APPLICATION OF GRACE DATA FOR QUANTIFYING MESOSCALE GROUNDWATER STRESS – URUCUIA AQUIFER SYSTEM, NORTHEASTERN BRAZIL

Abstract:

The Gravity Recovery and Climate Experiment (GRACE) mission provides a couple of applications in hydrology research such as total water storage (TWS) changes monitoring, quantitative water cycle components estimation, drought monitoring and hydrological modelling. Limited spatial resolutions of gravity measurements and noise contamination can cause errors and uncertainty of the study objective. Therefore, several GRACE studies recommend application of GRACE data retrievals to areas of interests only larger 200,000 km².

The Urucuia Aquifer System (UAS) represents a major strategic water resource for Brazil. UAS is located in the drought-stricken northeast of Brazil and its discharge covers about 30% of the São Francisco River water (4^th largest river in South America). Hydrological monitoring of the UAS is of increased importance to guarantee future river water supply and related ecosystem services for the territories crossed.

A pre-processed GRACE three-model-ensemble was used to account for TWS changes and a negative balance was revealed for the UAS territory indicating potential water stress. Individual water cycle components needed to be excluded from the total GRACE signal using supplemental data sets to characterize the remaining storage term equivalent to ‘water stress’. Comprehensive hydrological ground measurements of precipitation, river discharge, hydraulic heads plus further climate remote-sensing data sources were taken into account trying to distinguish natural from anthropogenic groundwater stress. Consideration of climate data from global hydrological models showed an insufficient accuracy which is related to spatial scaling issues whereas the inclusion of available ground data could increase the overall significance of the GRACE signal for this study.

GRACE-based TWS retrievals were applied successfully in combination with comprehensive hydrological monitoring data to quantify potential groundwater storage changes of the 120,000 km² large UAS.