Local to Regional Hydrological Model Calibration for the Okavango River Basin From In-Situ and Spaceborne Gravity Data
Christiansen, L.; Krogh, P. E.; Bauer-Gottwein, P.; Andersen, O.; Leiriao, S.
Technical University of Denmark
The Okavango Delta in Botswana, Southern Africa, is one of the World’s largest wetlands. Placed in a semi-arid region, the Delta and its rich flora and fauna are under constant pressure due to human water abstraction and climate variations. The recently started Hydrograv research project (www.hydrograv.dk) focuses on the use of gravity data for hydrological model calibration at continental to local scales with the Okavango Delta as one out of two model areas.
Preliminary results suggest that, at the continental scale, space-borne data from the GRACE mission can be used to calibrate a hydrological model of the Okavango River Basin. GRACE data products from the five available data-centers, will be evaluated and compared with hydrological model output. Forward calculation of in-situ time-lapse gravimetry shows the utility of ground-based gravity surveys to estimate actual evapotranspiration and changes in groundwater levels following seasonal flooding and rainfall.
For both continental and local scale, appropriate filtering and inverse routines must be developed in order to assimilate space-borne and in-situ gravity observations into hydrological models in the future. Simple conceptual models demonstrate the utility of joint inversion of gravity data together with traditional hydrological data (water levels, discharge, soil moisture). The sampling footprint of space-borne and ground-based gravity measurements differs by orders of magnitude, which allows for the monitoring and calibration of hydrological processes acting over a range of scales.