| Songnen grassland is located in the northeast of China's northern grassland,has the best water and heat conditions,and occupies an important position in China's temperate grassland,is also an important pastoral area and owns the fine grazing pastures.Vegetation is lush and productive.With the global warming,grassland drought and other disasters caused by climate change are occurrence frequently and grassland ecological environment deterioration is more and more seriously.Grassland droughts is one of the disasters that are slow to occur,effects wide area and have serious impact on people's living,production and sustainable development in grassland pastoral areas.In recent years,extreme climate events caused by global climate change(such as drought,floods,low temperature chilling,etc.)are frequent,and the deterioration of ecological environment has threatened the terrestrial ecosystem constitution and development.China is located in the Asian monsoon climate zone,is one of the world's major climate fragile areas,also suffer most serious disaster in the world.Drought is one of the highest rates of recurrence,the most extensive impact,causing the most serious loss of natural disasters in China.Grassland ecosystems are the most vulnerable open systems in all types of ecosystems and are vulnerable to damage by natural disasters.Therefore,the risk assessment and management of grassland drought disaster will be the focus of this paper.This study,conducting drought identification of grassland,the vulnerability assessment of grassland drought disaster,the dynamic risk assessment of grassland drought disaster and the insurance preium rate were carried out by combining field experiment and EPIC growth process simulation model based on the multi-source data,the theory of regional disaster system and the theory of natural disaster risk from "weather-vegetation-soil" continuum body,to improve the management of grassland drought disaster for Songnen grassland.The main conclusions and innovations are as follows:(1)In this study,the temperature vegetationdrought index(TVDI)as an early identification index to identify the grassland drought.Based on the MOD11A2 data and MOD13A1 data,the TS / NDVI spatial model was established and the TVDI was retrieved.The results showed that there was a significant correlation between TVDI and the measured soil water content.So,the temperature vegetation drought index was used to identify the 2001,2004,2007 and 2009 four typical historical cases of drought years in Songnen grassland.The drought was the most serious and the drought area was the largest in the turning stage.In the flowering stage,the drought area was reduced and the drought degree was the smallest,and the drought area began to expand at the maturity stage.The southwest of the Songnen grassland has the most severe drought.The results show that the temperature vegetation drought index can fully reflect the coupling relationship of "weather-vegetation-soil" continuum,and can be applied to real-time monitoring of drought and drought dynamic monitoring.(2)The dynamic vulnerability assessment model of drought disaster in Songnen grassland was established by fitting the vulnerability curve between drought index and key index loss rate in different growth stage.In this study,the key indicators of drought resistance were determined by field experiment.The growth process and yield formation process of grass in typical drought years were simulated by EPIC growth process simulation model at 11 kmkm × grid scale.The dynamic vulnerability assessment model of drought disaster in Songnen grassland was established by fitting the vulnerability curve between drought index and key index loss rate in different growth stage.The vulnerability of each growth stage is turning stage-flowring stage,flowring stage-maturity stage and matuaity stage-drying stage.The turning stage-flowering stage was the most sensitive to drought stress.This study not only realizes the transformation from statistical grassland drought research to disaster mechanism research,but also realizes the transformation from risk assessment of grassland drought disaster to dynamic risk assessment of grassland drought,and breaks through and perfected traditional method restrictions and incompleteness,which establish vulnerability curve only select the loss of production as a loss of key indicators.(3)Based on the theory of natural disaster risk formation,this paper establishes the grassland drought risk concept framework,and takes the interannual scale and the growth stage scale as the time scale and the 11 kmkm × grid scale as the spatial scale,to carries out the dynamic assessment risk model for grassland drought disaster.At the growth stage scale,the drought disaster risk area decreased gradually according to the turning green stage-flowering stage,flowering stage-maturity stage,maturity stage and drying stage.The turning green stage-flowering stage is the critical period of grass growth and easy to suffer severe drought risk.Therefore,it is great significance to reduce the grassland drought by taking appropriate drought prevention and mitigation measures and drought risk management in this growth stage and to stable development of animal husbandry in the grassland pastoral areas.The mature stage-drying stage is the critical period of grass production,which is the least affected by drought disaster risk during whole growth period.Therefore,it is impossible to take defensive measures for the grassland drought disaster risk,with the least economic input to obtain the greatest economic benefits.At the regional scale,the southwest of the Songnen grassland has high risk of drought disaster.At the county-level cities level,regardless of which drought year and growing stage,Tongyu County,Longjiang County,Changling County and Duerbert Mongolian Autonomous County are suffer higher risk of drought disaster,these high risk areas should be attention and precautions.This study not only breaks and completes the one-sidedness and completeness of the traditional methods from theory,but also updates the historical statistical data and the limited site observation data from the data acquisition method.The results of this study can provide effective theoretical basis and scientific guidance for the early warning of drought disaster,drought management migitation in grassland.(4)Based on the grassland drought disaster risk allocation,the pure rate of grassland insurance premium rate is determined by the administrative unit at county level as the basic space unit,and purium rate value is taken as the main zoning index.Songnen grassland drought disaster insurance premium rate is 2.27% to 12.49%.The pure rate is divided into three grades: high rate,middle rate and low rate.The pure rate value is 8.48-12.49,4.97-8.47 and 2.27-4.96 respectively.The spatial distribution is significant difference.High risk region have high insurance premium rate and the low risk region have low insurance purium rates.This study has broken through and perfected the limitations and incompleteness of the traditional method which determine drought disaster insurance rates by the average annual loss rate.In this paper,we use the expected loss rate to determine the insurance premium rate of grassland drought disaster.In order to avoid the base difference risk,the regional characteristics of the disaster are taken into account when the insurance premium rate is determined.The results of the study provide guidance and reference for the insurance companies to draft the grassland drought disaster insurance premium rate according to local conditions. |
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