| The development of the Yellow River basin has an important impact on China's economy,agriculture,water conservancy and other aspects.The govern,development,protection and management of the Yellow River are of great strategic significance to the sustainable development of social economy and the protection of ecological environment in China.In recent years,ecological protection and high-quality development of the Yellow River basin have become a major national strategy.It has become an important direction and strategic demand for the development of the Yellow River to strengthen the research on major issues of the Yellow River and realize the coordinated and green development of the Yellow River.In recent years of study,GEE,Google Earth Engine)as a new research has been used at home and abroad,its relative to traditional geographic information science research tools is quick,convenient and lower cost a lot of advantages,in the long time series of land cover and water detection plays an increasingly important.In this paper,based on the on-the-spot investigation,combined with satellite high image of the Yellow River Beach Areas in Henan province borders and water to cover frequency image,from 1987 to2018,the analysis of water cover change research area.We also are internal differences between different cities of the Yellow River Beach Areas in Henan province were analyzed,and to describe the Yellow River in Henan province belt cover the surface waters in 32 years the change of space form.According to the water cover frequency changes in the study area.We divide them into three categories: tidal flats,seasonal waters,permanent waters,its annual water cover frequency threshold value of 0 to 25%,25% and 75%,75% to 100%,and then concludes three kinds of water body cover types during1987 to 2018 to get specific area's morphological changes and the details.The tidal flat area expanded by57.55km2 in 32 years,and the seasonal water area decreased by 104.36km2 in 32 years.Area of PermanentWaters After expanding by 82.91km2 between 1987 and 1990,then this area shrank by a sharp 170.50km2 between 1990 and 1991,after those changes,Area of Permanent Waters increased by 134.39km2 between1991 and 2018.By analyzing the spatial distribution of various water cover types of 32 years,it can be concluded that in the Yellow River beach area of Henan Province,which accounts for 61.76%,as a continuous beach,the water cover pattern has not changed in 32 years,and both seasonal and permanent waters are in a drastic change.In the past 32 years,the specific mutual transformation among the three types of water cover to took place in the seasonal water area as the transition area,and the direct mutual transformation between the tidal flat and the permanent water area rarely occurred.The study area's water cover can be divided into before the Drying-up Period from 1987 to 1990,drying-up period from 1991 to2001,from 2001 to 2018,after the completion of Xiaolangdi Reservoir.they have significant difference between the three.During the Drying-up Period from 1991 to 2000,the surface water cover in the study area changed dramatically every year,and an average of 62.66% of the permanent water area changed to other types of water cover every year.After the Xiaolangdi Reservoir is completed,all kinds of water cover volatility in the study area are stabilized,at the same time,the area of continuous permanent water increased from 0.27km2 to 4.60km2,with an average annual permanent water retention ratio also increased to 70.61%from 37.34%.And the areas of the continuous permanent waters also have great differences,those areas in the After Xiaolangdi Reservoir Completed are 16.74 times as much as the Drying-up Period.In the comparison of the change range of each city in the study area,the smallest difference between the ratio of the largest area and the smallest area in the tidal flat of each city is 1.04:1 in Xinxiang City,and the largest is 1.30:1 in Zhengzhou City.The smallest gap in seasonal waters is 1.67:1 in Xinxiang City,the largest gap is 6.64:1 in Puyang City,the smallest gap in permanent waters is 2.72:1 in Xinxiang City,and the largest gap is 7.18:1 in Puyang City.Tidal flats in various cities are relatively stable,and theproportion of their area presents a more obvious staircase sequence.The annual average area of tidal flats in Xinxiang City,the largest area,is 784.74km2,and the minimum average area of tidal flats in Luoyang City is only 57.91km2.Seasonal waters and permanent waters are in dramatic changes.The coefficients of variation of the tidal flats,seasonal waters,and permanent waters in the study area are 0.03,0.36,and 0.39,respectively.The coefficients of variation of the cities are generally greater than the overall level of the research area,especially the seasonal waters and permanent waters,the range of change is even more dramatic.In the comparison of the changes of water cover types of each city,the changes of some cities play a leading role in the overall changes.The total contribution rates of Zhengzhou and Xinxiang in the overall changes of water cover types of beach land and seasonal waters are 85.90% and 74.25% respectively.The contribution rate of Kaifeng,Xinxiang and Zhengzhou to the total change of permanent water area is 98.68%.By analyzing the change trajectory of the three types of water cover in the leading cities,we can see that the trajectory of water cover's change is consistent with that of the entire Yellow River Beach Area.The area of continuous tidal flat in the study area is 1649.49km2,accounting for 69.78% of the Yellow River tidal flat area in Henan Province.It is mainly distributed in xinxiang,Puyang,Jiaozuo and other cities on the left bank of the Yellow River.The continuous tidal flat in each city presents an obvious trend of concentration.In last tidal flat risk classification,luoyang has more high-risk areas ratio,jiaozuo,xinxiang's continuous tidal flat has more ratio to low risk area.Among them,wen County,Meng County of Jiaozuo city and Changyuan County of Xinxiang city have large low-risk areas gathering,while high-risk areas are concentrated on Wuzhi County of Jiaozuo city,Yuanyang County of Xinxiang City,Lankao County of Kaifeng City and other areas. |
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