Relative humidity based model for estimation of reference evapotranspiration for western plateau and hills region of India

Abstract

As an important constituent of hydrological cycle, estimation of Reference Evapotranspiration (ETo) is essential for planning of projects related to water resources. This article compares the results obtained from the available pan evaporation based equations to estimate ETo from pan evaporation (Ep) and proposes a new simplified methodology for estimation of ETo, which needs only the data of relative humidity (H). The resulting model is based upon the collected meteorological data of a selected study area i.e. Nagpur District in Maharashtra State, which lies in western plateau and hills region of India. In the proposed methodology, Ep rates are adjusted to the values expected for 50 % relative humidity. Then, the relationship between ETo and the adjusted Ep is established. The validation of the proposed new model has been carried out by comparing its results with the results obtained by the pan evaporation method, for the study area as well as for the data set of another area. This new model is found to be reasonably accurate for estimation of reference evapotranspiration for the study area and as such, is expected to be applicable to the river basins located in the regions having climatic conditions similar to that of the study area. Although, if the conditions are different then another site specific model can be developed by adopting the methodology proposed in this article.