Dataset description This long-term repository provides daily river ice concentration (RIC) and annual river ice phenology for six major Arctic rivers—the Yukon, Mackenzie, Ob, Yenisey, Lena, and Kolyma—covering hydrological years 2001–2024 (hydrological year runs from October 1 to September 30 of the next calendar year). To capture the initial pre–freeze-up period of hydrological year (HY) 2001, daily RIC begins on 2000-08-01. All files are GeoTIFF in WGS 84 / Arctic Polar Stereographic (EPSG:3995). File organization For each river, four ZIP archives are provided (24 ZIPs in total). After unzipping, you will obtain: Daily RIC time series Contents: One GeoTIFF per day for the river mask, spanning 2000-08-01 through the end of HY2024 Variable: RIC (floating point) Value range: 0–1 (fractional ice concentration) No data: pixels outside the river mask are set to NaN Annual freeze-up date Filename pattern: freezeup_DOHY_yyyy.tif Definition: freeze-up date for hydrological year "yyyy", DOHY = Day Of the Hydrological Year, starting from October 1 as index 1 Annual breakup date Filename pattern: breakup_DOHY_yyyy.tif Definition: breakup date for hydrological year "yyyy", DOHY as above Annual river ice duration Filename pattern: ice_duration_DAY_yyyy.tif Definition: number of ice-covered days of hydrological year "yyyy"