Dataset - Frequent but Predictable Droughts in East Africa Driven By A Walker Circulation Intensification

The decline of the eastern East African (EA) March-April-May (MAM) rains
poses a life-threatening ‘enigma’, an enigma linked to sequential droughts
in the most food insecure region in the world. The MAM 2022 drought was
the driest on record, preceded by three poor rainy seasons, and followed
by widespread starvation. Connecting these droughts is an interaction
between La Niña and climate change, an interaction that provides exciting
opportunities for long lead prediction and proactive disaster risk
management. Using observations, reanalyses, and climate change
simulations, we show here, for the first time, that post-1997 OND La Niña
events are robust precursors of: (1) strong MAM ‘Western V Gradients’ in
the Pacific, which help produce (2) large increases in moisture
convergence and atmospheric heating near Indonesia, which appear
associated with (3) regional shifts in moisture transports and vertical
velocities, which (4) help explain more frequent dry EA rainy seasons.
Understanding this causal chain will help make long-lead forecasts more
actionable. Increased Warm Pool atmospheric heating and moisture
convergence sets the stage for dangerous sequential droughts in EA. At
20-yr time scales, we show that these Warm Pool heating increases are
attributable to observed Western V warming, which is in turn largely
attributable to climate change. As energy builds up in the oceans and
atmosphere, we see stronger convergence patterns, which offer
opportunities for prediction. Hence, linking EA drying to a stronger
Walker Circulation can help explain the ‘enigma’ while underscoring the
predictable risks associated with recent La Niña events.