Indian J. Phys. Vol. 85, No. 8, pp 1277-1285, August, 2011 © 2011 IACS Estimation of forest evapotranspiration over Uttarakhand hills, India P D Semalty* 1 , K Dev 1 , S Kumar 1 , S Kimoti 1 and M M Kimothi 2 1 Department of Physics, HNB Garhwal University Campus, Badshahithaul, Tehri-Garhwal-249 199, India 2 Department of Science and Technology, Uttarakhand Space Application Centre, Dehradun-248 001, India E-mail : semalty@rediffmail.com Received 21 June 2009, accepted 12 April 2011 Abstract : Potential evapotranspiration (PET) in the Uttarakhand forests has been estimated using the Modified Prestly-Taylor Method [1]. The estimated PET has been used to determine the actual evapotranspiration (AET) based on the limitation in available water (soil moisture) on the ground. The required meteorological data used in the estimation of ET is obtained from field measurements at three forest sites which includes Deodar (Cedrus deodara), Pine (Pinus roxburghii) and Oak (Quercus spp.) forests located within an area of five km radius in the district Tehri Garhwal. The meteorological data including daily sun shine hours, humidity, air temperature and soil moisture for one year from July, 2005 to June, 2006 were recorded and used in the estimation of ET. The daily average ET was highly influenced by the sunshine hours and soil moisture. A significant seasonal variation in the ET is observed. The results of seasonal variation in ET can be used as an indicator of possible forest fire events and helpful in prevention and management of forest fire in the hilly areas of Uttarakhand state of India. Keywords : Evapotranspiration, forest, radiation, moisture. PACS Nos. : 92.40.Je, 92.60.Jc 1. Introduction Evapotranspiration is the single largest component of the global hydrological and carbon cycles which ultimately affect the climate [2] since nearly two third of rain fall on earth is returned to the atmosphere by the process of evapotranspiration. Evapotranspiration (ET) in the forest is a complicated physical process. It includes transpiration by the green mass of the trees (canopy), evaporation from the soil and, evaporation of intercepted precipitation. The present study aims to estimate the evapotranspiration over a typical * Corresponding Author