Nilza Maria dos Reis Castro

Land use change effects on runoff and erosion from plot to catchment scale on the basaltic plateau of Southern Brazil

In the region of the basaltic plateau in Southern Brazil, problems of runoff and erosion on the deep ferrallitic soils are becoming increasingly recognized. Land use change from conventional tillage using disk plough to no-tillage on residues without terracing occurred at the beginning of the 1990s and it spread very quickly. Measurements of runoff and sediment concentrations on 1 m2 plots receiving natural rainfall and simulated rainfall under different crops with different stages of growth and different tillage systems, field surveys and measurements of rills and gullies in nested experimental catchments indicate a relative decrease of runoff on slopes but an increase of subsurface flow, and a marked decrease of sheet and rill erosion and soil loss from plot to catchment scales. Nevertheless, the extension of parts of the gully system is still continuing, strongly influenced by extreme rainfall. Copyright

Simplifying artificial neural network models of river basin behaviour by an automated procedure for input variable selection

The objective of the present work is to present a simplified and automated method for identifying and excluding unnecessary input variables, with a consequent reduction in dimensionality of ANN-based hydrological models. The proposed method is iterative and computationally efficient: it consists of perturbing the input variables, recording the change in model performance, establishing an index showing the contribution of each variable to the ANN (the relative contribution index, RCI) and excluding the least-influential variables that fall below a threshold. The method was used to simulate mean daily flow for a 20-year period 1989-2009 from four drainage basins nested at different scales ranging from 19.4km? to 9426km?, in the Southern Brazil. The main result of this method of simplifying ANN-based hydrological models was to increase the Nash-Sutcliffe (NS) coefficient and to reduce RMSE in all the simulations undertaken. The potential of ANN models was therefore improved by eliminating unnecessary and/or redundant variables. Simulating the intermediate basin with area 5414km? (Santo i?ngelo), for example, the initial performance (12 inputs; NS=0.894) improved when a simpler and more parsimonious model was used (4 inputs; NS=0.944). To validate the simplification procedure, a comparison was made between the proposed method (RCI) and the well-known methods of Overall Connection Weights (OCW) and Forward Stepwise Addition (FSA). For the comparison between RCI and OCW methods, in most cases, the ordering of selected variables was similar, confirming that the two procedures satisfactorily identify the more important variables, although the RCI is computationally more efficient giving a small advantage in the resulting model performance. In the FSA method, although the performance of the obtained models has also been satisfactory, the computational effort was much greater than with the other two methods because of the excessive number of the neural network training performed (117 training procedures in Combination 2, against only six for the RCI method, for example). An excessive number of input variables can reduce the efficiency of ANN simulation.A criterion was established by which input variables could be selected for exclusion.The proposed method satisfactorily identifies the most important variables.Simplification of the ANN improved performance of hydrological simulations.

Simulating transport of nitrogen and phosphorus in a Cambisol after natural and simulated intense rainfall.

Intense rainfall adversely affects agricultural areas, causing transport of pollutants. Physically-based hydrological models to simulate flows of water and chemical substances can be used to help decision-makers adopt measures which reduce such problems. The purpose of this paper is to evaluate the performance of SWAP and ANIMO models for simulating transport of water, nitrate and phosphorus nutrients, during intense rainfall events generated by a simulator, and during natural rainfall, on a volumetric drainage lysimeter. The models were calibrated and verified using daily time series and simulated rainfall measured at 10-minute intervals. For daily time-intervals, the Nash-Sutcliffe coefficient was 0.865 for the calibration period and 0.805 for verification. Under simulated rainfall, these coefficients were greater than 0.56. The pattern of both nitrate and phosphate concentrations in daily drainage flow under simulated rainfall was acceptably reproduced by the ANIMO model. In the simulated rainfall, loads of nitrate transported in surface runoff varied between 0.08 and 8.46 kg ha(-1), and in drainage form the lysimeter, between 2.44 and 112.57 kg ha(-1). In the case of phosphate, the loads transported in surface runoff varied between 0.002 and 0.504 kg ha(-1), and in drainage, between 0.005 and 1.107 kg ha(-1). The use of the two models SWAP and ANIMO shows the magnitudes of nitrogen and phosphorus fluxes transported by natural and simulated intense rainfall in an agricultural area with different soil management procedures, as required by decision makers.

