Statistical downscaling of GRACE products to improve the spatial resolution

Abstract:

The Gravity Recovery And Climate Experiment (GRACE) and GRACE Follow-on satellite missions record temporal variations in the gravity field, which is then related to water mass redistribution near the Earth's surface and disseminated as monthly fields of Total Water Storage Change (TWSC). TWSC represents an anomaly in the water mass stored in all three physical states, on and below the surface of the Earth. GRACE products are effective only above spatial scales of the order of 300 km. This limited their application in regional hydrological applications, and motivated researchers to optimize the processing of GRACE satellite data with an aim to obtain the best possible spatial resolution. At present, several GRACE products are available at 0.5° or 1° grid cells, but they are only an interpolated version of the coarse resolution GRACE products and do not offer additional physical information. In this study we implement a statistical downscaling approach that assimilates high resolution TWSC fields from the WaterGAP hydrology model (WGHM), precipitation fields from 3 models, evapotranspiration and runoff from 2 models, with GRACE data to improve its resolution. The downscaled product exploits dominant common statistical modes between all the datasets to inform the estimates of TWSC. An improvement in the spatial resolution is obtained from using WGHM that incorporates the geometry of various water compartments and simulates spatio-temporal changes in TWSC due to climate forcing, land use land cover change, and human intervention. Therefore, the downscaled product is able to capture physical attributes of water compartments at a better spatial resolution compared to the available GRACE products.