Assessment of new large-scale cloud cover and rainfall parameterizations for Regional Climate Modeling over the Upper Blue Nile basin

Abstract:

In this study we investigate the performance of new parameterizations of large-scale cloud and rainfall for use with climate models. Here, we apply these new parameterizations within MIT Regional Climate Model (MRCM), a modified version of Regional Climate Model, version 3 (RegCM3) including the land surface scheme Integrated Biosphere Simulator (IBIS) and recently developed parameterizations for the convective cloud cover and convective rainfall. The performance of the new parameterizations with MRCM is evaluated using 21-years regional climate model simulations over the upper Blue Nile basin. The new parameterizations improve the simulations of the water and energy budgets, and the simulations of the shape of the seasonal cycle and magnitude of rainfall over the basin compared to observations. On the other hand, the improvement in the simulations of cloud cover is reflected in the magnitudes of the simulated outgoing longwave radiation and planetary albedo, in comparison to satellite observations. The resulting increase in the net radiation at the surface increases the amount of evapotranspiration, impacting the simulated runoff over the basin bringing it closer to gauge observations.