Afternoon rain more likely over drier soils

C. Taylor, R.A.M. de Jeu, F. Guichard, P. Harris, W. Dorigo

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Land surface properties, such as vegetation cover and soil moisture, influence the partitioning of radiative energy between latent and sensible heat fluxes in daytime hours. During dry periods, soil-water deficit can limit evapotranspiration, leading to warmer and drier conditions in the lower atmosphere. Soil moisture can influence the development of convective storms through such modifications of low-level atmospheric temperature and humidity, which in turn feeds back on soil moisture. Yet there is considerable uncertainty in how soil moisture affects convective storms across the world, owing to a lack of observational evidence and uncertainty in large-scale models. Here we present a global-scale observational analysis of the coupling between soil moisture and precipitation. We show that across all six continents studied, afternoon rain falls preferentially over soils that are relatively dry compared to the surrounding area. The signal emerges most clearly in the observations over semi-arid regions, where surface fluxes are sensitive to soil moisture, and convective events are frequent. Mechanistically, our results are consistent with enhanced afternoon moist convection driven by increased sensible heat flux over drier soils, and/or mesoscale variability in soil moisture. We find no evidence in our analysis of a positive feedbackthat is, a preference for rain over wetter soilsat the spatial scale (50100 kilometres) studied. In contrast, we find that a positive feedback of soil moisture on simulated precipitation does dominate in six state-of-the-art global weather and climate modelsa difference that may contribute to excessive simulated droughts in large-scale models. © 2012 Macmillan Publishers Limited. All rights reserved.
Original languageEnglish
Pages (from-to)423-426
JournalNature
Issue number489
Early online date12 Sep 2012
DOIs
Publication statusPublished - 2012

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