The annual WMO State of Global Water Resources report provides important insights for water resource management, at the basin, continental and global scale. This has significant relevance, particularly for large-scale decision-making and policymaking, but also for informing and guiding intergovernmental discussions related to water resources. Moreover, producing annual summaries using consistent methods and formats will enable interannual comparisons that facilitate the differentiation of shorter-term variable effects on water from longer-term trends driving water distribution patterns.
As a first, ‘pilot’ edition, the present WMO State of Global Water Resources 2021 report is limited to the conditions of streamflow, terrestrial water storage and selected cryosphere parameters. Global Hydrological Modelling Systems and remotely sensed data were largely used in preparing the 2021 report, and the indicators obtained from these were compared and validated against observational data (where available). Despite a good correlation between modelled and observed results, the validation process would benefit substantially from utilizing further hydrological information.