Probability of afternoon precipitation in eastern United States and Mexico enhanced by high evaporation

• Published in: Nature geoscience Vol. 4; no. 7; pp. 434 - 439
• Main Authors: Findell, Kirsten L., Gentine, Pierre, Lintner, Benjamin R., Kerr, Christopher
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2011; Nature Publishing Group
• Subjects: 704/106; 704/2151/241; Earth and Environmental Science; Earth Sciences; Earth System Sciences; Evaporation; Evapotranspiration; Geochemistry; Geology; Geophysics/Geodesy; Hydrology; letter; Rainfall intensity; Sensible heat; Soil moisture; ASW, Mexico; USA, Mississippi
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo1174

Feedbacks between soil moisture and precipitation are among the most important land–atmosphere interactions. An analysis of evaporative fluxes over North America suggests that the probability of afternoon rainfall in Mexico and the eastern United States is increased during periods of enhanced evaporation. Moisture and heat fluxes from the land surface to the atmosphere form a critical nexus between surface hydrology and atmospheric processes, particularly those relevant to precipitation. Although current theory suggests that soil moisture generally has a positive impact on subsequent precipitation, individual studies have shown support both for 1 , 2 , 3 , 4 and against 5 , 6 , 7 this positive feedback. Broad assessment of the coupling between soil moisture and evapotranspiration, and evapotranspiration and precipitation, has been limited by a lack of large-scale observations. Quantification of the influence of evapotranspiration on precipitation remains particularly uncertain. Here, we develop and apply physically based, objective metrics for quantifying the impacts of surface evaporative and sensible heat fluxes on the frequency and intensity of convective rainfall during summer, using North American reanalysis data. We show that high evaporation enhances the probability of afternoon rainfall east of the Mississippi and in Mexico. Indeed, variations in surface fluxes lead to changes in afternoon rainfall probability of between 10 and 25% in these regions. The intensity of rainfall, by contrast, is largely insensitive to surface fluxes. We suggest that local surface fluxes represent an important trigger for convective rainfall in the eastern United States and Mexico during the summer, leading to a positive evaporation–precipitation feedback.