Assessment of uncertainty in river flow projections for the Mekong River using multiple GCMs and hydrological models

摘要

Hydrological model-related uncertainty is often ignored within climate change hydrological impact assessments. A MIKE SHE model is developed for the Mekong using the same data as an earlier semi-distributed, conceptual model (SLURP). The model is calibrated and validated using discharge at 12 gauging stations. Two sets of climate change scenarios are investigated. The first is based on a 2 °C increase in global mean temperature (the hypothesised threshold of 'dangerous' climate change), as simulated by seven GCMs. There are considerable differences in scenario discharge between GCMs, ranging from catchment-wide increases in mean discharge (up to 12.7%; CCCMA CGCM31, NCAR CCSM30), decreases (up to 21.6% in the upper catchments; CSIRO Mk30, IPSL CM4), and spatially varying responses (UKMO HadCM3 and HadGEM1, MPI ECHAM5). Inter-GCM differences are largely driven by differences in precipitation. The second scenario set (HadCM3, increases in global mean temperature of 1-6 °C) shows consistently greater discharge (maximum: 28.7%) in the upper catchment as global temperature increases, primarily due to increasing precipitation. Further downstream, discharge is strongly influenced by increasing PET, which outweighs impacts of elevated upstream precipitation and causes consistent discharge reductions for higher temperatures (maximum: -5.3% for the main Mekong). MIKE SHE results for all scenarios are compared with those from the SLURP catchment model and the Mac-PDM.09 global hydrological model. Although hydrological model-related uncertainty is evident, its magnitude is smaller than that associated with choice of GCM. In most cases, the three hydrological models simulate the same direction of change in mean discharge. Mac-PDM.09 simulates the largest discharge increases when they occur, which is responsible for some differences in direction of change at downstream gauging stations for some scenarios, especially HadCM3. Inter-hydrological model differences are likely attributed to alternative model structures, process representations and PET methods (Linacre for MIKE SHE and SLURP, Penman-Monteith for Mac-PDM.09).