Surface water balance estimation for a semi-arid region using a regional climate model and comparison of water balance components with global circulation model output and analysis data

Abstract

We have applied the regional climate model REMO, which is based on the Europa-Modell (EM) of the Deutscher Wetterdienst (DWD), to the Tropics. We have performed model runs using the so-called “nesting technique”. Results of a Global Circulation Model (GCM) with a T42 horizontal resolution, driven by observed Sea Surface Temperatures (SST's) covering the time-span December 1982 to December 1983 are used as initial and boundary conditions. Before using regional model results as driving forces for impact models, the model results have to be carefully validated in several steps. Here, we focus on the ability of both models in reproducing the surface water balance within the land-covered part of the model area shown in Fig. 1 as well as within a diagnosis area in Northeastern Brazil (NEB). We compare the model-simulated components contributing to this balance with analysis data. As an example, observations from a location in Central Piauí are used to relate modelled and analysed precipitation to real data. Conclusions are drawn on requirements for improved physical parametrizations and modified initial and boundary conditions. From the model comparison, it becomes clear that a comprehensive validation of the regional model for climate impact research using observations will only be possible if changed experimental conditions are applied. Therefore, it is intended to provide initial and lateral boundary conditions from analysis data to the regional model and to use a parametrization package which includes a large scale precipitation scheme as applied in the global models ECHAM3 and ECHAM4 in future investigations.