Development and validation of a global ensemble hydrological simulation system: TE-Global NEXRA

A novel global ensemble hydrological simulation system has been developed to enhance the accuracy of terrestrial water cycle simulations. This system integrates the Today’s Earth (TE) hydrological model with atmospheric forcing from the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) - the Local Ensemble Transform Kalman Filter (LETKF), Japan Aerospace Exploration Agency (JAXA) Research Analysis (NEXRA), using 128 ensemble members to account for uncertainties in land water and energy budgets and river dynamics. The system was validated against ground-based observations of snow water equivalent (SWE) and river discharge, key components in the hydrological cycle. Despite some limitations in data overlap, the results showed reasonable correlations in certain locations, with reduced errors and biases when compared to deterministic simulations. The study revealed that ensemble mean results improve overall accuracy, especially in SWE simulations where variability among members is diminished through seasonal accumulation. However, for river discharge, the variability among ensemble members affects peak flow estimates, highlighting the need for further refinement in ensemble spread and individual member analysis. Overall, the developed system, referred to as Today’s Earth - Global (TE-Global) NEXRA, demonstrates the potential for more reliable hydrological predictions through ensemble approaches, contributing to better understanding and management of water resources.