Historical Trends in Air Temperature, Precipitation, and Runoff of a Plateau Inland River Watershed in North China

Understanding historical trends in temperature, precipitation, and runoff is important but incomplete for developing adaptive measures to climate change to sustain fragile ecosystems in cold and arid regions, including the Balagaer River watershed on the Mongolian Plateau of northeast China. The objective of this study was to detect such trends in this watershed from 1959 to 2017. The detection was accomplished using a Mann-Kendall sudden change approach at annual and seasonal time scales. The results indicated that the abrupt changes in temperature preceded that in either runoff or precipitation; these abrupt changes occurred between 1970 and 2004. Significant (alpha = 0.05) warming trends were found at the minimum temperatures in spring (0.041 degrees C a(-1)), summer (0.037 degrees C a(-1)), fall (0.027 degrees C a(-1)), and winter (0.031 degrees C a(-1)). In contrast, significant decreasing trends were found in the precipitation (-1.27 mm a(-1)) and runoff (-0.069 mm a(-1)) in the summer. Marginally increasing trends were found in the precipitation in spring (0.18 mm a(-1)) and fall (0.032 mm a(-1)), whereas an insignificant decreasing trend was found in the runoffs in these two seasons. Both precipitation and runoff in the wet season exhibited a significant decreasing trend, whereas in the dry season, they exhibited a marginally increasing trend. Sudden changes in spring runoff and sudden rises in temperature are the main causes of sudden changes in basin rainfall.