EAGLE2006 – an intensive field campaign for
the advances in land surface hydrometeorological processes
– was carried out in the Netherlands from 8th to 18th June
2006, involving 16 institutions with in total 67 people from
16 different countries. In addition to the acquisition of multiangle
and multi-sensor satellite data, several airborne instruments
– an optical imaging sensor, an imaging microwave radiometer,
and a flux airplane – were deployed and extensive ground measurements were conducted over one grassland
site at Cabauw and two forest sites at Loobos and Speulderbos
in the central part of the Netherlands. The generated data
set is both unique and urgently needed for the development
and validation of models and inversion algorithms for quantitative
land surface parameter estimation and land surface
hydrometeorological process studies. EAGLE2006 was led
by the Department of Water Resources of the International
Institute for Geo-Information Science and Earth Observation
(ITC) and originated from the combination of a number
of initiatives supported by different funding agencies.
The objectives of the EAGLE2006 campaign were closely related to the objectives of other European Space Agency
(ESA) campaign activities (SPARC2004, SEN2FLEX2005
and especially AGRISAR2006). However, one important objective
of the EAGLE2006 campaign is to build up a data
base for the investigation and validation of the retrieval of
bio-geophysical parameters, obtained at different radar frequencies
(X-, C- and L-Band) and at hyperspectral optical
and thermal bands acquired simultaneously over contrasting
vegetated fields (forest and grassland). As such, all activities
were related to algorithm development for future satellite
missions such as the Sentinels and for validation of retrievals
of land surface parameters with optical and thermal
and microwave sensors onboard current and future satellite
missions. This contribution describes the campaign objectives
and provides an overview of the airborne and field campaign
dataset. This dataset is available for scientific investigations
and can be accessed on the ESA Principal Investigator
Meteorological measurements in the Walnut Gulch catchment in Arizona were used to synthesize a distributed, hourly-average time series of data across a 26.9 by 12.5 km area with a grid resolution of 480 m for a continuous 18-month period which included two seasons of monsoonal rainfall. Coupled surface-atmosphere model runs established the acceptability (for modelling purposes) of assuming uniformity in all meteorological variables other than rainfall. Rainfall was interpolated onto the grid from an array of 82 recording rain gauges. These meteorological data were used as forcing variables for an equivalent array of stand-alone Biosphere-Atmosphere Transfer Scheme (BATS) models to describe the evolution of soil moisture and surface energy fluxes in response to the prevalent, heterogeneous pattern of convective precipitation. The calculated area-average behaviour was compared with that given by a single aggregate BATS simulation forced with area-average meteorological data. Heterogeneous rainfall gives rise to significant but partly compensating differences in the transpiration and the intercepted rainfall components of total evaporation during rain storms. However, the calculated area-average surface energy fluxes given by the two simulations in rain-free conditions with strong heterogeneity in soil moisture were always close to identical, a result which is independent of whether default or site-specific vegetation and soil parameters were used. Because the spatial variability in soil moisture throughout the catchment has the same order of magnitude as the amount of rain failing in a typical convective storm (commonly 10% of the vegetation's root zone saturation) in a semi-arid environment, non-linearitv in the relationship between transpiration and the soil moisture available to the vegetation has limited influence on area-average surface fluxes.
This paper reports on a major UK initiative to address deficiencies in understanding the hydro-ecological response of groundwater-dominated lowland catchments. The scope and objectives of this national programme are introduced and focus on one of three sets of research basins ? the Pang/Lambourn Chalk catchments, tributaries of the river Thames in southern England. The motivation for the research is the need to support integrated management of river systems that have high ecological value and are subject to pressures that include groundwater abstraction for water supply, diffuse pollution, and land use and climate change. An overview of the research programme is provided together with highlights of some current research findings concerning the hydrological functioning of these catchments. Despite the importance of the Chalk as a major UK aquifer, knowledge of the subsurface movement of water and solutes is poor. Solute transport in the dual porosity unsaturated zone depends on fracture/matrix interactions that are difficult to observe; current experimental and modelling research supports the predominance of matrix flow and suggests that slow migration of a time-history of decades of nutrient loading is occurring. Groundwater flows are complex; catchments vary seasonally and are ill-defined and karst features are locally important. Groundwater flow pathways are being investigated using natural and artificial geochemical tracers based on experimental borehole arrays; stream-aquifer interaction research is using a combination of geophysics, borehole array geochemistry and longitudinal profiles of stream flow and solutes. A complex picture of localised subsurface inflows, linked to geological controls and karst features, and significant longitudinal groundwater flow below the river channel is emerging. Management implications are discussed. Strategies to control surface application of nutrients are expected to have little effect on groundwater quality for several decades, and new modelling tools for decision support have been developed to represent these effects. Conventional modelling approaches are limited by the complexities of the subsurface system; catchment areas are difficult to define, hence tracking pollutant pathways to stream receptors is also problematic. Conventional distributed groundwater models have difficulty in capturing key aspects of the groundwater system. This raises important questions concerning the confidence that can be placed in models as routinely used for decision support and the level of knowledge required for catchment management to be placed on a secure scientific foundation.
Much of the native forest in the highlands of western Kenya has been converted to agricultural land in order to feed the growing population, and more land is being cleared. In tropical Africa, this land use change results in progressive soil degradation, as the period of cultivation increases. Both rates and variation in infiltration, soil carbon concentration and other soil parameters are influenced by management within agricultural systems, but they have rarely been well documented in East Africa. We constructed a chronosequence for an area of western Kenya, using two native forest sites and six fields that had been converted to agriculture for up to 119 yr.
We assessed changes in infiltrability (the steady-state infiltration rate), bulk density, proportion of macro- and microaggregates in soil, soil C and N concentrations, as well as the isotopic signature of soil C (δ13C), along the 119-yr chronosequence of conversion from natural forest to agriculture. Infiltration, soil C and N decreased within 40 yr after conversion, while bulk density increased. Median infiltration rates fell to about 15% of the initial values in the forest, and C and N concentrations dropped to around 60%, whilst the bulk density increased by 50%. Despite high spatial variability, these parameters have correlated well with time since conversion and with each other.
In Northern Switzerland, an accumulation of large flood events has occurred since the 1970s, preceded by a prolonged period with few floods (Schmocker-Fackel and Naef, 2010). How have Swiss flood frequencies changed over the past 500 years? And how does the recent increase in flood frequencies compare with other periods in this half millennium? We collected historical flood data for 14 Swiss catchments dating back to 1500 AC. All catchments experienced marked fluctuations in flood frequencies, and we were able to identify four periods of frequent flooding in Northern Switzerland, lasting between 30 and 100 years. The current period of increased flood frequencies has not yet exceeded those observed in the past. We tested whether the flood frequency fluctuation could be explained with generalised climatic indices like solar activity or atmospheric circulation patterns. The first three periods of low flood frequency in Switzerland correspond to periods of low solar activity. However, after 1810 no relationship between solar activity and flood frequency were found. Nor could a relationship be established between reconstructed NAO indices or reconstructed Swiss summer temperatures. We found re-occurring spatial patterns of flood frequencies on a European scale, with the Swiss periods of frequent flooding often in phase with those in the Czech Republic, Italy and Spain and less often with those in Germany. The pattern of flooding in Northern Switzerland and the Czech Republic seem to be rather similar, although the individual flood events do not match. This comparison of flooding patterns in different European countries suggests that changes in large scale atmospheric circulation are responsible for the flood frequency fluctuations.
