Global Land Water Storage data set: recent updates and applications of a global GRACE/-FO data assimilation

GRACE and GRACE/-FO provide global measurements of surface and subsurface water storage in form of total water storage anomalies (TWSA). However, given that precipitation events, topography, and land surface conditions can be very local, the spatial resolution of GRACE/-FO of 300 km might be too coarse for applications such as hydrological drought monitoring. In the last decades, the GRACE/-FO TWSA were assimilated into hydrological for downscaling, to vertically disaggregate TWSA into compartmental storages such as soil moisture, surface water, and groundwater, and to improve the model's realism. Regional GRACE/-FO assimilation systems widely exist but only a few global data assimilation systems exist worldwide.

The Global Land Water Storage data set release 2 was developed by assimilating GRACE/-FO TWSA into the WaterGAP hydrological model. GLWS2 provides thus monthly TWSA, soil moisture, surface water, and groundwater on a spatial resolution of 0.5° from 2003 to 2019. Here, we present some recent updates of GLWS2. For example, we now incorporate spatial GRACE/-FO correlations into the assimilation framework, which – to our knowledge - are not included in other global assimilations so far. We will show that the new GLWS data inherits favorable properties of both the observations and the model simulation, and analyze hydrological dominant signatures in the different water compartments of soil moisture, surface water, and groundwater. To emphasize its use for drought monitoring applications, we present a methodology to extract the duration, severity, and timing of consecutive drought events, which could contribute to future risk assessments and drought monitoring systems based on GRACE/-FO and assimilation outputs.