The Evolution Of Drought And Its Effect On Vegetation Under Different Time Scale In The Loess Plateau

Drought is one of the most serious natural disasters all over the world, which hasbecome a serious problem to threaten the survival environment of mankind andbecome popular in science field. The loess plateau suited the inland of Eurasia and isone of the most drought place on the same latitude. The economy and society will beaffected if it continues to be drought. Therefore, it is significant to make a deep studyon the drought features of loess plateau, which can help improve and promote theeconomic development of loess plateau. SPE, fusing the influence of temperature onevaporation, is the new ideal index used for studying drought. This thesis employedthe monthly precipitation and average temperature from54representative weatherstations in loess plateau area from1959to2012. The author worked out the SPEI dataof the area when the time scale is three, six, twelve and forty-eight months. Combinedthe NDVI data and the meteorological data, the author analyzed the effect of climaticchange on vegetation, and then got the following conclusions:(1) SPEI can fully reflected the changes of degrees in drought when temperatureis going up.(2) The degrees of drought in spring, summer, and fall gradually become seriousin deferent speeds, which can be seen from the changing features in the past54yearsin loess plateau.(3) This thesis analyzed the features of drought in six different comprehensivetreatment regions during different time scale. The times of drought varies duringdifferent time scale. The drought mainly shows the vibration in season and year whenthe time scale is three or six months. However, for long time scale, the degree ofdrought become serious and last longer because of the cumulative effect, while thetimes of drought can be fewer.(4)NDVI increased by years with different speeds in loess plateau and sixcomprehensive treatment regions.(5) In order to study the relationship between NDVI during growth season anddegree of drought in different time scale in loess plateau.(6) The majority parts of the area has an increasing trend in vegetation except some ones, which can be seen from the changing trend of vegetation in loess plateau.(7) There is a positive and negative correlation between rainfall and vegetation inloess plateau. When positive correlation dominates, that means rainfall is the mainfactor to influence the growth of vegetation in this area; there is also a positive andnegative correlation between temperature and vegetation, while it is a negativecorrelation between temperature and rainfall in most places of this area. Theincreasing evaporation, soil-aridification can be caused by a rising temperature, whichwill be bad to the growth of vegetation.