Recent change of runoff and its components of baseflow and surface runoff in response to climate change and human activities for the Lishui watershed of southern China
Temporal change of baseflow and surface runoff, two components of river runoff, receives little attention though the runoff variation has long been an important concern worldwide. This study made a comparison of hydrological regimes in the Lishui river watershed, a mountain watershed in southern China between two periods of 1950s-1985 and 2007-2011. We examine not only the temporal change of runoff and its FDC (flow duration curve), but also the temporal change of its two components and their FDCs. The data used mainly involves the long-term observations at four gauging stations, 13 rainfall stations and two meteorological stations. Annual precipitation remains almost unchanged between the two periods compared with the former period. The latter period, however, was characterized by a high forest cover (about 70% in 2009) and numerous reservoirs. The substantial change in land surfaces induced by human activities makes no statistically significant difference both in annual runoff volume and its two components, which varies by about 10% between two periods. Human activities, however, play an important role at the daily time scale. Our examinations on FDCs show a differential response of the surface runoff and the baseflow to human activities. Responding to the reservoir operations and the high vegetating cover after 2007, the daily surface-runoff discharge decreases in the high-flow period and increases in other periods. The daily baseflow discharge remains insensitive to human activities, with FDCs after 2007 coinciding with those before 1985 except in the low-flow period. Out result may be typical of the humid southern China and is thus indicative of other rivers in southern China.