Study In Extreme Events Of Temperature And Precipitation Over Xinjiang, Northwest China During1960-2009

In the recent hundreds of years, with global warming, extreme climate eventsincrease obviously, which brings tremendous negative impacts to society andeconomy, so it is very important to study the characteristics for changes in extremeclimate, understand the rules and reasons for changes in extreme climate, and predictthe trends of extreme climate in future. Based on daily temperature (maximum,minimum and mean values) and daily precipitation at52meteorological stations overXinjiang, Northwest China observed by the China Meteorological Administrationfrom1960to2009, twelve indices of extreme temperature and ten ones of extremeprecipitation are studied. The results are as follows:(1) The regionally averaged occurrence of summer days, growing season length,tropical nights, warm spell duration indicator, warm nights and days have significantlyincreased by2.14,2.74,1.71,0.88,6.23and3.59days/decade, respectively. Over thesame period, the occurrence of extreme ice days, frost days, cold spell durationindicator, cold nights and days show statistically significant decreasing trends at ratesof-1.61,-3.69,-1.27,-6.57and-2.6days/decade, respectively. The diurnaltemperature range(DTR) exhibits a decreasing trend of0.26°C/decade. Averagemaximum with1-day and5-day precipitation, very wet and extremely wet dayprecipitation, number of10and20mm precipitation days, consecutive wet days andaveraged daily rainfall intensity show increasing trends whereas consecutive dry daysdecrease. In spite of the above-mentioned main trends in most parts, the differences inspatial distribution still exist significantly.(2) With the exception of diurnal temperature range, the other temperatureindices are strongly correlated with annual mean temperature. In the meantime, annualtotal precipitation shows positive correlations with precipitation indices exceptconsecutive dry days. The contribution of extreme precipitation to total precipitationincreased. Though the indices show patterns consistent with the other regions all overthe word, the differences still exist significantly. Compared with most regions, themagnitude of the trends is more obvious.(3) In winter, the differences between anticyclonic circulation and cycloniccirculation enhanced over the Eurasian continent have been strengthened. The southwesterly wind in northern Mongolia has been strengthened, which in turnweakens the southern extent of winter monsoon, limited its southward extension anddecreased incursions of colder air. This would explain why the cold temperatureextremes events have consistently decreased in Xinjiang, which is consistent withrapid warming in the region in winter. With regional warming, the magnitude of thetrends enhances during1993–2009as compared to1960–1992. Elevation hasinfluences on climate extremes, that is, cold days, warm days, tropical nights andsummer days are strongly correlated with elevation. In the meantime, maximum with1-day precipitation, number of10and20mm precipitation days, and very wet andextremely wet day precipitation are also strongly correlated with elevation. The periodof Sunspot, Moontide, mid-latitude westerlies and North Atlantic Oscillationinfluences on climate extremes in Xinjiang.(4) The trends of most extreme temperature and precipitation indices in futurewill generally be the same as the past with the exception of consecutive dry days usingR/S method. The results of Hurst Index experiment of extreme temperature inXinjiang show that indices of percentile-based annual extreme temperature includingwarm nights and days, and cold nights and days are no transition, and that summerdays and cold spell duration indicator exhibit transition in the rest indices. Similarly,the results of Hurst Index experiment show that there is transition in mostprecipitation indices, especially in wet days and consecutive dry days where theaccumulative Hurst Index are less than0.5.