Temporal Variation Analysis on Climate of Dry-Hot Valley Since 1950s in Upper Yangtze River Basin, China

Climate of dry-hot valley areas regarding their long term temporal changes are seldom studied. In this paper, climate change in lower reach of Yalongjiang River, a typical dry-hot valley area locating in upper Yangtze River Basin, was analyzed. Ten single meteorological factors were used to investigate basic climatic characteristics, and two integrated index (i.e. relative evapotranspiration(AET/P), standard precipitation evapotranspiration index(SPEI)) were selected to reflect changes from human activities and gauge climate drought regime. Mann-Kendall mutation test was applied to identify mutation year, and variation trends were diagnosed with linear regression and distance average analysis. Mean values were tested to find if there were significant changes resulting from a large artificial reservoir constructed in 1999. Results of mutation test showed that minimum temperature, relative humidity, and AET/P in two stations changed significantly in 2000s. Temperature increased since 1990s, and other single index fluctuated in recent 50 years. Precipitation decreased and temperature increased in autumn significantly, while precipitation in summer decreased slightly. The variation of SPEI implied that the area was humid from 1980s to 2000s, but drought in 2010s. The results of mean test indicated that 56% meteorological index changed significantly, which might be related to the construction of the large reservoir. This research not only reveals the climate change in a dry-hot valley, but also helps study concerning human activities especially the construction of cascade reservoirs in the future in this area.