Evaluation and Climate Change Projections of the Global Hydrological Cycle in IPCC AR4 Model Simulations

We will present results from ongoing research that involves assessing the realism of the global hydrological cycle (GHC) in a number of general circulation models (GCMs), with a particular focus on the models making contributions to the IPCC's 4th Assessment Report (AR4). This analysis includes evaluating the representation of the major reservoirs and flux components on annual and longer time scales over global and basin/continental scales. For validation, we draw on a number of reanalysis products (e.g., ERA-40, NCEP2) as well as state-of-the art satellite estimates where available/appropriate (e.g., SSM/I, SMRR, GPCP, AIRS, GRACE). In addition, we examine how the representation of the GHC changes under imposed conditions of climate change according to a number of AR4 scenarios (e.g., A2, B1). This includes an evaluation of how the residence times of the various reservoirs are effected and efforts to understand the principal physical mechanisms for these changes.