Uncertainties in monsoon precipitation projections over China: results from two high-resolution RCM simulations

A high-resolution climate change simulation at a grid spacing of 25 km was conducted over East Asia with the Abdus Salam International Centre for Theoretical Physics' (ICTP) regional climate model RegCM3, for the period 1951-2100.The model is driven at the lateral boundaries by the global model CCSR/NIES/FRCGC MIROC3.2_hires.Two time slices, 1961-1990 for present-day and 2071-2100 for future climate conditions were analyzed and compared with a previous high-resolution simulation of RegCM3 driven by the NASA/NCAR global model FvGCM.The focus of the present paper is on mean temperature and precipitation and their changes during the monsoon season (May-September).Overall, for present-day conditions, the regional model improves the simulation of both temperature and precipitation patterns compared to the driving global climate models, with greater agreement between the RegCM3 simulations than with the corresponding driving models.When driven by the 2 global models, RegCM3 simulates a consistent precipitation change pattern over western China, characterized by an increase over the northwest and a decrease over the Tibetan Plateau and Southwest China.These latter precipitation decreases have opposite signs compared those from the driving global models, and the causes of these differences (mostly associated with the different topographic representations) are discussed in the paper.This implies that over these regions the internal model physics and processes can be dominant factors.On the other hand, warming patterns are essentially driven by the large-scale boundary forcing.Our results show that precipitation change projections by current global models need to be considered cautiously and that the use of nested regional models adds an element of uncertainty which needs to be properly characterized.