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Spatial resolution of anthropogenic heat fluxes into urban aquifers
... Cologne is one of few cities where extensive groundwater temperature (GWT) monitoring has been performed since the 1970s [61][62][63] with an urban underground temperature anomaly of up to 4 K reported already in 1974. These early works date back more than three decades before the term SUHI was phrased [2] and are backed up by a variety of recent studies [5,35,[64][65][66][67][68][69]. We demonstrate how the thermal field develops and how the urban aquifer is charged by anthropogenic heat emission and climate change. ...
... This trailing equals rates that are typically found when comparing temperature in air to the shallow subsurface [65,80,81]. The underground temperature gradient in the city center is contrarily exceeding atmospheric temperature rise and can be attributed to higher anthropogenic heat fluxes caused by a higher building density, surface imperviousness, and more underground buildings in this area [64]. Subsurface temperature shift in the inner city reflects a transition between the rural outskirts and the city center. ...
... Even though heat storage is three magnitudes higher in the city center when compared to the outskirts, the heat stored in the aquifer each year equals only 1% of the thermal demand. These storage rates are also significantly lower than the average anthropogenic heat flux of 390 mW m −2 from the surface towards the aquifer that was calculated by Benz et al [64] using a 1D analytical model for this area. This implies that only about 5%-20% of the energy that is released into urban underground is also stored within the aquifer in the form of heat. ...
Meeting the rising energy demands of cities is a global challenge. Exploitation of the additional heat in the subsurface associated with the subsurface urban heat island (SUHI) has been proposed to address the heating demands. For the sustainable use of this heat it is crucial to understand how SUHIs evolve. To date, there have been no comprehensive studies showing how temperature anomalies beneath cities change over time scales of decades. Here, we reveal the long-term increase of temperatures in the groundwater beneath Cologne, Germany from 1973 to 2020. The rise in groundwater temperature trails atmospheric temperature rise in the rural areas and exceeds the rise in atmospheric temperature in the urban center. However, the amount of heat that is currently stored each year in the thin shallow aquifer reaches only 1% of the annual heating demand. The majority of the anthropogenic heat passes by the vertical extent of the aquifer or is discharged by the adjacent river. Overall the geothermal resource of the urban ground remains largely underused and heat extraction as well as combined heating and cooling could substantially raise the geothermal potential to supply the city’s demand.
... Consequently, subsurface temperatures, which are typically measured in shallow groundwater, are elevated under urban heat islands and in most places affected by human activity [11][12][13] . Due to their sheer number and ubiquity, heat lost from buildings and heat from sealed surfaces warmed by solar radiation are the main contributors to large-scale subsurface warming in a stable climate [14][15][16][17] . While less ubiquitous, even a single component of buried infrastructure can elevate ambient ground temperatures by several degrees Celsius 18 . ...
... Assuming energy extraction is focused on the groundwater table depth, this balance is achieved when the extraction rate is equivalent to the sum of conductive heat fluxes between the groundwater table and the natural and built environment at the surface. These fluxes have previously been determined for selected cities 14,19,36,37 . In three of these studies local infrastructure such as district heating networks and subsurface parking garages dominate on the smaller scale. ...
... Based on our highest estimates 14% or not feasible, 7% are potentially feasible, and 78% are likely feasible. Supplementary Fig. 4 further compares our results to existing studies quantifying both heating demand and heat input 14,15,19,20,37 . All of these are focused on larger cities and hence have high heating demands. ...
Despite the global interest in green energy alternatives, little attention has focused on the large-scale viability of recycling the ground heat accumulated due to urbanization, industrialization and climate change. Here we show this theoretical heat potential at a multi-continental scale by first leveraging datasets of groundwater temperature and lithology to assess the distribution of subsurface thermal pollution. We then evaluate subsurface heat recycling for three scenarios: a status quo scenario representing present-day accumulated heat, a recycled scenario with ground temperatures returned to background values, and a climate change scenario representing projected warming impacts. Our analyses reveal that over 50% of sites show recyclable underground heat pollution in the status quo, 25% of locations would be feasible for long-term heat recycling for the recycled scenario, and at least 83% for the climate change scenario. Results highlight that subsurface heat recycling warrants consideration in the move to a low-carbon economy in a warmer world.
... For example, heated ground cannot buffer hot summer days well and enhances heat waves in cities (Founda & Santamouris, 2017;Li & Bou-Zeid, 2013). Moreover, due to the high heat density of ground and groundwater, shallow geothermal energy is gaining attention as a renewable source for integrated heat and cold supply systems (Benz et al., 2015;Kammen & Sunter, 2016). We can consider heated ground not only as a resource but also as natural laboratories of the conditions to be expected in the future. ...
... a . b Benz et al. (2015). c . ...
... Although material properties have been studied (Popiel & Wojtkowiak, 2013), as well as the soil sealing effect on the urban climate (Murata & Kawai, 2018), the large scale impact on underground temperature is difficult to distinguish from other heat sources and has not been sufficiently investigated to date. However, several studies include elevated ground surface temperatures in the estimation of subsurface temperatures (Benz et al., 2015;Hemmerle et al., 2019;Tissen et al., 2021). Asphalt has been highlighted in the past as the material storing most solar energy (O'Malley et al., 2015), inducing the highest soil temperatures beneath it ( Cerm ak et al., 2017). ...
Anthropogenic warming of the atmosphere is one if not the most pressing challenge we face in the 21st century. While our state of knowledge on human drivers of atmospheric warming is advancing rapidly, little so can be said if we turn our view toward the Earth’s interior. Intensifying land use and atmospheric climate change condition the changing thermal state of the subsurface at different scales and intensities. Temperature is proven to be a driving factor for the quality of our largest freshwater resource: groundwater. But there is only insufficient knowledge on which sources of heat exist underground, how they relate in their intensity of subsurface warming, and which consequences this warming implies on associated environments, ecosystems and resources. In this review, we propose a differentiated classification based on (1) the geometry of the heat source, (2) the scale at which the subsurface is heated, (3) the process that generates the heat, and (4) the intention of heat release. Furthermore, we discuss the intensities of subsurface warming, the density of induced heat fluxes, as well as their abundance, and draw implications for depending processes and ecosystems in the subsurface and the potential of recycling this waste heat with geothermal installations.
... For the aforementioned city sites, the shallow mean annual groundwater temperature is 2-8°C warmer than in suburban areas and for some of them a warming trend was recognized due to global warming and urbanization effects. Benz et al. (2015) evaluated the thermal contribution of various anthropogenic heat sources for two European cities revealing the building basements and the elevated ground surface temperatures as the dominant heat sources on a citywide scale. ...
... The unsaturated layer between the ground surface and the water table can be considered a thermal resistant material able to dampen the temperature signal coming from the surface and to shift it in time. Thus, the downward heat propagation depends essentially on the thickness of the unsaturated soil and the thermal properties of the soil but, in a densely urbanized environment, the input signal from the surface can be altered by site-specific anthropogenic heat sources located at the surface (e.g., heat losses from building foundations, land use and land cover materials) or in the subsurface (e.g., heat losses from underground structures, infrastructures or geothermal installations and water leakage from sewage and district heating systems; Attard et al. 2016;Benz et al. 2015;Epting et al. 2017). ...
... Urban areas are characterized by a dense texture of structures and infrastructures that modify the water infiltration and groundwater flow processes, the heat transfer between the surface and the subsurface, and eventually the heat transport in the aquifer. In this context, the groundwater thermal regime is affected by several natural and human-activities-related factors already identified by many authors (Benz et al. 2015;Epting and Huggenberger 2013;Ferguson and Woodbury 2004;Menberg et al. 2013b;Taylor and Stefan 2009) such as: ...
Urban areas are major contributors to the alteration of the local atmospheric and groundwater environment. The impact of such changes on the groundwater thermal regime is documented worldwide by elevated groundwater temperature in city centers with respect to the surrounding rural areas. This study investigates the subsurface urban heat island (SUHI) in the aquifers beneath the Milan city area in northern Italy, and assesses the natural and anthropogenic controls on groundwater temperatures within the urban area by analyzing groundwater head and temperature records acquired in the 2016–2020 period. This analysis demonstrates the occurrence of a SUHI with up to 3 °C intensity and reveals a correlation between the density of building/subsurface infrastructures and the mean annual groundwater temperature. Vertical heat fluxes to the aquifer are strongly related to the depth of the groundwater and the density of surface structures and infrastructures. The heat accumulation in the subsurface is reflected by a constant groundwater warming trend between +0.1 and + 0.4 °C/year that leads to a gain of 25 MJ/m2 of thermal energy per year in the shallow aquifer inside the SUHI area. Future monitoring of groundwater temperatures, combined with numerical modeling of coupled groundwater flow and heat transport, will be essential to reveal what this trend is controlled by and to make predictions on the lateral and vertical extent of the groundwater SUHI in the study area.
... 40,41,42,43,44]. Menberg et al. [45] and Benz et al. [46] developed a 1D analytical and statistical heat flux model to estimate the mean annual heat flux and flow from anthropogenic heat sources. ...
... The GBA supplied average air temperatures from 2006 to 2016 as WFS with a spatial resolution of 1 km by 1 km. By combining air temperature with an offset depending on the surface material, the ground surface temperature (GST) is estimated [46]. The different offsets for grass, asphalt, bare soil and sand were determined by D ede cek et al. [67] and adapted to the land use categories described in the Urban Atlas [68]. ...
... The simulation of the vertical anthropogenic heat fluxes into the unsaturated zone is based on the method described by Benz et al. [46]. The heat flux q and heat flow Q calculation is accomplished on a regular grid with a 25 m by 25 m grid cell size, and comprises five steps (Fig. 2). ...
Decarbonising the heating sector is crucial for reducing CO2 emissions. This is in particular true for Central European cities such as Vienna, where 28% of the total CO2 emissions are caused by the energy supply for buildings. One promising option for environmental friendly heat supply is the use of shallow geothermal energy. To determine whether shallow geothermal systems are a feasible option to meet the urban heating demand, the Python tool GeoEnPy is developed and applied to a case study in Vienna. It allows the evaluation of the anthropogenic heat input into the subsurface, the theoretical sustainable potential, the technical geothermal potential, and the heat supply rate. The overall heat flow in Vienna is 17.6 PJ/a, which represents 38% of the current heating demand or indeed 99% once all buildings are thermally refurbished. The technical geothermal potential can satisfy the current heating demand for 63% (BHE system) or rather 8% (GWHP system) of the city area. GeoEnPy reveals that BHE systems are most feasible in the eastern and southern districts of Vienna. Our findings can guide integration of shallow geothermal use in spatial energy management focused on key locations to supply buildings with decentralised and sustainable heat from the subsurface.
... Energia je v podpovrchovej vrstve uskladnená v podobe zvýšených teplôt podzemnej vody (Benz et al. 2015). Výsledky ukazujú, že siete diaľkového vykurovania predstavujú bezpochyby najväčší zdroj tepelného toku s hodnotami vyššími ako 60 W/m 2 , pričom priestorové rozloženie celkového toku závisí hlavne od tepelného gradientu v nasýtenej zóne. ...
... kom vzájomného pôsobenia globálnej klimatickej zmeny a štruktúry miest (Zhu et al. 2015). Podobne ako v tejto štúdii, Benz et al. (2015) poukazujú na tepelný ostrov v podpovrchovej vrstve, ktorý je výsledkom priameho tepelného toku diaľkového vykurovania, únikov z odpadových systémov, vykurovania suterénov, koncentrácie kanalizačných systémov a tunelov (metra). Jednotlivé podpovrchové zdroje tak môžeme nepriamo vyjadriť pomocou antropogénnych prejavov na povrchu, pričom štruktúra vyjadrená pomocou krajinnej pokrývky a definovaním povrchových objektov poskytuje dostatočné množstvo informácií pre vyjadrenie vplyvu vertikálnej, ako aj horizontálnej štruktúry mesta na podpovrchové vrstvy. ...
... Zároveň je daný prístup použiteľný v oblastiach alebo miestach s nedostatočnou informáciou o jednotlivých podpovrchových vedeniach, ktoré najvýraznejšie ovplyvňujú teplotu podzemnej vody. Benz et al. (2015) Priebeh teploty podzemnej vody je v priemere asi o tri až päť mesiacov oneskorený v porovnaní s teplotou vzduchu (najnižšie teploty podzemnej vody sú v mesiaci apríl, a naopak najvyššie teploty v mesiaci október). Súhlasí to aj s výsledkami prezentovanými v štúdii Krčmář et al. (2017), kde autori poukázali na 4-až 5mesačný časový posun medzi teplotou v sledovaných vrtoch a teplotou vzduchu. ...
... In part, SUHIs can be regarded as the subsurface thermal imprint of the meteorological urban heat island (UHI) that causes elevated ground-surface temperature, but anthropogenic heat sources such as basement heating, underground thermal energy storage, sewers, and district heating, provide additional control on the development of a SUHI. Temperature-depth (TD) profiles obtained from borehole records allow one to describe the subsurface extent of SUHIs-examples of case studies that use such descriptions include mid-latitude cities in Canada (Ferguson and Woodbury 2004), Japan (Benz et al. 2018;Taniguchi et al. 2007Taniguchi et al. , 2009, and Europe (e.g., Benz et al. 2015;Epting and Huggenberger 2013;Menberg et al. 2013b;Mueller et al. 2018). In contrast to the UHI, the SUHI is a significant store for heat which accumulates at shallow depths and only slowly diffuses deeper into the subsurface. ...
