Natural disasters result from the complex relationships and interactions of the vulnerability of disaster-bearing bodies with the disaster-causing factors.The nature of natural disaster risk is described by the probability distribution which is associated with the magnitude and duration of the natural disaster.Evaluating a risk involves establishing a scientifically robust method to estimate the probability magnitude of a natural disaster risk.The mathematical theory of natural disaster risk assessment is essentially equivalent to an issue of probability and statistics,which can be described by the method of probability.The usual sample size required in probability-based statistical analyses is at least 30.However,in disaster risk assessment,especially when small areas are adopted as the evaluation unit,the data collection period is often short and statistics are incomplete.Therefore,it is difficult to reflect the variation in the risk of a disaster over certain study areas and big bias of computed results from observation often happen if we use traditional statistical methods to assess risk.
Drought is one of the most serious meteorological disaster and often causes considerable socioeconomic losses in the affected region.The Sichuan basin China is a very important agricultural production area.Researching and assessing the risk of agricultural drought in this region is helpful in making service decisions and carries huge social significance.However,risk assessment work on agricultural drought in the Sichuan basin has been minimal,and mainly focused at the city prefecture level.Agricultural disaster area is related to the disaster strength and scale,thus,the assessment of agricultural drought risk can be accomplished via a method‘disaster loss evaluation’.
Based on agricultural drought disaster data in Sichuan basin during 1984-2007 and information diffusion theory,the probability of agricultural drought,and its spatial distribution,are discussed under different risk levels.Accordingly,the risk of agricultural drought disaster in the Sichuan basin is separated(spatially) into a few of zones.Results show that the normal information diffusion method can provide a good fit for the agricultural drought disaster rate which is a proportion of the disaster area to the cultivated one.Further investigation shows that the difference in risk between Chongqing and Meishan,where the agricultural drought disaster rate is greater than or equal to 10% and 40%,respectively,increasing from the end of the 20th century to the beginning of the 21st century.An exceeding probability means an accumulated probability when the drought disaster rate is larger than a threshold,which is defined as 5% and 40% in this study,respectively.Cities such as Bazhong,Zhongjiang and Luxian are found to be high-risk regions.Low-risk regions are located in the western Sichuan basin,owing to its abundant precipitation.The research provides some useful decision-making information for those involved in disaster reduction and emergency management.
This study shows that small samples of disaster data can be applied in natural disaster risk assessment by using the information diffusion method.The accuracy and completeness of assessment data is probably the most crucial aspect in evaluating results.Due to the disaster data record being subjective and the sown area of the crop not completely matching the data in time,the result is not completely satisfactory.The method is a time-independent disaster risk assessment method that can be used to carry out statistical analysis of the disaster risk for a region where disaster events have occurred,and can also provide an indication of the natural disaster risk level of the region.Further research is necessary to help us make effective forecasts of long-term drought risk in the future.