Characteristics Of The Extreme Drought Events And Its Response To Climate Change In The Southwest China

Based on the daily data of temperature and precipitation of108meteorological stations in Southwest China from1960to2009, the author engaged in a spatial-temporal analysis of temperature and precipitation at first. Secondly, the surface humid indexes of months and years were calculated, as well as the extreme drought frequency. According to the data, the temporal and spatial characteristics of the extreme drought frequency in inter-annual, inter-decadal, summer monsoon and winter monsoon had been analyzed. Finally, this paper analyzed the response of the Extreme Drought Events to climate change.The results are indicated as follows:(1) In recent50years, the average temperature of the southwest China is increasing,1986is the turning point of the annual temperature increasing sharply; In general, the southwest of the areas is warming faster then the west and middle areas. The temperature of summer and winter monsoon are also significantly increased. In summer monsoon, the area is heating up after1993and the temperature increasing more significantly in the recent10years. In winter monsoon, the area is heating up after1982and the temperature reducing after enter21st century. The temperature of western is increasing faster then the eastern. In recent50years, the precipitation of the southwest China is decreasing. The rainfall decreased significantly at1980s, but increased rapidly and maintain in a higher level at1990s, and there was a sharply declining in the21century. The precipitation increased significantly in the western region, reduced rapidly in midland and gradually increased in the east. In addition, the precipitation of high altitudes areas increasing primarily, but most low altitude areas precipitation decreased. Monsoon period and the monsoon period of rainfall had constantly decreasing trend. The precipitation of summerand winter monsoon are also significantly decreased. The summer monsoon has the same climate characteristic with the annual precipitation. The changes in winter monsoon are not much in recent50years.(2) A severe drought, the most serious during the hundred years, occurred over Southwest region in the period from autumn of2009to spring of2010. This drought weather caused heavy losses to the industrial and agricultural production as well as people’s life and property in the Southwest. The Southwest China drought mainly happened from November2009to March2010, and lasted5months. This drought was very serious in autumn and winter of2009, and it has relieved in spring of2010. The eastern area of Yunnan, the western of Guizhou and the northwestern of Guangxi were the areas that the drought was most serious and continued most long time.(3) The temporal and spatial characteristics of the extreme drought frequency are that:In general, the southwest of Sichuan Basin, the southern part of Hengduan Mountains, southern coast of Guangxi and north of Guizhou are the areas in which the extreme drought frequency are significantly increased during the past50years. For the decadal change, the1990s is the most wettest decade and it turn wet over the whole area; In the2000s, the extreme drought frequency growth quickly, but the regional differences reduce. In summer monsoon, the extreme drought frequency is growing, always happened in the high mountains around Sichuan Basin, most part of Guangxi and "the broom shape mountains" and it is obvious that the altitude has impact on the extreme drought frequency of summer monsoon; in winter monsoon, the area is relatively wetter and the extreme drought frequency is decreasing. In summer monsoon, the abrupt change happened in2003, while the abrupt change of winter monsoon happened in1989, and the combine of abrupt in different period lead to the extreme drought frequency variation; The departure sequence vibration of annual extreme drought frequency is quasi5years, quasi12years.(4) A significant positive correlation exists between the extreme drought frequency and temperature precipitation, but the correlation between the extreme drought frequency and precipitation is negative strongly. In general, the extreme drought frequency response to the precipitation was better than the response to the temperature. Annual change of the response is the follow. The correlation between the extreme drought frequency and climate change in summer monsoon is weakly, but in winter monsoon the response is very strong and a significant positive correlation between the annual extreme drought frequency and annual temperature is exists in1963-1970and1998-2009. For the decadal change, the temperature and extreme drought has significantly enhanced after entering the21century, and a strong negative relationship between the precipitation and extreme drought frequency was presented all the time, especially in the1960s and the2010s. For the spatial distribution, there was more than half part of the areas has a strong relationship between the extreme drought frequency and the temperature in summer monsoon, and the area has strong relationship of winter monsoon is in the centre part of the Southwest China and the area of annual is in the Sichuan Basin. The correlation between the extreme drought frequency and precipitation is negative strongly in all the parts of the areas. In recent50years, the extreme drought frequency of the southwest China has a significant positive correlation with ENSO events. They have the same trend of changing. ENSO warming events (El Nino events) showed an increased probability of the extreme drought. ENSO cold events (La Nina events) showed a reduced probability of the extreme drought. At the same time, the response of the extreme drought frequency to ENSO events had the significant hysteresis quality. In general, the ENSO events and the extreme drought frequency had more significant and stronger relationship in summer monsoon then in winter monsoon.