... Consequently, the SUHI is often more pronounced than the UHI in terms of thermal intensity (Benz et al. 2017). The heat that is stored in SUHIs could be retrieved by geothermal energy systems (GES) and used for the heating of buildings, and in that way contribute to the offset of carbon emissions (e.g., Allen et al. 2003;Zhu et al. 2010;Menberg et al. 2013b;Menberg et al. 2015;Benz et al. 2015;García-Gil et al. 2015;Bayer et al. 2016;Epting et al. 2017). Bayer et al. (2019) review and categorize available studies on the geothermal potential of the urban subsurface; however, the long-term geothermal potential of a SUHI is expected to depend on the current extent, intensity and processes that maintain the SUHI (Benz et al. 2018). ...
... 5°C higher than the average annual SAT (Epting and Huggenberger 2013). In various German cities the inferred difference between highest and lowest observed groundwater temperatures is 4-8°C (Zhu et al. 2010;Menberg et al. 2013a, b, c;Menberg et al. 2015;Benz et al. 2015). Locally, subsurface temperatures have been raised to an even larger extent by groundwater heat pump systems or warm water injection-e.g. ...
Subsurface temperatures are substantially higher in urban areas than in surrounding rural environments; the result is a subsurface urban heat island (SUHI). SUHIs and their drivers have received attention in studies world-wide. In this study, a well-constrained data set of subsurface temperatures from Amsterdam, The Netherlands, is presented. The study demonstrates that, through modeling of centuries-long (from fourteenth to twenty-first century) urban development and climate change, along with the history of both the surface urban heat-island temperatures and ground surface temperatures, it is possible to simulate the development and present state of the Amsterdam SUHI. The results provide insight into the drivers of long-term SUHI development, which makes it possible to distinguish subterranean heat sources of more recent times that are localized drivers (such as geothermal energy systems, sewers, boiler basements, subway stations or district heating) from larger-scale drivers (mainly heat loss from buildings and raised ground-surface temperatures due to pavements). Because these findings have consequences for the assessment of the shallow geothermal potential of the SUHIs, it is proposed to distinguish between (1) a regional, long-term SUHI that has developed over centuries due to the larger-scale drivers, and (2) local anomalies caused by anthropogenic heat sources less than one century old.
... Among these are thermal pollution by wastewater [59], ground heating effects from asphalt [60,61], heat release from basements of buildings [29,62], thermal effects from tunnels [63], geothermal energy exchange [64,65], and case-specific impacts from brickworks [56]. For investigating causes of large-scale manifestations of SUHIs, comprehensive monitoring programs have been conducted for example in several German cities [25,66,67], which revealed the dominant heat flux from paved ground and buildings on the city scale. This is supported by estimations from Ferguson and Woodbury [52] based on their survey in Winnipeg and Attard et al. [29] in Lyon. ...
... A common choice are one-dimensional (1-D) analytical and numerical models for scrutinizing the role of land surface effects on temperature-depth profiles (e.g. [66,69,70]). Ferguson and Woodbury [52] inspected the heat release from basements of buildings via vertical two-dimensional (2-D) numerical models. ...
... The heat in place is considered as a basis for calculation of technical potential [102][103][104], but more detailed quantifications of theoretical potential under transient conditions are rare. Benz et al. [66] built upon the work of Zhu et al. [88] and compared estimated annual urban groundwater heat gains for the German cities of Cologne and Karlsruhe with the accumulated heat in place (assuming a ΔT = 4 K). The heat gain was computed based on 1-D vertical heat flux models that account for the various sources of SUHIs at the ground surface but neglect transient effects [25]. ...
What is the heat beneath our feet? There is a growing interest in the geothermal resources available at shallow depth beneath cities. However, there exists no general procedure for quantifying the low-temperature geo-thermal potential in urban ground and groundwater. This review categorizes previous work based on different definitions of the geothermal potential and compares the different assessment methods used. It is demonstrated that the theoretical potential of the available heat at a shallow depth is enormous, especially when not only the heat in place, but also compensating heat fluxes are considered. The technical potential describes the extractable heat by a specific technology. The methods to evaluate the extractable heat are manifold, including the use of technical performance standards, analytical and numerical simulation tools and mathematical regression procedures. These are different for groundwater well based open-loop systems and heat-exchanger-based closed loop systems, and the results depend on variable local factors, the density of systems applied and whether heat and/or cold is utilized. We contrast the published findings based on the power density and the relative contribution to the demand of a city. The broad span of the results highlights the need for a more consistent framework that distinguishes between the conceptual assumptions for calculating the technical geothermal potential and the local city-specific factors. This will be the basis for a reliable analysis of the economic geo-thermal potential of low-temperature geothermal applications on a local, district or city scale. This will also enhance the reliability and the trust in these technologies, and thus the public acceptance reflected in the acceptable geothermal potential.
... Primarily, heat loss from buildings and higher ground surface temperatures resulting from changed land use are held accountable for elevated subsurface temperatures (Ferguson and Woodbury, 2004;Reiter, 2007;Benz, 2018;Hemmerle et al., 2019). Furthermore, previous work successfully introduced methods to quantify anthropogenic heat fluxes through analytic calculations (Menberg et al., 2013a;Benz, 2015). ...
... Following the indirect observation of Dohr and Gruban (1999), we were able to identify a small influence of the heating grid. This finding is in line with Benz (2015) and Tissen et al. (2019), however, a differentiation must be made between Munich's modern heating grid and the older steam grid with a higher supply temperature. Thus, we suggest reviewing the influence of the heating grid in the future to gain a clearer view of the underlying dependencies. ...
Shallow aquifers beneath cities are highly influenced by anthropogenic heat sources, resulting in the formation of extensive subsurface urban heat islands. In addition to anthropogenic factors, natural factors also influence the subsurface temperature. However, the effect of individual factors is difficult to capture due to high temporal dynamics in urban environments. Particularly in the case of shallow aquifers, seasonal temperature fluctuations often override the influence of existing heat sources or sinks. For the city of Munich, we identify the dominant anthropogenic and natural influences on groundwater temperature and analyse how the influences change with increasing depth in the subsurface. For this purpose, we use depth temperature profiles from 752 selected groundwater monitoring wells. Since the measurements were taken at different times, we developed a statistical approach to compensate for the different seasonal temperature influences using passive heat tracing. Further, we propose an indicator to spatially assess the thermal stress on the aquifer.
A multiple regression analysis of four natural and nine anthropogenic factors identified surface sealing as the strongest and the district heating grid as a weak but significant warming influence. The natural factors, aquifer thickness, depth-to-water and Darcy velocity show a significant cooling influence on the groundwater temperature. In addition, we show that local drivers, like thermal groundwater uses, surface waters and underground structures do not significantly contribute to the city-wide temperature distribution. The subsequent depth-dependent analysis revealed that the influence of aquifer thickness and depth-to-water increases with depth, whereas the influence of Darcy velocity decreases, and surface sealing and the heating grid remain relatively constant. In conclusion, this study shows that the most critical factor for the mitigation of future groundwater warming in cities is to minimize further sealing of the ground, to restore the permeability of heavily sealed areas and to retain open landscapes.
... Visser et al. (2020) linked the development of the SUHI in the city of Amsterdam with the progressive city expansion and climate change of the last century. Benz et al. (2015) and Menberg et al. (2013b) evaluated analytically the thermal contribution of specific natural and anthropogenic heat sources, their temporal evolution in the last decades and the total heat content in the aquifer of Cologne and Karlsruhe. 2017b) and Bidarmaghz et al. (2020) proposed large-scale FEM modeling approaches to capture the subsurface temperature elevation resulting from anthropogenic heat sources in the city of Basel and a London district, respectively. ...
... These values are very similar to previous quantitative studies, e.g. Benz et al. (2015) estimated analytically a total heat accumulation of 2.1 and 1.0 PJ/y for the Karlsruhe and Cologne aquifers in Germany, with buildings and elevated ground surface temperature contributing to 88 and 70%, respectively. Given the assumed heating and cooling thermal power of geothermal installations, the net annual thermal contribution of shallow geothermic is low (0.08 PJ/y) compared to other sources since they are used both for heating and cooling. ...
Knowledge on the intensity and extension of current subsurface urban heat islands (SUHI) is not only based on the availability of spatiotemporal high-resolution and long-term groundwater monitoring data but also in-depth investigations on the role of single natural and anthropogenic factors. A holistic city-scale 3D FEM model is presented to introduce possible thermal management applications in the Milan metropolitan area such as: (1) understanding the hydro-thermal regime of the urban aquifer disentangling the thermal contribution of natural and anthropogenic heat sources, (2) quantifying the geothermal potential and (3) investigating the effects of urbanization and climate change scenarios. Focusing on the most relevant heat sources (boundaries) and transport mechanisms (parameters), this work deals with (I) the reconstruction of large-scale aquifer heterogeneities to consider the advective dominated heat transport, (II) the accurate definition of the upper thermal boundary by a coupled analytical solution and (III) the integration of natural and human-related fluid/heat sources as transient boundary conditions. The model was calibrated against 15 groundwater head and temperature time series and validated in space and time by temperature profiles at 40 additional observation wells. Thus, a fluid and heat budget analysis revealed the most relevant natural and anthropogenic sources at the city-scale. The heat flow from buildings, surface infrastructures and tunnels contribute to 85% of the net annual heat accumulation in the subsurface which totals to 1.4 PJ/y. The results of the simulations were used to evaluate the geothermal potential of the shallow aquifer and to localize promising and critical areas that should be further investigated for an effective thermal management. Finally, it was demonstrated that possible future climate change and city expansion scenarios could lead to the highest thermal energy increment in the subsurface compared to shallow geothermics development which, for this reason, should be highly supported.
... Obwohl Dahlem (2000) bereits feststellte, dass der Wärmeverlust durch die advektive Grundwasserströmung im Vergleich zu rein konduktiven Wärmeverlusten einen Faktor 10 ausmachen kann, untersuchten nur wenige Studien den Einfluss der Grundwasserströmung auf den Wärmeverlust beheizter Gebäudestrukturen. Auf städtischer Ebene haben Menberg et al. (2013a) und Benz et al. (2015) analytische Wärmeflussmodelle und einen GIS-Ansatz (Geographisches Informationssystem) verwendet, um zu zeigen, dass Untergrundstrukturen einen signifikanten Anteil der gesamten anthropogenen Wärmelast von urbanen Grundwasserleitern ausmachen. Epting et al. (2017a) präsentierten eine systematische Bewertung der thermischen Auswirkungen von unterirdischen Gebäudestrukturen auf städtische Grundwasserressourcen. ...
... In Menberg et al. (2013a) resultierten aus einer räumlichen Analyse der Wärmelasten von Untergrundstrukturen Werte im Bereich von -0,1 und > 10 W m -2 . In Benz et al. (2015) werden anthropogene Wärmelasten von Untergrundstrukturen in der Größenordnung von 3,61 ± 3,37 W m -2 für Karlsruhe und von 0,57 ± 0,47 W m -2 für Köln vorgestellt. Rees et al. (2000) und Thomas und Rees (1999) dokumentieren Wärmelasten durch Erdgeschossplatten von Gebäuden zwischen 0 und 20 Wm -2 und Ferguson und Woodbury (2004) schätzten den Wärmeverlust unter einem Gebäude auf~2 W m -2 . ...
Zusammenfassung
In Basel (CH) wurde mit Monitoringsystemen der thermische Einfluss unterschiedlicher Untergrundstrukturen, einschließlich fünf Tiefgaragen sowie einem Autobahntunnel, auf die urbanen Grundwasserressourcen untersucht. Die Daten wurden anschließend mit gemessenen Meteo- und Grundwassertemperaturdaten sowie Resultaten einer Wämetransportmodellierung zusammenhängend ausgewertet.
In den Tiefgaragen wurden auch über die Wintermonate deutlich erhöhte durchschnittliche Temperaturen zwischen 18,8 und 21,1 °C erfasst. Über den weitaus größten Zeitraum emittieren die Tiefgaragen somit Wärme in den Untergrund. Die Messdaten im Autobahntunnel hingegen deuten darauf hin, dass in den Sommermonaten zwar auch Wärme in den Untergrund emittiert, im Winterhalbjahr aber Wärme aus dem Untergrund absorbiert wird.
Zudem zeigen die Temperaturverläufe in den Tiefgaragen eine klare Abhängigkeit von der Nutzungsart: bei höherem Aufkommen täglicher Ein- und Ausfahrten konnten größere tägliche Temperaturanstiege nachgewiesen werden, mit Unterschieden von bis zu 2 °C in den Tagesmittelwerten. Besonders deutlich wird dies im Zeitraum des „Lockdowns“ während der COVID-19-Pandemie zwischen März und Mai 2020.
... Decreases in areas of vegetation and water surface will result in a decrease in latent heat flux in the output component of the surface energy balance . In addition, a large amount of anthropogenic heat from buildings, transportation, and industrial production is released into the atmosphere (Benz et al., 2015;Salamanca et al., 2014). This can contribute to the proportion of sensible heat flux out of the total energy output, forming a heat island effect. ...
... The selected variables explained 34e45% of the changes in urban LST in each season. In addition to the 12 factors, factors such as meteorology, transportation, industrial emissions, and heating methods have been shown to impact the spatial distribution of surface heat radiation (Benz et al., 2015;Chen et al., 2016;Huang and Cadenasso, 2016;Salamanca et al., 2014;Wang et al., 2014), which should be introduced into future research. Here, spatially uniform sampling was used in this study to obtain an ideal result. ...
Environmental factors such as urban landscape patterns, local climate, topography, and socioeconomic conditions have significant impacts on land surface temperature (LST), especially through the urban heat island effect. At present, in-depth studies on the mechanisms determining LST in different seasons in winter cities are lacking. In this study, we used structural equation modeling for 12 environmental factors to characterize how these factors affect the temporal and spatial heterogeneity of the LST in the winter city of Shenyang, China. We found that the most critical factors affecting LST varied with season. Specifically, the distances from the nearest water body and nearest green space had the largest impacts on the LST in spring and summer, with path coefficients of 0.51 and 0.19 for spring and 0.42 and 0.21 for summer, respectively. In winter, the main factors affecting LST were elevation, slope, and population density, with respective path coefficients of -0.5, -0.41, and 0.29. Our findings suggest that the urban thermal environment in this winter city can be improved by: optimizing the landscape pattern of green spaces and water bodies; and reducing the population density by establishing satellite cities. This study highlights how landscape pattern can be used to regulate the urban thermal environment and mitigate predicted climate change impacts on the quality, health, and safety of urban living.
