The Response Relationship Of Hydrological And Agricultural Drought To Meteorological Drought In The Lower Reaches Of Nenjiang River

In the past century,the global climate has been experiencing significant warming,leading to frequent droughts,which has a profound impact on human social and economic development.Since precipitation deficit is the leading factor of drought,in order to reduce the impact of drought,it is necessary to improve the understanding of the propagating relationship between different drought types,understand the response and potential transmission mechanism of different drought types the potential transmission mechanism,so as to be able to carry out early warning of hydrological and agricultural drought based on meteorological drought.The Songnen Plain on both sides of the lower Nenjiang River is an important grain producing area in China,with extensive wetland and natural water conservation conditions.Under the influence of many factors such as climate change and uneven distribution of water resources,the problem of water shortage in the lower reaches of the Nenjiang River has become increasingly prominent.Therefore,quantitative analysis of drought propagation mechanism is of great significance to irrigation,water diversion and regional development planning in the lower reaches of the Nenjiang River.First of all,this paper uses the trend-free pre-whitening MK trend test method(TFPW-MK)to analyze the meteorological,hydrological,and agricultural drought trends in the lower reaches of the Nen River.Then,the meteorological and hydrological standardized drought index(SPI,SRI)thresholds were determined,and meteorological and hydrological drought events were identified through the run-length theory.Based on the Standardized Drought Index(SPI)and the Self-adjusted Palmer Drought Index(sc-PDSI),the spatio-temporal overlap method is used to identify meteorological and agricultural drought events.On this basis,analyze the regional drought development law,extract the corresponding characteristic variable pairs,establish the response relationship of meteorological to agricultural and hydrological drought characteristics,obtain the response threshold of drought characteristics,and comprehensively analyze the response relationship of hydrology and agriculture to meteorological drought.The main conclusions are as follows:(1)The monthly precipitation data from 15 meteorological stations,runoff data from 3hydrological stations and grid SC-PDSI drought index data in the lower reaches of Nenjiang River were selected to analyze drought characteristics.It was found that the distribution of meteorological drought in the lower reaches of the Nenjiang River was relatively discrete,with high occurrence frequency,short duration,and low intensity.Agricultural and hydrological droughts have strong continuity and obvious regularity.There are two periods of severe drought(1970?1980,2000?2010).Hydrological drought is aggravated from north to south,and the southwest is a disaster area prone to agricultural drought.(2)This paper uses the run theory to compare multiple scenarios when identifying drought events,and finds that the lower reaches of the Nenjiang River is more suitable for using different thresholds for rainfall concentrated months and non-intensive months.When identifying agricultural drought,multiple schemes are also compared,and-0.6 is selected as the agricultural drought threshold.According to the results of drought event identification,long-term agricultural continuous droughts mostly originated in the southwest,gradually spreading and migrating upwards along the northeast direction,and finally ended in the northeast or the middle,or spread and contraction finally ended in the southwest.Moreover,the migration rate of drought in the middle and upper parts of the lower reaches of the Nenjiang River is relatively fast,and drought events with a longer duration will experience multiple enhancement-weakening-re-enhancement-re-weakening processes.(3)Through quantitative research on drought propagation mechanism,it is found that the hydrological-meteorological and agricultural-meteorological drought response models have better simulation effects for medium-long duration,medium-high intensity,and medium-duration and intensity,respectively,and the average error is smaller.And the nonlinear model is more suitable to describe its response relationship than the linear model.According to the calculation results of the threshold,the hydrological drought in the lower reaches of the Nenjiang River from Jiangqiao to Dalai has a shorter response time to meteorological drought,and the intensity is smaller.The meteorological drought in this area is more likely to develop into hydrological drought.(4)The hydrological-meteorological drought duration and intensity response thresholds in the lower reaches of the Nenjiang River were 0.93 months and 1.16,respectively.The response thresholds of agricultural-meteorological drought duration,intensity and area are 1.05 months,1.31 and 3857.86 km~2 respectively.The order of drought is meteorological drought,hydrological drought and agricultural drought,and agricultural drought is followed by hydrological drought.Based on the matching results of drought events on the spatial and temporal scales,it is found that continuous meteorological droughts in summer have a greater impact on agricultural continuous droughts,while short-term meteorological droughts in autumn and winter rarely trigger new agricultural drought events.