Global seasonal dynamics of inland open water and ice

Abstract

Seasonal changes of temperature and precipitation cause inland open surface water and ice cover extents to vary dramatically through the year from local to global scales. These dynamics of land, water, and ice have a significant impact on climate and often are critical to natural ecosystem functioning. However, global seasonal dynamics of both water and ice extent have not been well quantified. Here, we present the quantification of monthly surface water and ice areas for 2019 with associated uncertainties. Time-series reference data were created for a probability sample of 10 m grid cells by interpreting the entire 2019 time-series of 10 m Sentinel-2 data and a subset of 3 m PlanetScope data in selected places with a mix of land and water. From the probability sample reference data, we estimate that 4.86 ± 0.16 million km2 had inland water presence at some point during the year. Globally, only 23% of the total area with water was permanent water that remained open year-round (1.13 ± 0.19 million km2). Permanent water with seasonal ice cover extended 1.97 ± 0.21 million km2, comprising 41% of the total area with water. Seasonal water-land transitions (both with and without ice/snow cover) covered the remaining 36% of the total area with water (1.76 ± 0.19 million km2). February had the maximum extent of ice over areas of inland permanent and seasonal water, totaling 2.49 ± 0.25 million km2, and January – March had a larger global extent of ice cover than of open water. To investigate the spatiotemporal distribution of ice cover and the suitability of Landsat, prototype maps of surface water ice cover phenology were created by integrating the ice/snow and no data labels from the quality assurance layer of the GLAD ARD of Potapov et al. (2020) with the monthly surface water layers of Pickens et al. (2020), both of which are Landsat-based. While limited by data availability, these maps reveal the high spatiotemporal variability of ice phenology. The near-daily observations near the poles and the 10 m resolution bands of Sentinel-2 provide unprecedented potential to examine surface water and ice dynamics for 2016 forward and to investigate the drivers and impacts of this variability.