| Water surface temperature is an important parameter for assessing the status,function and process of lake ecosystems.It directly or indirectly affects the physical,chemical,biological and ecological processes in lake.Based on the in-situ observation data of the Lake Taihu Eddy Flux Network?2011?2019?and MODIS surface temperature products?2003?2019?,the temporal and spatial variaitons in water surface temperature of Lake Taihu were investigated.Then,the influencing factors of interannual variaitions in surface temperature of Lake Taihu were decomposed with the principle of surface energy balance.The effects of atmospheric forcing,energy redistribution on water surface temperature of Lake Taihu were analyzed.The research results not only provide data support for ongoing Lake Taihu ecosystem protection,but also give scientific reference for pursuing green water in Lake Taihu.The main findings are summarized as follow:The water surface temperature of Lake Taihu shows a single-peak diurnal variation pattern.The annual average daily maximum value?293.0 K?and minimum value?289.0 K?appear at 14:00 and 8:00 Beijing time,respectively,with a diurnal variation range of 4.0 K.The surface temperature of Lake Taihu shows the seasonal variation characteristics with high value in summer and low value in winter.The average surface temperature in spring,summer,autumn and winter is 290.4 K,301.4 K,293.1 Kand 279.5 K,respectively.The summer surface temperature is 22.0 K higher than that in winter.The lowest value of the monthly average water surface temperature from 2011 to 2019 was 278.3 K,which appeared in January,and the highest value of the multi-monthly average monthly average was 302.9 K,which appeared in July.Every year from March to June is the rising period of Lake Taihu surface temperature and from August to December is the decreasing period of Lake Taihu surface temperature.MODIS observations show that the temperature of the Lake Taihu surface increased year by year from 2003 to 2019,with a rate of 0.5 K 10a-1.The minimum annual average value is 288.9 K,which appeared in 2011,and the maximum annual average value is 290.4 K,which appeared in 2019.The average annual surface temperature of Lake Taihu increased by 0.9 K in 17 years.Spatially,the surface temperature of Lake Taihu is generally characterized by high in the coastal area and low in the center of the lake.The water surface temperature along the coast of Lake Taihu and shallow regions increases as the season shifting from winter to summer.While the change in the deep regions of the lake is relatively slow.The water surface temperature decreases from the east of the Lake Taihu to the west and from the shore to the center of the lake.In summer,the temperature of the entire Lake Taihu is higher,and the maximum value?304.4 K?appears in July.In winter,the temperature of the entire Lake Taihu is lower,and the minimum value?275.9 K?appears in January.The maximum spatial temperature gradient?9.3 K?appeared in July,and the minimum gradient?5.0 K?appeared in January.During 17 years,the maximum spatial temperature gradient?4.0 K?of Lake Taihu surface appeared in 2005 and 2018.Then,the spatial variation range of water surface temperature was from 287.9 to 291.9 K in 2005 and from 289.5 to 293.4 K in 2018.The minimum spatial gradient?1.9 K?appeared in 2007 and the spatial variation of water surface temperature in that year was from 289.3 to 291.2 K.The MODIS product corrected by observations shows that the surface temperature of Lake Taihu is increasing from 2003 to 2019,with a rate of 0.52 K 10a-1.With 2011 value as a baseline,the mean interannual temperature fluctuation of Lake Taihu surface from 2003 to2019 is 0.738±0.498 K,and the result of decomposition?0.736±0.530 K?is consistent with the observation.Among the five contribution factors,temperature has the largest contribution?0.454±0.401 K?to the interannual change of Lake Taihu surface temperature with a contribution of 62%.Followed by the change of Bowen ratio?0.292±0.178 K?,which contribute 40%of interannual variation in surface temperature.The effects of atmospheric radiative forcing?downward short wave and downward long wave?and the energy redistribution caused by roughness on the interannual temperature change of Lake Taihu are less than 0.1 K.The interannual change of the surface temperature of Lake Taihu is mainly caused by the change of air temperature and the change of Bowen ratio.The contribution of the two factors can completely explain the interannual change of the surface temperature of Lake Taihu. |
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