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

An 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.