REGIONAL CLIMATE CHANGE AND ITS POSSIBLE EFFECTS ON RIVER RUNOFF IN QIANTANG RIVER BASIN-PAST AND FUTURE

This paper presents the historical changes in temperature, precipitation, evaporation and its possible effects on runoff of Qiantang River Basin, and estimated their possible future regional variations using Bias Correction and Spatial Disaggregation (BCSD) downscaled Coupled Model Intercomparison Project phase 5 (CMIP5) projections under RCPs 2.6, 4.5 and 8.5, respectively. The results confirm the increase of annual mean temperature and evaporation in the historical dataset, this upward trend is expected to continue and accelerate in the CMIP5 projections. The historical annual average precipitation fluctuates with decreasing trend, whereas CMIP5 projections indicate an opposite rise in the future. The drought-flood cycle is relatively robust before 1970, but exhibits shorter transition time, stronger magnitude and higher occurrence frequency of extremes then, especially in the CMIP5 projections. The fluctuation is also indicated in the runoff with an upward trend during 1961-2005. As for the future, the potential impacts assessment shows that the streamflow would possibly experience the reduction in the first half of 21st century, and then a positive variation in the second half. Furthermore, the spatial variation pattern of these four variables was also discussed, those large sub-basin and important areas with the high possibility to experience notable climate change or extreme events were also pointed out. In addition, the uncertainty stemming from climate mitigation scenario and the inter-model variability was identified and explored. Generally, statistical positive changes are indicated for temperature, precipitation and evaporation ordered by the amount of radiative forcing under three RCP scenarios, and the inter-model uncertainty grows with both time and variation magnitude.