PNNL

Abstract

The East African March-April-May (MAM, “long rains”) precipitation decline in recent decades remains a puzzle marked by various proposed large-scale drivers. Here, the interannual variability of the long rains and their recent drying trend are examined using global model simulations and observations. Comparison of a control simulation and a series of re-initialized simulations in which land-surface feedback is suppressed shows that much of the long rains deficit experienced between 1980 and 2014 is synchronized with the warming of the northwestern Asian landmass. In agreement with the modeling results, multiple observational datasets reveal a strong correlation between MAM mean East African rainfall amount and the surface temperature over northwestern Asia. Idealized simulations further indicate that warming in northwestern Asia introduces atmospheric divergence that diverts the monsoonal transport of moisture poleward away from Eastern Africa toward Europe and southern Africa, highlighting the role of remote land surface warming on the observed precipitation decline