Variability of East African rainfall based on multiyear Regcm3 simulations

Abstract

Abstract:The International Center for Theoretical Physics (ICTP) regional climate model version 3 (ICTP-RegCM3) multiyear simulations of East Africa rainfall during the October-December, short rains season are evaluated. Two parallel runs; based on NCEP reanalysis and NASA FvGCM lateral boundary conditions are performed. The simulated monthly and seasonal rainfall climatology as well as the interannual variability are found to be fairly consistent with the observations. The model climatology over specific homogeneous climate subregions, except central Kenya (CKE) highlands, also reasonably agrees with the observed. The latitude-time evolution (intraseasonal variability) of the simulated seasonal rainfall exhibits two distinct modes of behavior. The first is a quasistationary mode associated with high rainfall throughout the season within the equatorial belt between 1°S and 2°N. The second mode is associated with the intertropical convergence zone (ITCZ)-driven southward migration of regions of rainfall maxima as the season progresses, which is also consistent with the observed. Furthermore, observed rainfall variability over distinct homogeneous climate subregions is also fairly reproduced by the model, except over central Kenya highlands and northeastern parts of Kenya. The spatial correlation between the simulated seasonal rainfall and some of the global teleconnections (DMI and Nino3.4 indices) shows that the regional model conserves some of the observed regional 'hot spots' where rainfall-ENSO/DMI associations are strong. At the same time, unlike observations, the model reveals that along the East Africa Rift Valley and over western parts of the Lake Victoria Basin, the association is weak, perhaps an indication that nonlinear interactions between local forcing (captured by the model) and large-scale systems either suppress or obscur the dominant influence of the teleconnections on rainfall over certain parts.

The influence of El Niño–Southern Oscillation regimes on eastern African vegetation and its future implications under the RCP8.5 warming scenario

“…Here we used a different method, EOT analysis, to quantitatively calculate the ENSO contribution, and found the spatial correlation patterns over the eastern Africa region to be in agreement with previous studies which independently looked at Pacific SST drivers for eastern African precipitation (Anyah and Semazzi, 2007). The ENSO signal identified through this method also shows strong correlation with the NOAA Niño-3.4 Index, which means the EOT method was a suitable choice for our analysis.…”

“…Southern Oscillation (ENSO) influence has long been at the centre of attention as a driver of these interannual fluctuations in eastern African rainfall (Indeje et al, 2000;Anyah and Semazzi, 2007;Nicholson, 2015); however, it is still an ongoing endeavour to qualify and quantify the future behaviour of ENSO regimes under the predicted future warming (Vecchi and Wittenberg, 2010;Miralles et al, 2014). In this study we aim to identify and quantify the ENSO contribution to the eastern African rainfall variability in order to increase our understanding of the future response of eastern African vegetation to rainfall variability related to changing ENSO regimes and climate, which can have dire consequences in this region in terms of food and social security.…”

Indigenous climate knowledge in southern Uganda: the multiple components of a dynamic regional system

“…The dry period that runs through June, July and August is longer than the one in January and February; the average monthly rainfall during these dry seasons is 43 mm, which is insufficient for agriculture. As in other parts of East Africa (Anyah and Semazzi 2006), there is significant variability in the timing and amount of rainfall in both seasons. In recent years, meteorologists have improved their ability to forecast this variability, drawing on historical analogies and on regional models that include ENSO indices, Indian Ocean sea surface temperatures, conditions in the Congo Basin and the Arabian Peninsula, and other factors.…”

Evaluation of the performance of CORDEX regional climate models in simulating present climate conditions of Tanzania

“…However, seasonal interactions within the ITCZ, perturbations in global climate circulation and changes in local circulation systems (which are influenced by complex topographical features) all contribute to high local climate variability. The seasonal rainfall is modulated by changes in the global sea surface temperatures (SSTs) especially over the equatorial Pacific and Indian oceans (Black et al 2003, Black 2005, Anyah and Semazzi 2007.…”