Article

Taking the higher ground: deviation between projected and observed precipitation trends varies with altitude

Abstract and Figures

Variation in the amount and intensity of precipitation is one of the most important factors determining how biological systems respond to anthropogenic climate change. Moreover, given the importance of climate projections for influencing (inter)national policy, there is a pressing need to contextualise contemporary projections with observed trends to better inform environmental strategy and planning. In this study we examine trends from one of the longest paired time series of upland (>300m) and lowland precipitation records (1879 – 2012), and shorter-term observations (1961 – 2015) from multiple upland locations in South West (SW) England (Dartmoor National Park). In the period 1879 – 2012, total precipitation in the upland site increased by more than 10% for spring, autumn, winter, and annually; for the lowland site, only spring experienced a significant increase (8%) in precipitation. Increases in autumn, winter and annual precipitation were recorded at upland sites since the 1960s. We compare observed precipitation trends with the latest UK climate projections (UKCP18) for the region across two timeframes (60 and 90 years). Changes in the 30 year average between reference (1981 – 2010) and observed and projected precipitation totals were compared and deviations calculated. Comparisons between model projections and observed trends show large deviation for spring, summer and autumn precipitation in the mid to late 21st century, with the deviation greatest in upland localities. Winter projections however, were broadly consistent with observed trends. Results suggest uncertainties in future precipitation change are greatest in the uplands where the impacts on ecosystem services are the largest.
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... The 'uplands', typically >250-300 m amsl in the UK (Bunce, Wood, & Smart, 2018), are particularly vulnerable and important for managing this risk. Not only have these areas experienced greater increases in precipitation compared with lowland sites (Burt & Holden, 2010;Murphy, Hanley, Ellis, & Lunt, 2019), as the source of 68% of the UK's freshwater, they represent the principal areas of river flow generation (Robinson, Rodda, & Sutcliffe, 2013;Van der Wal et al., 2011). ...
... Consequently, vegetation in DNP is dominated by acid grassland and Atlantic heath with relatively sparse tree cover over most of the area (Mercer, 2009). In addition to this long history of (over) grazing and associated soil compaction (Sansom, 1999), the area naturally receives high levels of precipitation, with extreme rainfall events set to increase into future decades associated with climate change (Fowler & Wilby, 2010;Murphy et al., 2019). The many small streams and rivers that rise on the open moorland form 'flashy' (or 'torrential') catchments, naturally vulnerable to spate flooding (Perry, 2014). ...
... The degraded nature of soils in many UK upland pastoral catchments Sansom, 1999), alongside elevated precipitation trends in these areas (Murphy et al., 2019) highlights the importance of hydrological integrity and soil recovery in flood risk management. Our results show that native woodland establishment in upland pasture areas offers a viable, and potentially rapid (7-15 years) means to reduce surface soil compaction and bulk density with concomitant benefits to Ksat and 'wetness threshold"'(i.e., soil water holding capacity). ...
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Extreme rainfall and flood events are predicted to increase in frequency and severity as a consequence of anthropogenic climate change. In UK upland areas, historical over‐grazing and associated soil compaction have further exacerbated peak flood levels and flash‐flood risk along many river catchments. As a result, the reinstatement of upland woodland is increasingly seen as a key component of an integrated suite of options forming part of Natural Flood Management (NFM) associated with a “public money for public goods” approach to European agriculture. Nevertheless, understanding the impact of native woodland establishment on upland soil hydrology remains relatively poor. We compare physical and hydrological properties from the surface soils of establishing woodland and grazed pasture across four flood vulnerable upland headwater catchments in Dartmoor National Park, SW England. We show upland native woodland establishment is a viable soil recovery option, with a doubling of soil saturated hydraulic conductivity, increased “wetness threshold” and reduced surface soil compaction and bulk density within 15 years of establishment. Our study supports the establishment of native woodland as an effective tool to improve the hydrological functioning of soils in upland pastoral catchments and the provision of flash‐flood mitigation “ecosystem services”. We caution however, that land managers and policy makers must consider past and present management, soil type and catchment location when planning new NFM schemes if environmental benefits are to be maximised and “public money for public goods” are to be commensurate with outcomes. This article is protected by copyright. All rights reserved.
... In recent years land-use management, particularly in the uplands (>250-300 m above sea level in the UK) has been increasingly debated as an effective method of NFM. The management of upland areas is crucial to managing future flood risk (Murphy et al., 2020) as these regions are experiencing greater increases in precipitation compared to lowland areas (Burt & Holden, 2010;Murphy et al., 2019) and play a principal role in river flow generation (Robinson et al., 2013). Many upland soils are often in poor condition, due to a legacy of soil compaction from long-term over grazing (Holden et al., 2007;Murphy et al., 2020;Sansom, 1999). ...