... Arola et al. [91] reported elevated groundwater temperatures due to urbanization, combined with shallow seasonal thermal fluctuation zone. Underground car parks, multi-story basements, road tunnels or district heating pipes could be potential heat sources that affect the aquifer temperature [92]. Several short-distance tunnels, partially burrowed in the aquifer, are found along the lateral boundaries of the model area. ...
... Improving the model presented here with heat flux estimations from buildings based on other studies could help [70,93,94]. In unconfined aquifers, heat flux through the unsaturated zone to the saturated zone originates from anthropogenic sources and structures resulting in a significant heat transfer processes to the aquifer [83,92]. Groundwater flow and heat transport simulations were previously performed in the semi-confined alluvial aquifer in Liège by neglecting the effect of the temperature sources of urban structures [30]. ...
In the context of energy transition, new and renovated buildings often include heating and/or air conditioning energy-saving technologies based on sustainable energy sources, such as groundwater heat pumps with aquifer thermal energy storage. A new aquifer thermal energy storage system was designed and is under construction in the city of Liège, Belgium, along the Meuse River. This system will be the very first to operate in Wallonia (southern Belgium) and should serve as a reference for future shallow geothermal developments in the region. The targeted alluvial aquifer reservoir was thoroughly characterized using geophysics, pumping tests, and dye and heat tracer tests. A 3D groundwater flow heterogeneous numerical model coupled to heat transport was then developed, automatically calibrated with the state-of-the-art pilot points method, and used for simulating and assessing the future system efficiency. A transient simulation was run over a 25 year-period. The potential thermal impact on the aquifer, based on thermal needs from the future building, was simulated at its full capacity in continuous mode and quantified. While the results show some thermal feedback within the wells of the aquifer thermal energy storage system and heat loss to the aquifer, the thermal affected zone in the aquifer extends up to 980 m downstream of the building and the system efficiency seems suitable for long-term thermal energy production.
... Human activities like the heat emitted from homes, vehicles, and industries elevate temperature in urban regions. The results are consistent with those of some other studies (Benz et al., 2015;Balew and Korme 2020;Chaka and Oda 2021). Further, a rise in water and vegetation cover reduced LST, and vice versa. ...
Climate change and urbanization along with uncontrolled development in less developed countries have led to an increased ecosystems’ thermal environment. Some factors such as environmental indices and landscape pattern changes can alter Land Surface Temperature (LST). Thus, the accurate evaluation of the relationship between these factors and LST is considered important for managing ecosystems, especially fragile ones under high stress. The southeast of Iran has witnessed many destructions in the environmental dimension in the past years. Moreover, this region has a low socio-economic situation, which increases the need to study in this region. In the present study, we used Landsat TM5 satellite images (1989), Landsat 8 OLI/TIRS ones (2019), and Google Earth Engine (GEE) system to prepare the maps of temporal-spatial LST changes, Land Use/Land Cover (LULC), and selected environmental indices including Normalized Difference Vegetation (NDVI), Built-up (NDBI), Water Indices (NDWI), Land Surface Moisture (LSM) and albedo. Then, the correlation levels of LST with the aforementioned indices were assessed by using Geographically Weighted Regression (GWR), as well as assessing LST variation following LULC change. In addition, the Moran index was used to analyze global and local spatial autocorrelation. The results represented an 8.67-degree increase in the mean LST during 1989–2019. Urban and built-up areas had a significant effect on increasing the temperature of the region. Additionally, water bodies and vegetation cover in the region were the most crucial parameters in LST reduction. All of the applied indices were strongly related to LST (>0.70), while some exhibited more correlation in each year. Further, the highest correlation of LST was observed with LSM and NDBI in 1989, as well as with NDVI and NDWI during 2019. In addition, the Moran index value reduced from 1989 to 2019 (from 0.93 to 0.89). Finally, the region rehabilitation based on sustainable development principles played an important role in the direct and indirect decrease in LST.
... Structures built into the ground and the associated heat flux from these are known to impact ground temperatures, with anomalous temperatures propagating particularly far through groundwater flow (Ferguson and Woodbury, 2004;Bidarmaghz et al., 2020). Such temperature anomalies can have knock-on effects, impacting cooling and heating requirements to maintain underground spaces at comfortable levels (particularly due to groundwater not transporting away as much heat (Blum et al., 2021)), groundwater quality, and the functioning of underground biospheres (Benz et al., 2015;Attard et al., 2016;Bayer et al., 2019;Krcmar et al., 2020). ...
Understanding the subsurface is crucial in building a sustainable future, particularly for urban centers. Importantly, the thermal effects that anthropogenic infrastructure, such as buildings, tunnels, and ground heat exchangers, can have on this shared resource need to be well understood to avoid issues, such as overheating the ground, and to identify opportunities, such as extracting and utilizing excess heat. However, obtaining data for the subsurface can be costly, typically requiring the drilling of boreholes. Bayesian statistical methodologies can be used towards overcoming this, by inferring information about the ground by combining field data and numerical modeling, while quantifying associated uncertainties. This work utilizes data obtained in the city of Cardiff, UK, to evaluate the applicability of a Bayesian calibration (using GP surrogates) approach to measured data and associated challenges (previously not tested) and to obtain insights on the subsurface of the area. The importance of the data set size is analyzed, showing that more data are required in realistic (field data), compared to controlled conditions (numerically-generated data), highlighting the importance of identifying data points that contain the most information. Heterogeneity of the ground (i.e., input parameters), which can be particularly prominent in large-scale subsurface domains, is also investigated, showing that the calibration methodology can still yield reasonably accurate results under heterogeneous conditions. Finally, the impact of considering uncertainty in subsurface properties is demonstrated in an existing shallow geothermal system in the area, showing a higher than utilized ground capacity, and the potential for a larger scale system given sufficient demand.
... Modellergebnissen zufolge scheint ein Temperaturanstieg um insgesamt 3-4 K in oberflächennahen Aquiferen möglich (Taylor, et al., 2008). In Ballungsgebieten (unter Großstädten) werden in solchen Aquiferen bereits heute durch den zusätzlichen Wärmeeintrag unterirdische Infrastruktur und Verkehrswege lokale Temperaturanstiege um 3-7 K beobachtet (Menberg, et al., 2013a;Benz, et al., 2015). ...
Environmentally compatible use of geothermal heat storage
To reduce fossil energy consumption, underground thermal energy storage (UTES), also called geothermal heat storage (GTS), is a building block in the transformation of heating and cooling. Such storage facilities are to be fed by renewable energy sources and other waste heat. The groundwater is thermally influenced.
The thermal impact space of UTES has been systematically investigated and illustrated with nu-merical simulations for seasonal buffering and heat storage, building air-conditioning and use of excess electricity (power-to-heat). Effects of temperature change on hydro-and geochemical processes and groundwater ecology were investigated by including extensively researched literature.
In oxygen-rich (oxic) freshwater aquifers in unconsolidated rocks, the high temperature sensi-tivity of groundwater fauna necessitates tighter temperature thresholds for their precautionary protection and maintenance of their ecosystem services to keep impacts minor. Less restrictive temperature thresholds can be derived for low-oxygen (anoxic) aquifers, where a microbiome can adapt more flexibly to changes in groundwater temperature and properties.
With the derived thermal thresholdsof insignificance, sustainable groundwater management is also possible with geothermal heat storage. The examples shown make it easier for involved planners and experts in the fields of geology, hydrogeology, groundwater ecology, geothermal energy as well as in authorities to estimate the thermal insignificance. Thermal insignificance means that the use of geothermal reservoirs has no adverse environmental impact on ground-water.
... N. Mijani et al. Advances in Space Research xxx (xxxx) xxx (Chow and Roth, 2006;Benz et al., 2015;Doan et al., 2019), hence further investigation and understanding of their relationship is worthwhile. Investigating the effect of COVID-19 pandemic lockdowns on LST and SUHI can be useful for drawing conclusions that provide solutions for climate change mitigation. ...
COVID-19 pandemic has had a major impact on our society, environment and public health, in both positive and negative ways. The main aim of this study is to monitor the effect of COVID-19 pandemic lockdowns on urban cooling. To do so, satellite images of Landsat 8 for Milan and Rome in Italy, and Wuhan in China were used to look at pre-lockdown and during the lockdown. First, the surface biophysical characteristics for the pre-lockdown and within-lockdown dates of COVID-19 were calculated. Then, the land surface temperature (LST) retrieved from Landsat thermal data was normalized based on cold pixels LST and statistical 2 parameters of normalized LST (NLST) were calculated. Thereafter, the correlation coefficient (r) between the NLST and index-based built-up index (IBI) was estimated. Finally, the surface urban heat island intensity (SUHII) of different cities on the lockdown and pre-lockdown periods was compared with each other. The mean NLST of built-up lands in Milan (from 7.71 °C to 2.32 °C), Rome (from 5.05 °C to 3.54 °C) and Wuhan (from 3.57 °C to 1.77 °C) decreased during the lockdown dates compared to pre-lockdown dates. The r (absolute value) between NLST and IBI for Milan, Rome and Wuhan decreased from 0.43, 0.41 and 0.16 in the pre-lockdown dates to 0.25, 0.24, and 0.12 during lockdown dates respectively, which shows a large decrease for all cities. Analysis of SUHI for these cities showed that SUHII during the lockdown dates compared to pre-lockdown dates decreased by 0.89 °C, 1.78 °C, and 1.07 °C respectively. The results indicated a high and substantial impact of anthropogenic activities and anthropogenic heat flux (AHF) on the SUHI due to the substantial reduction of huge anthropogenic pressure in cities. Our conclusions draw attention to the contribution of COVID-19 lockdowns (reducing the anthropogenic activities) to creating cooler cities.
... This is because GWHP systems are less expensive and more efficient than GCHP systems, due to the relative higher thermal conductivity of water than the antifreeze used in GCHP systems. However, despite the fact that urban aquifers can be considered as massive energy reservoirs, the intensive use of geothermal energy is leading to thermal overexploitation of urban aquifers (Bayer et al., 2019;Benz et al., 2015;Previati et al., 2022;Rivera et al., 2017;Visser et al., 2020;Zhu et al., 2010). Thermal interference between systems might comprise technical sustainability of the GWHP systems, especially in urban environments where shallow geothermal systems are affected by and contribute to subsurface urban heat island (SUHI) effects (García-Gil et al., 2020bMenberg et al., 2013;Zhu et al., 2010). ...
The growing interest in shallow geothermal resources is compromising geothermal energy availability and groundwater quality in urban areas. This makes it necessary to search for new methodologies that facilitate urban geothermal resources management. In this work, a novel methodology based on polar coordinates to assess the geothermal impacts caused by shallow geothermal installations on urban aquifers is proposed and applied to a real case study. This methodology facilitated the definition of three key parameters (Tmax, Tmin and ANTI -Annual Net Thermal Impact-) for geothermal impact assessment and allowed classification of geothermal impacts on urban aquifers into five patterns (seasonally balanced, cooling/heating dominated impact, single cooling/heating impact, unrecovered cooling/heating impact and upward/downward linear impact).
It was possible to establish the most frequent impact patterns in temperate to hot climates, where the use of the geothermal installations for cooling dominates, by applying this methodology to the Zaragoza city aquifer (Spain). The holistic view of the urban aquifer showed an average delay of four to five months between the production peak of the geothermal installations and the peak of the triggered thermal impact on the aquifer. The results showed that the increasing use of shallow geothermal energy is leading to an increase in temperature of aquifers which, in the case of the Zaragoza aquifer, was quantified at 0.20 °C/yr in the past five years. These results demonstrate the effectiveness of this methodology to assess thermal impacts on urban aquifers and facilitate thermal management in cities.
... The aquifers below more densely populated and older urban areas (e.g., city centres) often have higher temperatures than those below rural, undisturbed regions where the temperatures can be more than 5 K colder. Most relevant anthropogenic heat sources were observed to be sealing of ground surface, built-up-areas, and underground structures (e.g., basements, tunnels) (Benz et al., 2015;Böttcher and Zosseder, 2022;Previati et al., 2022). Locally, hot spots of more than 10 K elevation in temperature have been reported Ferguson and Woodbury, 2007;Hemmerle et al., 2019;Huang et al., 2009). ...
Groundwater fauna (stygofauna) comprises organisms that have adapted to the dark subterranean environment over a course of thousands and millions of years, typically having slow metabolisms and long life cycles. They are crucial players in the groundwater of oxygenic aquifers, and contribute to various ecosystem services. Today's knowledge of their sensitivity to anthropogenic impacts is incomplete and a critical analysis of the general relevance of local findings is lacking. In this review, we focus on those areas with the highest interference between humans and stygofauna: cities. Here is where local pollution by various contaminants and heat strongly stresses the unique groundwater ecosystems. It is demonstrated that it is difficult to discern the influence of individual factors from the findings reported in field studies, and to extrapolate laboratory results to field conditions. The effects of temperature increase and chemical pollution vary strongly between tested species and test conditions. In general, previous findings indicate that heating, especially in the long-term, will increase mortality, and less adapted species are at risk of vanishing from their habitats. The same may be true for salinity caused by road de-icing in cold urban areas. Furthermore, high sensitivities were shown for ammonium, which will probably be even more pronounced with rising temperatures resulting in altered biodiversity patterns. Toxicity of heavy metals, for a variety of invertebrates, increases with time and chronic exposure. Our current knowledge reveals diverse potential impacts on groundwater fauna by urban pollution, but our insights gained so far can only be validated by standardized and long-term test concepts.
