Study On Drought Disaster Risk Assessment Theory And Method

Due to the limitations of specific historical conditions,cognitive level,and technical means,drought disaster crisis management has occupied the dominant position for a long period,and also played an important role in mitigating the drought impacts and losses.However,with the increase of population and the promotion of industrialization and urbanization,food security,water security and ecological security are facing with more pressures and challenges.It is urgent to promote drought disaster risk management,by making a transition from mitigating drought losses to mitigating drought disaster risk.As the core content and key element of risk management,drought disaster risk assessment has got more and more concern from researchers.At present,a great deal of research has been carried out in the field of natural disaster risk management,a relatively systematic and complete theoretical and technical system has been established.Particularly,great progress has been made in the field of flood disaster risk management.A large number of achievements have been recognized and adopted by the state and relevant departments.However,since drought is a gradual disaster,different from floods,earthquakes,and other sudden disasters,it is essential to establish a theoretical and technical system for drought disaster risk assessment by taking its unique disaster characteristics and risk formation mechanism into consideration.As a matter of fact,the theoretical system for drought disaster risk assessment has not yet been established currently,and the assessment techniques are still in its infancy.In other words,the needs of drought disaster management cannot be satisfied.With the aim to provide theoretical and technical support for further implementation of drought disaster risk management,this study focuses on answering the following three questions:What is the theoretical basis of drought disaster risk assessment?Whether there exists a quantitative assessment method of drought disaster risk based on physical processes?And how to dynamically assess drought disaster risk?Liaoning Province,the main grain production areas in Northeast China,has been selected as the research area.The main contents and achievements of this research are given as follows:?1?Theoretical framework for drought disaster risk assessment and management has been established.As a fundermental part of drought disaster risk management theory,the drought-related concepts needs to be clarified,namely aridity,drought,and drought disaster.These concepts have been discussed and compared systematically from different points of view,including definition,formation mechanism,measure function and fundamental characteristics.On the basis of summarizing existing researches on disaster risk,the concept,connotation and classification method of drought disaster risk are proposed in this study.The formation mechanism of drought disaster risk is studied from two different perspectives,while one from the perspective of regional disaster system theory,and the other from the persperctive of physical process.The principle of drought disaster risk assessment is also discussed.And the current major drought disaster risk assessment methods are summarized.Based on the summarization of the existing disaster management models,the concept and connotation of drought disaster risk management are clarified,and differences between the drought disaster crisis management and risk management are systematically analyzed.Finally,the overall framework of drought disaster risk management are put forward in this study.?2?An quantitative drought disaster risk assessment technique based on the drought event process has been put forward.Taking the definition of drought disaster risk and its physical formation process into consideration,the principle of drought disaster risk assessment based on the drought event process was illustrated.Accordingly,the framework of quantitative drought disaster risk assessment technique based on the drought event process was put forward.Firstly,drought frequency or return period needs to be calculated by identifying all drought events through hydrological and meteorological factors and extracting drought characteristic variables;Then,the potential loss of each drought event needs to be evaluated by using a statistical model or a mechanistic model;Finally,the quantitative relationship of drought frequency-potential loss-drought resistance ability needs to be established on the basis of all drought events.Taking Liaoning province as an example,a case study on this method was conducted.In this case,drought frequency calculation method based on Copula multidimensional joint distribution was adopted,and the agricultural drought loss model based on the APSIM model was established.Then,the quantitative relationship between drought frequency and drought loss rate were established for 14 prefecture-level cities of Liaoning Province.The results show that there is a good correlation between the drought frequency and drought loss rate in all cities,with the coefficient of determination R² ranging between 0.6 and 0.8.By comparing with the statistical data of drought losses after drought,the rationality of this method was verified.?3?An dynamic assessment technique for drought disaster risk based on crop growth model and scenario simulation technology has been proposed.The dynamic assessment of drought disaster risk refers to predicting the potential impact of future droughts in an area in advance based on real-time drought information and possible future development trend analysis.Based on the understanding of dynamic drought disaster risk,the principle of dynamic assessment of agricultural drought disaster risk was studied,and the technical framework of this method was put forward.Firstly,the crop growth process under different scenarios,including different drought ensemble forecast scenarios,different typical year scenarios or hypothetical scenarios,needs to be simulated with the help of crop growth model and scenario simulation technology;Then,potential drought-induced grain loss under different scenarios needs to be estimated on behalf of dynamic drought disaster risk.A case study was carried out about the summer-autumn drought in 2009 in Liaoning province.Taking the growth process of maize in Liaoning province into consideration,three time points were choosen as the current assessment time t,June 1^st,July 1^st and August 1^st respectively.The crop yield was dynamically simulated by the crop growth model APSIM under different scenarios that external condition W is k:nown before time t and external condition U is unknown after time t.As for the unknown external conditions U,8 scenarios were set,including 5 hypothetical scenarios?no effective precipitation in the next 5 days,10 days,20 days,30 days,50 days?and three typical year scenarios?drought year,normal year,and wet year?.Then the potential drought-induced grain loss rates under different scenarios at three assessment time were calculated,and the dynamic drought risk distribution maps were drawed.