Spatial And Temporal Variations Of Extreme Temperature And Extreme Precipitation Events In Southwestern China During 1962-2012

In recent years, the magnitude of global warming was more serious than before, which increased the occurrence frequency of drought, frost and other natural disasters. In Southwestern China, persistent snow, ice storms and persistent drought events attracted a lot of attention since 2008. Therefore, it is very important to investigate the variation of extreme temperature events and its mechanism. By using daily maximum, minimum temperature and daily precipitation data at 90 meteorological stations in Southwestern China in the period between 1962 and 2012 provided by China Meteorological Administration, temporal and spatial variation of extreme temperature events were investigated with the methods of regression analysis, Mann-Kendall rank correlation and inverse distance weighted interpolation. Eight indices of extreme temperature were studied. The results indicated that extreme temperature indices are obviously different in spatial distribution. The indices of warm days, warm nights, cold nights, and extra-minimum air temperature decreased gradually from southeast to northwest, with change rate 13.1～36.3℃,-1～23.5℃,-15～15.2℃ and -30.6～6.7℃, respectively. Nevertheless the index of frost days increased in the same direction with maximum change over the northwest of Sichuan. Both the distributions of cold days index and extra-maximum air temperature are like a saddle, with the highest values over the southwest and northeast. There were few number of high temperature days over most area. Obvious gradient of hot day index only can be seen over central Yunnan. The indices of cold day, frost days and cold nights have significantly decreased by the rate of 2.7d/10a,3.5d/10a and 4.9d/10a, respectively. Warm days indices, warm nights indices, extra-minimum air temperature and extra-maximum air temperature have significant increased by the rate of ld/10a,4.7d/10a,0.4℃/10a and 0.1℃/10a, respectively. Only hot days indices did not change significantly. The magnitudes of changes in cold indices are much greater than those in warm indices. The change ranges of night indices were larger than those of day indices, which indicated that the changes of day and night temperature were asymmetrical. The variation of extreme cold indices showed a downward trend, and that of extreme warm indices showed an upward trend. Their overall performance was a warming trend over Southwestern China. Whereas, the variation range of extreme temperature events was less than other regions of China which reflected the unique feature of climate change over Southwest China.The annual daily maximum precipitation amount and extreme precipitation ratio decreased from 103-118mm and 39-43% in East areas to 25.4-46.7mm and 23-25% in West areas respectively. Extreme precipitation amount, extreme precipitation intensity and annual 5-days maximum precipitation decreased from 508～610mm、 55-64mm/d and 158-190mm in southeast areas to 118～220mm、17～28mm/d and 53-85mm in northwest areas respectively. Variation coefficient of annual daily maximum precipitation amount is the largest and up to 38.5%, followed by that of Extreme precipitation amount, extreme precipitation intensity, annual 5-days maximum precipitation and extreme precipitation ratio, while that of extreme precipitation days is the smallest and only 18.8%. Variation coefficient of extreme precipitation events were stronger that indicated the larger differences of extreme precipitation events in the southwestern region. Among extreme precipitation events during 1962～2012, sites of upward trend among annual daily maximum precipitation amount, extreme precipitation intensity and ratio accounted for 60%,64% and 61% respectively in which a significant upward trend reached 12%,10% and 13% respectively. Sites of extreme downward trend and significant downward trend of extreme precipitation days accounted for 52% and 4% respectively. On the whole, extreme precipitation events appeared upward trend overall but not significantly on account of ocean temperature anomalies changes and complex geographical environment.