... An average heat flux into the subsurface during the building's usage period was equal to 0.34 W/m 2 . For comparison, in Karlsrohe the anthropogenic heat flux from buildings to the subsurface was equal to 3.61 ± 3.37 W/m 2 , in Köln it was 0.57 ± 0.47 W/m 2 (Benz et al., 2015). In Basel Epting et al. (2013) estimated heat fluxes from different buildings in the range of 0.18 to 16 W/m 2 . ...
The paper deals with the analysis of the subsurface urban thermal field using temperature logging in boreholes. The method for the separation and quantification of temperature anomalies in an urban subsurface induced by climate change and the building construction at the local area has been described. The differences in the penetration dynamics for climate and local anomalies afford to estimate their contributions separately. The study was carried out by the example of the borehole IGF-280 located in Yekaterinburg, Russia. It was found that the value of local temperature anomaly caused by the building construction is much higher than that induced by climate change (11 K versus 1.4 K). But the climate temperature anomaly penetrates deeper than the local one (140 m for the climate anomaly versus 90 m for the local one). We also assessed changes in heat content due to climatic changes and building operation. The heat content of the rocks increased by 15.6·107 J/m2 due to climate change over the past 150 years. The building input to the heat content increase is more than twice as higher – 38.6·107 J/m2. About 40% of the heat content gain caused by climate change is concentrated in the 20-meter layer of rocks, and 97% of that – in the upper 100 m. 74% of the heat content gain due to the building influence are concentrated in the upper 20 m.
... The temperature of the near surface is controlled principally by two main sources of heat which have been stored over geological time; solar radiation and the inherent heat flux from the Earth's hot core to the surface. Climate variations clearly have a secondary influence and recently, urban settings are seeing an anthropogenic signal known as the Urban Heat Island Effect (Benz et al., 2015;Rivera et al., 2015;Bayer et al., 2019). The seasonal solar flux controls the temperature of the near surface [~10-20 m depth (Rybach and Sanner, 2000;Rybach and Eugster, 2010)], with warmer seasons seeing heat energy conduct downwards into the near surface, and during colder seasons heat is lost from the surface. ...
Decarbonisation of heating represents a major challenge in efforts to reach Net Zero carbon emissions, especially for countries that rely heavily on the combustion of carbon-based fossil fuels to meet heating demand such as the United Kingdom. In this paper we explore the use of near surface low enthalpy geothermal energy accessed via commercial and domestic heat pump technology. These resources may become increasingly important in decarbonisation efforts but, while they are renewable, their sustainability is contingent on appropriate management. Here, we introduce a new geothermal circular heat network concept, known as a “geobattery,” which redistributes recyclable heat from emitters to users via elevated permeability pathways in the subsurface and offers a platform to manage shallow geothermal resources. If successfully implemented the concept has the potential to provide low carbon, resilient, low-cost heating that is sustainable both in terms of heat pump performance and the shallow geothermal resource. We demonstrate the concept based on the cooling requirements of a case study data centre with existing high energy use and the potential to inject the generated heat into elevated permeability pathways in the shallow subsurface. We show that thermal recharge under these conditions has the potential to arrest subsurface temperature declines associated with closely spaced borehole heat exchangers, ensure the long-term sustainability of shallow geothermal resources for generations to come, and play an important role in the decarbonisation of heating.
... Existing studies that compare some type of geothermal potential and its capacity to meet demand can be divided into 2 categories: (1) studies that assess the geothermal potential based on actual or estimated energy needs (the heating needs of typical residential buildings in different geographical and climatic conditions can be met by a specific technical project); (2) studies that calculate a specific type of geothermal potential, such as theoretical or technical, for a given situation, and then compare the energy extracted with the value of energy demand [7,16]. The estimated capacity to meet demand is significantly reduced if focus is on the heat flow either in the subsurface [26] or in the aquifer [27] which is replenished annually by natural and anthropogenic heat resources. ...
Geothermal energy is a collective term referring to Earth heat extraction and use of the ground capacity to absorb and store thermal energy to supply heat or cold. Thermal ground exchange or shallow geothermal energy has been increasingly used in the housing sector to sustain comfortable room temperature. Increasing utilization of geothermal energy, particularly in urban areas, requires integration into urban planning processes. The question of subsurface planning, or underground space integration into land-use planning, or three-dimensional planning has been an emerging research theme in this decade. This paper will focus on specific issues that pertain to geothermal energy use in land use planning in urban areas. These issues include (1) holistic vision of underground space as a resource, (2) geothermal energy technologies in terms of using space, (3) multiple users and installations of heat pumps and their interaction, (4) possible conflicts and interference with other subsurface users and functions, (5) demand and suitability of geothermal use in housing, (6) urban densities and geothermal energy feasible use, (7) and general principles of urban geothermal land use planning. A feasibility case study of using heat pumps to provide heating for a typical historic residential multifamily building in the Petrogradsky district of the city of St. Petersburg, Russia is given.
... Given the human-induced heat fluxes that are introduced into the subsurface formation below the urban locales, the increased groundwater temperatures would further enhance the available geothermal resource. Particularly, these anthropogenic heat fluxes have been estimated to sustain 32% and 9% of the annual space heating in the residential sector in Karlsruhe and Cologne, Germany, respectively (Benz et al., 2015). ...
Among the main components of a smart city, the energy system plays a vital and core role in the transition towards a sustainable urban life. Furthermore, the utilization of renewable energy sources has been demonstrated as a significant contribution to reducing pollutant emissions and enhancing the quality of the living environment. Therefore, designing the energy systems based on clean and renewable criteria is considered a sustainable solution for smart cities. Indeed, the deep and rapid penetration of renewable energy-based technologies have been believed to very well fit into a smart city under various scales, this could supply a secure basis for a modern society with a low-carbon economy. In this review paper, the main components and roles of renewable energy resources (such as solar, wind, geothermal, hydropower, ocean, and biofuels) for the smart city were fully introduced. Besides, integrating the renewable sources form into the energy systems of smart cities was thoroughly analyzed on the basis of technical and economic criteria. Finally, existing challenges and future scenarios were also discussed in detail to clarify the progress and perspective of smart renewable energy systems for the smart city. In general, the integration of renewables into energy systems of the smart city is a sagacious perspective and solution aiming to achieve cleaner process and more sustainable development. However, the optimization issues of the energy system for integrating of renewable components, ensuring good stability, maximizing the operating range, and minimizing the investment costs should be critically evaluated in the future works.
... Epting et al. (2017) measured increased GWT by up to 6 and 8 K in commercial and industrial areas of Basel, Switzerland (Table 1). In two German cities, Karlsruhe and Cologne, Menberg et al. (Menberg et al., 2013b) and Benz et al. (2015) could demonstrate that the dominant heat fluxes responsible for the development of the SUHI are increased ground surface temperatures mainly due to sealing and basements of buildings. Hence, these studies showed that in SUHI groundwater temperatures typically increase by up to 6 K (Table 1). ...
Thermal use of the shallow subsurface and its aquifers (< 400 m) is steadily increasing. Currently, more than 2800 aquifer thermal energy storage (ATES) systems are operating worldwide alongside more than 1.2 million ground source heat pump (GSHP) systems in Europe alone. These rising numbers of shallow geothermal energy (SGE) systems will put additional pressure on typically vulnerable groundwater systems. Hitherto, suitable criteria to control the thermal use of groundwater in national and international legislations are often still at a preliminary state or even non-existing. While the European Union (EU) Water Framework Directive (WFD) defined the release of heat into the groundwater as pollution in the year 2000, the cooling of groundwater for heating purposes is not explicitly mentioned yet. In contrast, some national legislations have stricter guidelines. For example, in Germany, detrimental changes in physical, chemical and biological characteristics have to be avoided. In the Swiss water ordinance, it is even recommended that the groundwater biocenosis should be kept in natural state. However, exact definitions of ‘detrimental changes’ and ‘natural state’ are still missing. Hence, the current study provides an overview on natural and affected thermal groundwater conditions and international and national legislations of the thermal use of groundwater. Also, it presents recent studies on groundwater ecosystems and proposes a sustainable policy framework for the thermal use of groundwater. In addition to geothermal heat sources, other anthropogenic heat sources such as climate change, underground car parks, heated basements, district heating systems, land fills, wastewater treatment plants and mining are considered, although no legislation on these anthropogenic heat sources and their impact on groundwater is currently in place. Finally, we intend to answer the above question and provide recommendations for the further discussions on the joint use of shallow groundwater systems for drinking water production and thermal use.
... They show positive temperature anomalies in the subsurface up to several Kelvin [3][4][5][6][7][8][9][10][11]. Main causes for the warming include soil surface sealing, heat input through surfaces and buildings, as well as infiltration of heated rain and wastewater [12][13][14][15][16]. Simultaneously, proportions of vegetation and water surfaces decrease and thus further reduce cooling effects caused by evapotranspiration. ...
In urban areas, the human influence on the city-ecosystem often results in a Subsurface Urban Heat Island (SUHI), which can be used geothermally. Unfortunately, a model of a SUHI does not consider the geology and hydrogeology of the subsoil. These can vary significantly over short distances, and are of considerable importance for the energy balance. In this work, we calculated the energy and its density stored in the subsoil via a SUHI. For this so-called energy-SUHI (e-SUHI), we evaluated the geology and its physical parameters for the first 20 m below ground level in the German city of Nuremberg and linked them to measured underground temperatures in a GIS application. This approach revealed stored energy of 1.634 × 1010 MJ within the soil and water for the study area with an area of 163 km2 and a volume of 3.26 × 109 m3. It corresponds to an average energy density of 5.0 MJ/m3. The highest energy density of 16.5 MJ/m3 was found in the city center area and correlated well to increases in subsurface temperature. As expected, our model reacts sensitively to thickness changes in the geological layers and the unsaturated zone.
... Since we aim to analyze U of WTMs based on measurements of the UGT, care is taken to ensure thermal equilibrium of the BHE fluid with the surrounding ground, as pointed out by Gehlin and Nordell (Gehlin and Nordell, 2003). However, anthropogenic heat fluxes have already caused an increase in the groundwater temperatures in Karlsruhe (Benz et al., 2015;Menberg et al., 2013). To qualitatively compare the WTMs, we additionally record T-logs with the Distributed Temperature Sensing (DTS) method using two fiber optic cables. ...
The reliability of temperature measurements in open and closed geothermal systems is closely related to their design, quality control and performance evaluation. Thus, wireless and miniaturized probes, which provide highly resolved temperature profiles in borehole heat exchangers (BHEs), experience a growing interest in research. To ensure quality assurance and reliability of these emerging technologies, errors and uncertainties relating to wireless temperature measurements (WTMs) must be determined. Thus, we provide a laboratory analysis of random, systematic and dynamic measurement errors, which lead to the measurement uncertainties of WTMs. For the first time, we subsequently transfer the calculated uncertainties to temperature profiles of the undisturbed ground measured at a BHE site in Karlsruhe, Germany. The resulting precision of 0.011 K and accuracy of -0.11 K ensure a high reliability of the WTMs. The largest uncertainty is obtained within the first five meters of descent and results from the thermal time constant of 4 s. The fast and convenient measurement procedure results in substantial advantages over Distributed Temperature Sensing (DTS) measurements using fiber optics, whose recorded temperature profiles at the site serve as qualitative comparison. We additionally provide recommendations for technical implementations of future measurement probes. Our work will contribute to an improved understanding and further development of WTMs.
... However, the temporal variability and sensitivity to the extreme weather events of AH fluxes have not been adequately studied. Most commonly, two-dimensional statistical heat fluxes from buildings are aggregated with spatial distributions, fed as the input of static simulations with urban heat balance equations to analyze the sensitivity of regional weather to AH [22][23][24][25]. Other climate models (those coupled with urban canopy models) consider heat emissions from buildings as a diurnal profile based on pre-assumed waste heat inventories [26,27] or collected energy statistics. ...
More frequent and longer duration heat waves have been observed worldwide and are recognized as a serious threat to human health and the stability of electrical grids. Past studies have identified a positive feedback between heat waves and urban heat island effects. Anthropogenic heat emissions from buildings have a crucial impact on the urban environment, and hence it is critical to understand the interactive effects of urban microclimate and building heat emissions in terms of the urban energy balance. Here we developed a coupled-simulation approach to quantify these effects, mapping urban environmental data generated by the mesoscale Weather Research and Forecasting (WRF) coupled to Urban Canopy Model (UCM) to urban building energy models (UBEM). We conducted a case study in the city of Los Angeles, California, during a five-day heat wave event in September 2009. We analyzed the surge in city-scale building heat emission and energy use during the extreme heat event. We first simulated the urban microclimate at a high resolution (500 meters [m] by 500 m) using WRF-UCM. We then generated grid-level building heat emission profiles and aggregated them using prototype building energy models informed by spatially disaggregated urban land use and urban building density data. The spatial patterns of anthropogenic heat discharge from the building sector were analyzed, and the quantitative relationship with weather conditions and urban land-use dynamics were assessed at the grid level. The simulation results indicate that the dispersion of anthropogenic heat from urban buildings to the urban environment increases by up to 20% on average and varies significantly, both in time and space, during the heat wave event. The heat dispersion from the air-conditioning heat rejection contributes most (86.5%) of the total waste heat from the buildings to the urban environment. We also found that the waste heat discharge in inland, dense urban districts is more sensitive to extreme events than it is in coastal or suburban areas. The generated anthropogenic heat profiles can be used in urban microclimate models to provide a more accurate estimation of urban air temperature rises during heat waves.
