Heterogeneous Precipitation and Streamflow Trends in the Xiangxi River Watershed, 1961–2010

Abstract

This study aims to perform a comprehensive trend analysis of precipitation and streamflow at the watershed scale. Multiple techniques were employed to examine the temporal trends in annual, seasonal, and monthly precipitation as well as streamflow in the Xiangxi River watershed, China. Results showed that heterogeneous trends existed in precipitation and streamflow. To be specific, statistically insignificant trends in annual and seasonal precipitation were discovered, but varying monthly precipitation exhibited complex changes, especially for the decreasing precipitation in September. Annual and autumn average streamflow in addition to monthly streamflow in April, May, September, October, and November were found to experience a downward trend. Also, negative trends were detected in all low flow statistics, including annual minimum instantaneous streamflow; Q10, Q30, monthly, seasonal-minimum, and annual-minimum daily-mean streamflow; and 7-, 14-, and 30-day consecutive minimum streamflow. For high flow statistics, monthly maximum streamflow showed a slight upward tendency in dry months (December, January, and February), while its values in April, May, September, and October indicated a decreasing trend. In addition, Q70 and Q90 were found to have a statistically significant negative trend. Sequential Mann-Kendall (MK) test revealed an earlier beginning of the trends in low flow statistics than the other stream flows. Change point analysis suggested that changes in streamflow statistics had occurred since 1989, and accordingly, a new relation between precipitation and streamflow was established after 1988. Anthropogenic activities, especially small hydropower development, were found to be mainly responsible for changes in streamflow regime during the last 50 years. Thus, the obtained findings would help to better implement hydrologic engineering design and water resources planning and management over the watershed under changing environment.