Simulation And Spatial-temporal Variation Of Ice Thickness In Qinghai Lake Based On Multi-source Data

Ice thickness is an important physical parameter of a lake in the freezing period,which not only reflects the energy exchange intensity and material migration process at the water-air interface,but also has important ecological and economic value.Qinghai Lake is one of the important resource to maintain ecological security in the northeast of Qinghai-Tibet Plateau,as the increase of tourism heat in winter,research on spatial-temporal variation characteristics of ice thickness of Qinghai lake has great theoretical and practical significance to understand the spatiotemporal characteristics of lake ice,which helps study how lake ice responds to climate under the background of global warming.And it has practical significance for formulating scientific and reasonable management measures of Qinghai Lake.Based on the 0.01°temperature dataset of the Qinghai-Tibet Plateau,ERA5 Climate Reanalysis temperature dataset,MODIS MOD09GQ data product,and ice borehole and radar thickness measurements in 2019,the thickness of lake ice in Lake Qinghai between 2000 and 2020 was reconstructed by using the Degree-day model and the CLIMo model and the spatial-temporal variation characteristic was analyzed.The results showed that:(1)The accuracy of the two models was different and the degree-day ice growth model was more accurate.The average growth rate of ice thickness in March(0.3 cm/d)was faster than that in February(0.12 cm/d)based on the field survey data,the average growth rate of ice thickness in Lake Qinghai from November 2018 to March 2019 was0.34 cm/d simulated by the Degree-day model,with the ice thickness error of±2 cm compared with the actual observation data.However,the error was large at the entrance of the river and the south side of Lake Qinghai.Meanwhile,the simulation of ice thickness was overestimated before the mid-March but underestimated later.The average growth rate of ice thickness was 0.81 cm/d of 0%snow cover scenario and 0.67 cm/d of 100%snow cover scenario based on CLIMo model.And the simulation error of 0%snow cover scenario was 6.37 cm,which was generally overestimated between March 3 and generally underestimated in late March.The simulation error was 7.82 cm of 100%snow cover scenario,the simulation results all overestimated the measured ice thickness during the whole simulation process.There was a high correlation between the simulated ice thickness and the measured ice thickness of two scenarios(R~2>0.8).(2)The temporal variation characteristics of lake ice thickness in Qinghai Lake based on the two models were heterogeneous.Based on the Degree-day model,the average annual ice thickness of Qinghai Lake from 2000 to 2018 was 29?35 cm,and the annual variation showed fluctuating trend.The ice from 2001 to 2005 first thinned and then stabilized,2009-2014 was the period of severe fluctuations,and from 2015 to 2018,the ice cover first experienced sharp decline and then recovered.The ice thickness increased rapidly in the early freezing period,with the growth rate of 0.41 cm/d in December and 0.37 cm/d in January.After February,the growth rate of ice thickness slowed down after February,with the growth rate of 0.26 cm/d in February and 0.12 cm/d in March.The average relative error percentage of annual ice thickness was 14.53%for the two scenarios based on CLIMO model.For 0%snow cover scenario,the average annual ice thickness was between 30?55 cm,and the maximum ice thickness was between40?75 cm.For 100%snow cover scenario,the average annual ice thickness was between20?55 cm,and the maximum ice thickness was between 25?75 cm.0%snow cover scenario with the growth rate of 1.36 cm/d in December and 0.8 cm/d in January and decreased rate of 0.6 cm/d in February and 0.07 cm/d in March and 6.6 cm/d in April.100%snow cover scenario with the growth rate of 1.37 cm/d in December and 0.68 cm/d in January and decreased rate of 0.42 cm/d in February and 0.017 cm/d in March and 5.12cm/d in April.(3)The average ice thickness of Qinghai Lake was significantly different in space.The average ice thickness showed a spatial pattern of being thicker in the north and east,whereas being thinner in the south and west.The annual mean ice thickness of the whole lake showed a trend of thickening after thinning from 2000 to 2008,a continuous thickening trend from 2008 to 2014,and reached a low value in 2015 and then picked up again.During the study period,the average annual ice thickness of Qinghai Lake was unevenly distributed in space,ranging from 21 cm to 39 cm in general,and the maximum ice thickness in space ranged from 31 cm to 58 cm,and the years of spatial change were more stable in the east than in the west.(4)The average thickness of lake ice was positively correlated with complete freezing duration and the freeze-up period.The MODIS images for date of freeze-up and break-up was high consisted with the lake ice phenology characteristics based on two scenario of CLIMo model.The maximum absolute error of FUS,BUS and BUE of 0%snow scenario was 9,8 and 8 d,respectively,the maximum absolute error of FUS,BUS and BUE of 100%snow scenario was 10,12 and 9 d.The duration of freezing,melting and the duration of lake ice were positively correlated with the average ice thickness.The variation of the average thickness of lake ice had a high correlation with the duration of freezing duration and the duration of lake ice,little correlation with the duration of melting.