Research On Rapid Evaluation Ofthe Grassland Drought Disaster Loss

Meteorological disasters tend to become more frequency and intensity in China,in the context of global warming.These meteorological disasters have caused great negative impacts on human lives and socioeconomic wealth.As one of the major meteorological disasters,drought disaster poses a great threat to food security and restricts the sustainable development of agricultural and animal husbandry economy.The current studies and obtained achievements of drought are mainly focused on the traditional agricultural field about risk assessment.However,the grassland drought disaster and its impact on the animal husbandry economy is less well understood.China is a country with abundant grassland resources and ranks second in the world for the grassland area.Grassland system has an important ecological and economic value.However,significantly affected by human activities and climate change,the natural disasters occur frequently,especially grassland disaster,and cause the severe damages to the society in the grassland region.Therefore,this study proposes a topic on rapid evaluation of the grassland drought disaster loss,which aims to provide the scientific and important basis for developing policies of timely and effective disaster prevention and mitigation.Songnen Grassland was taken as a case study area,and the grassland was selected as the main hazard-bearing body.Based on the theory of regional disaster system,the impacts of grassland drought disaster on grassland yield and carrying capacity was rapid quantitatively evaluated by analyzing the relationships between the various drought intensity and the corresponding fluctuation of grassland NPP.This study set the following specific research contents: to analyze the background of grassland drought disaster from three aspects: hazard factor,hazard-formative environment,and hazard-bearing body;to investigate the spatial and temporal variations by the Standardized Precipitation-Evapotranspiration Index(SPEI)used to represent drought intensity;to estimate the monthly vegetation net primary product(NPP)using the Carnegie-Ames-Stanford Approach(CASA)model based on the MODIS NDVI dataset and meteorological data during 2005-2014,and analyze the spatiotemporal variations of vegetation NPP in the growth season of grassland(from April to September);to construct the loss rate curves of grassland drought disaster based on the CASA model and the field and indoor experiment in each growing stage;and to achieve the rapid quantitatively evaluation of the grassland drought disaster loss for grassland yield and carrying capacity in typical case year in each growing stage based on the loss rate curves and the conversion relation between grassland NPP and grassland yield.The Main results are as follows:(1)The SPEI-6 indicated a decreasing but not significant during the growing season,with a rate of 0.12 /10 a.The break analysis showed the sharpest and significant drop rate was detected from 1970 to 2009 of 0.38 /10 a.There was a clear change point in 1993 from analysis of abrupt changes,at which the evident decreasing trend began.Moreover,wavelet analysis revealed that SPEI-6 exists 10-11 years in periodic variation over the Songnen Grassland.(2)From a spatial perspective,the SPEI-6 had the highest decreasing rate in the southern region,on the whole,ranging from 0.51 to 0.41 /10 a.Monthly,grassland drought tends to be alleviated in the northern and central regions for the past 55 years.However,the southern,western and northwestern regions are still experienced drought stress.(3)The result of CASA model validation for estimation of monthly vegetation NPP shows good accuracy in growing season over 2005-2014.The spatial pattern of vegetation NPP indicated higher values in the northeast and lower values in the southwest,and in general,the northern part of the vegetation NPP is higher than that in the south.The higher value of NPP is mainly concentrated in the period from June to July.The vegetation NPP in the mountainous area is higher than that in the southwestern plains,and that is attributed to the distribution of forest land in the mountainous area.In addition,the vegetation NPP in the cultivated area is higher than that in grassland.(4)The vegetation NPP showed an increasing trend in May,June,and September in the growing season from 2005 to 2014,and annual vegetation NPP was experienced an increasing trend in the whole region.The result of variation analysis of annual vegetation NPP gravity center indicated that the gravity center moved to the southwest.It could be concluded that the annual vegetation NPP experienced an evident increasing trend in the southwestern regions.(5)By selecting typical case year,estimating the monthly grassland NPP based on CASA model,and utilizing the loss rate curves of grassland drought disaster,this study have achieved the rapid quantitatively evaluation of the grassland drought disaster loss for grassland yield and carrying capacity based on monthly SPEI index.The results showed that,from analysis of those case year,both the loss of grassland yield and carrying capacity caused by grassland drought indicated higher values in the north and lower values in the south areas.The high-value areas of grassland drought loss were mainly distributed in Qiqihaer city,Lindian county,and Fuyu county.(6)In July 2009,for example,the whole region was experienced the light drought and moderate drought,but the losses caused by that mild grassland drought were still high.In the view of the rapid evaluation results,the reduction of grassland yield has reached about 14263.15×104 kg,resulting in economic losses of about18542.09×104 yuan.The corresponding losses of theoretical grassland carrying capacity has reached roughly 105.03×104standard sheep(weight 50 kg),resulting in economic losses of about115025.39×104 yuan.On this basis,countermeasures and suggestion for mitigating the impact of grassland drought disaster are provided and discussed.