Spatial and temporal variation of drought patterns over East Africa

Understanding historical patterns of changes in drought is essential for drought adaptation and mitigation.
While the negative impacts of drought over east Africa have attracted increasing attention,
a comprehensive and long-term spatiotemporal assessment of drought is still lacking. Here, we provided
a comprehensive spatiotemporal drought pattern analysis during the period of 1964–2015 over
the GHA. The Standardised Precipitation-Evapotranspiration Index (SPEI) at various timescales (1 month
(SPEI-01), 3 month (SPEI-03), 6 month (SPEI-06), and 12 month (SPEI-12)) was used to investigate drought
patterns on a monthly, seasonal, and interannual basis. The results showed that despite regional differences,
an overall increasing tendency of the drought was observed across the GHA over the past 52 yr, with trends of
change of -0.0017 yr^-1, -0.0036 yr^-1, -0.0031 yr^-1, and -0.0023 yr^-1 for SPEI-01, SPEI-03, SPEI-06, and
SPEI-12, respectively. Droughts were more frequent, persistent, and intense in Sudan and Tanzania, while
more severe droughts were found in Somalia, Ethiopia, and Kenya. Droughts occurred frequently before
the 1990 s, and then became intermittent with large-scale impacts occurred during 1973–1974, 1984–
1985, and 2010–2011. A turning point was also detected in 1989, with the SPEI showing a statistically significant
downward trend during 1964–1989 and a non-statistically significant downward trend from 1990
to 2015. Seasonally, droughts exhibited an increasing trend in winter, spring, and summer, but a decreasing
trend in autumn. The research findings have significant implications for drought adaptation and mitigation
strategies through identifying the hotspot regions over east Africa at various timescales. Area-specific
efforts are required to alleviate environmental and societal vulnerabilities to drought events.