Impacts of Land-Use and Climate Changes on Hydrologic Processes in the Qingyi River Watershed, China

The impacts of human-induced land-use and climate changes on hydrologic processes have become a great challenge and attracted widespread attention of many researchers. Dramatic changes in land use and climate have occurred in the mountainous Qingyi River watershed in southwest China in the last three decades. Variable infiltration capacity (VIC), a large-scale hydrologic model, was used in this study to assess the impacts of land-use and climate changes on surface runoff, base flow, streamflow, and evapotranspiration (ET) of this watershed. The analysis for this study includes (1)investigation of change in historical land-use patterns, (2)detection of climate change (precipitation and mean temperature), and (3)simulation and assessment of hydrologic responses to these changes. The Mann-Kendall test was used to identify the long-term monotonic trends in precipitation and temperature for the period of 1980-2005. The results suggest no significant change in annual precipitation and a significant increase in annual temperature, particularly in February, April, July, and September. The analysis of three land-use maps reveals that the conversions between forest and shrubland/grassland were the predominant land-use change over the past three decades. Hydrologic simulations show that the influence of climate change on hydrologic processes was stronger than those of land-use change. Monthly variation of the river flow was mainly attributed to seasonal variation in precipitation. However, ET responded significantly to the land-use change in several subwatersheds where single land cover conversion occurred dominantly. The decrease in surface runoff and base flow caused by climate change was enhanced by changes in land use, whereas the reduction in ET was offset by reforestation over the study period. Furthermore, the impact of deforestation or reforestation on hydrologic processes was more significant in the dry season than other seasons. The results from this study can be a useful reference for decision making in land-use planning and water resource managements in this region. (C) 2013 American Society of Civil Engineers.