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Application of Global Circulation Model (GCM) results in simulating future rainfall in East Africa

Congress: 2008

Keyword(s): global circulation model, climate scenario, rainfall, downscaling
AbstractClimate change refers to any change in climate over time, whether due to natural variability in surface temperature or as a result of human activity. However, today, the term ‘climate change’ is almost the synonym of ‘global warming’, which is caused by the increase of greenhouse gases trapped in the atmosphere. The General Circulation Models (GCMs, also known as Global Climate models) are known as the only currently available tools for simulating the response of the global system to increasing greenhouse gas concentrations. Due to the coarse resolution of the GCMs results, downscaling is the common practice. However, how good is a GCM results in at a local scale? Does downscaling improve the GCM results? This paper aims to compare GCMs simulated rainfall with with the observed rainfall, and compare downscaled GCMs simulated rainfall with the observed rainfall. GCM simulated rainfall from five GCMs’ experiment based on IPCC SRES A2 scenario are used. Observed daily rainfall for five catchments in Lake Victoria, East Africa has been used. The five catchments are Nzoia, Yala, Sondu, Gucha and Mara. The LARS-WG weather generator has been used as temporal downscaling tool. The results shows inter-model disparities in GCMs simulated rainfall though the models were based on similar climate change scenario. The GCMs simulated rainfall have no features and trend of the local rainfall, which may be caused by the failure of current available models to simulate convective rainfall that is common in East Africa. Downscaling results successfully incorporated future climate changes to station-based perturbations. Downscaled rainfall shows seasonal rainfall trend to the observed. This method shows good consistency in maintaining mean and standard deviation but the wet spell and dry spell estimations are less convincing.
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