AS INCERTEZAS ASSOCIADAS ÀS CONDIÇÕES CLIMÁTICAS OBTIDAS PELO MODELO ETA CPTEC/HADCM3: AVALIAÇÃO COMPARATIVA ENTRE OS DADOS SIMULADOS E OBSERVADOS DE PRECIPITAÇÃO, EVAPOTRANSPIRAÇÃO E VAZÃO NA BACIA HIDROGRÁFICA DO RIO IJUÍ, BRASIL.

This study aims to evaluate the climate scenarios simulated by the Eta CPTEC/HadCM3 model, conducted by four members of the HadCM3 global climate model (CNTRL, LOW, MID and HIGH), at the Ijui River Basin, Brazil. The used control period was from 1961 to 1975, looking for the assessment of climate scenarios and river flow during the 1976 and 1990 period. The task was divided into five stages: spatial interpolation of climate data, correction of simulated climatic variables series (bias correction), calculation of reference evapotranspiration, hydrological simulation of monthly river flow, comparison between simulated and observed conditions of precipitation, evapotranspiration and river flow. Although the correction methods used to eliminate the simulated climate series biases have originated very different scenarios, neither methods presented a better performance in all examined criteria. Sometimes, the differences between the simulated values based on the Eta Model and the observed values were higher than 20%, both in both rainfall and river flow resulting from the hydrologic modeling processes. Therefore, one must consider that these uncertainties will propagate to future scenarios, when analyzing the effects of climate change on water availability.

Evapotranspiration from Remote Sensing to Improve the Swat Model in Eastern Amazonia

In this study, we estimated the evapotranspiration from orbital images - MODIS (Moderate Resolution Imaging Spectroradiometer) for assimilation in the hydrological modeling of the SWAT (Soil Water Assessment Tools) model. The data used include the period between October 2003 and December 2006 of the sub-basin of the Lajeado River, located in the Tocantins-Araguaia River basin in Tocantins state. Overall, the results of the use of heat flows estimated by remote sensors in the SWAT model can be considered satisfactory. The values of the COE (coefficient of efficiency of Nash-Sutcliffe) ranged from -0.40 to 0.91 in the comparison with the daily flow data and from 0.17 to 0.77 with the monthly flow data, with the assimilation of evapotranspiration from orbital images. These results indicate benefit to the model adjustment due to improvement in the data assimilated of approximately 0.91 in the COE on daily scale and 0.60 in the CEO on monthly scale.

Evapotranspiração a partir de Sensoriamento Remoto para Assimilação no Modelo Swat no Leste da Amazônia / Evapotranspiration from Remote Sensing to Improve the Swat Model in Eastern Amazonia

In this study, we estimated the evapotranspiration from orbital images - MODIS (Moderate Resolution Imaging Spectroradiometer) for assimilation in the hydrological modeling of the SWAT (Soil Water Assessment Tools) model. The data used include the period between October 2003 and December 2006 of the sub-basin of the Lajeado River, located in the Tocantins-Araguaia River basin in Tocantins state. Overall, the results of the use of heat flows estimated by remote sensors in the SWAT model can be considered satisfactory. The values of the COE (coefficient of efficiency of Nash-Sutcliffe) ranged from -0.40 to 0.91 in the comparison with the daily flow data and from 0.17 to 0.77 with the monthly flow data, with the assimilation of evapotranspiration from orbital images. These results indicate benefit to the model adjustment due to improvement in the data assimilated of approximately 0.91 in the COE on daily scale and 0.60 in the CEO on monthly scale.

