Study On Change Of Trend Coefficient Of Extreme Temperature And Precipitation In East Of Hexi Corridor

Since twentieth century, global extreme events have occurred frequently, caused serious impact and losses to the society, economy and people’s life, and a direct threat to the survival of mankind and the ecological environment, which are one of the most far-reaching influence on the global environmental problems in the modern world. This paper mainly used daily extreme maximum, minimum temperature, and precipitation(daily precipitation≥0.1mm) data of five stations in eastern Hexi Corridor during1961-2005, daily extreme maximum, minimum temperature thresholds and extreme precipitation threshold were defined by percentile method in different stations. Based on the thresholds of extreme events, occurring frequencies of yearly extreme temperature and precipitation events were counted in different stations during recent45a, and the time series were established. Then by using the least square estimation, mean frequencies of extreme maximum, minimum temperature and precipitation trend were linearly analyzed. Meantime, the reasons of extreme temperature and precipitation changes were also analyzed by correlation coefficient method. Further different time variation periods were analyzed by Morlet wavelet method, and finally M-K mutation detection were used. Results show as follows:(1)Because of the influence of geographical location, altitude and local weather system, from1961to2005, the spatial distribution of extreme maximum, minimum temperature increased from south to north in eastern Hexi Corridor, but extreme precipitation in spatial distribution decreased on the contrary.(2)With global warming, the extreme maximum, minimum temperature and extreme precipitation showed an increasing trends in eastern Hexi Corridor. The extreme maximum temperature time series were shown as6-7a,9-10a and2-3a periodic response, the extreme minimum temperature time series were shown as2-3a periodic response, the extreme precipitation index time series were shown as6-7a and9-10a periodic response. The extreme temperature and extreme precipitation index occurred mutation phenomenon.(3)When the Western Pacific subtropical high rose in the west and strengthened, and the Tibetan Plateau was controlled by high pressure, the values of extreme maximum temperature, minimum temperature and maximum temperature frequency increased, but extreme minimum temperature frequency decreased in eastern Hexi Corridor. When Asia polar vortex intensity index, Asian zonal circulation index and India Burma trough were strengthened, extreme maximum temperature, minimum temperature and extreme maximum temperature frequency decreased, on contrary extreme minimum temperature frequency increased. There was a certain relationship between extreme precipitation in the eastern part of the Hexi Corridor and the advance or retreat of the West Pacific subtropical high ridge line and the intensity of cold air. The West Pacific Ocean and the East India Ocean SST was lower, the extreme maximum temperature, minimum temperature and extreme precipitation were smaller. The main climate factors of affecting extreme maximum temperature were evaporation and maximum temperature, as well as that of affecting extreme minimum temperature were average air temperature and average soil temperature. The main climate factor of affecting extreme precipitation intensity, precipitation frequency and the total amount of precipitation was the average rainfall over the same period.