The hydrologic effects of land use changes, dams, and irrigation in North America and Asia over the past 300 years are studied using a macroscale hydrologic model. The simulation results indicate that the expansion of croplands over the last three centuries has resulted in 2.5 and 6 percent increases in annual runoff volumes for North America and Asia, respectively, and that these increases in runoff to some extent have been compensated by increased evapotranspiration caused by irrigation practices. Averaged over the year and the continental scale, the accumulated anthropogenic impacts on surface water fluxes are hence relatively minor. However, for some regions within the continents human activities have altered hydrologic regimes profoundly. Reservoir operations and irrigation practices in the western part of USA and Mexico have resulted in a 25 percent decrease in runoff in June, and a 9 percent decrease in annual runoff volumes reaching the Pacific Ocean. In the area in South East Asia draining to the Pacific Ocean, land use changes have caused an increase in runoff volumes throughout the year, and the average annual increase in runoff is 12 percent.
This paper compares event-based and continuous hydrological modelling approaches for real-time forecasting of river flows. Both approaches are compared using a lumped hydrologic model (whose structure includes a soil moisture accounting (SMA) store and a routing store) on a data set of 178 French catchments. The main focus of this study was to investigate the actual impact of soil moisture initial conditions on the performance of flood forecasting models and the possible compensations with updating techniques. The rainfall-runoff model assimilation technique we used does not impact the SMA component of the model but only its routing part. Tests were made by running the SMA store continuously or on event basis, everything else being equal. The results show that the continuous approach remains the reference to ensure good forecasting performances. We show,however, that the possibility to assimilate the last observed flow considerably reduces the differences in performance. Last, we present a robust alternative to initialize the SMA store where continuous approaches are impossible because of data availability problems.
The aim of this paper is to analyse interaction between Paris and the Seine during the industrial era, 1790–1970, a period marked by strong population growth, changes in techniques, and the absence of specific legislation on environmental issues. The viewpoint focuses on exchanges of waters and wastes between city and river, quantifying them and tracing evolution in the light of the strategies implemented by the stakeholders in charge. The study combines industrial ecology, local history and the history of technology. From 1790 to 1850, waste matters, and especially excreta, were considered as raw materials, not refuse: they generated real profits. The removal of human excreta aimed not only at improving urban hygiene, but at producing the fertilizers needed in rural areas. Discharging them into the river was out of the question. But after the 1860s, several factors upset this exploitation, notably domestic water supply. Even so, Parisian engineers continued to process sewage using techniques that would not only ensure hygiene but also conciliate economic and agricultural interests. Both of these early periods are thus noteworthy for a relative limitation of the river's deterioration by urban wastes. Not until the 1920s, when domestic water supply had become the rule and excreta came to be considered as worthless waste, was the principle of valorisation abandoned. This led to important and long-lasting pollution of the Seine, aggravating the industrial pollution that had been in evidence since the 1840s. Analysing the priorities that led to the adoption of one principle or another in matters of urban hygiene and techniques, with the causes and consequences of such changes, enables us to understand the complex relations between Paris and the Seine. From raw material to waste matter, from river to drain, the concept of quality in environment remains the underlying theme.
As products of both natural and social systems, rivers are highly complex historical objects. We show in this paper that historical analysis works on two different levels: one level, which we call "structural", shows the materiality of the riverine environment as the spatial-temporal product of natural factors and human impacts (bed and course alterations, pollution, etc.). On a second level –"semiotic" – we show that river systems are also social constructs and the subjects of ancient and diverse management practices. The quality of a river will be a function of the dialectical interaction between both levels. Historical analysis can uncover the inherited constraints that bear upon current management practices. To help substantiate this analytical framework, we analyse the case of the Moselle river in eastern France by using archival sources and statistical data. Severely impaired by industrial discharges from iron, coal and salt industries between the 1875s and the early 1980s, the waters of the Moselle became the subject of a social consensus between stakeholders that prevented the implementation of efficient pollution management policies until the 1990s. The example urges caution on the pervasiveness of participatory approaches to river management: social consensus does not necessarily benefit the environment.
Major fluxes of sulphur and dissolved inorganic nitrogen were estimated in Central European mountain ecosystems of the Bohemian Forest (forest lakes) and Tatra Mountains (alpine lakes) over the industrial period. Sulphur outputs from these ecosystems were comparable to inputs during a period of relatively stable atmospheric deposition (10-35 mmol m<sup>-2</sup> yr<sup>-1</sup>) around the 1930s. Atmospheric inputs of sulphur increased by three- to four-fold between the 1950s and 1980s to ~140 and ~60 mmol mm<sup>-2</sup> yr<sup>-1</sup> in the Bohemian Forest and Tatra Mountains, respectively. Sulphur outputs were lower than inputs due to accumulation in soils, which was higher in forest soils than in the sparser alpine soils and represented 0.8-1.6 and 0.2-0.3 mol m<sup>-2</sup>, respectively, for the whole 1930-2000 period. In the 1990s, atmospheric inputs of sulphur decreased 80% and 50% in the Bohemian Forest and Tatra Mountains, respectively, and sulphur outputs exceeded inputs. Catchment soils became pronounced sources of sulphur with output fluxes averaging between 15 and 31 mmol m<sup>-2</sup> yr<sup>-1</sup>. Higher sulphur accumulation in the forest soils has delayed (by several decades) recovery of forest lakes from acidification compared to alpine lakes. Estimated deposition of dissolved inorganic nitrogen was 53-75 mmol m<sup>-2</sup> yr<sup>-1</sup> in the Bohemian Forest and 35-45 mmol m<sup>-2</sup> yr<sup>-1</sup> in the Tatra Mountains in the 1880- 1950 period, i.e. below the empirically derived threshold of ~70 mmol m<sup>-2</sup> yr<sup>-1</sup>, above which nitrogen leaching often occurs. Dissolved inorganic nitrogen was efficiently retained in the ecosystems and nitrate export was negligible (0-7 mmol m<sup>-2</sup> yr<sup>-1</sup>). By the 1980s, nitrogen deposition increased to ~160 and ~80 mmol m<sup>-2</sup> yr<sup>-1</sup> in the Bohemian Forest and Tatra Mountains, respectively, and nitrogen output increased to 120 and 60 mmol m<sup>-2</sup> yr<sup>-1</sup>. Moreover, assimilation of nitrogen in soils declined from ~40 to 10-20 mmol m<sup>-2</sup> yr<sup>-1</sup> in the alpine soils and even more in the Bohemian Forest, where one of the catchments has even become a net source of nitrogen. In the 1990s, nitrogen deposition decreased by ~30% and DIN output decreased to < 70 and 35 mmol m<sup>-2</sup> yr<sup>-1</sup> in the Bohemian Forest and Tatra Mountains, respectively. New steady-state conditions, with negligible nitrogen export, could be reached in future but at lower nitrogen depositions than in the 1930s.
Keywords: emission, deposition, acidification, nitrogen-saturation, recovery, sulphate, nitrate, ammonium, mountain lakes
The aim of this study was to analyse the reproducibility of off-axis integrated cavity output spectroscopy (OA-ICOS)-derived δ<sup>2</sup>H and δ<sup>18</sup>O measurements on a set of 35 water samples by comparing the performance of four laser spectroscopes with the performance of a conventional mass spectrometer under typical laboratory conditions. All samples were analysed using three different schemes of standard/sample combinations and related data processing to assess the improvement of results compared with mass spectrometry. The repeatability of the four OA-ICOS instruments was further investigated by multiple analyses of a sample subset to evaluate the stability of δ<sup>2</sup>H and δ<sup>18</sup>O measurements.
