Climate models are the main tools for predicting future climate and for creating credible future climate change scenarios. However, prior to their use to simulate future climate conditions, we need evaluate their skill in simulating the current and past climates.
The hydrological cycle of climate models over major African basins is not well simulated. This requires that for any climate change study that aims to predict changes in future flows, climate models should be evaluated before their use. The proposed evaluation method is based on verifying the water balance of the land-atmosphere system in climate models and reanalysis products and testing their ability to represent the seasonal cycle of stream flow over large basins. This method can be used in the future to identify climate models that best simulate the hydrological cycle and are best candidates to study future changes in stream flow over such basins.
(a) (b)
Spatial distribution of the annual average of: a) Convergence of atmospheric moisture (mm/day) overlaid by the moisture fluxes field (Kg/ms), b) Simulated Runoff (mm/day)
The long-term average of the runoff is exactly balanced by the long-term average convergence of atmospheric moisture which is a key variable of the atmospheric water balance. The ability of climate model to simulate the seasonal cycle of the convergence of moisture is a good diagnostic measure of the climate models accuracy to simulate the hydrological cycle.
Average seasonal cycle of the convergence of atmospheric moisture and difference of precipitation and evaporation using the ERA-Interim Reanalysis product comapred to observations for: a) The Upper Blue Nile basin and b) The Congo basin
Reference:
Siam, Mohamed S., Marie-Estelle Demory, Elfatih A. B. Eltahir, 2013: Hydrological Cycles over the Congo and Upper Blue Nile Basins: Evaluation of General Circulation Model Simulations and Reanalysis Products. J. Climate, 26, 8881–8894. doi: http://dx.doi.org/10.1175/JCLI-D-12-00404.1