Edson Wendland

Trends in water balance components across the Brazilian Cerrado

We assess the water balance of the Brazilian Cerrado based on remotely sensed estimates of precipitation (TRMM), evapotranspiration (MOD16), and terrestrial water storage (GRACE) for the period from 2003 to 2010. Uncertainties for each remotely sensed data set were computed, the budget closure was evaluated using measured discharge data for the three largest river basins in the Cerrado, and the Mann-Kendall test was used to evaluate temporal trends in the water balance components and measured river discharge. The results indicate an overestimation of discharge data, due mainly to the overestimation of rainfall by TRMM version 6. However, better results were obtained when the new release of TRMM 3B42 v7 was used instead. Our results suggest that there have been (a) significant increases in average annual evapotranspiration over the entire Cerrado of 51 ± 15 mm yr−1, (b) terrestrial water storage increases of 11 ± 6 mm yr−1 in the northeast region of the Brazilian Cerrado, and (c) runoff decreases of 72 ± 11 mm yr−1 in isolated spots and in the western part of the State of Mato Grosso. Although complete water budget closure from remote sensing remains a significant challenge due to uncertainties in the data, it provides a useful way to evaluate trends in major water balance components over large regions, identify dry periods, and assess changes in water balance due to land cover and land use change.

Performance evaluation of rainfall estimates by TRMM Multi‐satellite Precipitation Analysis 3B42V6 and V7 over Brazil

Time series precipitation data generated by the Tropical Rainfall Measuring Mission (TRMM) have been used as a possible solution for providing rainfall information for ungauged regions. We evaluated the quality of TRMM Multi-satellite Precipitation Analysis (TMPA) Version 6 (3B42V6) and Version 7 (3B42V7) products on a daily and monthly basis for a 14 year time series by comparing with gridded ground-based rainfall data from ~3625 rain gauges distributed throughout Brazil. The results show that daily estimates are inaccurate for both Versions 6 and 7 (the refined index of agreement, dr, was less than 0.6 in most of the analyzed pixels). In general, both versions perform well on monthly basis (dr > 0.75), but no significant improvement between them could be identified with the exception of local areas. TMPA performed poorly in the northwest region, where rainfall depths are higher in Brazil; however, the quality of the ground-based data is poor in this region because of low gauge density. Based on a seasonal analysis, we found that TMPA performed better during the dry seasons and that some improvements, although not significant, between successive versions took place over the northeast, southeast, and south regions. This study shows the value of remote sensing precipitation for providing reliable, spatiotemporally continuous precipitation at monthly timescales.

Recharge contribution to the Guarani Aquifer System estimated from the water balance method in a representative watershed

The contribution of recharge to regional groundwater flow systems is essential information required to establish sustainable water resources management. The objective of this work was to determine the groundwater outflow in the Ribeirão da Onça Basin using a water balance model of the saturated soil zone. The basin is located in the outcrop region of the Guarani Aquifer System (GAS). The water balance method involved the determination of direct recharge values, groundwater storage variation and base flow. The direct recharge was determined by the water table fluctuation method (WTF). The base flow was calculated by the hydrograph separation method, which was generated by a rain-flow model supported by biweekly streamflow measurements in the control section. Undisturbed soil samples were collected at depths corresponding to the variation zone of the groundwater level to determine the specific yield of the soil (drainable porosity). Water balances were performed in the saturated zone for the hydrological years from February 2004 to January 2007. The direct recharge ranged from 14.0% to 38.0%, and groundwater outflow from 0.4% to 2.4% of the respective rainfall during the same period.

Integração de modelos espaciais e temporais para predições de níveis freáticos extremos

Abstract – The objective of this work was to evaluate extreme water table depths in a watershed, using methods for geographical spatial data analysis. Groundwater spatio-temporal dynamics was evaluated in an outcrop of the Guarani Aquifer System. Water table depths were estimated from monitoring of water levels in 23 piezometers and time series modeling available from April 2004 to April 2011. For generation of spatial scenarios, geostatistical techniques were used, which incorporated into the prediction ancillary information related to the geomorphological patterns of the watershed, using a digital elevation model. This procedure improved estimates, due to the high correlation between water levels and elevation, and aggregated physical sense to predictions. The scenarios showed differences regarding the extreme levels – too deep or too shallow ones – and can subsidize water planning, efficient water use, and sustainable water management in the watershed.Index terms: groundwater, geostatistics, geoinformation, water resource management, uncertainty, digital elevation model.

Estimativa da evapotranspiração a partir de variação de nível estático de aquífero

A quantificacao da evapotranspiracao e uma tarefa essencial para o gerenciamento dos recursos hidricos em uma bacia hidrografica, ja que e variavel importante no ciclo hidrologico. Entretanto, estimar a evapotranspiracao real e uma tarefa dificil, e os pesquisadores usam, geralmente, mais de um metodo a fim de validar os resultados. Este trabalho apresenta um metodo para a determinacao da evapotranspiracao real com base na variacao da precipitacao, do escoamento de base e do nivel de agua subterrânea medidas na bacia hidrografica. Usando o metodo proposto em uma bacia hidrografica piloto, a evapotranspiracao real foi estimada em 900 mm por ano. Esse resultado foi comparado com a evapotranspiracao potencial, calculada pelos metodos empiricos e semiempiricos, baseados em dados climatologicos. O metodo de Thornthwaite, com evapotranspiracao potencial de 936 mm por ano, apresentou o valor mais proximo ao metodo de balanco hidrico. O metodo do balanco hidrico, baseado em medidas hidrogeologicas, mostrou-se apropriado para estimar a evapotranspiracao real na bacia hidrografica. Entretanto, e necessario observar as hipoteses e as limitacoes descritas neste estudo para aplicar este metodo a outra bacia hidrografica.

