Climate Changw Of The Wei River Basin In Last60Years

Climate change is not only one of the focuses of earth science researches nowadays, butalso the precondition to analyze regional resources, environment and ecological processwhich are affected by the characteristics and process of climate change. Wei River Basin islocated in southeast of loess plateau of China, where fragile ecological environment leads tohigh occurrence rate of droughts and floods, Wei River Basin is facing many ecological andenvironmental problems. Based on the annual atmospheric temperature, precipitation,monthly climatic data and monthly and yearly potential evapotranspiration of Wei River Basinwith FAO Penman-Monteith Equation of45weather stations around Wei River Basin duringthe period of1951-2009, with the methods of tendency analysis, spatial interpolation,Mann-Kendall method, Empirical Orthogonal Function decomposition, wavelet analysis,traditional statistics and accumulated variance analysis, which can be used to analyze themeteorological elements trend, catastrophe character, spatial distribution characteristics ofWei River Basin and so on. The main conclusions are as follows:(1) The temperature of the Wei River Basin showed an increasing trend between1951and2009. The annual mean temperature was rising at the rate of0.252℃/10a. The rising trendof annual mean minimum temperature (0.261℃/10a) was larger than the annual meanmaximum temperature's rising rate(0.255℃/10a).The turning points of the mean annual temperature and the mean minimum temperaturewere around the late1980s and early1990s; while the mean annual maximum temperaturewas around1994. With the method of Morlet analysis, the results showed that the periodicityof temperature were about19years,33years, and mainly periodicity was33years.The annual mean temperature decreased from east to west, and from south to north, thatshowed a similar trend. While the position of isotherm changed in different years, base on thearea of region which is encompassed by basin boundary and isotherm. The threshold of themean temperature is9.5℃, which was the mean temperature of the last decades. Theproportion of the area where the average annual temperature was more than9.5℃increasedfrom34.67%in1960s to69.10%after2000,3℃was the threshold of average annual minimum temperatures of the past years. The area of region with the average annualminimum temperatures more than3℃increased from68.55%in1950s to85.75%after2000.Diurnal temperature showed a decreasing trend from1950s to1970s and after1980s whichshowed an slight increasing trend. The proportion of the area where average diurnal range intemperature was more than11℃decreased from55.96%in1950s to41.58%in1980s, thenincreased to61.07%after2000.(2) Most precipitation happened in summer and autumn in a year in Wei River Basin.The precipitation showed a descending trend from1950s to after2000, with the falling rate of14.6mm/10a.The precipitation turning point in northwest regions is located in2007, while theprecipitation turning point in southern region and western region located in1970and1986respectively. The precipitation in Wei River Basin was affected by the large-scale weathersystems. The characteristics of the abnormity of precipitation in Wei River Basin wereconsentaneous, Still, there were different between the south and north, the east and west.Morlet wavelet transmission showed that the periodicity of precipitation were about19years,32years, and mainly periodicity was32years. It was accordance with the periodicity oftemperature change.The analysis on the accumulative anomaly of annual precipitation indicated that Duringthe period of1951to1957,1993to2002, and2004to2009, the precipitation in most stationswas less than the mean value in the past, while from1951to1968, the precipitation in moststations was more than the mean value in the past, and in other times, the precipitationfluctuated around the mean value.(3) The amount of potential evapotranspiration of spring and summer were most, whilethe amount of potential evapotranspiration in winter was less in Wei River Basin. Thepotential evapotranspiration showed an ascending trend from1950s to after2000, thepotential evapotranspiration was rising at the rate of5.08mm/10a. Morlet wavelettransmission showed that the periods for potential evapotranspiration were19years,32years,and the main periods was32years. It was also the same as temperature. The potentialevapotranspiration in most stations was less than the mean value, from1951to1968and1983to1993, the potential evapotranspiration from1969to1982and1995to2009in most stationswas more than the mean value.