Study On Changes Of Lake Area And Vegetation Coverage In Hulun Lake Based On Landsat Data

Based on 10 Landsat images every three years from 1991 to 2018,this thesis uses the maximum likelihood method to classify the land cover types,extract the area of Hulun Lake and analyze its changes,and extract the vegetation coverage area and analyze its changes based on NDVI pixel dichotomy model;The relationship between the area of Hulun Lake and the vegetation coverage and the main meteorological factors in this area was discussed.The main results are as follows(1)The change of Hulun Lake area can be divided into three stages.From 1991 to1997,the average annual increase of Hulun Lake area was 0.11%;From 1997 to 2012,the average annual decrease was 1.65%,which was a continuous shrinking period;From 2012to 2018,the average annual increase is 2.74%,which is the recovery period.The smallest Lake area of Hulun Lake was 1750.36km~2in 2012,and the largest lake area was2326.81km~2in 1997;During the 28 years,the area of Hulun Lake decreased by 273.92 km~2,with an average annual decrease of 0.43%.The water area of the south bank was obviously restored,and the water area of the small lake in the Northeast disappeared.(2)From 1991 to 2018,the coverage area of medium and high coverage vegetation was getting smaller and smaller,but it accounted for more than 70%of the total vegetation area in each period.The change rate of vegetation coverage area of middle and high coverage was 10.44%in the stable period,31.93%in the continuous shrinking period and54.03%in the recovery period.(3)From 1991 to 2018,the average annual temperature and winter temperature in Hulun Lake region decreased,while the temperature in other seasons increased;Annual evaporation and spring,summer and autumn evaporation increased,while winter evaporation decreased;The annual precipitation and summer precipitation decreased,while the other seasons increased;The relative humidity decreased in all seasons.Generally,it tends to be warm and dry.(4)In summer,the increase of average temperature,the decrease of precipitation,the decrease of average relative humidity and the increase of evaporation are the main factors leading to the shrinkage of Hulun Lake area.(5)There is a significant positive correlation between the area of Hulun Lake and the area of medium and high vegetation coverage.