CS(AR)-9/99-2000 : Crop water requirements for Krishnai Irrigation Project (medium) of Assam

Abstract

An attempt has been made to estimate the design mean monthly reference crop evapotranspiration (ETo) for Krishnai Irrigation Project of Assam. For this analysis the mean monthly climatological and physiographical data for the period of 1986 to 1994 have been collected from the Indian Meteorological Department, Borjhar. Since the ETo value depends on large number of climatological, physiographic and other data and manual estimation is highly tedious and time consuming, so use of computer software is very essential. A computer program given in FAO-24 developed by Doorenbos and Pruitt (1977) has been modified and used for estimation of ETo by seven different empirical methods viz. Blaney & Crridle, Radiation, Penman, Modified Penman, Pan Evaporation, Hargreave and Thomthwaite. Modified Penman Method of ETo estimation is the most elaborate and rational but requires a large number of data. Often such data is very scanty forcing the use of some other empirical methods. Therefore the study is further extended to evaluate regional relationships for Krishnai Irrigation Project relating the ETo values of Modified Penman and of six other climatological methods. The developed relationships are useful in determining the rational value of ETo which will correspond to the ETo value by Modified Penman method even in the situation of scanty data. Finally crop water requirements calculated on the basis of mean monthly ETo values received from Modified Penman method.