Global observational diagnosis of soil moisture control on the land surface energy balance

Belen Gallego‐Elvira,Sonja S Folwell,Darren Ghent,Christopher M Taylor,Phil P Harris,Karen L Veal

doi:10.1002/2016gl068178

Abstract

AbstractAn understanding of where and how strongly the surface energy budget is constrained by soil moisture is hindered by a lack of large‐scale observations, and this contributes to uncertainty in climate models. Here we present a new approach combining satellite observations of land surface temperature and rainfall. We derive a Relative Warming Rate (RWR) diagnostic, which is a measure of how rapidly the land warms relative to the overlying atmosphere during 10 day dry spells. In our dry spell composites, 73% of the land surface between 60°S and 60°N warms faster than the atmosphere, indicating water‐stressed conditions, and increases in sensible heat. Higher RWRs are found for shorter vegetation and bare soil than for tall, deep‐rooted vegetation, due to differences in aerodynamic and hydrological properties. We show how the variation of RWR with antecedent rainfall helps to identify different evaporative regimes in the major nonpolar climate zones.

Highlights

Soil moisture (SM) plays a central role in the partition of available energy at the land surface
There are large variations in the number of dry spell days and events according to our definition, due to the diversity of regional hydroclimates (Figure 2a)
Since daily variations in solar radiation and wind speed are minimal during our dry spells, the observed surface warming can be associated with water stress; positive Relative Warming Rate (RWR) indicate an increase of H during dry spells

Summary

Introduction

Soil moisture (SM) plays a central role in the partition of available energy at the land surface. Precipitation deficits have been linked to hot extremes [Hirschi et al, 2011; Mueller and Seneviratne, 2012; Vautard et al, 2007], with established SM deficits interacting with the large-scale circulation to amplify summertime temperature variability [Haarsma et al, 2009; Miralles et al, 2014; Quesada et al, 2012]. This atmospheric warming can in turn affect SM through changes in humidity deficit, cloud cover, and precipitation [Fischer et al, 2007; Taylor et al, 2012]. Such soil moisture-atmosphere interactions are projected to strengthen under future climate change [Dirmeyer et al, 2013]

Methods

Results

Conclusion