Analysis On The Characteristics And Driving Factors Of Surface Water Temperature Variation Of Major Large Lakes In China

In the context of global warming,lake surface water temperature(LSWT)has risen rapidly.In urban areas with rapid economic development,the LSWT has not only changed due to climate warming,but also continuously rising due to the influence of regional human activities.Since the change of LSWT would affect the watershed ecological environment,exploring its causes is the basis for protecting and improving the water environment of urban lakes.Therefore,it is very important to carry out attribution analysis of LSWT.China's six major urban lakes(Chaohu Lake,Dianchi Lake,Taihu Lake,Hongze Lake,Poyang Lake and Dongting Lake)play an important role in ecological environment of the basin and the development of the social regional economy.Under the dual influence of global warming and human activities,LSWT has changed significantly,and the water quality has not been effectively improved.LSWT is one of the most important physical properties of lakes,and exploring its variation characteristics and driving mechanisms can provide theoretical support for lake governance and sustainable development of watersheds.This study based on MODIS surface temperature product data,and selected six lakes that have a significant impact on China's social and economic development as the study area.The trend analysis,correlation analysis and stepwise multiple regression analysis method were used to explore the variation characteristics and interrelations between LSWT and driving factors at different time scales,and quantify the contribution rate of each driving factor to the LSWT change,and attribution analysis was carried out for the LSWT change of different lake types.The main contents and conclusions are as follows:(1)On the whole,from 2001 to 2018,the mean comprehensive change rate of LSWT-day and LSWT-night of six important lakes in China was 0.31 ?/10 a,which was obviously higher than the NSAT in the study area(0.10 ?/10a).At the same time,the comprehensive change rate of each lake showed an upward trend,and the warming rate was higher than that of NSAT.It shows that besides air temperature,other factors also lead to the change of lake surface water temperature.(2)Form the lakes,the daily average change rate(the mean of day and night value)of the LSWT in the six lakes showed an upward trend from 2001 to 2018,and the warming rate was higher than that of NSAT,and the LSWT change rate of stable lakes increased faster than fluctuating lakes.Meanwhile,the analysis of the change characteristics of the driving factors and LSWT shows that the two are closely related.For example,the research results of Chaohu Lake and Dianchi Lake show that in the context of the impervious surfaces expansion,changes in natural factors would affect the effect intensity of thermal runoff on the lake surface water temperature.(3)On an annual scale,the impact of driving factors on all lakes was consistent.LSWT were significantly positively correlated with the NSAT,and the correlation coefficients were higher than other driving factors,which was consistent with the contribution results.Natural factors explain the LSWT to a higher degree than anthropogenic factors.Air temperature was the most important driving factor,but anthropogenic factors,especially the role of impervious surface expansion on LSWT changes,cannot be ignored.In addition,the effect of anthropogenic factors on stable lakes was higher than that of fluctuating lakes.Second,the contribution strength of driving factors to LSWT differed between daytime and nighttime.The contribution rate of natural factors to LSWT at night was lower than that in daytime.The contribution rate of anthropogenic factors to LSWT at night was higher than that during daytime,and in some lakes its influence strength exceeded natural factors.For stable lakes,the effect intensity of anthropogenic factors on the LSWT-day was affected by the annual average air temperature and precipitation.The contribution rate to the LSWT-night was related to the growth rate of the impervious surface area in the basin.For fluctuating lakes,there were differences in the influence of anthropogenic factors.(4)On the seasonal scale,the daily average change rate(the mean of day and night value)of LSWT in most lakes had a strong correlation with natural factors in spring,autumn and winter.The contribution rate results show that the LSWT is mainly affected by natural factors in these three seasons,especially with air temperature.The contribution rate of anthropogenic factors to the LSWT in summer was higher than that of the other seasons,but it was still lower than the contribution rate of natural factors.For a single lake,the impact of driving factors on the LSWT-day and LSWT-night was different.For the LSWT-day,in spring,autumn and winter,all lakes were all strongly influenced by natural factors,especially air temperature.In summer,due to the different types of lakes,the driving factors of LSWT were different.Among the stable lakes,the contribution of anthropogenic factors was higher than that of natural factors,and the lakes with higher average air temperature and precipitation had a significant effect.In fluctuating lakes,although the influence of anthropogenic factors on the LSWT in summer was higher than in other seasons,its contribution rate was still lower than natural factors.For the LSWT-night,except for Poyang Lake and Taihu Lake,the contribution rate of natural factors to other lakes was higher than that of anthropogenic factors in the four seasons.(5)This study shows that the contribution rate of natural factors to the LSWT is higher than that of anthropogenic factors,especially the air temperature is still dominant.However,the contribution of anthropogenic factors was increasing with the intensification of human activities,especially in summer due to the influence of surface thermal runoff,the impact of anthropogenic factors was significantly larger than other seasons.