This project examines the rainy seasons of East Africa, including their interannual variability and connections to rainfall variability in other parts of Africa. The region considered is roughly Tanzania, Uganda, and Kenya. Most of the rainfall in this region comes in two seasons, the "long rains" occurring between March and May, and the "short rains" during the October to December season. Of the two, the short rains account for most of the interannual rainfall variability and have much stronger connections to sea surface temperature. The project addresses a set of four general topics. First, the research will examine the causes of the general aridity of the region, which is unusual for an equatorial region. Second, the role of the Turkana jet in determining the regional precipitation climatology and the year-to-year variability of the rains will be considered. The Turkana jet is a low-level jet that flows through a narrow gap between the Ethiopian and East African highlands, and has not been extensively studied. Third, the extent to which a local intertropical convergence zone (ITCZ) is responsible for the seasonality and interannual variability of rainfall will be determined. The seasonality and variability of rainfall over much of Africa is commonly attributed to ITCZ movement, but this paradigm is problematic over East Africa. Fourth, the research will provide an examination of interannual variability of the rainy seasons, both for the short and long rains, seeking to understand the relative roles of Indian (particularly the Indian Ocean Dipole Mode), Pacific (El Nino), and Atlantic Ocean variability in determining rainfall variability, and the reasons for dipole teleconnection patterns between rainfall anomalies in East Africa and in other parts of Africa. The work would also consider the possibility that the climate of the region has changed in recent years. A novel aspect of the work is the use of a rain gauge record extending back to 1874, along with semi-quantitative precipitation time series for several regions of East Africa extending back to 1820.
The work has societal impact through its focus on the behavior of droughts and floods in East Africa, which take a heavy toll on the people of the region. The work could lead to statistical relationships between rainfall and sea surface temperature which could be useful for forecasting variations in the rainy seasons, including prolonged periods of flood and drought. In addition, the project supports two graduate students, thereby training the next generation of researchers in the field.
