Modern Environmental Science and Engineering (ISSN 2333-2581) June 2018, Volume 4, No. 6, pp. 537-545 Doi: 10.15341/mese(2333-2581)/06.04.2018/007 Academic Star Publishing Company, 2018 www.academicstar.us Remote Sensing Drought Indices for the Semi-Arid Region of Southeast Brazil Antônio H. de C. Teixeira 1 , Janice F. Leivas 2 , Fulvio R. Simão 3 , and João B. R. S. Reis 3 1. Embrapa Coastal Tablelands, Brazil 2. Embrapa Satellite Monitoring, Brazil 3. Minas Gerais Agricultural Research Institute, Brazil Abstract: The semi-arid region of the Minas Gerais state, Southeast Brazil, has experienced some events of drought, while arising large irrigation schemes in some areas increasing water withdrawn from the rivers. These scenarios demand large-scale water balance studies to subsidize water resources policies. The visible, infrared and thermal bands from Landsat 8 satellite images were used together with a net of agrometeorological stations to test drought indices in this region, during the year 2015, classifying irrigated areas and natural vegetation, aiming mitigations for climatically water scarcity. The ET r index (i.e., the ratio of actual – ET to reference – ET 0 evapotranspiration) was obtained by using the SAFER (Simple Algorithm for Evapotranspiration Retrieving) algorithm, while the SUREAL (Surface Resistance Algorithm) algorithm was applied to estimate the surface resistance to water vapor transfer (r s ). The highest and lowest ET r and r s values, meaning better root-zone moisture conditions, above 0.90 and bellow 800 s m -1 , respectively, happened in the counties with the largest concentrations of irrigation area, resulting in an increment on ET of 3.0 mm d -1 , because of the replacement of natural vegetation by irrigated crops. On the other hand, outside the rainy period, natural vegetation showed ET r values close to 0.00 and r s very high, above 1000 s m -1 . Between the two drought indices, r s detected better the different soil moisture conditions. The results are relevant for monitoring drought events under the additional environmental consequences of land use change in semi-arid environments. Key words: evapotranspiration, soil moisture, water resources 1. Introduction Drought events can occur in any agro-ecosystems, from a range of hydrometeorological processes that suppress precipitation and/or limit the root-zone water availability, creating conditions that are significantly drier than normal or otherwise limiting moisture availability to a potentially damaging extent. Agrometeorological indices may be used to help track drought events, depending on the spatial and time scale [1]. Drought impacts are significant and widespread in many hydrological basins, increasing disputes over Corresponding author: Antõnio Heriberto de Castro Teixeira, Ph.D.; research areas/interests: agrometeorology, environmental sciences, remote sensing. E-mail: heriberto.teixeira@embrapa.br. their water resources. Under these conditions, more conflicts are expected as populations expand, economies grow, and the competition for the scarce water supplies during these drier events intensifies [2]. Aiming a sustainable exploration of the water resources, water managers should consider the large-scale water balance conditions of the mixed agro-ecosystems in the hydrological basins, to subsidize policies that minimizes the water use by agriculture while maintaining the water availability [3]. Drought events can adversely affect agriculture and food security and their impacts can vary by region and by season. Agriculture in the North of Minas Gerais state, Southwest Brazil, has been highlighted by increasing water demands for irrigation, with fast replacement of natural vegetation by irrigated crops.