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Afternoon rain more likely over drier soils

Taylor, Christopher M.; de Jeu, Richard A. M.; Guichard, Francoise; Harris, Phil P.; Dorigo, Wouter A.. 2012 Afternoon rain more likely over drier soils. Nature, 489. 423-426. 10.1038/nature11377

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Abstract/Summary

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, a soil-water deficit can limit evapotranspiration, leading to increased surface heating ofwarmer and drier conditions in the lower atmosphere and affecting the climate. 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 feedback—that is, a preference for rain over wetter soils—at the spatial scale (50–100 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 models—a difference that may contribute to excessive simulated droughts in large-scale models.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1038/nature11377
Programmes: CEH Topics & Objectives 2009 - 2012 > Biogeochemistry > BGC Topic 2 - Biogeochemistry and Climate System Processes > BGC - 2.3 - Determine land-climate feedback processes to improve climate model predictions
CEH Sections: Reynard
ISSN: 0028-0836
Additional Information. Not used in RCUK Gateway to Research.: This document is the author’s final manuscript version of the journal article following the peer review process. Some differences between this and the publisher’s version may remain. You are advised to consult the publisher’s version if you wish to cite from this article. www.nature.com/
Additional Keywords: climate science, environmental science
NORA Subject Terms: Hydrology
Meteorology and Climatology
Atmospheric Sciences
Date made live: 13 Sep 2012 15:18
URI: http://nora.nerc.ac.uk/id/eprint/19573

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