SWELTER-21 stands for “Soil water – climate feedbacks in Europe in the 21st Century”. This project has been using a state-of-the-art computer model of the land surface and atmosphere, combined with new compilations of data obtained from satellites, to improve our understanding of how soil wetness influences rainfall.
We are using observations from periods of drought to see directly how temperatures rise as soil water declines. We also use satellite imagery to examine whether local storms are more likely to develop under certain soil conditions within Europe. This knowledge is being applied to improve the description of the water cycle within the UK Met Office model used both for climate and seasonal prediction.
Computer predictions of future climate agree that rising concentrations of greenhouse gases will warm the earth's surface over the 21st century. There is less consensus concerning how this will affect the climate in a region such as Europe, in particular when considering changes in rainfall. Broadly speaking, northern Europe is likely to get wetter, particularly during the winter, and central and southern Europe are expected to experience drier and hotter summers.
Uncertainty in our predictions of rainfall and drought arises from the inadequate description of key processes in climate models. One key area which this project focusses on is the relationship between the atmosphere and the land. During summer, soils dry, which in many parts of Europe limits evaporation of soil moisture into the atmosphere. When this happens, less solar energy absorbed by the land surface is used for evaporation and more is used to warm the atmosphere directly. This "feedback" can affect the development of clouds and rainfall, especially the occurrence of local summertime storms which develop during the afternoon. Furthermore, when soil dries out over a large region, as happened for example across much of Western and Central Europe during 2003, the lack of land evaporation can affect much larger-scale weather systems. Indeed some studies have suggested that 2003 may illustrate the shape of summers to come, with drier spring soils favouring summer drought and heat-waves.
Modeling soil moisture-precipitation feedback in the Sahel: Importance of spatial scale versus convective parameterization
2013. Geophysical Research Letters, 40 (23), 6213–6218. DOI: 10.1002/2013GL058511
Improved evaporative flux partitioning and carbon flux in the land surface model JULES: Impact on the simulation of land surface processes in temperate Europe
2013. Agricultural and Forest Meteorology, 181, 108–124. DOI: 10.1016/j.agrformet.2013.07.011
Dr Chris Taylor, Centre for Ecology and Hydrology
Prof Pier-Luigi Vidale, University of Reading
Dr Anne Verhoef, University of Reading
Prof John Remedios, University of Leicester
Dr Sean Milton, Met Office