Analysis On Drought Disaster Risk In Eastern Agricultural Areas Of Qinghai Province

Eastern agricultural areas of Qinghai province is the barn of Qinghai.Affected by the change of global climate,drought in this area has aggravating trend.Eastern agricultural areas of Qinghai province as the research area, two methods were used to evaluate drought Disaster risk. The drought risk assessment method based on fuzzy-grey theory evaluated the drought risk of long time series, the drought assessment method based on cloud model and the entropy weight method evaluated the drought risk in typical year(2005).The combination of the two kinds of methods could be more comprehensive to evaluate the drought disaster risks.This study has guiding significance to the drought resistance and disaster reduction work in local area.According to meteorological data of 13 meteorological stations in the eastern Qinghai agricultural area, from 1959 to 2005, such as precipitation, air temperature, evaporation, drought disaster situation in history and social-economic data of the study area, many theories were used in the study, such as the fuzzy theory, grey theory, cloud model, the entropy method, Arcgis spatial analysis tool and the drought disaster risk system theory. The drought risk level distribution of the study area in 2 time scale were evaluate: from 1959 to 2005 and typical year(2005). Main results obtained are as follows:(1)Drought risk assessment based on fuzzy-grey theory. According to the 1959-2005(long time series) of precipitation and temperature data, the theory of fuzzy information diffusion method was used to deal with the growing season SPEI value of 6 months scale, from March to August, and combining with historical disaster situation from 1959-2005, grey risk evaluation models were established to evaluate long time sequence drought risks of each level in eastern Qinghai province. The result shows: drought which occurs most frequent in most areas in Qinghai province are moderate drought and heavy drought; drought which occurs most frequent in northern and central part of study area is moderate drought, the drought in southern is heavier.The conclusion is similar to the real situation, it proved this method is feasible.(2) Analysed the historical drought occurrence regularity in the study area, the following characteristics can be concluded: 1) the drought occurrence frequency rencently is much higher than that of the historical period, the drought situation is grim; 2) Drought happens most frequently in three periods: from March to August, from June to August and from March to May; 3) the drought which happens frequently in most regions is moderate drought;Among 13 areas of eastern agricultural area, the total frequency of drought disaster of Xining was markedly lower than other regions(the occurance frequency is lower than 40%).So Xining belongs to low drought disaster areas, In other parts, the times of drought disaster in different levels were between 10-14 times, total drought frequency is between 55.6% and 77.8%, these areas belongs to drought prone areas.(3) The paper made preliminary analysis on agricultural drought hazard mechanism of the study area, it is concluded that the fundamental causes of agricultural drought in eastern Qinghai province is a special geographical environment and natural climate conditions which lead to less precipitation, high evaporation capacity, uneven distribution of space and time. In addition, the relatively high cultivated land rate as well as low effective irrigation rate, poor drought-resistant ability are also the main reasons for agricultural drought in eastern Qinghai province.(4)According to the analysis of characteristics of drought and drought hazard mechanism in Qinghai province, based on cloud model, the entropy weight method, risk assessment of drought disaster risk system, 16 evaluation index were choosen from four selection criteria layer: dangerous hazard-formative factors, exposure of hazard-affected bodies and damage sensitivity, drought-resistant ability and drought risk assessment index system were set. According to precipitation and evaporation data from 2004 to 2005, social and economic statistical data in 2005, normal cloud model was used to calculate the membership degree of each drought grade, and the entropy weight method was used to determine weight of the indexes in each rule layer, agricultural drought disaster risk evaluation model was established, then the drought risk of each eastern agricultural regions of Qinghai province in 2005 was evaluated. The evaluation results show that the drought risk in most regions of Qinghai province in 2005 is light to medium risks, belonging to a lesser risk level as a whole. Light risk areas are: Menyuan, Da Tong, Huangyuan, Huangzhong, Ledu Jianzha and Minhe. Moderate risk areas include: Huzhu, Hualong, Guide and Huangnan. Light risk areas include: Xining, Xunhua. The overall drought risk distribution is that northern regions is lighter, in southern regions is relatively heavier. The evaluation results of this method is in accordance with the actual drought situation and the overall trend of the drought in different regions of the eastern agricultural regions of Qinghai province in 2005.(5) Comparing two methods from the aspects of application, advantages and disadvantages. The first method is suitable for the evaluation of long time series of drought risk,it requires less data, but unable to evaluate drought risk of only one year; The second method is suitable for the evaluation of a typical years of drought risk, the disadvantage is the index selection of high data volume requirements. The two methods above are suitable for long sequence, the typical years of drought risk assessment respectively. The combination of the two methods could make the evaluation of the drought risk of long time or any typical year, and the applicaion is much wider.