Effects of Climate Variations and Human Activities on Runoff in the Zoige Alpine Wetland in the Eastern Edge of the Tibetan Plateau

AbstractThe Zoige alpine wetland on the eastern edge of the Tibetan Plateau is an important headwater area for the Yellow River Basin. The White and Black Rivers are two major tributaries in the Zoige Basin. However, the alpine wetland has experienced a rapid degradation due to human and other recent environmental changes in the region. The effects of climate variations and human activities on runoff in this region are still unclear. In this study, those changes in runoff were quantified and categorized using the hydrologic sensitivity analysis method and a monthly water balance model. The temperature index-based snow melting submodel was integrated into a monthly water balance model to account for the considerable snow meltwater from the wetland in the summer season. The nonparametric Mann-Kendall test was used to analyze the annual and seasonal climatic trends in the Zoige Basin. Results suggest that during the past 55 years (1957–2011), annual precipitation was significantly decreasing at a rate of −0.978 mm/year while the air temperature and potential evapotranspiration (PET) have increasing trends at the rates of 0.029°C/year and 0.755 mm/year, respectively. Using three change-point detection methods, one change point was detected at 1989 in the annual streamflow series (1960–2011) and was adopted to divide the data set into two study periods—the baseline period (1960–1989) and the human-induced period (1990–2011). The mean annual runoff depth from the White (Black) River in the baseline period was 448.9 mm (151.5 mm), while the mean of the human-induced period decreased by 28% (35%). It was determined that decreases in runoff between the two periods can be attributed to 55% (64%) from climate variations and 45% (36%) from human activities in the White River (Black River). Thus, climatic impact exerted more important influence on runoff decline in the Zoige wetland basin as compared to human activities. This study enhances our understanding of the changes caused by climate variations and runoff (and their contributing factors) in the alpine wetland.