| As an extreme weather event and a major natural disaster,drought is one of the most widespread and costly types of extreme weather events and is considered one of the most serious natural disasters in the world.As a result of climate change,droughts in the Northeast are intensifying and persisting,with negative impacts on socioeconomic and agricultural production,and the Northeast Transboundary Basin is located in the border area of Northeast China,which is an important border support area and a new strategic maritime pivot point in the “Belt and Road” cooperation strategy in Northeast Asia.The ecological security of this area will also become a key issue in the ecological network of Northeast Asia.Therefore,it is important to analysis the spatial and temporal distribution characteristics of droughts in the Northeast cross-border watershed region,and to clarify the extent of droughts and the main land cover types in the cross-border watersheds of Northeast China,so as to provide scientific and reasonable theoretical support for coping with droughts in the region.Based on this,this paper takes the cross-border watersheds of Northeast China as the study area,and analyses the climate change background,drought and drought in both time and space scales by calculating the meteorological drought index-SPEI index based on station data,and the remote sensing drought index-VCI index based on remote sensing data,sampling linear trend method,inverse distance weight interpolation method,travel theory,Sen+MK trend analysis method,superposition analysis and other methods.The spatial and temporal evolution of SPEI index and VCI index were analyzed from both temporal and spatial scales.Finally,the SPEI and VCI indices were combined to analysis the drought levels in different land cover types in Northeast China cross-border watershed region.The main results are as follows.(1)Characteristics of temperature and precipitation changes in the cross-border watersheds of Northeast China: Temperature and precipitation show an overall upward trend.The multi-year average of temperature shows a clear north-south variability,while the multi-year average rate of temperature change shows an upward trend,with only the northwestern part of the Heilongjiang basin showing a clear downward trend.Precipitation shows mainly east-west variability,with the rate of change of precipitation in the Heilongjiang and Ussuri river basins showing a downward trend,and the Tumen and Yalu river basins showing an upward trend.(2)The spatial and temporal evolution of drought the cross-border watersheds of Northeast China: the SPEI and VCI indices have both shown an increasing trend over the past 20 years;the drought intensity of the SPEI index is in the range of moderate drought and mild drought,with the frequency of drought mainly concentrated between8 and 16 times,and drought is more frequent;moderate drought is mainly distributed in the Heilongjiang River basin and the Russian side of the Ussuri River basin.The overall trend of the VCI vegetation status index is very significantly increasing,the drought level is mainly moderate drought and mild drought,and the frequency of drought is mainly concentrated between 51% and 75%,and drought is frequent.(3)Analysis of the combined SPEI and VCI indices revealed that the cross-border watersheds of Northeast China are dominated by moderate drought levels,and the main land use type in the study area is woodland.The “high” and “very high” levels of drought are mainly found in forest land,accounting for 17.91% and 10.76% of the total area of the study area respectively,followed by cropland.The “high” and “very high”drought levels account for 37.41% of the total area of the study area.The drought levels in the Heilongjiang and Ussuri River basins are mainly “medium” drought levels,while the drought levels in the Tumen and Yalu River basins are mainly “low” and “very low”. |
