High Resolution Climate Simulations over Africa: Past, Present, and Future

Abstract

The horizontal resolution is a prominent constraint on the accuracy of simulating synoptic and sub-synoptic scale rainfall. High resolution General Circulation Models are signi cantly better than Regional Climate Models and conventional coarse resolution General Circulation Models in their representation of atmospheric circulation and precipitation. In this study two monsoon systems over Africa, the features associated with them, and their future are examined using a high resolution Atmospheric General Circulation Model, HiRAM. HiRAM, which is developed at Geophysical Fluid Dynamics Laboratory, employs a cubed-sphere nite volume dynamical core and uses shallow convective scheme for moist convection and stratiform cloudiness instead of a deep convective parameterization. Future projections are conducted using the representative concentration pathway, RCP 8.5 from 2076 to 2099 at C360 ( 25 km)resolution. The study explores three important climate features of the region: West African Monsoon, Southern African Monsoon, and African Easterly Waves. These climate systems particularly bene t from high resolution simulations since they involve several multiscale processes and are in uenced by coastlines and complex topography. The study shows that, in the RCP 8.5 scenario, elevated areas of Sahel and western Sahara experience robust warming of >4K by the end of the 21st century. Precipitation increases over the equatorial Atlantic and the Guinean coast, while the southern Sahel appears drier. The wave activity of the region also shows a signi cant increase. The examination of the future projections of southern Africa reveals increased precipitation over central Africa and contrasting anomalies over northern Madagascar while Kalahari desert experience signi cant warming. The rainfall change in a global warming scenario is not unidirectional, unlike the temperature which increases almost everywhere and this emphasizes the need for more projection studies.