... The main drivers of SUHIs are heat fluxes between urban structures (e.g., buildings, roads) and the ground F I G U R E 1 Heat and water process differences in urban and forested environments, with the size of the arrows indicating proportional differences between urban and forested heat flux (radiative flux, heat transfer, evapotranspiration) and water flow (runoff, infiltration). In this figure, UHI refers to urban heat island, red arrows represent heat flux, and blue arrows represent water flow [Color figure can be viewed at wileyonlinelibrary.com] (Benz, Bayer, Menberg, Jung, & Blum, 2015). The infiltration of warmed surface water may also influence groundwater temperature, as well as stream baseflow temperatures (Beltrami, Bourlon, Kellman, & González-Rouco, 2006). ...
Green infrastructure (GI) and other stormwater management practices are commonly designed to reduce stormflow volume and pollutant loads by using infiltration, retention , and evapotranspiration to capture stormwater. Although these methods are be designed to reduce impacts of stormwater volumes and pollutant loads, they may not be designed to mitigate thermal load from stormwater runoff in urban areas. This review of literature identifies key drivers of stream temperature in urban streams, including heat transference from stormflow and effects of pipe networks and evapo-transpiration on baseflow. Recent simulation studies indicate the need for more than bioretention, increased infiltration, and tree canopy mitigation practices to reduce heat stress in urban streams. These studies show greatest reductions in thermal load by applying cool surfaces as a single thermal mitigation practice (TMP) and comprehensive applications of TMPs to all available areas at the watershed scale. This review of available literature suggests that incorporating TMPs into current and future GI designs will help maintain water resources, water quality, aquatic ecosystems , and coldwater stream species across the landscape. Further research is needed on the most effective ways to implement TMPs as part of our current and future GI designs for stormwater and how to best incorporate these measures into urban design concepts at larger spatial scales. K E Y W O R D S bioretention, coldwater fish, cool surfaces, effective impervious, forest canopy, thermal load, urban stormwater
... The land use of the test site is mainly agricultural, and the density of buildings and paved surfaces is expected to be negligible for the local thermal regime, as conversely occurs in urban areas (e.g. Taniguchi et al. 2007;Menberg et al. 2013;Benz et al. 2015;Garzena et al. 2019). ...
A 3-year high-resolution monitoring of shallow subsurface temperature (unsaturated and saturated zones) was performed in the experimental site of Mezzi Po (Po River plain, NW Italy) to investigate the thermal behaviour of subsurface and the dependency with the atmospheric (air) temperature. The unsaturated zone of the test site is mainly constituted by sands and silts, and the unconfined aquifer below is hosted in coarse sediments (mainly sands and gravels) with shallow depth to water table (5 m b.g.l). The monitoring results allowed for identifying two main phenomena correlated with the propagation of the atmospheric heat through the subsurface. First, the amplitude of temperature fluctuation during the year, calculated as the difference between maximum and minimum temperature value, reduces with increasing depth, with a maximum range (31.1 °C) in air and a minimum (2.0 °C) in the saturated zone, at 7.00 m below ground level (b.g.l.). Furthermore, a lag of mean temperatures in the subsurface respect to air occurs. The delay is as much longer as the depth increases. Mainly, the time shift ranges between 1 week in the shallow soil (at 0.60 m b.g.l.) and 17 weeks in the saturated zone (7 m b.g.l.). These results are consistent with a 1-D heat diffusion model, through which the thermal subsoil properties were derived for 0.60–7 m depth interval. More specifically, thermal diffusivity is 8.12 × 10–7 m2/s, and thermal conductivity is 1.40 W/mK.
... Recent studies have considered the application of this technology to tunnel linings, investigating feasibility and efficiency issues ( Barla et al., , 2019Barla and Perino, 2014;Di Donna and Barla, 2016;Franzius and Pralle, 2011;Lee and Lam, 2012;Mimouni et al., 2013;Nicholson et al., 2013;Tinti et al., 2017;Zhang et al., 2013). Very few cases of real implementation or site-scale experiments of energy tunnels are known (Adam and Markiewicz, 2009;Barla et al., 2017; 2010-2015(modified after Mueller et al. (2018). Below: Sketch of the cross section of the lower and right part of the planned railway tunnel (T1), including the location chosen for the setup of local-scale 3D-TH models where the railway tunnel is located in the bedrock (Model BR) and the groundwater (Model GW) saturated zone. ...
This work presents preliminary evaluation elements for geothermal potential assessment and thermal influences of planned tunnel infrastructures for the urban agglomeration of Basel (Switzerland). In dependence of the tunnel type (motorway or railway) as well as its location related to the geological and hydrogeological settings different solutions for shallow geothermal energy systems (SGE) are investigated. ‘Passive’ and ‘active’ SGE have been evaluated, including heat-exchanging segments installed in tunnel lining structures and thermal exploitation of water circulating in culvert systems.
First results suggest that thermal activation of a planned railway tunnel is most efficient where it is located within groundwater-saturated zones of the unconsolidated rock deposits. In summer, thermal power of 3.7 and 1.4 MW can be exchanged from two 736 and 284 m-long tunnel sections, respectively. Accordingly, in standard heat pump operating conditions a thermal energy of 10.4 and 3.8 GWh can be delivered for ‘cooling’. In winter, thermal power of 1.9 and 0.7 MW can be exchanged, respectively, and a thermal energy of 5.2 and 1.9 GWh can be delivered for ‘heating’.
SGE within culverts reveals to be favorable in heating mode only and for sections where the motorway tunnel runs perpendicular to the regional groundwater flow field and where ambient groundwater temperatures are high. Under such conditions along a 320 m-long tunnel section thermal power of up to 0.4 MW can be provided in summer and 0.8 MW in winter, respectively, and thermal energy of 1.1 GWh in summer and 2.1 GWh in winter, can be delivered.
... Increased surface temperatures due to artificial, sealed surfaces 60 and underground structures, raise the groundwater temperature beneath cities leading to 61 so-called subsurface urban heat islands (SUHI) [36][37][38][39]. These SUHIs are often quantified by 62 3 A c c e p t e d M a n u s c r i p t measuring the urban heat island intensity, which is defined as the difference between GWT in the urban area and in the rural background. In Germany, Menberg et al. [23] determined 64 average SUHI intensities of about 3 to 7 K, but also detected local hot spots with GWT up 65 to 20 K warmer than the rural background temperature. ...
As groundwater is competitively used for drinking, irrigation, industrial and geothermal applications, the focus on elevated groundwater temperature (GWT) affecting the sustainable use of this resource increases. Hence, in this study GWT anomalies and their heat sources are identified. The anthropogenic heat intensity (AHI), defined as the difference between GWT at the well location and the median of surrounding rural background GWTs, is evaluated in over 10 000 wells in ten European countries. Wells within the upper three percentiles of the AHI are investigated for each of the three major land cover classes (natural, agricultural and artificial). Extreme GWTs ranging between 25 °C and 47 °C are attributed to natural hot springs. In contrast, AHIs from 3 to 10 K for both natural and agricultural surfaces are due to anthropogenic sources such as landfills, wastewater treatment plants or mining. Two-thirds of all anomalies beneath artificial surfaces have an AHI > 6 K and are related to underground car parks, heated basements and district heating systems. In some wells, the GWT exceeds current threshold values for open geothermal systems. Consequently, a holistic management of groundwater, addressing a multitude of different heat sources, is required to balance the conflict between groundwater quality for drinking and groundwater as an energy source or storage media for geothermal systems.
... UUHI and its impact on underground climate, in particular, groundwater flow network and temperature have been studied in varies cities ( Attard et al., 2016a;Menberg et al., 2013;Benz et al., 2015b;Attard et al., 2016b;Taniguchi et al., 2009;Ferguson and Woodbury, 2007;Ferguson and Woodbury, 2004;Epting et al., 2017;). The heat flux into the subsurface as the heat input into shallow urban aquifers is caused by various anthropogenic heat sources. ...
... Accordingly, the investigation of SUHIs enables a determination of the initial period of urbanization in a certain region [30,31]. In addition to building basements, groundwater flow, surface cover, and man-made climate change influence groundwater temperatures [32][33][34][35][36]. Moreover, anthropogenic heat sources like subsurface infrastructure, power plants, landfills, or geothermal installations can have an impact on the spatial distribution of subsurface temperatures [14]. ...
Subsurface temperature data is usually only accessible as point information with a very limited number of observations. To spatialize these isolated insights underground, we usually rely on interpolation methods. Unfortunately, these conventional tools are in many cases not suitable to be applied to areas with high local variability, like densely populated areas, and in addition are very vulnerable to uneven distributions of wells. Since thermal conditions of the surface and shallow subsurface are coupled, we can utilize this relationship to estimate shallow groundwater temperatures from satellite-derived land surface temperatures. Here, we propose an estimation approach that provides spatial groundwater temperature data and can be applied to natural, urban, and mixed environments. To achieve this, we combine land surface temperatures with anthropogenic and natural processes, such as downward heat transfer from buildings, insulation through snow coverage, and latent heat flux in the form of evapotranspiration. This is demonstrated for the city of Paris, where measurements from as early as 1977 reveal the existence of a substantial subsurface urban heat island (SUHI) with a maximum groundwater temperature anomaly of around 7 K. It is demonstrated that groundwater temperatures in Paris can be well predicted with a root mean squared error of below 1 K by means of satellite-derived land surface images. This combined approach is shown to improve existing estimation procedures that are focused either on rural or on urban conditions. While they do not detect local hotspots caused by small-scaled heat sources located underground (e.g., sewage systems and tunnels), the findings for the city of Paris for the estimation of large-scale thermal anomalies in the subsurface are promising. Thus, the new estimation procedure may also be suitable for other cities to obtain a more reliable insight into the spatial distribution of urban ground and groundwater temperatures.
... Further, the leakage model may be coupled to a heat transport model [e.g. Hein et al., 2016] to investigate the contribution of pipe leakage to warming of urban GW (which is known to be significant [Benz et al., 2015]). Warming of urban GW is related to economic and ecological advantages for the use of shallow geothermal systems [Allen et al., 2003]. ...
Pipe leakage related to defect urban sewer and stormwater pipe networks may lead to
subsurface contamination, reduction of groundwater recharge or a significant decrease of
the groundwater table. The quantification of pipe leakage is challenging, mostly due to the
uncertain forming of a colmation layer in the defect vicinity and inaccessibility of both,
pipe defects and the surrounding soil. Numerical models can be used to quantify leakage.
At present times, only few physically-based pipe leakage models exist, all of which either
neglect or simplify variably-saturated flow.
In the present dissertation, a novel and unique three-dimensional physically-based pipe
leakage model for variably saturated soil is presented. The model consists of the newly
implemented coupling between the pipe flow simulator HYSTEM-EXTRAN and the
unsaturated-saturated flow simulator OpenGeoSys. The coupling is based on updating
of boundary conditions and source terms. The interprocess data transfer is realized using
a shared-memory. The pipe leakage model is successfully validated and verified using a
newly generated benchmark library for pipe leakage models. Benchmarks are based on two physical experiments described in literature and two newly derived analytical solutions.
A novel method for upscaling pipe leakage is presented. The method enables to significantly reduce the local refinement of spatial discretization in the pipe vicinity, which
leads to a substantial reduction of computational costs. The method is based on leakage
functions. Two leakage functions representing both, sewer and stormwater pipe leakage
are presented. Accuracy and time efficiency of the upscaling method is demonstrated by
comparing results from a fully discretized model and an upscaled model.
In the present dissertation, the pipe leakage model is applied to several case studies to
investigate the pipe leakage process. Model setups represent (i) a single defect, (ii) a leaky sewer pipe of 30 m length, and (iii) a 53 km long defect stormwater pipe network in an urban catchment.
Results of the single defect and leaky sewer pipe model (models i,ii) show that leaky pipes can hydraulically disconnect from groundwater. It is found that, for a given pipe water level, pipe water exfiltration converges as the groundwater table is lowered. Further, it is found that pipe water exfiltration increases as the intensity and duration of pipe flow events increase. The temporal distribution of pipe flow has a negligible effect on pipe
water exfiltration.
Results of the model representing a defect stormwater pipe network in an urban catchment (model iii) show the impact of pipe leakage on urban groundwater. It is shown that groundwater infiltration into a largely defect pipe network may be in the order of annual groundwater recharge. Further, it is shown that groundwater infiltration may reduce the groundwater table by several meters and that the groundwater table may be lowered to the elevation of the pipe network.
... Also, higher ground and groundwater temperatures positively affect the heat extraction rate. The studies by Benz et al. (2015), Zhu et al. (2015) and Menberg et al. (2013) show that groundwater temperatures beneath cities are up to 7 K higher compared to rural areas. Due to this so-called subsurface heat island effect, the exploitation rate can be raised from 13 to 33% (Rivera et al. 2017). ...
Thermal energy for space heating and for domestic hot water use represents about a third of the overall energy demand in Germany. An alternative to non-renewable energy-based heat supply is the implementation of closed and open shallow geothermal systems, such as horizontal ground source heat pump systems, vertical ground source heat pump (vGSHP) systems and groundwater heat pump systems. Based on existing regulations and local hydrogeological conditions, the optimal site-specific system for heat supply has to be identified. In the presented technical feasibility study, various analytical solutions are tested for an urban quarter before and after building refurbishment. Geothermal heat supply rates are evaluated by providing information on the optimal system and the specific shortcomings. Our results show that standard vGSHP systems are even applicable in older and non-refurbished residential areas with a high heat demand using a borehole heat exchanger with a length of 100 m or in conjunction with multiple boreholes. After refurbishment, all studied shallow geothermal systems are able to cover the lowered heat demand. The presented analysis also demonstrates that ideally, various technological variants of geothermal systems should be evaluated for finding the optimal solution for existing, refurbished and newly developed residential areas.
