Seasonal changes of temperature and precipitation cause inland open surface water and ice cover extents to vary dramatically through the year at both local and global scales. These dynamics of land, water, and ice have a significant impact on climate and often are critical to natural ecosystem functioning. However, the seasonal dynamics of surface water globally have not been well quantified, with area estimates only for the total area of seasonal water and not the distribution through the year. Further, global water studies have ignored ice cover on inland water bodies by treating it as no data or not mapping the high latitudes during winter months. However, through a stratified random sample of 10 m Sentinel-2 and 3 m PlanetScope data for 2019, we found that globally only 23% of the total 4.86 ± 0.16 million km2 with some water presence in 2019 was permanent liquid water (1.13 ± 0.19 million km2). 1.97 ± 0.21 million km2 of permanent inland water froze seasonally, totaling 41% of the total water area, and January-March had more ice cover than liquid water. Seasonal water-land transitions covered the remaining 36% of the total water area (1.76 ± 0.19 million km2). In parallel, we developed prototype Landsat-based monthly maps of ice/snow over areas with surface water. These maps show multiple month disparities in ice melt timing of neighboring lakes of different sizes. Given the vastly different ecosystem services and climate impacts of open versus frozen surface water, these spatially explicit prototype maps of ice cover phenology and monthly area estimates and associated uncertainties of inland surface water and ice cover extent provide important insights into the current state of the global water system.

 

Highlights:

  • First combined global area estimates of surface water and ice with uncertainty bounds
  • 64% of permanent inland water froze seasonally
  • Liquid open surface water extent in June was almost 2.5x larger than that of January
  • 1.76 ± 0.19 million km2 had seasonal water and land presence
  • Only 23% of the area with some water presence in 2019 was permanent liquid water

 

View maps online: https://glad.earthengine.app/view/global-water-ice

Reference data:

Table of cluster location and stratum: clusterTable.csv

Table of reference data per secondary sampling units (10 grid cells): referenceData.csv. The individual date labels have been summarized at the monthly level as percent water, calculated as the counts of water / (water + land + ice), with a range of 0-100. Month labels of 200 denote ice was present in ≥50% of the observations. Month labels of 201 denote that there were no observations in the given month, but based on the images from the surrounding months, that month was determined to have persistent ice cover.

Citation:

Pickens, A.H., Hansen, M.C., Stehman, S.V., Tyukavina, A., Potapov, P., Zalles, V., Higgins, J., 2021. Global seasonal dynamics of inland water and ice. (in review)