Tropical drivers of interannual vegetation variability in eastern Africa

Here, we use idealized climate model simulations to elucidate the governing processes for eastern African interannual hydroclimate and vegetation changes and their relationship to the El Niño-Southern Oscillation (ENSO). Our analysis focuses on Tanzania. In the absence of ENSO-induced sea surface temperature anomalies in the Tropical Indian Ocean, El Niño causes during its peak phase negative precipitation anomalies over Tanzania due to a weakening of the tropical-wide Walker circulation. Resulting drought conditions increase wildfires and decrease vegetation cover. Subsequent wetter La Niña conditions reverse the trend, causing a gradual 1-year-long recovery phase. The 2-year-long vegetation response in Tanzania can be explained as a double-integration of local rainfall, which originates from the seasonally-modulated ENSO Pacific-SST forcing (ENSO Combination mode). In the presence of interannual TIO SST forcing, the southeast African ENSO precipitation and vegetation responses are muted due to Indian Ocean warming and the resulting anomalous upward motion in the atmosphere.