Effects of Alpine Swamp Wetland Change on Rainfall Season Runoff and Flood Characteristics in the Headwater Area of the Yangtze River

Alpine swamp wetlands (ASW), which are dominated by alpine swamp meadows, are particularly dense in the headwater area of the Yangtze River (HYR). Typically, hydrological conditions determine both the attributes and spatial distribution of wetlands, while wetlands themselves influence the water cycles and hydrological processes of regions and basins, respectively. Global climate change has affected natural ecosystems significantly worldwide, particularly wetland ecosystems, whose sensitivity to global climate change has accelerated their degradation. However, the link between changes in alpine swamp wetland and the river hydrological process has not been adequately investigated and quantified. Moreover, although ASW is the most important alpine wetland in HYR, few studies have documented changes in this wetland type in response to climatic change; accordingly, the effects of ASW change in particular on hydrological processes in HYR remains unclear.

Therefore, it is critical to detect the effect of ASW change on runoff and flood characteristics in the rainfall season in HYR. To address this, researchers investigated the changes in ASW in HYR from 1975 to 2004 based on remote sensing data. In particular, they also aimed to determine the effects of ASW change on runoff and flood characteristics (i.e., peak flow, rising time, duration and flood runoff coefficient) during the rainfall season based on observations from meteorological and hydrologic stations.

The results indicated that the area of ASW decreased by 28.22% and 30.54% at Zhimenda (ZMD) and Tuotuohe (TTH), respectively, from 1975 to 2004. Moreover, 76% and 71% of the decreases at ZMD and TTH, respectively, occurred during the period from1990 to 2004. Both runoff and the runoff coefficients decreased at ZMD and increased at TTH with decreasing ASW in the rainfall season. The effects of ASW on runoff and runoff coefficients were more pronounced at ZMD than at TTH. A slightly lower maximum peak flow and a greater frequency of moderate and small peak flows were observed at ZMD. Conversely, maximum peak flow increased and the frequency of maximum and moderate peak flows increased at TTH. Flood events increased at both ZMD and TTH, whereas both the rising time and duration decreased at both sites. Overall, the volume of snowmelt water increased and the ability to conserve water decreased in response to decreased ASW and permafrost were responsible for the observed changes in flood characteristics.

This study was published in Catena in April 2015.