Study On Temporal And Spatial Variation Of Drought Characteristics Based On Multi Source Data In Arid Zone Of Middle Ningxia

Drought is a hot issue in the study of global climate change.According to statistics,the global economic loss caused by drought up to 6-8 billion dollars each year,far more than other disasters.However,China is a country with frequent agricultural disasters,the most serious agricultural disasters among them caused by drought,the average affected area up to 22 million square hectares annually.Ningxia is one of the highest province of drought rate and hazard rate in China,the most serious drought of it is in the central arid zone.lt has been a great obstacle for social and economic development in the arid zone of middle Ningxia that sustained and critical drought has caused serious problemssuch as agriculturereduction,desertification and ecological environment deterioration.Therefore,study on temporal and spatial variation characteristics of drought in the arid zone of middle Ningxia,can not only provide help for the drought disaster of the local government,but also can provide scientific basis for the development of regional agriculture and animal husbandry.The method of drought monitoring are based on climatological data of traditional monitoring methods and remote sensing of modern monitoring techniques,both of them have their own advantages and disadvantages.So,organic combine this two kinds of monitoring methods will enhance the extractability of drought spatio-temporal information entirely.Therefore,my study uses monthly meteorological data in Yanchi,Zhongning and Tongxin from 1960 to 2012 to calculate the Standardized Precipitation Index(SPI)and Palmer Drought Severity Index(PDSI),then base on the Ensemble Empirical Mode Decomposition(EEMD),Power spectrum analysis and Hurst index to analyse the characteristics of drought multi scale transformation in the central arid zone in recent 50 years.At the same time,constructed the ALST-NDVI feature space by using medium resolution imaging spectrometer(MODIS)from 2000 to 2014 to obtain the monthly D-value of day and night surface temperature(ALST)and Normalized Difference Vegetation Index(NDVI)data.Besides,improved the Temperature Vegetation Dryness Index(TVDI)model and study on the characteristics of drought in arid zone of middle Ningxia from two dimensions of time and space in recent 15 years.The conclusions are as follows:(1)Drought events in Yanchi,Zhongning and Tongxin from the Arid zone of middle Ningxiashow that more than 30%of drought events,which happened in arid zone of middle Ningxia,are moderate drought or even more intensity.The situation of three counties in the case of extreme drought showed similar temporal characteristics.And the multi-scale decomposition of drought period show that there are four time scales in different intensity of drought,which include 0.5a,la,3a and 10a change cycle respectively to mild drought,moderate drought,severe drought and extreme drought.The SPI analysis show that the inter-annual fluctuation of drought in arid zone of middle Ningxia mainly derived from a 3.25-4a period which has more than 65%contribution to the whole variance and another 14%contribution came from a 5.78-6.5a period.Trend analysis shows that the drought trend in the arid zone of middle Ningxia is generally in the enhanced trend,but the drought intensity in different seasons showed a difference.The average drought intensity is increasing,but the extreme drought events have a tendency to weaken.On the whole,the increasing trend of annual average drought intensity in the central arid zone has a long-term dependence,that is to say,the drought will continue in the future.(2)My study using ALST and NDVI data from 2000 to 2014,set up two-dimensional feature space of land surface temperature and vegetation index,improve dry and wet edge fitting process of Temperature Vegetation Dryness Index model by statistical method.First of all,determine the "tail"phenomenon of ALST when NDVI is in low value area through the statistical method,eliminate the"tail" point on the basis of it and to fit dry edge equation.At the same time,using the method of Box-plot to calculate the outliers in the wet side scattered points,eliminate the influence of the data on the wet edge fitting by removing outliers.Compared with the results of TVDI drought monitoring before and after the improvement of the model,found that the original Temperature Vegetation Dryness Index will overestimate the drought situation.(3)Doing spatial analysis to TVDI of recent 15 years in arid zone of middle Ningxia,we can find that although the drought occurrence is uncertain in Arid Zone of Middle Ningxia,but the overall drought intensity is very high.Among of them,the most serious drought situation is in the southwest of Haiyuan County,the northern of Shapotou District,the part of Tongxin county and Yanchi County.Besides,there are three drought process from 2002 to 2005,2007 to 2010 and 2012 to 2014 are all beginning in Yanchithen spread to Tongxin and even cover the whole central arid zone.From this drought trend,it is concluded that the drought in 2015 may be mild,but there will be a severe drought in the year of 2016.Tongxin,Hongsipu and Lingwu will have an enhance drought trend in the future fora strong continue,but Yanchi will have amoderate sustained weakeningina weakened area and a weak sustained trend will in drought enhanced area.