Analysis On Extreme Temperature And Precipitation In Shaanxi Province During The Recent50Years

With the further research of global climate change, it has been gradually realizedthat the impact of extreme climate events is more significant than that of long-termclimate change, which displayed in the human daily production and living, as well asthe socio-ecological environment.Based on the data of daily maximum temperature, minimum temperature,average temperature and precipitation at21meteorological stations in ShaanxiProvince from1961to2010, the extreme temperature and precipitation were studied.Several statistical methods were used to analyze, such as linear trend, anomalies,Morlet wavelet analysis and so on. The main results were as follows:1. The basic features of temperature and precipitation during the recent50yearsin Shaanxi Province:(1) The average temperature increased with a rate of0.28℃perdecade, which was more obvious in north than that in south. Seasonally, the warmingin winter was significant, and that in summer was weak. Across the province, thetemperatures in different seasons showed different spatial characteristics, and summeris the only season of cooling. An alternation between cold and warm with a cycle ofapproximate15years existed in the average temperature.(2) The average annualprecipitation decreased with16.75mm per decade, and the rate was the largest inGuanzhong Plain and the smallest in North Shaanxi. The precipitation mainlyoccurred in summer, followed by winter, spring and autumn, decreasingly. Across theprovince, the precipitation in different seasons varied spatially, and the precipitationin summer and winter increased at most areas. The average annual precipitationshowed an approximate12-year cycle of alternation.2. The results of extreme temperature were as follows:(1) The extreme hightemperature days increased significantly, but it was contrary for extreme lowtemperature days. During the recent50years, daily maximum temperature andminimum temperature all showed an increasing trend significantly, especially for theminimum temperature.(2) The extreme high temperature days during1960~1980were below the average, and positive anomalies occurred since the1990s, which wasopposite for the extreme low temperature days. With the increasing of extreme hightemperature days and the decreasing of extreme low temperature days since the1990s, it was evidenced that the regional temperatures was in a warming trend.(3) Theextreme temperature of Shaanxi Province exhibited significantly spatial differences.The defined indices of extreme high temperature increased at most areas, and theextreme low temperature indices decreased at most areas, while the spatialdistribution for each index was quite different.(4) For the extreme temperaturesevents, the cycle analysis indicated that there was a period of5to15years.3. The results of extreme precipitation were as follows:(1) the extremeprecipitation days, rain days, moderate rain days and continuous rain days decreased,respectively, which can result in the increasing of sustained drought days. Heavy raindays, daily precipitation maximum and extreme precipitation displayed an increasingtrend, indicating the decreasing of extreme precipitation and increasing of its intensity.(2) The rain days, moderate rain days, continuous rain days decreased in the recent20years, and the continuous dry days increased significantly. In the background ofclimate warming, the precipitation reduced, and the extreme precipitation and its days,heavy rain days, and daily precipitation maximum varied among different decadeswithout significant regulations, which showed that extreme precipitation eventstended to be extremalization, and the drought or flood events increase.(3) Theextreme precipitation distributed spatially in different regions, the extremeprecipitation and its days roughly showed a "decreasing-increasing” trend from northto south. The rain days, moderate rain days and continuous rain days reduced with asmall rate of decreasing in North Shaanxi. The heavy rain days and daily precipitationmaximum in South Shaanxi showed an increasing trend.(4) With the cycle analysis ofextreme precipitation events, it was found that there were a cycle of5~20years.