Study On Dynamic Changes Of Hongjiannao Based On Remote Sensing

Hongjiannao is located in the arid and semi-arid region of northwest China,which plays an important role in local climate regulation,water resource balance and biodiversity conservation.However,the area of Hongjiannao has been shrinking continuously,which affects its ecological,economic and social functions in recent years.This paper took Hongjiannao as the study area,adopted the Soil Moisture Monitoring Index(SMMI)combined OTSU to obtain the lake area based on 359 Landsat images from 1986 to 2020.Based on lake area and waterline method,we obtained the lake water level from 1986 to 2020 by ASTER GDEM(V2.0).The area and water level were combined to acquire the water volume variation over the 34 years in Hongjiannao.We analyzed the variation trend of the area,water level and water volume variation of Hongjiannao in the past 34 years.The Net Shoreline movement(NSM)and Linear Regression Rate(LRR)in DSAS(Digital Shoreline Analysis System)were applied to quantitatively evaluate the variation trend of lake area in spatial location.Finally,we established the water balance model of Hongjiannao lake and basin to calculate the change of lake groundwater and water quantity.The results were as follows.(1)The variation trend of the area,level and volume of Hongjiannao lake between 30a can be divided into fluctuation(1986-1997,from 57.4km2,1211.28m,-2×105m3 to 56.94km2,1211.19m,-5.42×106m3,respectively)--rapid decrease(1997-2016,from 56.94km2,1211.19m,-5.42×106m3 to 30.14km2,1205.86m,-2.33×108m3,respectively)--increase(2016-2020,from 30.14km2,1205.86m,and-2.33×108m3 to 38.68km2,1207.43m,and-1.84×108m3,respectively).From the perspective of spatial variation trend,we can get that from 1986 to 1997,the mean NSM and the mean LRR of the Hongjiannao were 77.6m and 4.69m/a respectively.The shrinking trend is obvious at the three vertices of the triangular lake.From 1997 to 2015,the mean NSM and the mean LRR was of the Hongjiannao was 900m and 44.3m/a respectively.The decreasing trend is most obvious at the three vertices of triangular lake especially at the southeast Angle.From 2015 to 2020,the mean NSM of the Hongjiannao was-278.7m,and the mean LRR was-57.9m/a.The expansion trend is more obvious at the three vertices of the triangular lake.The variation trend of the area in this paper is similar with other studies after comparison,which proves that the results obtained in this paper are reliable.The area,water level and volume variation of Hongjiannao were at a high level from 1986 to 1997,and the changes were small and stable,mainly because the meteorological conditions of Hongjiannao were stable during this period.The decrease of water quantity between 1997 and 2016 is mainly affected by human factors,among which industrial output value is the main factor.The Economic bulletin of Yuliin city shows that the output value of coal accounted for more than 70%of the total output value for many years.Therefore,it is speculated that coal mining is the main cause of groundwater loss.Since 2016,the main reasons for the increase in the area,water level and volume of Hongjiannao are the sluice release of the upstream river,the increase in rainfall and the closure of small coal mines.(2)The Hongjiannao lake basically fluctuated from 1986 to 1997,which was regarded as the equilibrium stage,the mean area was 54.3km2.The maximum groundwater supply was 9.81 ×106m3 during this stage.From 1997 to 2015,Hongjianao lake declines fastly during 1997-2015.Therefore,during this period of reduction,the groundwater was negative,indicating that the recharge from the lake to the groundwater was-2.17×106m3.From 2016 to 2019,the water quantity of Hongjiannao lake continued to increase,and the water quantity in Hongjiannao basin showed an increasing trend.During this period,the groundwater was replenished to the lake,with a supply of 4.97×105m3.Water quantity ?S in Hongjiannao basin is negative from 2000 to 2015,and there is a trend of rising to falling from 2000 to 2007,?S was change from-1.46×108m3 to-1.32×108m3.From 2008 to 2015,?S shows an upward trend of fluctuation,?S was change from-7.63×107m3 to-3.45×107m3.From 2016 to 2018,the change trend of ?S in Hongjiannao basin is upward to downward,and ?S is positive and the water quantity is positive,change from 4.62×107m3 to 1.51×10m3.On the whole,the water quantity change in Hongjiannao basin is on the rise from 2000 to 2018,and climate change is the main reason for the increase of water quantity in Hongjiannao basin in recent years.