Curve number estimation from Brazilian Cerrado rainfall and runoff data

The Curve Number (CN) method has been widely used to estimate runoff from rainfall events in Brazil; however, CN values for use in the Brazilian savanna (Cerrado) are poorly documented. In this study we used experimental plots to measure natural rain-fall-driven rates of runoff under undisturbed Cerrado and under the main crops found in this region, and derive associated CN values from the measured data using five different statistical methods. Curve numbers obtained from the standard USDA Natural Resources Conservation Service (NRCS) table were suitable to estimate runoff for bare soil, soybeans (Glycine max [L.] Merr.), and sugarcane (Saccharum L.). However, CN values obtained from measured rainfall-runoff data (CN calibrated) provided better runoff estimates than the CN values from the standard table. The best CN values for the bare soil (hydrologic soil group B), soybeans, and sugarcane were 81.2 (78.5 to 83.9), 78.7 (75.9 to 81.5), and 70.2 (67.8 to 72.6). The CN method was not adequate to estimate runoff for the undisturbed Cerrado, bare soil (hydrologic soil group A), pasture, and millet (Pennisetum glaucum).

Land use and climate change impacts on runoff and soil erosion at the hillslope scale in the Brazilian Cerrado

Land use and climate change can influence runoff and soil erosion, threatening soil and water conservation in the Cerrado biome in Brazil. The adoption of a process-based model was necessary due to the lack of long-term observed data. Our goals were to calibrate the WEPP (Water Erosion Prediction Project) model for different land uses under subtropical conditions in the Cerrado biome; predict runoff and soil erosion for these different land uses; and simulate runoff and soil erosion considering climate change. We performed the model calibration using a 5-year dataset (2012-2016) of observed runoff and soil loss in four different land uses (wooded Cerrado, tilled fallow without plant cover, pasture, and sugarcane) in experimental plots. Selected soil and management parameters were optimized for each land use during the WEPP model calibration with the existing field data. The simulations were conducted using the calibrated WEPP model components with a 100-year climate dataset created with CLIGEN (weather generator) based on regional climate statistics. We obtained downscaled General Circulation Model (GCM) projections, and runoff and soil loss were predicted with WEPP using future climate scenarios for 2030, 2060, and 2090 considering different Representative Concentration Pathways (RCPs). The WEPP model had an acceptable performance for the subtropical conditions. Land use can influence runoff and soil loss rates in a significant way. Potential climate changes, which indicate the increase of rainfall intensities and depths, may increase the variability and rates of runoff and soil erosion. However, projected climate changes did not significantly affect the runoff and soil erosion for the four analyzed land uses at our location. Finally, the runoff behavior was distinct for each land use, but for soil loss we found similarities between pasture and wooded Cerrado, suggesting that the soil may attain a sustainable level when the land management follows conservation principles.

Recharge estimates for various land uses in the Guarani Aquifer System outcrop area

ABSTRACT The Guarani Aquifer System (GAS) is a subsurface reservoir that contains the largest volume of fresh groundwater in South America. Despite the relevance of the GAS, a lack of attention has been paid to land use effects on its recharge. We present the most detailed long-term (2004–2011) results of land-use effects on recharge in an outcrop area of the GAS. Water table fluctuations (WTFs) were measured at 11 monitoring wells, which are distributed between different land uses (i.e. eucalyptus, sugarcane, citrus and grassland). Recharge was estimated using a point-scale method (WTF) for each monitored well. The annual recharge estimates for different land uses are eucalyptus forest (135 mm year-1), sugarcane (248 mm year-1), citrus areas (296 mm year-1) and grassland (401 mm year-1). The results indicate that the evapotranspiration seems to be a key parameter in the assessment of recharge in the study area.

A hybrid numerical scheme for multi-phase flow in heterogeneous porous media

This work describes a numerical scheme for simulation of two-phase flow in heterogeneous porous media. The system of governing equations is transformed into an equivalent problem, as proposed by Peaceman (1977) . For the numerical solution, the operator split technique is used, separating the advection-diffusion equation in a hyperbolic and a parabolic part. The Finite Element and Finite Volume Methods are used for the spatial discretization of the problem. The reliability of the scheme is demonstrated for a typical problem of Petroleum Engineering, showing better performance than a commercial software.

Coupling one-dimensional recharge solution to analytic element model: an approach for coastal aquifers in Brazil

An important aquifer in the Brazilian northeastern coast with a long strait strip shape was modeled using the Analytic Element Method (AEM). For the recharge effect, a solution of the one-dimensional flow with accretion was applied. Boundary conditions at the coast and inland were specified by means of image method, with special care to line-doublets and head-given elements. The model was constructed with GNU TimSL code and compared with finite element results showing good agreement.