Results demonstrated an overall agreement between OA-ICOS-based and mass spectrometry-based measurements for the entire dataset. However, a certain degree of variability existed in precision and accuracy between the four instruments. There was no evident bias or systematic deviations from the mass spectrometer values, but random errors, which were apparently not related to external factors, significantly affected the final results. Our investigation revealed that analytical precision ranged from ±0.56‰ to 1.80‰ for δ<sup>2</sup>H and from ±0.10‰ to 0.27‰ for δ<sup>18</sup>O measurements, with a marked variability among the four instruments. The overall capability of laser instruments to reproduce stable results with repeated measurements of the same sample was acceptable, and there were general differences within the range of the analytical precision for each spectroscope. Hence, averaging the measurements of three identical samples led to a higher degree of accuracy and eliminated the potential for random deviations.
An analysis of riverine outflow into the Baltic Sea is presented for the years 1901 ? 1990. The monthly outflows were calculated from the measurements in a number of representative rivers. The analysis included estimation of seasonal and multi-year characteristics of riverine outflows and periodic structure, as well as stochastic and statistical indicators characterising the influence of riverine water on the variability of the sea level and water volume in the basin. The article presents prognostic characteristics determined using analysis of parametric stochastic processes. The results obtained are related to oceanographic characteristics of the Baltic Sea.
Keywords: Baltic volume; Baltic balance; river outflow; river seasonality
Changes in the flooded area of ponds in the Gourma region from 1950 to present are studied by remote sensing, in the general context of the current multi-decennial Sahel drought. The seasonal and interannual variations of the areas covered by surface water are assessed using multi-date and multi-sensor satellite images (SPOT, FORMOSAT, LANDSAT-MSS, –TM, and -ETM, CORONA, and MODIS) and aerial photographs (IGN). Water body classification is adapted to each type of spectral resolution, with or without a middle-infrared band, and each spatial resolution, using linear unmixing for mixed pixels of MODIS data. The high-frequency MODIS data document the seasonal cycle of flooded areas, with an abrupt rise early in wet season and a progressive decrease in the dry season. They also provide a base to study the inter-annual variability of the flooded areas, with sharp contrasts between dry years such as 2004 (low and early maximal area) and wetter years such as 2001 and 2002 (respectively high and late maximal area).The highest flooded area reached annually greatly depends on the volume, intensity and timing of rain events. However, the overall reduction by 20% of annual rains during the last 40 years is concomitant with an apparently paradoxical large increase in the area of surface water, starting from the 1970's and accelerating in the mid 1980's. Spectacular for the two study cases of Agoufou and Ebang Mallam, for which time series covering the 1954 to present period exist, this increase is also diagnosed at the regional scale from LANDSAT data spanning 1972-2007. It reaches 108% between September 1975 and 2002 for 91 ponds identified in central Gourma. Ponds with turbid waters and no aquatic vegetation are mostly responsible for this increase, more pronounced in the centre and north of the study zone. Possible causes of the differential changes in flooded areas are discussed in relation with the specifics in topography, soil texture and vegetation cover over the watersheds that feed each of the ponds. Changes in rain pattern and in ponds sedimentation are ruled out, and the impact of changes in land use, limited in the area, is found secondary, as opposed to what has often been advocated for in southern Sahel. Instead, major responsibility is attributed to increased runoff triggered by the lasting impact of the 1970-80's droughts on the vegetation and on the runoff system over the shallow soils prevailing over a third of the landscape.
Rainfall erosivity refers to the ability of precipitation to erode soil,
and depends on characteristics such as its total volume, duration, and
intensity and amount of energy released by raindrops. Despite the
relevance of rainfall erosivity for soil degradation prevention, very
few studies have addressed its spatial and temporal variability. In this
study the time variation of rainfall erosivity in the Ebro Valley (NE
Spain) is assessed for the period 1955-2006. The results show a general
decrease in annual and seasonal rainfall erosivity, which is explained
by a decrease of very intense rainfall events whilst the frequency of
moderate and low events increased. This trend is related to prevailing
positive conditions of the main atmospheric teleconnection indices
affecting the West Mediterranean, i.e. the North Atlantic Oscillation
(NAO), the Mediterranean Oscillation (MO) and the Western Mediterranean
The Plynlimon experiment in mid-Wales, designed to determine the extent to which coniferous plantation increases evaporation losses and reduces streamflow relative to upland grassland, has now been yielding data since 1969 from the grassland Wye and the 67% forested Severn catchments. Water balance analyses of the early data indicated significantly higher evaporation rates from the forested catchment and studies of the hydrological processes involved attributed this to the high loss rates of precipitation intercepted by the forest canopy. Models based on these process studies predicted losses from the forested catchment that were similar but marginally higher than those determined by the catchment water balance.
As the data sets from the catchments increased in length and a detailed reassessment of the ratings of the streamflow gauging structures was completed the updated water balances continued to show a significantly greater evaporation loss from the forested catchment, but the gap between the forest water balance and the model predictions widened. Furthermore Hudson and Gilman (1993), using the best data sets then available, identified downward trends in the evaporation from both catchments which the models did not reproduce and for which no obvious physical or physiological explanation was forthcoming.
This dictated a major reassessment of the longer data sets, using the more powerful data processing techniques now available, to identify and eliminate any errors and inconsistencies. This paper describes the reassessment of the precipitation data and the estimates of potential evaporation and presents the water balance results emerging from the revised data sets.
The revised results indicate that the evaporation losses from the grassland Wye catchment remained broadly similar to the potential evaporation estimates throughout the 1969-1995 period. The losses from the forested area of the Severn catchment declined from a level some 61% above that of the grassland in 1972 to a level only 18% higher before the start of felling in 1985. This downward trend continued as the felling and re-planting progressed. Over the period since 1990 the forest catchment losses appear to have stabilised at some 5-10% below those of the grassland catchment.
Using the revised precipitation and potential evaporation data, process based models over-predict the forest catchment evaporation throughout the period and do not mirror the re-felling decline. Possible reasons for this apparent decline in evaporation rates are discussed.
This paper reviews research into the hydrological impacts of UK upland forestry and updates the water balance of the Plynlimon research catchments for the period 1972-2004. Comparison of this network of densely instrumented coniferous forest and grassland catchments builds upon previously reported differences in annual evaporation of the two land uses and, most crucially, provides evidence of systematic, age-related, variations in forest evaporation losses over a managed plantation forest cycle. In comparison with the grassland catchment, the additional water use of the 70% forested catchment fell from 250 to 150 mm yr<sup>-1</sup> because of increasing forest age; this is equivalent to a decline from 370 mm to 210 mm extra evaporation from a complete forest cover. At present, with up to half of the forest area felled or only recently replanted, the difference in evaporation between the forest and grass catchments is negligible. Knowledge of the period of maximum tree water use may be critically important for the future management of multi-use forests. This is also being investigated by micro-meteorological measurements at the scale of the forest stand using eddy covariance, in conjunction with the long-term catchment monitoring.
Two methods for modelling regional responses of lake water quality to changes in acidic deposition in southernmost Norway were examined. Both methods are based upon the MAGIC model but differ in mode of regional application; one uses site-specific while the other uses Monte-Carlo methods for model calibration. The simulations of regional responses from both methods were compared with observed responses based on data from three lake surveys in southernmost Norway conducted in 1974, 1986 and 1995.
