Impacts Of Climate And Land Use Change On Streamflow A Case Study In The Poyang Lake Basin

With the deep research on global warming, the influences of climate change and landuse/land cover change(LUCC) become a new issue. Both climate change and LUCC havealready lead to a series of ecological problems, and is likely to have significant effects on thehydrological cycle. Poyang Lake is the largest freshwater lake in China, and plays animportant role in the Yangtze River basin, which exchanges water with the Yangtze River aswell as receiving surface and groundwater flow from five sub-basins. In2011, Poyang Lakesuffered the worst drought in recent60years, and the lake area shrank to twenty percent ofthat in the same historical period. Therefore, assessing hydrological responses to climatechange and LUCC will be greatly helpful for flood and drought control plan and also forestablishing the long-term strategy of water resources uselisation. In this study, the dailytempreture, precipitation, evaporation and streamflow sreies from five main tributaries of thePoyang Lake Basin were selected to investigate the correlation between climatic variables andstreamflow. The annual and seasonal trends of climatic variables and streamflow over the past50years were analyzed by using both the parametric and non-parametric methods. There isgenerally a good agreement between the results of the trend analysis using the linearregression method and the MK method. It was found that temperature, precipitation andstreamflow have increasing trend with rates of0.11℃,22.5mm and14.6mm perdecadeseparately. On the contrary, evaporation shows a notable reducing trend in the past50years.The seasonal analysis suggests that temperature rises significantly in winter and precipitationincrease in summer.The upstream of Ganjiang River basin is selected as case study to investigate thehydrological responses to climate changes and LUCC in the Poyang Lake basin by applyingthe Soil and Water Assessment Tool (SWAT) model for runoff simulation. With the support ofSWAT model, the598HRUs are automatically delineated by Digital Elevation Model (DEM)and drainage network. The model are calibrated and validated with daily observed dischargedata from1985to2000. Nash-Suttcliffe coefficient and correlation coefficient are greater than0.6, suggesting a good agreement between observed and simulated streamflow. The results indicated that the SWAT model could be successfully used for runoff simulation.Hydrological responses to climate changes and LUCC are examined in this study byapplying the SWAT model with different scenarios of climate and LUCC. The results showthat climate change was the dominant factor influencing the streamflow, which played greaterrole than that of LUCC. Climate variability contributed95%to the annual mean streamflowwhile LUCC occupied5%. The streamflow is more sensitive to the wet climate condition thanto dry and normal climate condition.The study applies the SDSM model to investigate the correlation between theatmospheric variables and the predictands. The maximum temperature, minimum temperatureand precipitation were selected as predictands. The future climate data generated from A2andB2scenarios of HadCM3model is downscaled by the SDSM method. The results show thatthere are significant increasing trends for the maximum temperature and minimumtemperature, and slight upward trend for precipitation in this area. Impacts of climate changeson streamflow are simulated by using SWAT model with input downscaled climate variablesduring3future periods (2020s,2050s and2080s). Fluctuated reduction in streamflow isdetected in the next3decades while the trend is not significant.The study will improve our understanding of impacts of climate change and LUCC, andprovide a scientific basis for water resources management and utilization in the Poyang Lakebasin.