Preprints
https://doi.org/10.5194/essd-2022-138
https://doi.org/10.5194/essd-2022-138
 
15 Jun 2022
15 Jun 2022
Status: this preprint is currently under review for the journal ESSD.

GLOBMAP SWF: a global annual surface water cover frequency dataset during 2000–2020 for change analysis of inland water bodies

Yang Liu1, Ronggao Liu1, and Rong Shang2 Yang Liu et al.
  • 1State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing, 100101, China
  • 2Key Laboratory for Humid Subtropical Eco-geographical Process of the Ministry of Education, School of Geographical Sciences, Fujian Normal University, Fuzhou, 350007, China

Abstract. The extent of surface water has been changing significantly due to climatic change and human activities. However, it is challenging to capture the interannual changes of inland water bodies due to their high seasonal variation and abrupt change. In this paper, a global annual surface water cover frequency dataset (GLOBMAP SWF) was generated from the MODIS land surface reflectance products during 2000–2020 to describe the seasonal and interannual dynamics of surface water. Surface water cover frequency (SWF) was proposed as the percentage of the time period when a pixel is covered by water in a year. Instead of determination of the water directly, the SWF was estimated indirectly by identifying land observations among annual clear-sky observations to reduce the influence of clouds and variability of water bodies and surface background characteristics, which helps to improve the applicability of the algorithm for different regions across the globe. Regional analysis demonstrates that our estimation results show better performances on frozen water, saline lake, bright surface and cloud-frequent regions compared with the two high-frequent surface water datasets derived from MODIS data. Compared with the high-resolution SWF maps extracted from Sentinel-1 data in four regions that cover lake, river and wetland, the R2 reaches 0.83 to 0.97, RMSE is ranging from 7.24 % to 11.28 %, and MAE is between 2.07 % and 7.15 %. In 2020, the area of global maximum surface water extent is 3.38 million km2, of which the permanent surface water accounts for approximately 54 % (1.83 million km2) and the other 46 % is intermittent surface water (1.55 million km2). The area of global maximum and permanent surface water has been shrinking since 2001, with a change rate of -7577 km2/yr and -4315 km2/yr (p < 0.05), respectively; while the intermittent surface water with the SWF above 50 % has been expanding (1368 km2/yr, p < 0.01). This dataset can be used to analyze the interannual variation and change trend of highly dynamic inland waters extent with consideration of its seasonal variation. The GLOBMAP SWF data are available at https://doi.org/10.5281/zenodo.6462883 (Liu and Liu, 2022).

Yang Liu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on essd-2022-138', Anonymous Referee #1, 01 Jul 2022
  • RC2: 'Comment on essd-2022-138', Anonymous Referee #2, 29 Jul 2022

Yang Liu et al.

Data sets

GLOBMAP SWF: a global annual surface water cover frequency dataset since 2000 for change analysis of inland water bodies Ronggao Liu, Yang Liu https://doi.org/10.5281/zenodo.6462883

Yang Liu et al.

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Short summary
A global annual surface water cover frequency (SWF) dataset was generated to analyze the interannual changes and trends of inland waters extent with consideration of its seasonal variation. The dataset show reasonable performances on frozen water, saline lake, bright surface and cloud-frequent regions. Intermittent waters account for 46 % of global maximum water. Global maximum and permanent water areas have shrunk since 2001, while intermittent surface water with the SWF above 50 % has expanded.