The regional responses of the two modelling approaches were quite similar and agreed well with the observed regional distributions of lakewater chemistry variables. From 1974 to 1986 the observed data indicated that despite a decline of approximately 10% in sulphate (SO<sub>4</sub>) deposition, the mean acid neutralizing capacity (ANC) of lakes in southernmost Norway declined by approximately 6 μeq l<sup>-1</sup>. Both modelling approaches simulated no change or a very small decline in mean ANC for that period. From 1986 to 1995 the observed data indicated that, in response to an approximate 40% decline in SO<sub>4</sub> deposition, the mean ANC of lakes in southernmost Norway increased by 11-16 μeq l<sup>-1</sup>. The modelling approaches simulated increases of 9-10 μeq l<sup>-1</sup> in mean ANC for the same period. Both simulations and observations indicate that > 65% of lakes in southernmost Norway were acidic in 1974 and 1995. Both simulation methods predict that >65% of the lakes in southernmost Norway will have positive ANC values within 10 years of reductions of SO<sub>4</sub> deposition to 20% of 1974 levels.
Of the two regionalization methods the site-specific method appears preferable, because whereas the Monte-Carlo method gives results for a region as a whole, the site-specific method also reveals patterns within the region. The maintenance of a one-to-one correspondence between simulated and observed systems means that simulation results can be mapped for a geographically explicit presentation of model results. The ability to examine geographic patterns of response is becoming increasingly important in regional assessments.
The Galloway region of south-west Scotland has historically been subject to long-term deposition of acidic precipitation which has resulted in acidification of soils and surface waters and subsequent damage to aquatic ecology. Since the end of the 1970s, however, acidic deposition has decreased substantially. The general pattern is for a rapid decline in non-marine sulphate in rainwater over the period 1978-1988 followed by stable concentrations to the mid-1990s. Concentrations of nitrate and ammonium in deposition have remained constant between 1980 and 1998. Seven water quality surveys of 48 lochs in the Galloway region have been conducted between 1979 and 1998. During the first 10 years, from 1979, there was a major decline in regional sulphate concentrations in the lochs, which was expected to have produced a decline in base cations and an increase in the acid neutralising capacity. But sea-salt levels (as indicated by chloride concentrations) were approximately 25% higher in 1988 than in 1979 and thus short-term acidification due to sea-salts offset much of the long-term recovery trend expected in the lochs. During the next 10 years, however, the chloride concentrations returned to 1979 levels and the lochs showed large increases in acid neutralising capacity despite little change in sulphate concentrations. From the observed decline in sulphate deposition and concentrations of sulphate in the lochs, it appears that approximately 75% of the possible improvement in acid neutralising capacity has already occurred over the 20-year period (1979-1998). The role of acid deposition as a driving factor for change in water chemistry in the Galloway lochs is confounded by concurrent changes in other driving variables, most notably, factors related to episodic and year-to-year variations in climate. In addition to inputs of sea-salts, climate probably also influences other chemical signals such as peaks in regional nitrate concentrations and the sharp increase in dissolved organic carbon during the 1990s.
Keywords: acidification, recovery, Galloway, sulphur, nitrogen
Considerable work has been done to examine the relationship between
environmental constraints and vegetation activities represented by the
remote sensing-based normalized difference vegetation index (NDVI).
However, the relationships along either environmental or vegetational
gradients are rarely examined. The aim of this paper was to identify the
vegetation types that are potentially susceptible to climate change
through examining their interactions between vegetation activity and
evaporative water deficit. We selected 12 major vegetation types along
the north-south transect of eastern China (NSTEC), and tested their time
trends in climate change, vegetation activity and water deficit during
the period 1982-2006. The result showed significant warming trends
accompanied by general precipitation decline in the majority of
vegetation types. Despite that the whole transect increased atmospheric
evaporative demand (ET0) during the study period, the actual
evapotranspiration (ETa) showed divergent trends with
ET0 in most vegetation types. Warming and water deficit exert
counteracting controls on vegetation activity. Our study found
insignificant greening trends in cold temperate coniferous forest
(CTCF), temperate deciduous shrub (TDS), and three temperate herbaceous
types including the meadow steppe (TMS), grass steppe (TGS) and
grassland (TG), where warming exerted more effect on NDVI than offset by
water deficit. The increasing growing season water deficit posed a
limitation on the vegetation activity of temperate coniferous forest
(TCF), mixed forest (TMF) and deciduous broad-leaved forest (TDBF).
Differently, the growing season brownings in subtropical or tropical
forests of coniferous (STCF), deciduous broad-leaved (SDBF), evergreen
broad-leaved (SEBF) and subtropical grasslands (STG) were likely
attributed to evaporative energy limitation. The growing season water
deficit index (GWDI) has been formulated to assess ecohydrological
equilibrium and thus indicating vegetation susceptibility to water
deficit. The increasing GWDI trends in CTCF, TCF, TDS, TG, TGS and TMS
indicated their rising susceptibility to future climate change.
Surveys of 485 lakes in Norway conducted in 1986 and again in 1995 reveal widespread chemical recovery from acidification. Sulphate concentrations in lakes have decreased by 40% in acidified areas in southern Norway. This decrease has been compensated about 25% by decreases in concentrations of base cations and of 75% by increased Acid Neutralising Capacity (ANC). The increased ANC in turn reflects lower concentrations of acidic cations Aluminum (AL<sup>n+</sup>) and Hydrogen (H<sup>+</sup>). A sub-set of 78 of the 485 lakes sampled yearly between 1986 and 1997 shows that, at first most of the decrease in non-marine sulphate (SO<sub>4</sub><sup>*</sup>) was compensated by a decrease in base cations, such that ANC remained unchanged. Then as SO<sub>4</sub><sup>*</sup> continued to decrease, the concentrations of non- marine calcium and magnesium ((Ca+Mg)<sup>*</sup>) levelled out. Consequently, ANC increased, and H<sup>+</sup> and Al<sup>n+</sup> started to decrease. In eastern Norway, this shift occurred in 1989?90, and came slightly later in southern and western Norway. Similar shifts in trends in about 1991?92 can also be seen in the non-acidified areas in central and northern Norway. This shift in trends is not as pronounced in western Norway, perhaps because of the confounding influence of sea-salt episodes on water chemistry. This is the first documented national-scale recovery from acidification due to reduced acid deposition. Future climate warming and potentially increased N-leaching can counteract the positive trends in recovery from acidification.
A detailed trend analysis of 12 years of data (1988-2000) for 22 surface waters in acid-sensitive regions of the United Kingdom, in which individual site data have been combined to identify national-scale trends, has shown strong common patterns of temporal variation. Results suggest a widespread reduction in sulphate concentrations, hydrogen ion and inorganic aluminium species, and increases in acid neutralising capacity. Many chemical changes have not been linear. However, the first five years were characterised by high concentrations of marine ions and relatively stable pollutant sulphate concentrations and the remaining period by lower concentrations of marine ions and declining sulphate. Genuine 'recovery', in terms of declining acidity in response to reduced anthropogenic sulphur deposition is only apparent, therefore, for the latter part of the monitoring period. Reductions in calcium concentrations appear to have partially offset the influence of sulphate reductions on acidity, as have increases in organic acidity associated with strong and widespread rising trends in dissolved organic carbon. Fluctuations in a number of climatic factors over the monitoring period have led to significant inter-annual variability in nitrate, which exhibits little long-term trend, marine ions and acidity, emphasising the need for long monitoring periods if underlying trends are to be correctly identified.
