Abstract 182

Abstract ID: 182

Drivers of S2S Forecast Errors of the East African Short Rains

Lead Author: Erik W. Kolstad
NORCE, Bjerknes Centre for Climate Research, Norway

Keywords: Rainy season, East Africa, Forecast errors

Abstract: In East Africa, the rainfall is usually concentrated in specific periods of the year. One of these periods occurs between October and December and is called the ‘short rains’. Failure of the short rains can have disastrous effects on farmers and pastoralists, as there exists little infrastructure for irrigation in the region. Similarly, too heavy rains can yield devastating floods. Advance knowledge of the timing and nature of the short rains is therefore crucial for planning and preparedness. However, the usefulness of any prior information is contingent on accurate forecasts, which are mainly based on numerical models. Here we study the relationship between initial-state sea surface temperatures and sub-seasonal rainfall forecast errors in the ECMWF model in the region. We demonstrate that the initial mode of the Indian Ocean Dipole (IOD) is a partial control on the rainfall error in weeks 3–4. This relationship is also clear on the seasonal scale, exemplified by too-wet forecasts during the 2015 season when the IOD was positive, and too-dry forecasts in 2010 when it was negative. Our results provide an entry point for model improvement, and we show that a priori forecast corrections based on the initial IOD index are feasible.

David MacLeod (Cardiff University, UK)
Teferi D. Demissie (NORCE, and Bjerknes Centre for Climate Research, Norway)