Lake ice is a robust indicator of climate change. The availability of information contained in Moderate Resolution Imaging Spectroradiometer (MODIS) daily snow products from 2000 to 2017 could be greatly improved after cloud removal by gap filling. Thresholds based on open water pixel numbers are used to extract the freeze‐up start and break‐up end dates for 58 lakes on the Tibetan Plateau (TP), 18 lakes are also selected to extract the freeze‐up end and break‐up start dates. The lake ice durations are further calculated based on freeze‐up and break‐up dates. Lakes on the TP begin to freeze‐up in late October and all the lakes start the ice cover period in mid‐January of the following year. In late March, some lakes begin to break‐up, and all the lakes end the ice cover period in early July. Generally, the lakes in the northern Inner‐TP have earlier freeze‐up dates and later break‐up dates (i.e. longer ice cover durations) than those in the southern Inner‐TP. Over 17 years, the mean ice cover duration of 58 lakes is 157.78 days, 18 (31%) lakes have a mean extending rate of 1.11 d yr‐1 and 40 (69%) lakes have a mean shortening rate of 0.80 d yr‐1. Geographical location and climate conditions determine the spatial heterogeneity of the lake ice phenology, especially the ones of break‐up dates, while the physico‐chemical characteristics mainly affect the freeze‐up dates of the lake ice in this study. Ice cover duration is affected by both climatic and lake specific physico‐chemical factors, which can reflect the climatic and environmental change for lakes on the TP.
1 December 2017 in Science of The Total Environment
Accurate multitemporal glacier change investigations and analyses are lacking on the southeastern Tibetan Plateau (SETP). A combination of photogrammetry, optical remote sensing and synthetic aperture radar (SAR) datasets can accurately identify large-scale glaciers; In the present study, glaciers in three periods on the SETP (1970s, 2000, 2020) were identified from multisource remote sensing data based on a deep learning method and manual visual interpretation, and multitemporal glacial inventory data from relatively high-frequency source imagery. Totals of 11648, 12993, and 11875 glaciers were identified in the 1970s, 2000, and 2020, with total areas of 13372.08 km 2 , 11692.31 km 2 , and 10612.94 km 2 , respectively. The general distribution of SETP glaciers was identified to be typical of alpine glaciers dominated by small-sized glaciers. The average elevation of glaciers was approximately 5000 m; the slopes were mostly lower than 40°, and the main aspect was southeast, followed by south and southwest. The glaciers retreated from the 1970s to 2020, and a total glacier area of approximately 2759.14 km 2 was degraded during this time, with an average annual melting rate of 0.45% yr -1 . Rising summer temperatures may be the driving force behind the continuous decline in the glacier area. Overall, the results obtained in this study showed relatively low uncertainty involved in the identification of glaciers compared to some previous studies. The results can provide accurate glacier information for glacier monitoring and modeling studies on the SETP.
The color of lakes is an essential indicator of the local ecological state, and the corresponding changes can reflect the physical and biochemical processes of lakes. However, worldwide changes in lake color and their drivers remain largely unknown. Here, we analyze the long‐term color distributions and changes of 67,579 lakes worldwide from 1984 to 2021 by utilizing 32 million consistent satellite observations. Blue lakes (<495 nm) were primarily located in high‐latitude and high‐elevation areas. Green lakes (495–560 nm) were more prevalent in densely populated middle‐latitude regions, while most red and yellow colors (≥560 nm) were located in the Southern Hemisphere. Our findings reveal distinct temporal patterns of lake color changes, with the majority of global lakes shifted toward shorter wavelengths. This phenomenon is more common in Warm Temperate and Boreal zones. Lake color changes are closely linked to basin vegetation conditions, population, water volume change, and lake area. Our study provides essential references for monitoring the ecological status of global lakes, further supporting the sustainable development of water resources in the future.