Keywords: acidification, recovery, long-term trends, climate, Dissolved Organic Carbon, United Kingdom Acid Waters Monitoring Network
This paper reported a dramatic channel incision (>10 m in the deepest cut) during the past 10 y or so in the lower Pearl River, the second largest river in terms of water discharge in China. The channel incision had caused changes both in the channel geometry as well as in the river hydraulics. Also, the water exchange between the two major tributaries of the Pearl River, the Xijiang and Beijiang, had been significantly changed due to the channel incision. The rapid channel incision was principally the result of extensive sand mining in the lower Pearl River and the delta region due to the booming economy in the Pearl Delta region. Slight increase of water discharge and significant decrease of sediment load since the early 1990s in both the Xijiang and Beijiang also likely contributed to the observed dramatic river bed downcutting to some extent. This has important implications for river management, as the large Chinese rivers have seen a dramatic depletion of sediment fluxes due to the combined effects of declining rainfall, dam constructions, water diversion, reforestation and afforestation, and sediment mining over the recent decades.
Whether the global runoff (or freshwater discharge from land to the
ocean) is currently increasing and the global water cycle is
intensifying is still a controversial issue. Here we compute
land-atmosphere and ocean-atmosphere water budgets and derive two
independent estimates of the global runoff over the period 1993-2009.
Water storage variations in the land, ocean and atmosphere reservoirs
are estimated from different types of data sets: atmospheric reanalyses,
land surface models, satellite altimetry and in situ ocean temperature
data (the difference between altimetry based global mean sea level and
ocean thermal expansion providing an estimate of the ocean mass
component). These data sets are first validated using independent data,
and then the global runoff is computed from the two methods. Results for
the global runoff show a very good correlation between both estimates.
More importantly, no significant trend is observed over the whole
period. Besides, the global runoff appears to be clearly impacted by
large-scale climate phenomena such as major ENSO events. To infer this,
we compute the zonal runoff over four latitudinal bands and set up for
each band a new index (combined runoff index) obtained by optimization
of linear combinations of various climate indices. Results show that, in
particular, the intertropical and northern mid-latitude runoffs are
mainly driven by ENSO and the Atlantic multidecadal oscillation (AMO)
with opposite behavior. Indeed, the zonal runoff in the intertropical
zone decreases during major El Niño events, whereas it increases
in the northern mid-latitudes, suggesting that water masses over land
are shifted northward/southward during El Niño/La Niña. In
addition to this study, we propose an innovative method to estimate the
global ocean thermal expansion. The method is based on the assumption
that the difference between both runoff estimates is mainly due to the
thermal expansion term not accounted for in the estimation of the ocean
mass. We find that our reconstructed thermal expansion time series
compares well with two existing data sets in terms of year-to-year
fluctuations but somewhat differs on longer (multi-year) time scales.
Possible explanations include non negligible steric variations from the
Detailed plot-scale observations of basic hydrometeorological variables represent valuable data for assessing the quality of the soil moisture module and evapotranspiration scheme in hydrological models. This study presents the validation of soil moisture and evapotranspiration (ET) simulation during the special observing period (R-SOP) of the Riviera Project (July?November 1999), a sub-project of the Mesoscale Alpine Programme (MAP). The location investigated was a sandy soil plot at the edge of a corn field. The hydrological model PREVAH was driven using three meteorological data sets: hourly data from an experimental tower in the Riviera Valley (southern Switzerland), hourly data interpolated for the Riviera site during the R-SOP period from permanent automatic stations (MeteoSwiss network) and interpolated daily data (1980?2000). The quality of the interpolated meteorological data was evaluated with respect to data collected at an experimental tower. The interpolated data proved fairly representative for the location under investigation. The hydrological simulations were compared with recorded observations of soil moisture and latent heat flux (LE). The simulation of soil moisture was accurate in case of all three meteorological data sets. The results of ET simulations with three simple parameterisations showed high correlation to LE derived using the Bowen ratio and measured through eddy correlation. The quantitative agreement between observed and simulated LE was poorer because of the presence of a fully developed wind valley system during periods of good weather. This wind system claims part of the available energy and therefore reduces the amount of energy available for LE. The 21-year simulation at daily time step shows that the R-SOP period in 1999 was warm and wet compared to the last 21 years.
Keywords: MAP-Riviera Project, soil moisture, evapotranspiration, hydrological modelling, model evaluation
Knowledge of the water fluxes within the soil-vegetation-atmosphere
system is crucial to improve water use efficiency in irrigated land.
Many studies have tried to quantify these fluxes, but they encountered
difficulties in quantifying the relative contribution of evaporation and
transpiration. In this study, we compared three different methods to
estimate evaporation fluxes during simulated summer conditions in a
grass-covered lysimeter in the laboratory. Only two of these methods can
be used to partition total evaporation into transpiration, soil
evaporation and interception. A water balance calculation (whereby
rainfall, soil moisture and percolation were measured) was used for
comparison as a benchmark. A HYDRUS-1D model and isotope measurements
were used for the partitioning of total evaporation. The isotope mass
balance method partitions total evaporation of 3.4 mm d-1
into 0.4 mm d-1 for soil evaporation, 0.3 mm d-1
for interception and 2.6 mm d-1 for transpiration, while the
HYDRUS-1D partitions total evaporation of 3.7 mm d-1 into 1
mm d-1 for soil evaporation, 0.3 mm d-1 for
interception and 2.3 mm d-1 for transpiration. From the
comparison, we concluded that the isotope mass balance is better for low
temporal resolution analysis than the HYDRUS-1D. On the other hand,
HYDRUS-1D is better for high temporal resolution analysis than the
isotope mass balance.
The operational system known as MORECS which provides estimates of evaporation, soil moisture deficit and effective precipitation under British climatic conditions has been revised as version 2.0. An overview of the new system is described with emphasis on the new additions. The major changes from the older version (Thomson, Barrie and Ayles, 1981) include the introduction of the crop oil-seed rape, a revised treatment of soils and available water capacity and a land use data base which is representative of the 1990s.
During the autumn of 2000, England and Wales experienced the wettest conditions for over 270 years, causing significant flooding. The exceptional combination of a wet spring and autumn provided the potential for soil structural degradation. Soils prone to structural degradation under five common lowland cropping systems (autumn-sown crops, late-harvested crops, field vegetables, orchards and sheep fattening and livestock rearing systems) were examined within four catchments that experienced serious flooding. Soil structural degradation of the soil surface, within the topsoil or at the topsoil/subsoil junction, was widespread in all five cropping systems, under a wide range of soil types and in all four catchments. Extrapolation to the catchment scale suggests that soil structural degradation may have occurred on approximately 40% of the Severn, 30–35 % of the Yorkshire Ouse and Uck catchments and 20% of the Bourne catchment. Soil structural conditions were linked via hydrological soil group, soil condition and antecedent rainfall conditions to SCS Curve Numbers to evaluate the volume of enhanced runoff in each catchment. Such a response at the catchment-scale is only likely during years when prolonged wet weather and the timing of cultivation practices lead to widespread soil structural degradation. Nevertheless, an holistic catchment-wide approach to managing the interactions between agricultural land use and hydrology, allowing appropriate runoff (and consequent flooding) to be controlled at source, rather than within the floodplain or the river channel, should be highlighted in catchment flood management plans.
