Impacts of projected climate change on runoff in upper reach of Heihe River basin using climate elasticity method and GCMs.

Understanding the impacts of climate change on runoff is of great importance for water resource assessments and adaptation strategy developments especially for the areas where scare and unevenly distributed water are available. Compared to the hydrological modelling method, the climate elasticity method is more flexible with the advantage of using few data in addressing the issue of investigating the effects of climate change on runoff. This study employed Budyko-based climate elasticity method, combined with temperature-based Blaney-Criddle equation, to obtain the elasticities of runoff to two major climate variables, and then applied this methodology to the upper reach of Heihe River basin, China. The runoff elasticity to precipitation in the study area was estimated to be 0.56-0.57, and the elasticity to temperature was -0.017 to -0.018. Precipitation increases showed a positive effect to runoff increases, and temperature increases showed a negative effect. Performances of 18 General Circulation Models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5) were assessed and the best GCMs were selected based on the entropy weighted TOPSIS approach. CSIRO-Mk3.6.0, CCSM4, and CanESM2 were ranked the first three with the best performances in simulating the observed precipitation and temperature over the study area. Climate projections from the above three GCMs showed that precipitation increased by 10% and 12% on average during the two periods of 2021-2050 and 2051-2080, producing 5.6% and 6.7% decreases in the projected long-term runoff compared to those in baseline period (1961-1990). Temperatures were projected to be increased by 2.0 °C and 2.9 °C for the two periods, resulting in the future long-term runoff decreased by nearly 2.0% and 2.9%, respectively.