Seasonal and Long-term Variability in the Atmospheric Moisture Budget and Transport over East Africa

While the climatic characteristics and controlling mechanisms across parts of Africa, notably the Sahel, have been extensively studied, a lot less is known about the climate across the complex terrain of East Africa. In recent decades, East Africa has experienced major climatic changes, in particular, a significant decline in precipitation during the “long rains" (March-May). In addition, current future precipitation projections over East Africa are subject to great uncertainty, hampering policy planning and calling into question the reliability of state-of-the-art climate models. A better understanding of the mechanisms involved in East African climate variability and change is therefore a necessity.

This study is part of the Future Climate For Africa’s HyCRISTAL project that aims to understand the variability and change of the East African hydrological cycle. We exploit multiple observational and reanalysis products to explore the processes involved in the inter-annual variability and long-term trends of seasonal rainfall over East Africa, with a focus on the atmospheric water budget terms, precipitation recycling and large-scale atmospheric moisture transport. Our initial findings indicate that model reanalyses, often used a trusted reference for atmospheric fields, capture some aspects of the observed rainfall variability but fail to capture the observed rainfall trends, raising concerns over the reliability of these data sets for understanding long-term changes in the climate. Further analyses are underway to scrutinise each reanalysis individually and determine what useful information can be obtained. Our analyses will eventually be extended to the CMIP5 suite of models to better understand climate model deficiencies.