... In the city of Turin's aquifer temperatures are 0.6 ÷1.6 °C higher than in rural sectors. This groundwater warming is linked to the urban heat island effect, which is mainly driven by the typical artificial land use (i.e., Benz et al., 2015). Sparse warmer outliers (16-20 °C) are in some cases connected to documented point heat sources, such as GSHP systems, industrial districts and landfills. ...
This work is a multidisciplinary synthesis of geological and hydrogeological researches on the subsoil of Turin and suburbs, summarizing the existing previous studies and also using new data specially collected, aimed at bringing together the different aspects of the subsoil in a single contribution. The stratigraphic setting of the Turin Plain, as examined through numerous boreholes (wells, piezometers and geognostic drillings) shows an erosional surface essentially shaped on the fine Villafranchian succession and locally on the Pliocene and pre-Pliocene sediments, on which the Quaternary gravelly outwash and fluvial cover rests. This cover, which is mainly fed by the Dora Riparia River, is relatively thin (thickness between 5 and 57 m) and highly variable in terms of facies and cementation degreee. The most recent excavation activities are also taken into consideration, which locally allowed the direct observation of the shallow subsoil stratigraphy. The geological literature reports that the setting of Turin subsoil is strictly conditioned by the Quaternary uplift of Turin Hill. The structural causes of this geological evolution and its relationship with seismicity are here summarized. The stratigraphy of Turin subsoil is also connected to the recent deviation of the Po River, which flowed south of Turin Hill (through the southern slope of Turin Hill and the Poirino Plateau) during the Middle-Upper Pleistocene and only recently develops at the NW foot of Turin Hill. A new reading of this Po deviation as an overflow is made, based both on a re-examination of all the existing data and new collected data. The hydrogeological features of the Turin subsoil are also reported, characterized by two superimposed main groundwater flow circuits, as well as the thermal regime of shallow groundwater and its geothermal potential. This work can help professional geologists for conducting geological, hydrogeological and geotechnical appraisals on Turin and suburbs. It can also be useful to researchers to reconstruct the geological and hydrogeological features of the Turin territory.
... Geothermal heat can be regarded as a strategic urban resource (Lund et al. 2011; Herbert et al. 2013); since underground structures can significantly affect groundwater temperatures(Epting et al. 2013), this impact of urbanisation can be important. According toBenz et al. 2015, buildings reaching into or close to the groundwater generate a major part of the total anthropogenic heat flux received by groundwater. ...
... Although shallow ground is considered as a large energy reservoir, geothermal energy availability in urban areas is limited and overexploitation of the ground is becoming a major concern for authorities [18][19][20]. The increase in the number of GWHP systems and the increase of thermal interferences between these systems enforces the need for new criteria to develop subsurface energy policies that allow to plan their spatial distribution and to limit their operation regimes. ...
The steady increase of geothermal systems using groundwater is compromising the renewability of the geothermal resources in shallow urban aquifers. To ensure sustainability, scientifically-based criteria are required to prevent potential thermal interferences between geothermal systems. In this work, a management indicator
(balanced sustainability index, BSI) applicable to groundwater heat pump systems is defined to assign a quantitative value of sustainability to each system, based on their intrinsic potential to produce thermal interference. The BSI indicator relies on the net heat balance transferred to the terrain throughout the year and the maximum seasonal thermal load associated. To define this indicator, 75 heating-cooling scenarios based in 23 real systems were established to cover all possible different operational conditions. The scenarios were simulated in a standard numerical model, adopted as a reference framework, and thermal impacts were evaluated. Two polynomial regression models were used for the interpolation of thermal impacts, thus allowing the direct calculation of the sustainability indicator developed as a function of heating-cooling ratios and maximum seasonal thermal loads. The BSI indicator could provide authorities and technicians with scientifically-based criteria to establish geothermal monitoring programs, which are critical to maintain the implementation rates and renewability of these systems in the cities.
... Suitable geological conditions, i.e. relatively high hydraulic conductivity are necessary to provide adequate groundwater flow. Urbanisation has significantly elevated groundwater temperatures under cities (Benz, et al. 2015;Memberg, et al. 2013), also in Finland . ...
... This is not simply a consequence of urban heat islands in the atmosphere that are thermally coupled with the ground (Kataoka et al. 2009) (Fig. 1a). Recently, attention to the so-called subsurface urban heat islands (Ferguson and Woodbury 2007) has been growing, especially because in cold and moderate climates such as those found in central Europe, large scale thermal anomalies are found beneath cities (Menberg et al. 2013;Benz et al. 2015;Bayer et al. 2016;Mueller et al. 2018). Compared with their counterpart in the atmosphere, much more pronounced permanent thermal anomalies are measured, and thus subsurface urban heat islands have a substantial geothermal potential (Zhu et al. 2010;Radioti et al. 2017;Rivera et al. 2017). ...
Environmental indices and landscape pattern changes alter Land Surface Temperature (LST). Thus, the accurate evaluation of the relationship between these factors and LST is considered as important for managing ecosystems, especially the fragile ones under high stress. In the present study, Landsat TM5 satellite images (1989), Landsat 8 OLI/TIRS ones (2019), and Google Earth Engine (GEE) system were used to prepare the maps of temporal-spatial LST changes, Land Use/Land Cover (LULC), and selected environmental indices including Normalized Difference Vegetation (NDVI), Built-up (NDBI), Water Indices (NDWI), Land Surface Moisture (LSM) and albedo. Then, their correlation with LST was assessed. The results represented an 8.67-degree increase in the mean LST during 1989–2019. Urban and built-up areas had a significant effect on increasing the temperature of the region. Additionally, water bodies and vegetation cover in the region were the most crucial parameters in LST reduction. All of the applied indices were strongly related to LST (> 0.70), while some exhibited more correlation in each year. Further, the highest correlation of LST was observed with LSM and NDBI in 1989, as well as with NDVI and NDWI during 2019. Finally, the region rehabilitation based on the sustainable development principles played an important role in the direct and indirect decrease in LST.
The subsurface beneath urban areas worldwide is warming up, leading to so-called subsurface urban heat islands. Despite many investigations, limited knowledge is available on the sources (e.g., localized drivers) of subsurface urban heat islands. This paper presents an unprecedented Internet of Things facility to unravel key features characterizing localized drivers of subsurface urban heath islands: a network composed of >150 wireless temperature sensors deployed in surface and subsurface environments across the Chicago Loop district. Through this facility, the study unravels a subsurface urban heat island in the Loop and indicates marked and highly heterogeneous temperatures for localized drivers of such underground climate change. The temperatures of localized drivers characterizing the monitored subsurface heat island can exceed by >25 °C the ground temperature, involving a continuous heat transfer towards this medium. The temperatures of such drivers can further differ by >15 °C across the studied district, not only when different drivers are examined, but also when different locations within the same driver are considered. The identified features of localized drivers of subsurface urban heat islands arguably characterize many cities worldwide, requiring adequate modeling approaches and uncertainty quantifications in future simulation studies on such pervasive phenomena.
Shallow groundwater temperatures have been subject to a variety of different research projects and studies on local to global scale. Especially within the last 10 years the studies focused on the effects of anthropogenic factors and climate change on shallow groundwater bodies. However, regionalized groundwater temperature data are scarce, especially in the required appropriate spatial resolution. In any case, the means for adequate calculation taking into account the various influencing factors and boundary conditions have not been established yet.
As a part of the big framework of the renewable energy transition particularly in Tyrol (Tirol 2050 energieautonom), it was decided that a comprehensive overview on the groundwater temperatures in Tyrol should be compiled in order to achieve a better understanding of the regional distribution of groundwater temperatures and local anomalies. This is considered to be especially relevant as the use of heat pump systems that use groundwater as a heat source play an important role for the future of innovative central heating systems. For such systems, the groundwater temperature is often a limiting factor, as Austrian guidelines like the ÖWAV-Regelblatt 207 constitute that the groundwater should not be cooled below 5 °C before being reinjected into the aquifer. As a consequence, such heat pump systems are not suited for areas where the groundwater temperature is not high enough during the heating period. If this is not investigated and evaluated regularly before the construction of a heat pump system, it can lead to massive performance problems and a subsequent shutdown of the heating system.
Thus, understanding the lateral and vertical distribution of the groundwater temperatures as well as the various influencing factors like air temperature and elevation, stream water temperature, measurement depth, groundwater level, river bank infiltration, anthropogenic factors and climate change is crucial for the estimation of the dynamics of groundwater temperatures and its possible use.
To this aim, the continuous groundwater temperature time series of more than 200 measurement sites distributed across various groundwater bodies in Tyrol were compiled, analysed and interpreted regarding the mean groundwater temperature and other statistical parameters as well as the above-mentioned influencing factors. Additionally, complementary data of single or regular measurements were used.
As a result, the 37 groundwater bodies of Tyrol were described with respect to the available groundwater temperature data, depth to groundwater table, seasonal temperature variations, possible influence of river bank infiltration and snow melt, ultimately leading to a classification highlighting the groundwater body's aptitude for heat pump systems and the limiting factors.
The study showed that in most bigger groundwater bodies in Tyrol the installation of groundwater heat pump systems is basically possible, although there are several site-related factors like proximity to surface waters and shallow withdrawal depth that can impair such applications.
Above altitudes of approximately 1.200 metres a.s.l., the groundwater temperatures are rather too low for efficient use, although there are exceptions as well. Furthermore, the study highlighted the large heterogeneity of groundwater temperatures even within a single, smaller groundwater body as well as the need for site-specific investigations. Even though the elevation-based regression line developed in this study mainly shows satisfactory results, the need for a better understanding and a more sophisticated calculation tool factoring in the main influencing parameters like measurement depth, river bed infiltration, urban heat islands and geothermal gradients has to be highlighted.
The main focus of the work was the compilation and evaluation of the groundwater temperature time series data currently monitored in Tyrol, Austria, in more than 200 groundwater probes. The analysis focused on finding characteristics that help to predict the mean groundwater temperature in Alpine regions for any given altitude and to understand the factors influencing the amplitude and phase of seasonal groundwater temperature variations.
The first statement that should be highlighted is the fact that shallow geothermal technology does not pose a generalized risk to the environment. Only specific situations must be considered, related to specific hydrogeological settings and the construction of geothermal heat exchangers (open and closed) to maintain pristine conditions of aquifers and underground environments. The following subsections discuss the potential impacts related to negligent use and/or use by untrained personnel of this renewable technology.
In order to understand the possibilities and advantages of using shallow geothermal energy, it is necessary to understand the origin and magnitude of heat transfer processes in the subsurface. This chapter provides an overview of the spatial and temporal temperature distribution in the underground, i.e., its thermal regime. The most important sources and sinks of heat in nature for the shallow subsurface domain are the sun, the atmosphere and the earth’s core. In the following subsections of this chapter, the energy balance in the atmosphere-earth system and the concept of the terrestrial geothermal gradient will be described, as well as other boundary conditions, in order to subsequently study the temperature profile in the subsurface.
Zusammenfassung
Ziel dieser Studie ist die Bestimmung der hydraulischen Durchlässigkeiten eines Sandsteins unter Berücksichtigung der Gesteinsmatrix sowie einer Einzelkluft unter Verwendung eines tragbaren Luftpermeameters. Hierfür wurde der fluviatil-äolisch abgelagerte Bebertaler Sandstein des Oberen Rotliegenden in Sachsen-Anhalt untersucht. Es wurden die Matrixpermeabilitäten der unterschiedlichen Faziesbereiche sowie die Kluftöffnungsweiten entlang einer Schichtfuge bestimmt. Die ermittelten hydraulischen Durchlässigkeiten der Sandsteinmatrix liegen dabei zwischen 1,0 · 10⁻⁷ und 9,2 · 10⁻¹⁰ m/s, allerdings weisen nur 3 von insgesamt 298 Messpunkten einen kf-Wert von > 7,4 · 10⁻⁸ m/s bzw. eine Permeabilität von > 10 mD auf. Diese gehören zur homogenen und höher durchlässigen äolischen Fazies. Die bestimmte mittlere Öffnungsweite der Schichtfuge liegt bei 82 ± 12 µm. Mithilfe der ermittelten hydraulischen Eigenschaften konnte somit die effektive hydraulische Durchlässigkeit des untersuchten Sandsteins bestimmt werden. Unsere Ergebnisse verdeutlichen die praktische und robuste Anwendbarkeit des verwendeten Luftpermeameters zur Bestimmung der hydraulischen Durchlässigkeiten von Sandsteinen sowohl im Labor als auch im Gelände.
Anthropogenic infrastructures in the shallow subsurface, such as heated basements, tunnels or shallow geothermal systems, are known to increase ground temperatures, particularly in urban areas. Numerical modelling helps inform on the extent of thermal influence of such structures, and its potential uses. Realistic modelling of the subsurface is often computationally costly and requires large amounts of data which is often not readily available, necessitating the use of modelling simplifications. This work presents a case-study on the city centre of Cardiff, UK, for which high resolution data is available, and compares modelling results when three key modelling components (namely ground elevation, hydraulic gradient distribution and basement geometry) are implemented either ‘realistically’, i.e. with high resolution data, or ‘simplified’, utilising commonly accepted modelling assumptions. Results are presented at a point (local) scale and at a domain (aggregate) scale to investigate the impacts such simplifications have on model outputs for different purposes. Comparison to measured data at individual locations shows that the accuracy of temperature outputs from numerical models is largely insensitive to simplification of the hydraulic gradient distribution implemented, while changes in basement geometry affect accuracy of the mean temperature predicted at a point by as much as 3.5 °C. At the domain scale, ground temperatures within the first 20 m show a notable increase (approximately 1 °C volume-averaged and 0.5 °C surface-averaged), while the average heat flux over the domain is about 0.06 W/m² at 20 m depth. These increased temperatures result in beneficial conditions for shallow geothermal utilisation, producing drilling cost savings of around £1700 per typical household system or about 9% increase in thermal energy potential. Simplifications of basement geometry and (to a lesser degree) the hydraulics can result in an overestimation of these temperatures and therefore over-predict geothermal potential, while the elevation simplification showed little impact.
