The use of triple collocation approach to merge satellite- and model-based terrestrial water storage for flood potential analysis

Terrestrial water storage anomaly (TWSA) retrieved from the Gravity Recovery and Climate Experiment (GRACE) mission can be used as a good indicator of flood potential, but it is limited to regional analysis due to the coarse resolution (∼300 km). This study proposed an optimal least square merging scheme to spatially downscale GRACE-based TWSA via integrating it with model-based TWSA estimates on to a finer resolution (0.125°) with associated uncertainty estimates. TWSA products estimated from GRACE, an advanced Land Surface Model (LSM), and reanalysis data were used in the merging process. Error uncertainties in each input data sets and the merged TWSA product were calculated based on the triple collocation approach. The merged TWSA was subsequently used to compute the flood potential index and results were compared against measured river discharge and historical flood records. Results showed that the merged TWSA provides a better representation of the spatial variability of TWSA at a sub-regional scale relative to GRACE-based TWSA along with improved uncertainties. Merged TWSA also showed improved capability in capturing flood events that occurred at sub-regional to local scales relative to GRACE-based TWSA when compared to historical flood records.