Simulation of impacts of changes in land use and cover on annual streamflow in the upper reach of Chaohe River Basin

This study investigated the precipitation, streamflow, land use and land cover changes during the period 1961-2000 in the upper Chaohe River Basin, one of the key water sources for Beijing, and simulated the impacts of land use and land cover changes on the annual streamflow. Results show that rainfall-streamflow evolution in the upper Chaohe watershed during the past 40 years can be divided into three periods: 1961-1978 (period I), 1979-1993 (period II) and 1994-2000 (period III). An analysis of land cover data of the three periods suggests that since the late 1980s obvious changes of land cover types occurred in the watershed: area of cultivated land increased by 7.47% from the period I to II and 0.35% from the period II to III; forestland area increased by 7.78% and 11.81% respectively. Dominant changes in land cover types are conversion from cultivated land to forestland and grassland; conversion from grassland to forestland or from forestland to grassland. Construction and use of many water conservancy and irrigation works also took place in period II. During period III, the change of land use and cover is largely characterized by a rapid increase of forestland area by 11.81%. Using period I as the reference period, annual streamflow during the period II and III was simulated by a lumped rainfall-runoff IHACRES model. By calculating the difference between the reference and gauged annual streamflow, a conclusion was reached that land cover changes in this watershed reduced annual streamflow; the impact degrees of land cover changes are 27.76% for period II and 26.15% for period III.