The Characteristics Of Temporal And Spatial Changes In The Ecological Conditions Of The Hunchun River Basin And The Local Impact Of The Construction Of Laolongkou Reservoir

The Hunchun River Basin is located at the junction of China,North Korea,and Russia.The main source of water,the Hunchun River,is a tributary of the Tumen River in China,which has important strategic significance.Reservoirs benefit human society in many aspects such as flood control and water supply,but at the same time they change the types of land use and the hydrological process of the river,and even have an impact on the local climate.This paper takes the Hunchun River Basin and Laolongkou Reservoir as the research objects,and uses geographic information technology,models and hydrological change index method(IHA)to carry out the impact of the watershed land use,the temporal and spatial characteristics of extreme climate and the local ecological and hydrological impacts of the Laolongkou Reservoir.Analysis and the following conclusions are reached:Through the combination of RS and GIS,it is found that from 1976 to 2017,Hunchun River Basin has a large cluster of woodlands,with high landscape connectivity,more uniform spatial distribution,and small changes in land use types.Reservoir construction has caused local land use types to change actively in a short period of time,and the conversion from bare land to reservoirs and ponds is the most obvious.Among them,the land occupation of the pivot project and the temporary land occupation for construction have transformed some dry land and woodland into artificial surfaces.At the same time,the forest was cut and the cultivated land was cleared to make it into bare land in preparation for later water storage.After the completion of the reservoir,the bare land was flooded,Temporary occupation of land for construction and part of nearby cultivated land,resulting in water area larger than the original bare land area.Based on the RClim Dex model to analyze the temporal and spatial characteristics of extreme climate events in the basin from 1979 to 2018,it is found that the basin is warming,and the occurrence of extreme climate events is on the increase with large inter-annual fluctuations,reaching a peak in the past 10 years.From a spatial point of view,extreme temperature events generally follow the law of higher latitude,fewer high temperature events,and more low temperature events.Extreme precipitation events show that over the past 10 years,excessive rainfall events and continuous humidity have declined from southwest to northeast,and continue to be dry.The situation is just the opposite.In the previous 30 years,the spatial distribution was uniform and there was no major change in the law.At the same time,the operation of the reservoir can inhibit local climate warming,reduce the occurrence of local extreme high temperature events,alleviate the local continuous dry weather,but also promote the occurrence of local extreme low temperature events at night.In general,the operation of the reservoir can alleviate local extreme weather phenomena and improve the productivity and stability of the ecosystem in the surrounding area.Establish a SWAT model suitable for the Hunchun River Basin to simulate the natural runoff information of the river and eliminate the impact of reservoir construction on the river's hydrological situation.Using the Hydrological Change Index Method(IHA),it is found that the operating height of Laolongkou Reservoir has changed the hydrological situation in the lower reaches of the Hunchun River.Reservoirs have less change to extremely high runoff than very low runoff,and at the same time,they are insufficient in dealing with long-term low runoff during the dry season.However,it plays an important role in regulation and storage during the snow-melting period,flood season and river freezing period,slowing down the phenomenon of river drought and flooding,and keeping the runoff as stable as possible,which is a beneficial change to the hydrological changes of the Hunchun River.At the same time,the runoff management behind the dam should pay more attention to the water release process of the reservoir to avoid frequent water release that causes the increase in the duration of high runoff pulses,which will have a greater adverse impact on downstream organisms.