Estimation of reference evapotranspiration using a user-friendly decision support system: DSS_ET

Due to wide application of evapotranspiration (ET) data, a number of indirect methods for estimation of reference ET (ETo) have been developed. Therefore, it becomes impractical for many users to select the best ETo estimation method for the available data and climatic condition. To overcome this problem, a decision support system (DSS_ET) was developed which supports 22 ETo estimation methods with varied options for calculation of various intermediate parameters, generalized data input format with copy–paste option from spreadsheet applications, visualize/check input data and results, features to estimate missing data, and user-friendly graphical user interface (GUI) that enhances its applicability as a handy research and teaching tool. Monthly meteorological data for 32 years (1971–2002) were procured from IMD, Pune, for 133 selected stations evenly distributed over five climatic ecosystems of India. Altogether 18 ETo estimation methods, including the globally accepted standard method FAO-56 Penman–Monteith (PM), were found applicable for the data availability conditions used in this study. In absence of lysimeter measured ETo data, the FAO-56 PM ETo values were used to estimate the normal monthly ETo for each station and climatic condition. Finally, ranks were assigned to each applicable ETo method based on weighted standard error of estimate (WSEE) with respect to the FAO-56 PM method for different climatic ecosystems. If, because of poor data availability condition, it becomes unavoidable to use methods other than FAO-56 PM, then these ranks can readily be used to select the best applicable method in the existing data and climatic conditions to get ETo values closer to FAO-56 PM estimates.

► A decision support system (DSS_ET) was developed which supports 22 indirect ETo estimation methods.
► Meteorological data for 32 years were used for 133 stations over five climatic ecosystems of India.
► Normal monthly ETo for each station and climatic ecosystem was estimated.
► Ranks were assigned to each applicable ETo method for different climatic ecosystems.