Urbanization and limited land availability have resulted in the increased utilization of underground structures including residential basements in largely populated cities such as London, with an average addition of 200 basements per year in some boroughs. Residential basements kept at a comfortable temperature level throughout the year significantly contribute to heat fluxes in the subsurface as well as an increase in ground temperature. Understanding the ground thermal status is crucial in managing the significant geothermal energy potential in urban areas as well as the sustainable development of the urban underground, and in maintaining the energy efficiency of underground structures. In this proof-of-concept study, a 3D finite element approach accounting for coupled heat transfer and groundwater flow in the ground was used to investigate the influence of ground conditions on the heat rejection rate from basements. A detailed analysis was made of ground, above ground and underground built environment characteristics. This study demonstrates that the amount of heat from basements rejected to the ground constitutes a significant percentage of the total heat loss from buildings, particularly in the presence of groundwater flow. The extent of thermal disturbance in the ground varies depending on the ground characteristics. The volume of thermally disturbance ground inversely correlates with the groundwater flow rate in ground mainly consisting of highly permeable material. However, a direct correlation exists when the thickness of permeable soil layer decreases. A larger horizontal to vertical ratio of ground thermal disturbance is observed when the thickness of permeable soil layer increases.
Repeated measurements of subsurface temperature-depth profiles have been conducted eight times between May 2000 and December 2015 at the Kawaguchi groundwater observation wells in southeastern Saitama Prefecture, Japan to evaluate distribution and causes of subsurface warming in an urban area. Additionally, monitoring has been conducted since April 2007 to observe long-term changes in subsurface temperature. Subsurface warming was observed at depths shallower than 40m. Subsurface warming decreased with depth, and at depths of 20m, 30m and 40m had rates of 3.4×10⁻²oC/year, 2.30×10⁻²oC/year and 1.93×10⁻²oC/year, respectively. Results of comparison between calculated temperatures and observed temperatures indicate that surface warming estimated by secular changes in air temperature, starting in 1983, has led to subsurface warming that has been observed after 2003.
Background: EU member states have concluded an agreement that renewable energy will cover 20% of the total energy production by 2020. To achieve this target, it is essential to investigate all possibilities for renewable energy production. We investigated whether groundwater could provide a shallow geothermal energy resource, and to what extent it could meet the demands for heating buildings in Finland. Our research focused on classified aquifers, namely, groundwater areas that are zoned for urban or industrial use. Methods: The heating potential of Finnish aquifers was estimated based on the flux, temperature and heat capacity of groundwater and the efficiency of heat pumps. The design power of residential buildings was then simulated. Finally, the design power was divided by the groundwater power to determine the ability of groundwater to heat buildings. Results: Approximately 56,500 ha of Finnish aquifers are zoned for urban or industrial land use. These aquifers contain 40 to 45 MW of power. In total, 55 to 60 MW of the heat load could be utilised with heat pumps, meaning that 25% to 40% of annually constructed residential buildings could be heated utilising groundwater in Finland. Conclusions: There are several hundred sites in Finland where groundwater could be used for energy utilisation, and groundwater could thus be a significant source of local renewable energy. However, because of geological and geographical factors, groundwater cannot be considered as a nationwide energy source. Future research should define the area-specific limiting factors for groundwater energy use.
Groundwater temperature measurements in a shallow coastal aquifer in Virginia Beach, Virginia, USA, suggest groundwater warming of +4.1 °C relative to deeper geothermal gradients. Observed warming is related to timing and depth of influence of two potential thermal drivers—atmospheric temperature increases and urbanization. Results indicate that up to 30 % of groundwater warming at the water table can be attributed to atmospheric warming while up to 70 % of warming can be attributed to urbanization. Groundwater temperature readings to 30-m depth correlate positively with percentage of impervious cover and negatively with percentage of tree canopy cover; thus, these two land-use metrics explain up to 70 % of warming at the water table. Analytical and numerical modeling results indicate that an average vertical groundwater temperature profile for the study area, constructed from repeat measurement at 11 locations over 15 months, is consistent with the timing of land-use change over the past century in Virginia Beach. The magnitude of human-induced warming at the water table (+4.1 °C) is twice the current seasonal temperature variation, indicating the potential for ecological impacts on wetlands and estuaries receiving groundwater discharge from shallow aquifers.
Soil temperature (t(B)) was determined down to 2 m below ground level at 8 locations in the city of Oberhausen, Ruhr area, Germany, between August 2010 and July 2011 to investigate the subsurface urban heat island (SUHI) and its impact on drinking water quality. The soil temperatures obtained in Oberhausen demonstrate typical location-dependent behaviour. At the depth of drinking water pipes (1 to 2 m subsurface), the daily average soil temperature ranges from 3 degrees C in the winter (at the coldest location) to 24 degrees C in the summer (at the warmest location). A maximum SUHI (70 cm below ground level) of almost 9 K on hourly average was found between the city centre station and the open country station. Soil temperatures were measured to be >20 degrees C at the drinking water pipeline level in the city centre over the course of 89 d, which could have an impact on drinking water quality.
The use of renewable energy can be enhanced by utilising groundwater reservoirs for heating and cooling purposes. The urbanisation effect on the peak heating and peak cooling capacity of groundwater in a cold groundwater region was investigated. Groundwater temperatures were measured and energy potentials calculated from three partly urbanised aquifers situated between the latitudes of 60° 25′N and 60° 59′N in Finland. The average groundwater temperature below the zone of seasonal temperature fluctuations was 3–4 °C higher in the city centres than in the rural areas. The study demonstrated that due to warmer groundwater, approximately 50–60 % more peak heating power could be utilized from populated areas compared with rural areas. In contrast, approximately 40–50 % less peak cooling power could be utilised. Urbanisation significantly increases the possibility of utilising local heat energy from groundwater within a wider region of naturally cold groundwater. Despite the warming in urban areas, groundwater still remains attractive as a source of cooling energy. More research is needed in order to determine the long-term energy capacity of groundwater, i.e. the design power, in urbanised areas of cold regions.
The thermal regime of the shallow subsurface is mainly governed by the heat flow from the Earth’s interior and the temperature at the surface. Thermal signals from temperature vari-ations at the surface penetrate through the unsaturated zone mainly by heat conduction and can perturb the temperature distribution in the deeper subsurface. Thus, shallow subsurface temperatures are prone to be influenced by various processes, which alter the ground surface temperature. In particular, the thermal environment under urban areas is profoundly changed by anthropogenic activities and under several cities an increase in groundwater temperatures is observed. However, little is known about the spatial extension and intensity of these ther-mal anomalies in the urban subsurface, and the individual influencing factors and driving forces are not yet comprehensively understood. Moreover, also in rural areas atmospheric temperatures exhibit an increasing trend due to climatic changes. Yet, the direct implications of increasing air temperatures, and consequently ground surface temperatures, for the long-term temperature development in shallow aquifers are still unclear.
The first part of this study deals with the thermal conductivity of unconsolidated sedi-mentary rocks as an important parameter for conductive heat transport. Different methods for the determination of the thermal conductivity are applied on samples obtained from a bore-hole or on a pilot borehole heat exchanger, which is installed in the borehole. Thermal con-ductivity is measured on core samples in the laboratory and a Thermal Response Test is car-ried out to determine a corresponding value in the field. Furthermore, the thermal conductivity is calculated with different theoretical models under consideration of several ground parame-ters that are determined by laboratory tests. The best agreement between measured and calcu-lated thermal conductivity values is obtained using the geometric mean model. The accuracy of the thermal conductivity calculation is lower than the accuracy of the laboratory and field measurements, but it nevertheless represents a more accurate method than, for instance, pa-rameter estimation based on published values.
Furthermore, a detailed spatial analysis of groundwater temperatures under several German cities is conducted. It reveals that extensive positive thermal anomalies exist under each of the studied cities, with the highest temperatures usually occurring under the densely urbanized city centers. Yet, often many local hot spots are found, which result in a very heter-
Abstract
ii
ogeneous temperature distribution. A comparison with the magnitude of atmospheric urban warming shows that the groundwater warming is more pronounced, which reflects the long-term accumulation of heat in the subsurface. The spatial correlation of the subsurface thermal anomalies with the atmospheric urban heat island and the population density indicates that increased ground surface temperatures and heat loss from subsurface infrastructure, such as basements of buildings, may act as dominant heat sources.
Based on the identified heat sources an analytical heat flux model is developed in order to quantify the individual heat flux processes, such as increased ground surface temperatures and heat loss from basements and other subsurface structures. By modeling the heat fluxes into the subsurface of the city of Karlsruhe for the years 1977 and 2011, the long-term trend of the heat flux processes can be assessed. The highest heat flux densities in both years occur from the increased ground surface temperatures and the basements. Although the magnitude of the individual heat flux densities changed significantly over the last decades. However, the total annual heat input into the shallow urban aquifer originating from the considered heat sources accounts up to around 1.5 × 1015 J in 1977 and 2011.
Finally, the coupling of air and groundwater temperature development is evaluated by statistically analyzing time-series of several decades with special regard to abrupt shifts in the long-term mean temperature. The observed positive shifts in the aquifer temperature are linked to preceding abrupt increases in regional air temperatures, which can be in turn associ-ated with changes in the global mean air temperature. The increase in groundwater tempera-tures is generally found to be more gradual than atmospheric warming, as the thermal signals from the surface are attenuated and delayed by conductive and advective heat transport in the subsurface. However, it is revealed that these signals can have a pronounced impact on the development of groundwater temperatures in economically important aquifers.
Thus, it is shown that anthropogenic alterations at and beneath the ground surface as well as increasing air temperatures can significantly and permanently elevate groundwater temperatures in shallow aquifers. These temperatures changes may have a negative impact on groundwater quality and thus implications for drinking water supply. On the other hand, the extensive heat anomalies in the urban groundwater contain a vast amount of stored thermal energy that is continuously recharged from above. Therefore, the understanding of the thermal processes in the urban subsurface provides a useful basis for a sustainable management of this attractive geothermal reservoir.
High-resolution numerical simulations of the urban heat island effect with the widely-used Weather Research and Forecasting (WRF) model are assessed. Both the sensitivity of the results to the simulation setup, and the quality of the simulated fields as representations of the real world, are investigated. Results indicate that the WRF-simulated surface temperatures are more sensitive to the planetary boundary layer (PBL) scheme choice during nighttime, and more sensitive to the surface thermal roughness length parameterization during daytime. The urban surface temperatures simulated by WRF are also highly sensitive to the Urban Canopy Model (UCM) used. The implementation in this study of an improved UCM (the Princeton UCM or PUCM) that allows the simulation of heterogeneous urban facets and of key hydrological processes, together with the so-called CZ09 parameterization for the thermal roughness length, significantly reduce the bias (< 1.5 ºC) in the surface temperature fields as compared to satellite observations during daytime. The boundary layer potential temperature profiles are captured by WRF reasonable well at both urban and rural sites; the biases in these profiles relative to aircraft-mounted senor measurements are on the order of 1.5 ºC. Changing UCMs and PBL schemes does not alter the performance of WRF in reproducing bulk boundary layer temperature profiles significantly. The results illustrate the wide range of urban environmental conditions that various configurations of WRF can produce, and the significant biases that should be assessed before inferences are made based on WRF outputs. The optimal set-up of WRF-PUCM developed in this paper also paves the way for a confident exploration of the city-scale impacts of urban heat island mitigation strategies in the companion paper (Li et al., 2014).
Long-term heating of shallow urban aquifers is observed worldwide. Our measurements in the city of Cologne, Germany, revealed that the groundwater temperatures measured in the city center are more than 5 K higher than the undisturbed background. To explore the role of groundwater flow for the development of subsurface urban heat islands (UHIs), a numerical flow and heat transport model is set up, which describes the hydraulic conditions of Cologne and simulates the transient evolution of thermal anomalies in the urban ground. A main focus is on the influence of horizontal groundwater flow, groundwater recharge and trends in local ground warming. In order to examine heat transport in groundwater, a scenario consisting of a local hot spot with a length of 1 km of long-term ground heating was set up in the center of the city. Groundwater temperature-depth (GWTD) profiles at upstream, central and downstream locations of this hot spot are inspected. The simulation results indicate that the main thermal transport mechanisms are long-term vertical conductive heat input, horizontal advection and transverse dispersion. Groundwater recharge rates in the city are low (< 100 mm a-1) and thus do not significantly contribute to heat transport into the urban aquifer. With groundwater flow, local vertical temperature profiles become very complex and are hard to interpret, if local flow conditions and heat sources are not thoroughly known. This article is protected by copyright. All rights reserved.
This study presents the development of tools for the sustainable thermal
management of a shallow unconsolidated urban groundwater body in the
city of Basel (Switzerland). The concept of the investigations is based
on (1) a characterization of the present thermal state of the urban
groundwater body, and (2) the evaluation of potential mitigation
measures for the future thermal management of specific regions within
the groundwater body. The investigations focus on thermal
processes down-gradient of thermal groundwater use, effects of heated
buildings in the subsurface as well as the thermal influence of
river-groundwater interaction. Investigation methods include (1) short-
and long-term data analysis, (2) high-resolution multilevel groundwater
temperature monitoring, as well as (3) 3-D numerical groundwater flow
and heat transport modeling and scenario development. The combination of
these methods allows for the quantifying of the thermal influences on
the investigated urban groundwater body, including the influences of
thermal groundwater use and heated subsurface constructions.
