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|Title:||Caracterização de mudanças paleoclimáticas no nordeste do Brasil utilizando modelagem hidrológica|
|Keywords:||Paleoclima; Hidrologia; Modelagem hidrológica de Lagos; Produção intelectual; Paleoclimate; Hydrology; Lake Hydrology Model|
|Abstract:||The aim of this study is to set up a model that represents hydrological processes at Caçó Lake - MA, targeting its use in past climate quantification on a regional basis. Understanding the physical processes acting on the flow from the hydrological basin at present and modeling the lake level response to climate changes, it is possible to estimate the precipitation and evaporation in the region using the lake level past reconstruction or climate changes from global models. The Caçó lake, located in the Northeast region of Brazil, has great sensitivity to climate variations. In this region, the precipitation occurs between the months of December and May, temperatures vary around 30oC and occur high rates of evaporation. The biome in the region is a transition between Cerrado and Amazon Forest. The Caçó lake has been object of several studies. To model the change in Caçó Lake level it is necessary to determine all the inflows and outflows of the lake. For this purmose, a hydrological model of river basins has been used. The chosen model was SWAT (Soil and Water Assessment Tool) since it is a distributed model that enable to assimilate climate change. Additionally, lake water balance model was built to simulate lake level changes. The daily data needed for modeling were provided by the National Water Agency (ANA), Research Center for Weather and Climate (CPTEC) and National Institute of Meteorology (INMET). Information from the soil types and texture characteristics were obtained from IBGE and RADAMBRASIL Project data bases. Vegetation cover informations were found in Eva et al. (2002) and land elevation data were obtained from SRTM (Shutle Radar Topography Mission). The daily lake levels and the water table monitoring have been made since 2001 by a field observer. The water stable isotopes monitoring is being conducted since 2006. The calibration and validation of SWAT model appear satisfactory, with Nash-Sutcliffe coefficients of 0.82 and 0.83, respectively. The lake water balance model was also satisfactory with Nash-Sutcliffe coefficients of 0.81 and 0.71 for validation and calibration periods. Simulations considering climatic conditions in 6,000 cal. years BP and the pre-industrial periods, using data from global models, were done. The simulations were: (i) using the SWAT climate change module and, (ii) using 30 years of daily data from IPSL global model. Both procedures showed similar results, showing that the lake level in the 6,000 cal. years BP would be around 17 to 23cm above the current level and that it is possible to use the SWAT climate change module for past climates situations. The modeling was applied to estimated climate conditions based on palaeoenvironmental studies of Caçó lake. The rainfall was percentually reduced compared to the current value, considering that precipitations are responsible for the large variations in the Caçó lake level. The rainfall was estimated at some stages since approximately 18,000 cal years BP. Finally, it was concluded that the hydrological modeling of lakes is a necessary tool to complete geochemical studies since it allows quantifying past climat changes.|
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