Investigating the response of terrestrial evapotranspiration to droughts in Africa : A combined remote sensing and modeling approach

Abstract: Climate change is posing a significant threat to terrestrial ecosystems worldwide, in part due to the more frequent occurrence of extreme climatic events such as droughts. While the importance of drought impacts on vegetation has been widely recognized, the time-dependent characteristics of drought-induced response remain insufficiently understood. In this study, we examine the sensitivity of terrestrial evapotranspiration (ET) to water availability in African biomes using a suite of satellite and geospatial data. By correlating a multi-scalar drought index with monthly ET anomalies between 1981 and 2016, the spatiotemporal effects of drought are evaluated and compared against simulations from a coupled vegetation-climate model. The coupling between water availability and ET is found to be largely dependent on aridity conditions and the evapotranspiration regime (energy- vs. soil moisture-limited). We also observed the dominant role of root zone storage capacity in mediating ET response among rainforests and savannas, whereas shrubs and grasslands tend to exhibit much more complex soil-plant interactions. Comparing between model simulations and observations, discrepancies in the magnitude and timing of ET response were evident. Our findings highlight the need for an explicit consideration of plant-available water to improve the representation of hydroclimatic processes in Earth system models.