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Management of upland land‐use has considerable potential for mitigating flood risk by increasing topsoil storage and slowing overland flow. Recent work has highlighted the potential for vegetation to impact the velocity of saturation‐excess overland flow. Woodland creation is widely proposed for Natural Flood Management (NFM), but data on saturation‐excess overland flow in woodland habitats is lacking. Here we measure soil properties and overland flow velocities in established broadleaf woodland and wood pasture with an understorey dominated by either grass or bracken. We show that wood pasture dominated by bracken has overland flow velocity 12‐20 % lower than established broadleaf woodland and 19‐27% lower than grass‐dominated wood pasture. Established woodland soils exhibited 8 times higher saturated hydraulic conductivity than bracken‐dominated wood pasture and 80 times higher than grass‐dominated wood pasture. We conclude that upland habitats can be managed to reduce flood risk, first by storing storm water in the soil and then by reducing overland flow velocity through rough surface vegetation. These factors combine to reduce floods by delaying the onset of overland flow runoff and slowing its delivery to streams. It is clear than Manning’s n is far from constant in these shallow overland flows, the development of overland flow datasets is, therefore, also beneficial for improving the theory and practice of hillslope rainfall‐runoff modelling. This article is protected by copyright. All rights reserved.
... As areas where agricultural economic returns are sustained only through agricultural subsidy (EU), UK upland pasture slopes represent ideal areas for woodland expansion to meet climate change commitments and UK environmental policy (Bunce et al., 2018b; Committee on Climate Change, 2019; Defra, 2018a). Moreover, when coupled with recent anthropogenic climate change-driven precipitation increases (Burt & Holden, 2010;Murphy et al., 2019), afforestation of over-compacted soils in upland river catchments has the potential to improve hydrological functioning and alleviate downstream flood risk (Murphy et al., 2020;Stratford et al., 2017). ...
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Abstract Woodland expansion is widely advocated for the mitigation of climate change and its impacts. This is supported by ambitious targets for increasing tree cover in the United Kingdom and elsewhere to aid carbon storage, flood mitigation and biodiversity provision. However, it remains unclear whether natural tree establishment can supply demand for expanded treescapes in remote, anthropogenically modified upland landscapes. We assessed natural establishment of NW‐European native oak (Quercus robur, Q. petraea) saplings (
... In Tel Aviv, however, intertidal trials revealed positive effects of physical complexity (Strain et al., 2021) that contrasted the neutral effects found in the subtidal here. Physical complexity in the intertidal zone was likely more important for reducing thermal stress in Tel Aviv, which is characterized by dry and hot conditions (approximately 500 mm mean annual rainfall; 14-26 • C air temperature; Striem, 1967;Azov, 1991) compared to Plymouth, which is characterized by rainy conditions and a temperate climate (approximately 1000 mm mean annual rainfall; 6-16 • C air temperature; Barrow and Hulme, 1997;Murphy et al., 2019). The differing effects of physical complexity between our subtidal experiments and previous intertidal experiments likely arose from differences in the key environmental stressors to which subtidal and intertidal communities are exposed. ...
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In response to the environmental damage caused by urbanization, Nature-based Solutions (NbS) are being implemented to enhance biodiversity and ecosystem processes with mutual benefits for society and nature. Although the field of NbS is flourishing, experiments in different geographic locations and environmental contexts have produced variable results, with knowledge particularly lacking for the subtidal zone. This study tested the effects of physical complexity on colonizing communities in subtidal habitats in two urban locations: (1) Plymouth, United Kingdom (northeast Atlantic) and (2) Tel Aviv, Israel (eastern Mediterranean) for 15- and 12-months, respectively. At each location, physical complexity was manipulated using experimental tiles that were either flat or had 2.5 or 5.0 cm ridges. In Plymouth, biological complexity was also manipulated through seeding tiles with habitat-forming mussels. The effects of the manipulations on taxon and functional richness, and community composition were assessed at both locations, and in Plymouth the survival and size of seeded mussels and abundance and size of recruited mussels were also assessed. Effects of physical complexity differed between locations. Physical complexity did not influence richness or community composition in Plymouth, while in Tel Aviv, there were effects of complexity on community composition. In Plymouth, effects of biological complexity were found with mussel seeding reducing taxon richness, supporting larger recruited mussels, and influencing community composition. Our results suggest that outcomes of NbS experiments are context-dependent and highlight the risk of extrapolating the findings outside of the context in which they were tested.