Keywords: flooding, soil structure, land management, Curve Number, runoff, agriculture
In August 2002, in the worst flooding in more than 100 years, the River Elbe destroyed built-up areas and caused widespread erosion and the relocation of soils and river sediments. To assess the pollutants entering the water, surveys of dissolved constituents and suspended particulate matter (SPM) were carried out daily during the flood at a monitoring station near Magdeburg. The sampling point is part of the network of the International Commission for the Protection of the Elbe (ICPE). The results were compared with those of previous flood studies which used the same sampling strategy. Unlike past floods, the 2002 flood was characterised by the transport of relatively fine suspended material with a low mass concentration. Owing to different input sources, the maxima of dry weight and of particle number concentration occurred at different times. Hg, Fe, Mn, Zn, Cu, Ni and Cr showed a maximum concentration concurrent with the dry weight of the SPM, whereas the maximum concentrations of As, Pb, and Cd coincided with the particle number concentration peak. The concentration of particulate matter decreased rapidly, unlike the concentrations of dissolved substances such as DOC and trace metals, as well as the values of UV extinction, all of which remained high for a longer period. Comparing the results of the 2002 flood with the winter floods in 1995, 1999 and 2000, revealed increased values of As and Pb as well as higher concentrations of dissolved compounds.
Keywords: river, flood, transport, suspended particulate matter, trace metals, dissolved compounds, Elbe
The extraordinarily warm and dry summer experienced in SW Europe in 2003 provides an interesting case study for the analysis of the response of regional-scale vegetation variables to drier and hotter conditions. SW Europe includes a boundary between phytogeographic and climatic regions (Oceanic and Mediterranean) that differ in terms of summer precipitation, which let us compare the response of different vegetation types. In addition, some scenarios predict summer conditions such as those of 2003 to be common by the latter decades of the 21st century in this region. We have analyzed a monthly series of regional fields of normalized difference vegetation index from the VEGETATION-SPOT5 instrument, from 1999 to 2003. We show that negative anomalies of vegetation index in summer 2003 were larger for herbaceous vegetation of the Oceanic climate region and for deciduous forests. The vegetation index of August 2003 in the Mediterranean climate region was also significantly lower than normal values in August 1999–2002, albeit the anomalies were small in absolute value. We compared August NDVI, as a measure of the vegetation response, to the difference between total summer precipitation and total summer potential evapotranspiration, as a measure of atmospheric water stress. Our results indicate that water stress is a major factor structuring the geographic variability of NDVI in this region. In accordance with these results, the analysis of the data of 2003 indicate that the increased water stress was a key factor of the observed anomalies of vegetation index.
The turbulent sensible and latent heat fluxes simulated in the operational weather forecast model LM have been checked with data from the field experiment LITFASS 2003 (Lindenberg Inhomogeneous Terrain - Fluxes between Atmosphere and Surface: a Long-term Study) using both single site measurements and grid box aggregated fluxes. SCE-UA (single objective) and MOSCEM-UA (multi-objective) approaches were applied to calibrate the land-surface scheme TERRA/LM for 11 single sites and for the aggregated fluxes. A large variation is seen among the parameter sets found by calibration but no typical classification according to vegetation type is obvious. This is attributed to the calibrated parameter sets correcting for model deficiencies and data errors rather than describing the physical characteristics of the measurement site. The measured fluxes were combined into a time series of aggregated fluxes by the tile method. Calibration of TERRA/LM with respect to the averaged fluxes resulted in a range of parameter sets which all simulated the area-averaged fluxes in much better agreement with the observed fluxes than the standard parameter set of the operational model. A modified Nash-Sutcliffe measure as a coincidence criterion fell from 0.3 to a range between 0.15 and 0.28 for the latent heat flux and from 0.43 to between 0.26 and 0.36 for the sensible heat flux when the calibrated parameter sets were used instead of the standard parameters.
This paper describes a new bio-indicator method for assessing wetland ecosystem health; as such, the study is particularly relevant to current legislation such as the EU Water Framework Directive, which provides a baseline of the current status of surface waters. Seven wetland sites were monitored across northern Britain, with model construction data for predicting eco-hydrological relationships collected from five sites during 1999. Two new sites and one repeat site were monitored during 2000 to provide model test data. The main growing season for the vegetation, and hence the sampling period, was May–August during both years. Seasonal mean concentrations of nitrate (NO<sub>3</sub><sup>-</sup>) in surface and soil water samples during 1999 ranged from 0.01 to 14.07 mg N l<sup> –1 </sup>, with a mean value of 1.01 mg N l<sup> –1 </sup>. During 2000, concentrations ranged from trace level (<0.01 mg N l<sup> –1 </sup>) to 9.43 mg N l<sup> –1 </sup>, with a mean of 2.73 mg N l–<sup> -1 </sup>. Surface and soil-water nitrate concentrations did not influence plant species composition significantly across representative tall herb fen and mire communities. Predictive relationships were found between nitrate concentrations and structural characteristics of the wetland vegetation, and a model was developed which predicted nitrate concentrations from measures of plant diversity, canopy structure and density of reproductive structures. Two further models, which predicted stem density and density of reproductive structures respectively, utilised nitrate concentration as one of the independent predictor variables. The models were tested where appropriate using data collected during 2000. This approach is complementary to species-based monitoring, representing a useful and simple tool to assess ecological status in target wetland systems and has potential for bio-indication purposes.
Keywords: bio-indicators, surface water, water quality, wetland vegetation
The tropical storm, floodwater, and the floodplain-sediment layer of a 100-year recurrence flood are examined to better understand characteristics of large monsoon floods on medium-sized rivers in northern Thailand. Storms producing large floods in northern Thailand occur early or late in the summer rainy season (May–October). These storms are associated with tropical depressions evolving from typhoons in the South China Sea that travel westward across the Indochina Peninsula. In late September, 2005, the tropical depression from Typhoon Damrey swept across northern Thailand delivering 100–200 mm/day at stations in mountainous areas. Peak flow from the 6355-km<sup>2</sup> drainage area of the Ping River upstream of the city of Chiang Mai was 867 m<sup>3</sup>s<sup>−1</sup> (river-gage of height 4.93 m) and flow greater than 600 m<sup>3</sup>s<sup>−1</sup> lasted for 2.5 days. Parts of the city of Chiang Mai and some parts of the floodplain in the intermontane Chiang Mai basin were flooded up to 1-km distant from the main channel. Suspended-sediment concentrations in the floodwater were measured and estimated to be 1000–1300 mg l<sup>−1</sup>.
The mass of dry sediment (32.4 kg m<sup>-2</sup>), measured over a 0.32-km<sup>2</sup> area of the floodplain is relatively high compared to reports from European and North American river floods. Average wet sediment thickness over the area was 3.3 cm. Sediment thicker than 8 cm covered 16 per cent of the area, and sediment thicker than 4 cm covered 44 per cent of the area. High suspended-sediment concentration in the floodwater, flow to the floodplain through a gap in the levee afforded by the mouth of a tributary stream as well as flow over levees, and floodwater depths of 1.2 m explain the relatively large amount of sediment in the measured area.
Grain-size analyses and examination of the flood layer showed about 15-cm thickness of massive fine-sandy silt on the levee within 15-m of the main channel, sediment thicker than 6 cm within 200 m of the main channel containing a basal coarse silt, and massive clayey silt beyond 200 m. The massive clayey silt would not be discernable as a separate layer in section of similar deposits. The fine-sand content of the levee sediment and the basal coarse silt of sediment within 200 m of the main channel are sedimentological features that may be useful in identifying flood layers in a stratigraphic section of floodplain deposits.
