Impact of Climate Change on Runoffs from Hanjiang and Ganjiang in the Yangtze River Basin

摘要

In the past few years, a modelling framework on assessment of climatic impact on water resources for four main basins in China has been established at National Climate Center (NCC) of China. This work aims at demonstrating the capability of one of the hydroiogical models in simulating observed river flow and in assessing the sensitivity of the steam flow to climate changes in two sub-basins of the Yangtze River. The study area includes Hanjiang and Ganjiang sub-basins. A distributed water balance model was used to simulate monthly water balance under present day and future climates. First, a control simulation for the period 1961-2000 using the observed climatic input was performed. A method to grid the station data into a 30X30 km grid system is described and tested, which provides the input to the hydrological model. A comparison between the simulated and measured runoff demonstrates capability of the model. A baseline period from 1961-1990 is chosen to represent the current climate. The potential impacts of future climate change are simulated by perturbing the observed driving climate variables (rainfall and temperature) during the baseline period and re-running the model for another two 30-year periods (2021-2050 and 2051-2080) with climate change scenarios estimated by the General Circulation Model (GCM). The scenarios were constructed from output of ECHAM4 and HadCM2 experiments. The experiments assume a 1% per year increase in atmospheric CO2 concentrations from 1990 to 2100. Monthly differences between 2021-2050 and 1961-1990, as well as between 2051-2080 and 1961-1990 were used to force the hydrological model. The results for the two sub-basins were analysed, focusing on the changed runoff. While temperature changes are essentially consistent between the two GCMs, precipitation change shows a relatively large difference, which causes different responses of runoff. This underlines the importance of uncertainties associated with GCM.