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Evaluation of remotely sensed data for estimating recharge to an outcrop zone of the Guarani Aquifer System (South America)

Lucas, Murilo, Oliveira, Paulo T. S., Melo, Davi C. D., Wendland, Edson
Hydrogeology journal 2015 v.23 no.5 pp. 961-969
aquifers, equations, evapotranspiration, groundwater, highlands, remote sensing, sandy soils, satellites, spatial data, streams, topographic slope, water table, watersheds, Brazil
The Guarani Aquifer System (GAS) is the largest transboundary groundwater reservoir in South America, yet recharge in the GAS outcrop zones is one of the least known hydrological variables. The objective of this study was to assess the suitability of using remote sensing data in the water-budget equation for estimating recharge inter-annual patterns in a representative GAS outcropping area. Data were obtained from remotely sensed estimates of precipitation (P) and evapotranspiration (ET) using TRMM 3B42 V7 and MOD16, respectively, in the Onça Creek watershed in Brazil over the 2004–2012 period. This is an upland flat watershed (slope steepness <1 %) dominated by sandy soils and representative of the GAS outcrop zones. The remote sensing approach was compared to the water-table fluctuation (WTF) method and another water-budget equation using ground-based measurements. On a monthly basis, the TRMM P estimate showed significant agreement with the ground-based P data (r = 0.93 and RMSE = 41 mm). Mean(±SD) satellite-based recharge (R ₛₐₜ) was 537(±224) mm year⁻¹. Mean ground-based recharge using the water-budget (R gᵣ) and the WTF (R wₜf) methods were 469 mm year⁻¹ and 311(±75) mm year⁻¹, respectively. Results show that 440 mm year⁻¹ is a mean (between R ₛₐₜ, R gᵣ and R wₜf) recharge for the study area over the 2004–2012 period. The latter mean recharge estimate is about 29 % of the mean historical P (1,514 mm year⁻¹). These results are useful for future studies on assessing recharge in the GAS outcrop zones where data are scarce or nonexistent.