Runoff from soils under different management and simulated rainfall regimes in southern Brazil

Abstract Surface runoff and drainage were evaluated for southern Brazilian soils subjected to different rainfall intensities and management practices. Soils received up to four applications of simulated rainfall in sequences with one application per day. Seven lysimeters, each of 1 m3 volume, were used to measure drainage volume, with measurement of initial and final water content, times at which surface runoff and lysimeter drainage began, and the volume rates of flow. At the end of the second test, soils were subjected to two levels of disturbance (denoted by low and high soil movement) by opening furrows. These cultivation treatments altered the times at which lysimeter surface runoff and drainage were initiated, the rates of surface runoff, the final infiltration and internal drainage, and the components of the water balance throughout the series of trials. Mean times at which surface runoff was initiated in lysimeters subjected to greater soil disturbance were longer than those with little soil disturbance. Final infiltration rates were greater in lysimeters with little soil disturbance. It was also found that lysimeter surface runoff generation was influenced by the state of development of maize grown in the lysimeter. Editor D. Koutsoyiannis; Associate editor G. Mahé

Estimation of soil water content in watershed using artificial neural networks

ABSTRACT Soil water content (SWC) is an important factor in transfer processes between soil and air, contributing to water and energy balances, and quantifying it remains a challenge. This study uses artificial neural networks (ANNs) to analyse spatial and temporal variation of SWC in a Brazilian watershed, based on climate information, soil physical properties and topographic variables. Thirty eight input variables were tested in 200 models. The outputs were compared with 650 gravimetric moisture measurements collected at 26 points (25 field studies). The results show that it is possible to estimate SWC efficiently (Nash-Sutcliffe statistic, NS = 0.77) using topographic data, soil physical properties and rainfall. If only climate information is considered, modelling is less efficient (NS = 0.28). Using many variables does not necessarily improve performance. Alternatively, SWC can be estimated by simplified models using rainfall and topographic maps information, although the performance is less good (NS = 0.65).

Análise de variâncias pluviométricas na bacia hidrográfica do rio Taboão - RS

The objective of this paper was to determine the probabilistic distribution that fits the variance of the precipitation data obtained in six stations located at Taboao river watershed, northwestern region of Rio Grande do Sul State, during a seven years period from 5/May/2003 to 9/May/2006 and from 1/July/2007 to 4/June/2011. Group patterns were determined in relation to the variance. The Shapiro-Wilk test was used for a comparison between the observed and theoretical distributions of the variance. After determining the Log Pearson and Gama distribution, the grouping of stations was performed based on theirs variances by the Euclidean distance using the Wards method. The evaluation with the ANOVA and Tukeys test showed that the proposed groupings were not sustainable, which implies the homogeneity among the mean values of the historical series variances from the six analyzed precipitation stations. The obtained results permit to conclude that the precipitation is homogeneous in the Taboao river watershed.

Fluvial carbon export and CO2 efflux in representative nested headwater catchments of the eastern La Plata River Basin

&NA; This study involved a baseline evaluation of fluvial carbon export and degas rates in three nested rural catchments (1 to 80 km2) in Taboão, a representative experimental catchment of the Upper Uruguay River Basin. Analyses of the carbon content in stream waters and the catchment carbon yield were based on 4‐year monthly in situ data and statistical modeling using the United States Geological Survey load estimator model. We also estimated pCO2 and degas fluxes using carbonate equilibrium and gas‐exchange formulas. Our results indicated that the water was consistently pCO2 saturated (˜90% of the cases) and that the steep terrain favors high gas evasion rates. The mean calculated fluvial export was 5.4 tC·km−2·year−1 with inorganic carbon dominating (dissolved inorganic carbon:dissolved organic carbon ratio >4), and degas rates (˜40 tC km−2·year−1) were nearly sevenfold higher than the downstream export. The homogeneous land use in this nested catchment system results in similar water‐quality characteristics, and therefore, export rates are expected to be closely related to the rainfall‐runoff relationships at each scale. Although the sampling campaigns did not fully reproduce storm‐event conditions and related effects such as flushing or dilution of in‐stream carbon, our results indicated a potential link between dissolved inorganic carbon and slower hydrological pathways related to subsurface water storage and movement.