The estimation of transient streamflow from stage measurements is indeed important and the study of Dottori, Martina and Todini (2009) (henceforth DMT) is useful, however, DMT seem to miss certain of its practical aspects. The goal is to infer the discharge from measurements of the stage conveniently and with accuracy adequate for practical work. This comment addresses issues of the applicability of the DMT method in the field. DMT also advocate their method as a replacement of the widely used Jones Formula. The Jones Formula was modified by Thomas (Henderson, 1966) to include the temporal derivative of the depth, instead of the spatial one, to specifically allow discharge estimation from at-a-section stage observations. The outcome of the comparison is not surprising in view of this approximation. However, this discussion intends to show that, properly evaluated, the praxis-oriented Jones Formula, which did well in the tests, can perform better than DMT imply. It will be also documented that the DMT methodology relates to a known method for computing flood depth profiles.
This paper presents a new reconstruction of the 20th century global hydrography using fully coupled water balance and transport model in a flexible modeling framework. The modeling framework allows a high level of configurability both in terms of input forcings and model structure. Spatial and temporal trends in hydrological cycle components are assessed under "pre-industrial" conditions (without modern-day human activities) and contemporary conditions (incorporating the effects of irrigation and reservoir operations). The two sets of simulations allow the isolation of the trends arising from variations in the climate input driver alone and from human interventions. The sensitivity of the results to variations in input data was tested by using three global gridded datasets of precipitation.
Our findings confirm that the expansion of irrigation and the construction of reservoirs has significantly and gradually impacted hydrological components in individual river basins. Variations in the volume of water entering the oceans annually, however, are governed primarily by variations in the climate signal alone with human activities playing a minor role. Globally, we do not find a significant trend in the terrestrial discharge over the last century.
The largest impact of human intervention on the hydrological cycle arises from the operation of reservoirs that drastically changes the seasonal pattern of horizontal water transport in the river system and thereby directly and indirectly affects a number of processes such as ability to decompose organic matter or the cycling of nutrients in the river system.
This study is an update of the information contained in the precipitation-frequency atlas published by the US National Weather Service in 1973. Data collection for the NWS study ended in 1966 while this study uses the current data base which more than doubles the record length used in the NWS study. Washington State has highly variable topography and climate; in particular Mean Annual Precipitation (MAP) varies from over 260 inches a year to less than 7 inches. Steep high mountain ranges provide very wet slopes as well as pronounced rain shadows with large climate changes occurring in relatively short distances. In addition there are four distinct sources for the atmospheric moisture needed for precipitation which gives rise to complex seasonal and spatial interactions. The PRISM mapping system used in this study has greatly improved the spatial mapping of precipitation and increased the reliability of estimates of precipitation in the broad areas between precipitation measurement stations. Further, the development and use of regional L-Moments has greatly improved the reliability of precipitation magnitude-frequency estimates, particularly for the rarer and more extreme storms. Washington State could be specified adequately by 12 regions for the purposes of estimating the 2-hour and 24 hour precipitation frequencies. Within each region algorithms were developed for L-CV and L-Skewness expressed as functions of the MAP. The GEV distribution was acceptable statistically for all regions up to the 1 in 500 recurrence interval, beyond which the four-parameter Kappa distribution is recommended. The estimated changes in precipitation magnitudes for a given frequency as regional boundaries were crossed were found to be small, and well within the expected differences likely from sampling errors. An interesting transition zone was observed at the eastern edge of the Cascade foothills, associated with the maxima having a seasonal change from autumn?winter synoptic scale general storms in the west to spring?summer maxima in the east that were produced by a mix of storm types. (Comment: storms were a mix of general storms and more-isolated convective storms).
An experiment comparing effects of sulphuric acid and reduced N deposition on soil water quality and on chemical and physical growth indicators for forest ecosystems is described. Six H<sub>2</sub>SO<sub>4</sub> and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> treatment loads, from 0 – 44 and 0 – 25 kmol<sub>c</sub> ha<sup>-1</sup> yr<sup>-1</sup>, respectively, were applied to outdoor microcosms of Pinus sylvestris seedlings in 3 acid to intermediate upland soils (calc-silicate, quartzite and granite) for 2 years. Different soil types responded similarly to H<sub>2</sub>SO<sub>4</sub> loads, resulting in decreased leachate pH, but differently to reduced N inputs. In microcosms of calc-silicate soil, nitrification of NH<sub>4</sub> resulted in lower pH and higher cation leaching than in acid treatments. By contrast, in quartzite and granite soils, (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> promoted direct cation leaching, although leachate pH increased. The results highlighted the importance of soil composition on the nature of the cations leached, the SO<sub>4</sub> adsorption capacities and microbial N transformations. Greater seedling growth on calc-silicate soils under both treatment types was related to sustained nutrient availability. Reductions in foliar P and Mg with higher N treatments were observed for seedlings in the calc-silicate soil. There were few treatment effects on quartzite and granite microcosm tree seedlings since P limitation precluded seedling growth responses to treatments. Hence, any benefits of N deposition to seedlings on quartzite and granite soils appeared limited by availability of co-nutrients, exacerbated by rapid depletion of soil exchangeable base cations.
Keywords: acidification, manipulation, nitrogen, ammonium, deposition, soil, drainage, pine, microcosms, forest
This article presents the use of new remote sensing data acquired from airborne full-waveform lidar systems for hydrological applications. Indeed, the knowledge of an accurate topography and a landcover classification is a prior knowledge for any hydrological and erosion model. Badlands tend to be the most significant areas of erosion in the world with the highest erosion rate values. Monitoring and predicting erosion within badland mountainous catchments is highly strategic due to the arising downstream consequences and the need for natural hazard mitigation engineering.
Additionally, beyond the elevation information, full-waveform lidar data are processed to extract the amplitude and the width of echoes. They are related to the target reflectance and geometry. We will investigate the relevancy of using lidar-derived Digital Terrain Models (DTMs) and the potentiality of the amplitude and the width information for 3-D landcover classification. Considering the novelty and the complexity of such data, they are presented in details as well as guidelines to process them. The morphological validation of DTMs is then performed via the computation of hydrological indexes and photo-interpretation. Finally, a 3-D landcover classification is performed using a Support Vector Machine classifier. The use of an ortho-rectified optical image in the classification process as well as full-waveform lidar data for hydrological purposes is finally discussed.
Stream waters in the Allt a'Mharcaidh catchment (Cairngorms, Scotland) have been monitored for flow, conductivity and pH at sub-hourly resolution; and for a range of chemical, biological and physical parameters, less intensively, since the mid-1980s. The Allt a'Mharcaidh stream is subject to acidic events (pH<5.5) triggered by both hydrology and sea-salt inputs from the atmosphere. This paper investigates the drivers of these acidic events using variables derived from sub-hourly monitored data. It also examines the influence of the North Atlantic Oscillation (NAO) on episode severity. Sub-hourly datasets are used to derive multiple regression models expressing stream H+ concentration as a function of the sea-salt conductivity and the peak instantaneous flow rate amongst other explanatory variables. The relationship between sea-salt conductivity and the NAO is significant but hidden due to issues such as time lags and the influence of atmospheric patterns other than the NAO.
