Examining evapotranspiration trends in Africa

Surface temperatures are projected to increase 3-4A degrees C over much of Africa by the end of the 21st century. Precipitation projections are less certain, but the most plausible scenario given by the Intergovernmental Panel on Climate Change (IPCC) is that the Sahel and East Africa will experience modest increases (similar to 5%) in precipitation by the end of the 21st century. Evapotranspiration (E-a) is an important component of the water, energy, and biogeochemical cycles that impact several climate properties, processes, and feedbacks. The interaction of E-a with climate change drivers remains relatively unexplored in Africa. In this paper, we examine the trends in E-a, precipitation (P), daily maximum temperature (T-max), and daily minimum temperature (T-min) on a seasonal basis using a 31 year time series of variable infiltration capacity (VIC) land surface model (LSM) E-a. The VIC model captured the magnitude, variability, and structure of observed runoff better than other LSMs and a hybrid model included in the analysis. In addition, we examine the inter-correlations of E-a, P, T-max, and T-min to determine relationships and potential feedbacks. Unlike many IPCC climate change simulations, the historical analysis reveals substantial drying over much of the Sahel and East Africa during the primary growing season. In the western Sahel, large increases in daily maximum temperature appear linked to E-a declines, despite modest rainfall recovery. The decline in E-a and latent heating in this region could lead to increased sensible heating and surface temperature, thus establishing a possible positive feedback between E-a and surface temperature.