Increasing annual streamflow and groundwater storage in response to climate warming in the Yangtze River source region
Climate warming has been driving hydrological changes across the globe, especially in high latitude and altitude regions. Long-term (1962-2012) streamflow records and permafrost data in the Yangtze River source region were selected to analyze streamflow variations and groundwater storage in response to climate warming. Results of Mann-Kendall test and Morlet wavelet analysis show that the anomalies of both annual streamflow and winter baseflow are near the year 2010, and their main period scales are 37 years and 34 years, respectively. The annual streamflow and the annual baseflow increased significantly, as assessed by the recursive digital filtering baseflow separation. Results of Pearson correlation coefficient indicate that the rising air temperature is the primary cause for the increased streamflow instead of precipitation and evaporation. By using the top temperature of permafrost model, the total permafrost area has decreased by 8200 km2 during the past 50 years, which causes groundwater storage to increase by about 1.62 km3 per year due to climate warming. More space has been made available to store the increasing meltwater during the permafrost thawing. Permafrost thawing and increasing temperature are the direct and indirect causes of the increasing groundwater storage. The results of the cumulative anomaly method and Pearson correlation coefficients show that permafrost thawing has a greater impact than increasing temperature on the increase of groundwater storage. Permafrost thawing due to climate warming show compound effects on groundwater storage-discharge mechanism, and significantly affects the mechanisms of streamflow generation and variation.