Abstract
ABSTRACTThe Tibetan Plateau houses numerous lakes, the phenology and duration of lake ice in this region are sensitive to regional and global climate change, and as such are used as key indicators in climate change research, particularly in environment change comparison studies for the Earth three poles. However, due to its harsh natural environment and sparse population, there is a lack of conventional in situ measurement on lake ice phenology. The Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Snow Index (NDSI) data, which can be traced back 20 years with a 500 m spatial resolution, were used to monitor lake ice for filling the observation gaps. Daily lake ice extent and coverage under clear-sky conditions was examined by employing the conventional SNOWMAP algorithm, and those under cloud cover conditions were re-determined using the temporal and spatial continuity of lake surface conditions through a series of steps. Through time series analysis of every single lake with size greater than 3 km2 in size, 308 lakes within the Tibetan Plateau were identified as the effective records of lake ice extent and coverage to form the Daily Lake Ice Extent and Coverage dataset, including 216 lakes that can be further retrieved with four determinable lake ice parameters: Freeze-up Start (FUS), Freeze-up End (FUE), Break-up Start (BUS), and Break-up End (BUE), and 92 lakes with two parameters, FUS and BUE. Six lakes of different sizes and locations were selected for verification against the published datasets by passive microwave remote sensing. The lake ice phenology information obtained in this paper was highly consistent with that from passive microwave data at an average correlation coefficient of 0.91 and an RMSE value varying from 0.07 to 0.13. The present dataset is more effective at detecting lake ice parameters for smaller lakes than the coarse resolution passive microwave remote sensing observations. The published data are available in https://data.4tu.nl/repository/uuid:fdfd8c76-6b7c-4bbf-aec8-98ab199d9093 and http://www.sciencedb.cn/dataSet/handle/744.
Highlights
Known as the “Roof of the World”, the Tibetan Plateau has an average elevation of more than 2,000 m and an abundance of lakes
The Normalized Difference Snow Index (NDSI) snow cover algorithm SNOWMAP (George & Dorothy) was used to estimate the daily lake ice on/off at a single pixel under clear sky, and a series of further processes was conducted under cloudy conditions based on spatial and temporal continuity of lake surface conditions
According to the Moderate Resolution Imaging Spectroradiometer (MODIS)-based lake ice phenology determination: the Freeze-Up End (FUE) is defined as the first day during the second half of the year when the lake ice coverage is greater than 0.9, whereas the Break-Up End (BUE) is the first day during the first half of the year when the lake ice coverage is less than 10% (Reed, Budde, Spencer, & Miller, 2009)
Summary
Known as the “Roof of the World”, the Tibetan Plateau has an average elevation of more than 2,000 m and an abundance of lakes This region contains 2,612 lakes with a surface area greater than 0.25 km, as estimated from the lake database (Messager, Lehner, Grill, Nedeva, & Schmitt, 2016) (Figure 1). Lake ice coverage under cloud cover conditions was identified using the spatial and temporal continuity of the lake surface conditions This method was used to calculate and classify the daily lake ice characteristics for the maximum number of lakes within the Tibetan Plateau from 2002 to 2018. A time series analysis of lake ice coverage, which included lakes with a surface area greater than 3 km, was carried out to provide a clear list of lakes where the lake ice phenology, i.e. Freeze-up Start (FUS), Freeze-up End (FUE), Break-up Start(BUS), or Breakup End(BUE), can be accurately estimated and retrieved
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