DT: daytime temperature (oC), NT: nighttime temperature (oC), DTD: diurnal temperature difference (oC). ASL: elevation above sea level (m).

4. Conclusions

The study demonstrated the utility of MODIS LST products to monitor the spatial, diurnal, seasonal, and annual variations of lakes water surface temperature (LWST) across Eurasia where long-term in-situmeasurements are very limited. In particular, this is an effective approach for monitoring LWST in some of the wild, inaccessible and protected areas in high latitude regions of the word. The inter-annual and intra-annual variations of LWST across Eurasia were derived from 11,978 maps of daytime and nighttime 8-day composite MODIS LST products during the period 2001-2015. Lakes in high latitude regions, especially those situated in the boreal or the Taiga biome displayed low LWST. Lakes in the Tibetan Plateau also exhibited low LWST. However, the LWST pattern in nighttime showed a more homogeneous distribution, and the pattern mostly resembled that of air temperature at Eurasian scale. Large spatial variations of DTDs were observed for large lakes in Eurasia. Small variations in DTDs were measured in high latitude lakes, and also in lakes situated in the tropical rainforest region. Several factors, e.g., lake depth and area (volume), altitude, and water source, may have contributed to the spatiotemporal variations in LWST. The shallow lakes showed a rapid response of LWST to solar and atmospheric forcing, while in the large deep lakes, the response time was much slower. Finally, it should be noted that LWST and ice-free duration can be influenced by water salinity and ground water input, but these factors were not considered in the present study. Further investigation is thus needed to assess the impact of these factors on the thermal dynamics of large water bodies across the Eurasian continent.

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