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

Abstract

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 waterbudget (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.

Aquifer Responses to Rainfall through Spectral and Correlation Analysis

“…On average, the baseflow (Qb/contributing area) represents ~25.0 ± 2.9% of the annual P , which agrees with the annual recharge rates (22% of P ), estimated by Lucas et al. () at the same basin. The runoff (Qs = Qt − Qb) in the OCB represents a small percentage (~2.0 ± 0.6%) of P ; hence, its contribution to Qt is almost negligible.…”

“…; Lucas et al. ) and indicates that the aquifer in the OCB has an important role in feeding the stream (Figure ). The baseflow index (Qb/Qt), calculated using the annual mean discharge values, ranged from 88% to 96% between 2003 and 2014.…”

Groundwater recharge decrease with increased vegetation density in the Brazilian cerrado

“…These results suggest that recharge tends to decrease with the increase in vadose zone thickness and vegetation density (grassland to woodland). Several authors have reported that land use and land cover have a strong influence on the groundwater recharge (Jobbágy & Jackson, ; Scanlon et al, ; Scott et al, ; Lucas et al, ); however, this is the first report regarding the influence of different cerrado physiognomies on recharge rates.…”

“…Considering that the IES site has similar hydrogeological characteristics (geology, and soil texture and structure) as the Onça Creek basin, we used a mean specific yield value of 12% (Wendland et al, ). As there are uncertainties in the recharge estimate by the WTF method, associated mainly with uncertainty in the Sy values (Coes, Spruill, & Thomasson, ), we applied an uncertainty factor of ±24% in recharge estimates according to results from a previous study conducted in the Onça Creek basin (Lucas et al, ).…”

“…To improve water availability in southeastern Brazil, the state and federal governments have studied the possibility of increasing groundwater use, mainly in the Guarani Aquifer System (GAS), the largest (~1.2 million km 2 ) transnational boundary groundwater reservoir in South America (Lucas, Oliveira, Melo, & Wendland, ). The GAS in the Brazilian territory covers part of the states of Goiás, Mato Grosso do Sul, Minas Gerais, São Paulo, Paraná, Santa Catarina, and Rio Grande do Sul.…”