Trends and Variability of Temperature and Evaporation Over the African Continent: Relationships with Precipitation

Abstract

This study analyzes changes in the long-term (1901-2015) monthly values of potential evapotranspiration (PET), precipitation, and minimum (Tmin) and maximum (Tmax) temperatures across Africa to quantify trends and assess covariability between these climatic variables. Both warming and drying trends were observed across the continent. The 1979-2015 warming was stronger than that from 1901 to 1940. Some cooling occurred from 1941 to the mid-1970s. The 1901-2015 annual Tmax, Tmin, and PET averaged over Africa exhibited increasing or drying trends across the continent at rates of 0.18 ºC, 0.22 ºC, and 3.5 mm per decade, respectively. The 1961-1990 annual precipitation averaged over the whole continent showed that Africa experienced drying at a rate of about –28 mm per decade. When considering the period 1961-2015, the rate of precipitation decrease was about –8 mm per decade. From 1901 to 1915, areas around Lake Victoria in East Africa and along the western coastline south of the equator experienced wetting rates of up to 36 mm per decade. Significant (p < 0.01) warming trends occurred in Sudan, Southern and Northern Africa. Positive PET trends were significant (p < 0.01) in the warm Mediterranean climate, and the western part of South Africa. Long-term temperature increase and precipitation decrease across northern Africa possibly indicated the Sahara Desert expansion over time. Except in the warm desert climate, the continent exhibited high precipitation variability. Equatorial climate experienced low temperature and PET variability. The strongest coherence between precipitation and temperature existed at multiple scales (6-8 years). Correlations between precipitation and PET (or temperature) were mostly negative and weak (p > 0.01). Because the sensitivity of Tmin to local influences is higher than that of Tmax, areas with strong negative correlation were larger in coverage for Tmax than those of Tmin. These results call for planned measures to tackle food insecurity in sub-Saharan Africa.