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In recognition of the need to address complex environmental problems, some ecological studies have adopted social research methods to better understand the complexity of social‐ecological systems management. The overwhelming majority of these studies stop short of fully embracing qualitative methodologies. The lack of integrative social and natural science data for a topic such as soil carbon farming is problematic as theoretical carbon sequestration opportunities identified through soil mapping and process‐based models can fail to deliver the sequestration levels promised when introduced on‐the‐ground. Such mapping needs to account for the human factors involved in delivering increased soil carbon on‐farm. Here, we develop a mixed methods mapping approach to explore the potential for increasing soil carbon stocks on upland farms in the UK. Our approach considers ecological and social complexity through application of soil science, ecology, participant observation, interviews and a focus group. Our maps revealed landscapes that are full of carbon farming opportunity, but contain previously hidden barriers to the delivery of increased soil carbon. For example, they revealed that carbon farming can be considered by farmers to work in opposition to perceived ‘good farming’ practices and be correlated with increased incidents of livestock disease. We also discovered that the use of maps in research can be problematic as they can close down discussion and exclude local representation of an area. Trialling an interdisciplinary mixed methods approach produced new, deeper and more richly‐textured understandings about how soil carbon management is produced socially as well as ecologically on upland livestock farms. Our findings have potential to improve the success of future carbon farming initiatives by incorporating farmer knowledge and social drivers of implementation. A plain language summary is available for this article. Plain Language Summary
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Global climate change is affecting and will continue to affect ecosystems worldwide. Specifically, temperature and precipitation are both expected to shift globally, and their separate and interactive effects will likely affect ecosystems differentially depending on current temperature, precipitation regimes, and other biotic and environmental factors. It is not currently understood how the effects of increasing temperature on plant communities may depend on either precipitation or where communities lie on soil moisture gradients. Such knowledge would play a crucial role in increasing our predictive ability for future effects of climate change in different systems. To this end, we conducted a multi‐factor global change experiment at two locations, differing in temperature, moisture, aspect, and plant community composition, on the same slope in the northern Mongolian steppe. The natural differences in temperature and moisture between locations served as a point of comparison for the experimental manipulations of temperature and precipitation. We conducted two separate experiments, one examining the effect of climate manipulation via open‐top chambers (OTCs) across the two different slope locations, the other a factorial OTC by watering experiment at one of the two locations. By combining these experiments, we were able to assess how OTCs impact plant productivity and diversity across a natural and manipulated range of soil moisture. We found that warming effects were context dependent, with the greatest negative impacts of warming on diversity in the warmer, drier upper slope location and in the unwatered plots. Our study is an important step in understanding how global change will affect ecosystems across multiple scales and locations.
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Forecasts of summer weather patterns months in advance would be of great value for a wide range of applications. However, seasonal dynamical model forecasts for European summers have very little skill, particularly for rainfall. It has not been clear whether this low skill reflects inherent unpredictability of summer weather or, alternatively, is a consequence of weaknesses in current forecast systems. Here we analyze atmosphere and ocean observations and identify evidence that a specific pattern of summertime atmospheric circulation--the summer East Atlantic (SEA) pattern--is predictable from the previous spring. An index of North Atlantic sea-surface temperatures in March-April can predict the SEA pattern in July-August with a cross-validated correlation skill above 0.6. Our analyses show that the sea-surface temperatures influence atmospheric circulation and the position of the jet stream over the North Atlantic. The SEA pattern has a particularly strong influence on rainfall in the British Isles, which we find can also be predicted months ahead with a significant skill of 0.56. Our results have immediate application to empirical forecasts of summer rainfall for the United Kingdom, Ireland, and northern France and also suggest that current dynamical model forecast systems have large potential for improvement.
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Sea surface temperatures in the northern North Atlantic have shown a marked decrease over the past several years. The sea surface in the subpolar gyre is now as cold as it was during the last cold phase of the Atlantic Multidecadal Oscillation index in the 1990s. This climate index is associated with shifts in hurricane activity, rainfall patterns and intensity, and changes in fish populations. However, unlike the last cold period in the Atlantic, the spatial pattern of sea surface temperature anomalies in the Atlantic is not uniformly cool, but instead has anomalously cold temperatures in the subpolar gyre, warm temperatures in the subtropics and cool anomalies over the tropics. The tripole pattern of anomalies has increased the subpolar to subtropical meridional gradient in SSTs, which are not represented by the AMO index value, but which may lead to increased atmospheric baroclinicity and storminess. Here we show that the recent Atlantic cooling is likely to persist, as predicted by a statistical forecast of subsurface ocean temperatures and consistent with the irreversible nature of watermass changes involved in the recent cooling of the subpolar gyre.
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