Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2008
Publication Date: 10/24/2008
Citation: Mello, C.R., Viola, M.R., Norton, L.D., Silva, A.M., Weimar, F.A. 2008. Development and application of a simple hydrologic model for water simulation for a Brazilian Headwater Basin. Catena. 75:235-247.
Interpretive Summary: The analysis of possible consequences of land-use changes on the hydrology of a basin is a global concern. This study focus on a theoretical and experimental investigation of the effects of a hypothetical land use change, from pastures into forests, on the Alto Rio Grande Basin, located in Minas Gerais, Brazil. The Alto Rio Grande Basin is of great socio-economic importance for Minas Gerais which is second most populous state in Brazil and fourth largest by area. It is a mountainous State, with many important rivers for hydroelectric energy production. Rio Grande Basin is responsible for great part of electric hydropower energy in Minas Gerais State, draining from a headwater region with more than 2,000 m above sea level. Application of hydrologic modeling to simulate the effects produced by different land-use is one the most relevant scientific investigation of hydrology and soil and water conservation. Many studies around the world have been carried out in last two years. However, in Brazil, this kind study has not been developed and we have serious problems with land-use change, specially, aforestation (grassland areas converted to eucalyptus plantation for pulp production) and the effects on water resources associated to this new scenario needs to be adequately treated. This work used two relevant contributions: 1 – a simple hydrologic model process based able to simulate adequately the water resources behavior, being a robust tool for environmental planning and management for the most important headwater region of southeast Brazil; 2 – to simulate the effects on water resources produced by converting grassland areas to eucalyptus on a basin which feed an important Hydropower Plant Facility Reservoir of southern Minas Gerais State. We found the approach to accurately predict the runoff in the watershed to a high level of confidence. This provided us the ability to predict the differences in runoff to the hydroelectric facility for generating power due to land use changes. The impact of this study is that this approach can be used by decision makers and planners to plan for future decreases in hydroelectric power production in the region due to land use changes.
Technical Abstract: Physically based hydrologic models for watershed are important tools to support water resources management and predicting hydrologic impacts produced by land-use change. Rio Grande Basin is located in south of Minas Gerais State, and the Rio Grande is the main tributary of basin which has 2080 km2 draining into the Camargos Hydropower Plant Reservoir (CEMIG). The objectives of this work were: 1) to create a semi-physically based hydrologic model, in lumped and semi-distributed to sub-basins approaches and based on GIS and Remote Sensing tools and, 2) to simulate the hydrologic responses of the Rio Grande basin, thus creating an important tool for management and planning of water resources for the region. The hydrologic model is based on the SCS Curve Number (SCS-CN) as modified by Mishra, et al. (2006), VIC-2L and Muskinghan-Cunge models, and structured into three hydrologic components: estimation of the flow components (quick runoff, hortonian and base flows), propagation into the respective soil reservoirs (surface, sub-surface and shallow saturated zone) and propagation into channels. Precipitation and discharge data sets were obtained from the Brazilian National Water Agency (ANA), summing, 10 pluviometric stations and 2 gauging stations in the basin. Reference evapotranspiration (ETo) data were obtained from the Brazilian National Meteorological Institute (INMET) for just one location. In order to estimate actual evapotranspiration, crop coefficient, soil moisture and satellite image interpretation were applied. Long-term hydrologic series were structured for period between 1990 and 2003. Model calibration phase was carried out applying data set of 1990–2000, using the Nash-Sutcliffe Statistical Coefficient (CNASH) to evaluate the model performance. A validation period (split simple test) was carried out applying the calibrated model to the period of 2001–2003. In addition, some hydrologic variables wree estimated by extracting from simulated hydrographs which were compared to observed values. The statistical precision showed that the model was able to simulate the hydrologic impacts produced by land-use change on Rio Grande Basin, with CNASH greater than 0.7 for both calibration and validation phases. The hydrologic impacts on Rio Grande basin produced from grassland area converted to eucalyptus under three specific scenarios were evaluated, which predicted annual runoff mean reductions up to 17.8%, due to an increase in evapotranspiration rate for the eucalyptus plantation.