EVAPOTRANSPIRATION AND RAINFALL SURPLUS IN BRAZILIAN SEMIARID WATER BASINS BY USING REMOTE SENSING DATA: A CASE STUDY OF PIRANHAS-AÇU RIVER BASIN
S-SEBI, SSEB, MODIS, Energy balance, Water resources
Research on hydrological cycle processes is crucial to water resources management in water basins, especially those located in semiarid regions. It is the case of Piranhas-Açu River Basin (PARB), where the occurrence of long draught periods associated with water resources allocation conflicts may put its water availability at risk, impacting human supply and agriculture development. Among hydrological cycle processes, evapotranspiration (ET) is of uttermost importance given its critical role in water, soil and vegetation interactions, hydrometeorological modelling and in the energy fluxes dynamics of semiarid regions. Remote sensing techniques for ET estimation have been developed in the past few decades, allowing its calculation in large spatial scales, such as water basins. Therefore, the objective of this study is to quantify daily and annual ET during 2011 and 2014 in all the PARB, by using remote sensing data and formulations based on the Simplified Surface Energy Balance Index (S-SEBI) and Simplified Surface Energy Balance (SSEB) algorithms. For the calibration and validation of the proposed algorithm, energy balance components data from a flux tower equipped with eddy covariance system will be used. In addition, land surface temperature and albedo data from MODIS sensor and solar radiation data from weather stations located in the basin will also be used. ET determination will allow its spatial analysis in relation with vegetation dynamics, by means of NDVI obtained from MODIS data, and with different land cover classes. This relationship will be evaluated seasonally, identifying changes in its behavior during dry and wet periods. Lastly, the annual rainfall surplus in the basin will be calculated by taking the difference between precipitation, obtained from TRMM satellite data, and evapotranspiration, in order to recognize the most vulnerable regions during extended draught periods.