Risk assessment and division of loss caused by drought for main crops in Longdong of Gansu Province.

【Objective】The drought risk of main crops in different areas of Longdong was studied to provide science gist for making rational distribution of planting to reduce loss of disasters effectivly.【Method】Based on the crops'yield loss caused by drought,using the long term yield data of main crops and meteorological data in Longdong area,the loss in history caused by drought(drought distribution,intensity and frequency,and distribution of loss caused by drought),percentage of planting area and local yield level of crops,etc.were analysed.【Result】There were more than 20% and 14% years respectively in most areas of Longdong in which the yield reduction caused by drought was more than 20%;The frequency of various types of drought occurred during the growth period of winter wheat and spring corn was 53%-94% and 34%-80% respectively.Huanxian was the place where the frequency of drought,especially that of the severve and extreme drought,was the highest;The maxium of loss rate in Longdong caused by drought appeared in Huanxian too,which was more than 30% and 20% respectively;According to the comprehensive risk division index,Longdong was divided into 4 risk areas:the lowest,the moderate,the higher and the highest,and the corresponding risk index of winter wheat was Ei≤0.1,0.1Ei ≤0.3,0.3Ei ≤0.5 and Ei0.5 respectively,and the corresponding risk index of spring corn was Ei≤0.2,0.2Ei ≤0.5,0.5Ei ≤0.7 and Ei0.7 respectively.【Conclusion】The results indicated that both risk distribution of loss caused by drought for winter wheat and spring corn increased from south to north.North of Longdong was the highest area,middle and north the higher area,and middle and south the moderate area,while the lowest area was located in south of Longdong.