Following the launch of the European Space Agency's Soil Moisture and
Ocean Salinity (SMOS) mission on 2 November 2009, SMOS soil moisture
products need to be rigorously validated at the satellite's
approximately 45 km scale and disaggregation techniques for producing
maps with finer resolutions tested. The Australian Airborne Cal/val
Experiments for SMOS (AACES) provide the basis for one of the most
comprehensive assessments of SMOS data world-wide by covering a range of
topographic, climatic and land surface variability within an
approximately 500 × 100 km2 study area, located in
South-East Australia. The AACES calibration and validation activities
consisted of two extensive field experiments which were undertaken
across the Murrumbidgee River catchment during the Australian summer and
winter season of 2010, respectively. The datasets include airborne
L-band brightness temperature, thermal infrared and multi-spectral
observations at 1 km resolution, as well as extensive ground
measurements of near-surface soil moisture and ancillary data, such as
soil temperature, soil texture, surface roughness, vegetation water
content, dew amount, leaf area index and spectral characteristics of the
vegetation. This paper explains the design and data collection strategy
of the airborne and ground component of the two AACES campaigns and
presents a preliminary analysis of the field measurements including the
application and performance of the SMOS core retrieval model on the
diverse land surface conditions captured by the experiments. The data
described in this paper are publicly available from the website: http://www.moisturemap.monash.edu.au/aaces .
The Chinese Loess Plateau is located in the north of China and has a significant impact on the climate and ecosystem evolvement over the East Asian continent. Estimates of evapotranspiration (ET) at a regional scale are in crucial need for climate studies, weather forecasts, hydrological surveys, ecological monitoring and water resource management. In this research, the ET of the Chinese Loess Plateau was estimated by using an energy balance approach and data collected during the LOess Plateau land-atmosphere interaction pilot EXperiments 2005 (LOPEX05). With the combined data of the Medium Resolution Imaging Spectrometer (MERIS), the Advanced Along-Track Scanning Radiometer (AATSR) and some other variables such as air temperature, crop height and wind speed, the instantaneous net radiation, sensible heat flux and soil heat flux were calculated; the instantaneous latent heat flux was derived as the residual term of energy balance, and then converted to daily ET value by sunshine duration. The calculated daily ET from the model showed a good match with the measurements of the eddy covariance systems deployed in LOPEX05. The minimum relative error of this approach is 9.0%, the cause of the bias was also explored and discussed.
The inland, mountainous marginal areas (land abandoned by farming and colonised by shrubs) of the Iberian Peninsular, Spain, generally receive a higher rainfall than the coastal areas (Lazaro and Rey, 1991) and may store water after cold season (autumn and winter) rainfall. By measuring runoff, change of soil water content and rainfall, this study tests the hypothesis that two shrubs on two sites on abandoned land do not use all the water available after cold season rainfall. One site was on an upper alluvial slope dominated by Anthyllis cytisoides and the other on a lower alluvial slope dominated by Retama sphaerocarpa . The root systems of A. cytisoides and R. sphaerocarpa penetrate to 3 m and 20 m, respectively. A. cytisoides senesces during the dry season and R. sphaerocarpa is evergreen. The water balance is dominated by high actual evapotranspiration (ET), which is limited by rainfall. Reference evapotranspiration was high; runoff was low and soil water storage occurred above 2 m depth. ET and water storage were highest under A. cytisoides shrubs. Runoff was lower on the ?Anthyllis' site. The spatial variability of soil water is high and the problems of its measurement are discussed. The quantity of rainfall infiltrated was greater under shrubs than grass-areas, suggesting that shrub roots facilitated preferential flow. The growing season of A. cytisoides began when water was available in the upper soil layers and senescence occurred when the upper soil layers dried to less than 4% water content. A. cytisoides , therefore, relies on water from these layers. The main growth of R. sphaerocarpa occurred when the upper soil layers were relatively dry, so that R. sphaerocarpa must extract water from deeper layers. Results suggest that A. cytisoides accumulates rainfall and runoff and directs water to lower layers for later use, while R. sphaerocarpa extracts water from deeper soil layers. By mid-summer both shrubs had extracted all the available water accumulated in the upper soil layers from cold season rainfall.
Keywords: water balance, neutron probe, patchy vegetation, mosaic vegetation, Spain, semi arid, Anthyllis cytisoides , Retama sphaerocarpa
Understanding catchment hydrological processes is essential for water resources management, in particular in data scarce regions. The Gilgel Abay catchment (a major tributary into Lake Tana, source of the Blue Nile) is undergoing intensive plans for water management, which is part of larger development plans in the Blue Nile basin in Ethiopia. To obtain a better understanding of the water balance dynamics and runoff generation mechanisms and to evaluate model transferability, catchment modeling has been conducted using the conceptual hydrological model HBV. Accordingly, the catchment of the Gilgel Abay has been divided into two gauged sub-catchments (Upper Gilgel Abay and Koga) and the un-gauged part of the catchment. All available data sets were tested for stationarity, consistency and homogeneity and the data limitations (quality and quantity) are discussed. Manual calibration of the daily models for three different catchment representations, i.e. (i) lumped, (ii) lumped with multiple vegetation zones, and (iii) semi-distributed with multiple vegetation and elevation zones, showed good to satisfactory model performances with Nash-Sutcliffe efficiencies Reff > 0.75 and > 0.6 for the Upper Gilgel Abay and Koga sub-catchments, respectively. Better model results could not be obtained with manual calibration, very likely due to the limited data quality and model insufficiencies. Increasing the computation time step to 15 and 30 days improved the model performance in both sub-catchments to Reff > 0.8. Model parameter transferability tests have been conducted by interchanging parameters sets between the two gauged sub-catchments. Results showed poor performances for the daily models (0.30 < Reff < 0.67), but better performances for the 15 and 30 days models, Reff > 0.80. The transferability tests together with a sensitivity analysis using Monte Carlo simulations (more than 1 million model runs per catchment representation) explained the different hydrologic responses of the two sub-catchments, which seems to be mainly caused by the presence of dambos in Koga sub-catchment. It is concluded that daily model transferability is not feasible, while it can produce acceptable results for the 15 and 30 days models. This is very useful for water resources planning and management, but not sufficient to capture detailed hydrological processes in an ungauged area.
Adoption of soil conservation structures (SCS) has been low in high
rainfall areas of Ethiopia mainly due to crop yield reduction, increased
soil erosion following breaching of SCS, incompatibility with the
tradition of cross plowing and water-logging behind SCS. A new type of
conservation tillage (CT) involving contour plowing and the construction
of invisible subsoil barriers using a modified Maresha winged
"subsoiler" is suggested as a means to tackle these problems as an
integral part of the SCS. We investigated the effect of integrating the
CT with SCS on the surface runoff, water-logging, soil loss, crop yield
and plowing convenience. The new approach of conservation tillage has
been compared with traditional tillage (TT) on 5 farmers' fields in a
high rainfall area in the upper Blue Nile (Abbay) river basin. Test
crops were wheat [triticum vulgare] and tef [eragrostis tef]. Farmers
found CT convenient to apply between SCS. Surface runoff appeared to be
reduced under CT by 48 and 15%, for wheat and tef, respectively. As a
result, CT reduced sediment yield by 51 and 9.5%, for wheat and tef,
respectively. Significantly reduced water-logging was observed behind
SCS in CT compared to TT. Grain yields of wheat and tef increased by 35
and 10%, respectively, although the differences were not statistically
significant apparently due to high fertility variations among fields of
participating farmers. Farmers who tested CT indicated that they will
continue this practice in the future.