The water balance of the large river basins of Northern Kazakhstan estimated by remote sensing and global datasets combined with hydrologic information

Kazakhstan is a large country located in the center of Eurasia.  The quantity and quality of its water resources strongly depend on the specific cold and dry climate conditions with strong continentality, and land-locked topography. The country faces significant climatic risks and water management challenges, yet comprehensive baseline data for its regional river basins remains fragmented and largely unknown to the global community. In this study, we address these gaps by evaluating the water balance of regional river basins of Northern part of Kazakhstan—Zhaiyk-Caspian, Tobyl, Torgai, Sarysu, Nura, Yesil, and Ertis and additional inter-basins, focusing on the recent period when Earth-Observation Satellite data became available (21st century). Consequently, this research integrates ground-based hydrometeorological observations (such as river runoff and precipitation) with satellite-based products for precipitation, terrestrial evaporation and total water storage (such as MSWEP, GLEAM and GRACE), as well as global climate reanalysis datasets (ERA5), to quantify water fluxes and storage over the last 20 years. Our results show that: 1) total terrestrial water storage inferred from GRACE remained in a steady state in the study region apart from Zhaiyk-Caspian basin where it decreased by approximately by 200 mm from 2002 to 2022; 2) the water budget is dominated, in terms of inputs, by cold season (October-March) precipitation and in the loss term by warm season (April-September) evapotranspiration, with strong evaporation control; 3) the water balance closure and storage change from P-E and GRACE show good correspondence; 4) new evaporation sensor data show that best global ET remote sensing product (GLEAM) and model output (ERA5) datasets overestimate terrestrial evaporation in the study region due to water limitation.