Journal of Agricultural Science; Vol. 11, No. 6; 2019 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 209 Water Balance in a Tropical Eucalyptus plantations in the Doce River Basin, Eastern Brazil A. Q. Almeida 1 , A. Ribeiro 2 , F. P. Leite 3 , R. Souza 4 , M. I. Silva Gonzaga 1 & W. A. Santos 1 1 Programa de Pós-graduação em Recursos Hídricos, Universidade Federal de Sergipe, São Cristóvão, Brazil 2 Departamento de Engenharia Agrícola, Universidade Federal de Viçosa, Minas Gerais, Brazil 3 Departamento de Pesquisa, CENIBRA, Belo Oriente, Minas Gerais, Brazil 4 Departamento de Energia Nuclaer, Universidade Federal de Pernambuco, Recife, Brazil Correspondence: A. Q. Almeida, Programa de Pós-graduação em Recursos Hídricos, Universidade Federal de Sergipe, Cidade Universitária Prof. José Aloísio de Campos, Av. Marechal Rondon, s/n, CEP: 49100-000, São Cristóvão, SE, Brazil. Tel: 55-793-194-6423. E-mail: andre.almeida@ufs.br Received: January 20, 2019 Accepted: March 3, 2019 Online Published: May 15, 2019 doi:10.5539/jas.v11n6p209 URL: https://doi.org/10.5539/jas.v11n6p209 Abstract The rapid expansion of Eucalyptus plantations in Doce river basin, eastern Brazil, by changing the grassland and the natural surface cover in the savanna ecosystem, can potentially cause significant changes to water resources of the region. Especially for the higher amount of water transpired by the trees. The objective of this work was to model the water balance in an area cultivated with clonal E. grandis × urophylla in the Doce river basin, state of Minas Gerais, Brazil. Between October 2007 and September 2010, the water balance model estimated the daily variation of available soil water as a function of the water loss via evapotranspiration. Components of the evapotranspiration process were estimated by modifying the stomatal resistance of the Penman-Monteith equation. Evapotranspiration (ET) and precipitation (P), during the three years, were 3,467 mm and 3,439 mm, respectively. The evapotranspiration/precipitation ratio (ET/P) was of 1.01. Precipitation input was approximately balanced by water losses to evapotranspiration, without significant changes to water stored in soil and groundwater. Keywords: Eucalyptus plantations, water balance, forestry, rutter model, interception 1. Introduction Eucalyptus is the most widely planted hardwood genus in the world, covering more than 19 million hectares (Albaugh, Dye, & King, 2013). Approximately 5.7 million hectares of the Brazilian territory in 2016 is cover with species of the genus Eucalyptus (IBÁ, 2017). Minas Gerais state alone accounts close 24% of the total planted area in Brazil, most planted in Doce river basin. In addition to existing plantations, the increase in the area planted with Eucalyptus forests in the Doce river basin is expected for the coming years, especially in areas currently destined for pasture land. However, any change in land use and land cover promotes changes in the energy and water cycles of a basin, especially in the evapotranspiration and flow components of the watercourses (Zhou et al., 2015, Almeida et al., 2016). As fast-growing species exhibit a high water consumption through the transpiration process, the increase in planted area is expected to cause a significant increase in total evapotranspiration in the basin (Maier et al., 2004, 2017), which can compromise the water resources. The many countries around the world there is much concern about their water consumption of Eucalyptus plantations, since forests play an important role in the capture and distribution of rainwater in the watersheds (Huang & Zhao, 2014; Jones et al., 2017). In areas cultivated with Eucalyptus plantations, we expect to see higher evapotranspiration rates, resulting in decreased runoff and therefore the supply of water input to aquatic ecosystems (Reichert et al., 2017). Studies have shown that reforestation of degraded areas with Eucalyptus will often increase water loss by evapotranspiration, reducing water flow in streams and rivers (Reichert et al., 2017). Modeling studies that assess components of the water balance in field cultivated with planted forests (mainly eucalyptus) are being conducted in various parts of the world, including South America (Smethurst, Almeida, &