Statistical estimation of the impacts of glaciers and climate change on river runoff in the headwaters of the Yangtze River

Abstract

Impacts of glacier and climate change on river runoff in the source region of the Yangtze River (SRYR) were investigated. The non-parametric Mann–Kendall test was used to detect monotonic trends in the glacier area, which was manually digitized from aerial photographs and satellite images. An exponential function between glacier volume and glacier area was established through glacier volume and area data at the SRYR, and glacier melt runoff was calculated on the basis of the function and glacier area change. Results showed that overall the climate of the SRYR became warmer and wetter during 1964–2009. During this period, the mean air temperature (MAT) showed a statistically significant increasing trend that showed a decrease before 1986 and a steady increase since 2001. The total glacier area loss from 1986 to 2009 was approximately 119.3 km2, i.e., 10.1% of the total area in 1986 and was mainly caused by an increasing trend of air temperature in the basin. The area of the glacier in the Geladandong region exhibited an increasing trend from 1964 to 1986, which was mainly caused by an increasing trend of precipitation as snowfall in the frozen season that led to increased glacier accumulation. The glacier melt runoff from 1986 to 2009 was 2.02 × 108 m3/10 y at the SRYR, which accounted for 17.5% of the total runoff changes. The increase in runoff induced by precipitation was 9.47 × 108 m3/10 y, and the evapotranspiration-induced runoff consumption was 39.95 × 108 m3/10 y, which accounted for 81.0% of precipitation. These results imply that less than 20% of precipitation could be transformed into runoff at the SRYR.