Subsequently, first implications for management strategies are
discussed, including minimizing further groundwater temperature
increase, targeting "potential natural" groundwater temperatures for
specific aquifer regions and exploiting the thermal potential.
For the planning and design of borehole heat exchangers systems, the
knowledge of the thermophysical ground parameters is essential. In this
study, several methods for the determination of thermal conductivity
were used on a borehole for a ground source heat pump system. Thermal
conductivity was measured on core samples using laboratory tests and
likewise a Thermal Response Test (TRT) was carried out. In addition,
several ground parameters, such as water content and carbonate content,
were determined by laboratory tests. With these parameters the thermal
conductivity was then calculated using different theoretical models. The
best agreement between measured and calculated values for thermal
conductivities was obtained using the geometric mean. The mean error of
these calculations in this study is about 12 %. Thus, the accuracy of
the calculation of thermal conductivity is lower than the accuracy of
the laboratory tests or TRTs, but it nevertheless represents a simple
and more accurate method than parameter estimations based on published
values.
The paper reports on detection and quantification of the impact of local anthropogenic structures and regional climatic changes on subsurface temperature field. The analyzed temperature records were obtained by temperature monitoring in a borehole in Prague-Spořilov (Czechia) and by repeated logging of a borehole in Šempeter (Slovenia). The observed data were compared with temperatures yielded by mathematical 3D time-variable geothermal models of the boreholes’ sites with the aim to decompose the observed transient component of the subsurface temperature into the part affected by construction of new buildings and other anthropogenic structures in surroundings of the boreholes and into the part affected by the ground surface temperature warming due to the surface air temperature rise. A direct human impact on the subsurface temperature warming was proved and contributions of individual anthropogenic structures to this change were evaluated. In the case of Spořilov, where the mean annual warming rate reached 0.034°C per year at the depth of 38.3 m during the period 1993–2008, it turned out that about half of the observed warming can be attributed to the air (ground) surface temperature change and half to the human activity on the surface in the immediate vicinity of the borehole. The situation is similar in Šempeter, where the effect of the recently built surface anthropogenic structures is detectable down to the depth of 80 m and the share of the anthropogenic signal on the non-stationary component of the observed subsurface temperature amounts to 30% at the depth of 50 m.
The paper demonstrates the relationship existing between the size of a village, town or city (as measured by its population), and the magnitude of the urban heat island it produces. This is accomplished by analyzing data gathered by automobile traverses in 10 settlements on the St. Lawrence Lowland, whose populations range from 1000 to 2 million inhabitants. The locations of these settlements effectively eliminate all non-urban climatic influences. The results are compared with previously published data.The analysis shows the heat island intensity under cloudless skies to be related to the inverse of the regional windspeed, and the logarithm of the population. A simple model is derived which incorporates these controls. In agreement with an extension of Summers' model the heat island appears to be approximately proportional to the fourth root of the population. With calm and clear conditions the relation is shown to hold remarkably well for North American settlements, and in a slightly modified form, for European towns and cities.
This study quantifies the contribution through energy consumption, to the heat island phenomena and discussed how reductions in energy consumption could mitigate impacts on the urban thermal environment. Very detailed maps of anthropogenic heat in Tokyo were drawn with data from energy statistics and a very detailed digital geographic land use data set including the number of stories of building at each grid point. Animated computer graphics of the annual and diurnal variability in Tokyo's anthropogenic heat were also prepared with the same data sources. These outputs characterize scenarios of anthropogenic heat emission and can be applied to a numerical simulation model of the local climate. The anthropogenic heat flux in central Tokyo exceeded 400Wm−2 in daytime, and the maximum value was 1590Wm−2 in winter. The hot water supply in offices and hotels contributed 51% of this 1590Wm−2. The anthropogenic heat flux from the household sector in the suburbs reached about 30Wm−2 at night. Numerical simulations of urban climate in Tokyo were performed by referring to these maps. A heat island appeared evident in winter because of weakness of the sea breeze from Tokyo Bay. At 8 p.m., several peaks of high-temperature appeared, around Otemachi, Shinjuku and Ikebukuro; the areas with the largest anthropogenic heat fluxes. In summer the shortwave radiation was strong and the influence of anthropogenic heat was relatively small. In winter, on the other hand, the shortwave radiation was weak and the influence of anthropogenic heat was relatively large. The effects of reducing energy consumption, by 50% for hot water supply and 100% for space cooling, on near surface air temperature would be at most −0.5°C.
The urban heat island effect has received significant attention in recent years due to the possible effect on long-term meteorological records. Recent studies of this phenomenon have suggested that this may not be important to estimates of regional climate change once data are properly corrected. However, surface air temperatures within urban environments have significant variation, making correction difficult. In the current study, we examine subsurface temperatures in an urban environment and the surrounding rural area to help characterize the nature of this variability. The results of our study indicate that subsurface temperatures are linked to land-use and supports previous work indicating that the urban heat island effect has significant and complex spatial variability. In most situations, the relationship between subsurface and surface processes cannot be easily determined, indicating that previous studies that relying on such a linkage may require further examination.
2 emission abstract In the current study the savings of CO2 emissions due to the use of ground source heat pump (GSHP) systems was investigated in comparison to conventional heating systems. Based on a subsidy program for GSHP systems in southwest Germany, the regional, average, and total CO2 savings of 1105 installed GSHP systems were determined on a regional scale. The emitted CO2 per kWh of heating demand for the studied scenario resulted in 149 g CO2/kWh for GSHP using the German electricity mix and 65 g CO2/kWh using the regional electricity mix, which results in CO2 savings of 35% or 72%, respectively. Similar CO2 avoidances of GSHP systems were found in American and European studies ranging between 15% and 77% strongly depending on the supplied energy for the heat pumps and the efficiency of installation. The resulting CO2 savings for one installed GSHP unit in the present study therefore range between 1800 and 4000 kg per year. Nevertheless, the minimum average total annual CO2 savings of all installed GSHP systems due to the subsidy program amounted to 2000 tons per year. The maximum regional avoided additional CO2 emissions are primarily associated with the affluent suburbs of the most densely popu- lated area in the region. In 2006 the total contribution of CO2 savings due to GSHP systems in Germany was only about 3.4% of the total renewable energies. However, continuously rising numbers of installed GSHP units and the increasing use of renewable electricity demonstrate that there is a fine opportunity to substantially avoid additional CO2 emissions associated with the provision of heating (and cooling) of buildings and other facilities.
Variations in the Earth's surface energy balance are recorded in the subsurface as perturbations of the steady state thermal field. Here we invert 558 temperature-depth profiles in the Northern Hemisphere (NH), in order to estimate the energy balance history at the continental surface from heat flux anomalies in the subsurface. The heat gain is spatially variable and does not appear to have been persistent for the last 200 years at all locations, but overall continental areas have absorbed energy in the last 50 years. Results indicate a mean surface heat flux of 20.6 mWm(-2) over the last 200 years. The total heat absorbed by the ground is 4.8 x 10(21)J and 13.3 x 10(21)J for the last 50 and 200 years respectively. We suggest that our results may be useful for state-of-the-art General Circulation Model (GCM) validation and for land-surface coupling schemes.
In the framework of the global energy balance, the radiative energy exchanges between Sun, Earth and space are now accurately quantified from new satellite missions. Much less is known about the magnitude of the energy flows within the climate system and at the Earth surface, which cannot be directly measured by satellites. In addition to satellite observations, here we make extensive use of the growing number of surface observations to constrain the global energy balance not only from space,but also from the surface. We combine these observations with the latest modeling efforts performed for the 5th IPCC assessment report to infer best estimates for the global mean surface radiative components. Our analyses favor global mean downward surface solar and thermal radiation values near 185 and 342 Wm-2, respectively, which are most compatible with surface observations. Combined with an estimated surface absorbed solar radiation and thermal emission of 161 and 397 Wm-2, respectively, this leaves 106 Wm-2 of surface net radiation available globally for distribution amongst the non-radiative surface energy balance components. The climate models overestimate the downward solar and underestimate the downward thermal radiation, thereby simulating nevertheless an adequate global mean surface net radiation by error compensation. This also suggests that, globally, the simulated surface sensible and latent heat fluxes, around 20 and 85 Wm-2 on average, state realistic values. The findings of this study are compiled into a new global energy balance diagram, which may be able to reconcile currently disputed inconsistenciesbetween energy and water cycle estimates.
The urban heat island effect and climate change have not only caused surface temperature increase in most urban areas, but during the last hundred years also enhanced the subsurface temperature by several degrees. This phenomenon yields aquifers with elevated temperature, which are attractive though underestimated thermal energy reservoirs. Detailed groundwater temperature measurements in Cologne (Germany) and Winnipeg (Canada) reveal high subsurface temperature distributions in the centers of both cities and indicate a warming trend of up to 5 • C. The case-specific potential heat content in urban aquifers and available capacities for space heating are quantified. The results show, for example, that, by decreasing the 20 m thick urban aquifer's temperature by 2 • C, the amount of extractable geothermal energy beneath Cologne is 2.5 times the residential heating demand of the whole city. The geothermal potential in other cities such as Shanghai and Tokyo is shown to supply heating demand even for decades.
During the Basel Urban Boundary Layer Experiment (BUBBLE) conducted in 2002, micrometeorological in-situ data were collected for different sites using a variety of instruments. This provides a unique data set for urban climate studies. Nevertheless, the spatial distribution of energy and heat fluxes can only be taken into account with remote sensing methods or numerical models. Therefore, multiple satellite images from different platforms (NOAA-AVHRR, MODIS and LANDSAT ETM+) were acquired, processed and analysed. In addition, a high resolution digital elevation model (DEM) and a 1 m resolution digital surface model (DSM) of a large part of the city of Basel was utilized. This paper focuses on the calculation and modelling of the ground (or storage) heat flux density using remotely sensed data combined with in-situ measurements using three different approaches. First, an empirical regression function was generated to estimate the storage heat flux from NDVI values second approach used the Objective Hysteresis Model (OHM) which is often used for in-situ measurements. The last method used information of the geometric parameters of urban street canyons, computed from the high resolution digital urban surface model.
Modelled and measured data are found to be in agreement within ±30 Wm−2 and result in a coefficient of determination (R2) of 0.95.
There are numerous approaches to the parameterization of the ground heat flux that use different input data, are valid for
different times of the day, and deliver results of different quality. Six of these approaches are tested in this study: three
approaches calculating the ground heat flux from net radiation, one approach using the turbulent sensible heat flux, one simplified
in situ measurement approach, and the force-restore method. On the basis of a data set recorded during the LITFASS-2003 experiment,
the strengths and weaknesses of the approaches are assessed. The quality of the best approaches (simplified measurement and
force-restore) approximates that of the measured data set. An approach calculating the ground heat flux from net radiation
and the diurnal amplitude of the soil surface temperature also delivers satisfactory daytime results. The remaining approaches
all have such serious drawbacks that they should only be applied with care. Altogether, this study demonstrates that ground
heat flux parameterization has the potential to produce results matching measured ones very well, if all conditions and restrictions
of the respective approaches are taken into account.
The urban heat island (UHI) is a result of urbanization, causing local microclimatologic changes such as increase in ambient temperature. Factors causing the UHI effect are anthropogenic energy release, energy absorption by concrete, tarmac structures and traffic, although the main factor is the replacement of vegetation with man-made structures. These factors cause heating of not only local air but also subsurface and groundwater. Observations of groundwater temperatures from the urban, southern part of Istanbul (Turkey) and the rural, northern part of Istanbul revealed that the urban groundwater temperatures were 3.5°C higher than the rural. Urbanization is a direct consequence of improvements in technology and modern life. However, this comes at the cost of an ever-increasing demand for energy. Exploitation of low-enthalpy geothermal energy is an attractive alternative to fossil fuel based energies. From the environmental point of view, clean and cheap energy is the most preferable, with heat pumps being the best choice for recovery purposes. Usage of elevated groundwater temperature in the heat pumps in urban areas increases the efficiency of the heat pump system and yields more thermal energy than that of rural groundwater. This system may be applicable to Istanbul.
Climatic measurements from almost 30 urban and suburban stations as well as specific measurements performed in 10 urban canyons in Athens, Greece, have been used to assess the impact of the urban climate on the energy consumption of buildings. It is found that for the city of Athens, where the mean heat island intensity exceeds 10°C, the cooling load of urban buildings may be doubled, the peak electricity load for cooling purposes may be tripled especially for higher set point temperatures, while the minimum COP value of air conditioners may be decreased up to 25% because of the higher ambient temperatures. During the winter period, the heating load of centrally located urban buildings is found to be reduced up to 30%. Regarding the potential of natural ventilation techniques when applied to buildings located in urban canyons, it is found that, mainly during the day, this is seriously reduced because of the important decrease of the wind speed inside the canyon. Air flow reduction may be up to 10 times the flow that corresponds to undisturbed ambient wind conditions.
The outflow of heat from the earth's interior, the terrestrial heat flow, and the temperature field at depth are determined by deep-seated tectonic processes. The knowledge of the re gional heat flow pattern is thus very important in geophysics and provides a useful tool for studying crustal and litho spheric structure and understanding the nature of their evo lution. In order to use the results of heat flow measurements for regional studies and/or to correlate the observed surface geothermal activity with other geophysical or geological fea tures, a map showing the surface distribution of heat flow is necessary. Since 1963, when the first comprehensive listing of all available heat flow data appeared (Lee, 1963), several at tempts have been made to up-date the list, to classify all the data and to interpret them with respect to tectonics, deep structure and to use them for constructing surface heat flow maps. The first listing was subsequently revised by Lee and Uyeda (1965); numerous new data which were published there after were included in successive catalogs compiled by Simmons and Horai (1968) and then again by Jessop et al. (1976). The map showing the surface heat flow pattern may also be of great value for practical purposes, in view of the recent world-wide search for applicable sources of geothermal energy.