Evaluation of reference evapotranspiration methods for the northeastern region of India

摘要

Highlights ? Radiation-based IRMAK3 and TURC models performed best among the selected models. ? FAO24 Blaney-Criddle is the only suitable temperature based method for the region. ? Performance of particular model is more subjected to it structure rather than type. ? In particular, FAO24BC and TURC performed better as compared to 1957MAKK model. ? Radiation and temperature extreme is the dominant factors to drive the ET0 process. Abstract The study planed to identify a suitable alternative to the FAO-56 Penman-Monteith (FAO56PM) equation for calculating reference evapotranspiration ( ET ₀) from chosen temperature and radiation based models utilizing monthly meteorological data from 30 destinations in diverse agro-ecological regions of the Northeast (NE) India i.e., Assam Bengal Plain (ABP), eastern Himalaya (EH), and the northeastern hilly (NEH) region. Radiation-based IRMAK3 most appropriate in the ABP (weighted root mean square deviation, WRMSD=0.17?mm?d?1, r 2=0.98, for Nagrakata), and TURC model being in the first three rank of most of the sites, with the lowest error and highest correlation in NEH (WRMSD=0.10?mm?d?1, r 2=0.92, for Shillong), and EH (WRMSD=0.23?mm?d?1, r 2=0.95, for Gangtok). Findings reveal that IRMAK3 and TURC models performed equally well and were observed to be the best among selected models for the majority of stations followed by FAO24 Blaney-Criddle (FAO24BC), and 1957MAKK. Pair-wise regression equations were developed for preferred FAO56PM ET ₀ estimates to ET ₀ estimates by alternative methods. Cross-correlation of eighteen chose methods demonstrated that the five equations (i.e. four radiation- and one temperature-based) performed exceptionally well when contrasted with the FAO56PM model, thus being advised for assessing ET ₀ under limiting data conditions as have yielded a better estimate of ET ₀ with a small error. Keywords Reference evapotranspiration ; Performance statistics ; Calibration and validation ; Empirical methods ; North East ; India prs.rt("abs_end"); 1. Introduction Evapotranspiration is the integrated process of evaporation and transpiration and is affected by meteorological variables, crop characteristics, and management practices, as well as environmental characteristics. ET ₀ is the water evaporated from a reference surface, and was presented to quantify evaporative demand of the atmosphere, independent of the crop growth parameters and management practices ( Allen, Pereira, Raes, & Smith (1998) and Zotarelli, Dukes, Romero, Migliaccio, & Morgan (2010) ). ET ₀ is a highly nonlinear variable controlling varieties of issues in water management, hydrology, agriculture, irrigation scheduling, and proper planning of available fresh water resources. Among the different components of the hydrological cycle, a precise approximation of evapotranspiration is perhaps most difficult due to its complex interactions with the soil–plant–atmosphere system. The reliable estimation of ET ₀ is essential to estimate the net irrigation requirement, regional water resources planning, and management and to model the climate change effect. The direct approach to quantify ET ₀ is using lysimeter measurement, or it could be indirectly calculated using the energy balance approach (or empirical models). However, the lysimetric approach is time-consuming and requires precise instrumentation. The indirect approach (methods) is based on site specific meteorological data, altitude, and latitude. The FAO56PM method is the most suitable indirect approach for accurate estimation of ET ₀ and evaluation of other empirical models ( Allen, Pereira, Raes, & Smith (1998) , Berti, Tardivo, Chiaudani, Rech, & Borin (2014) , Djaman et al. (2015) , Lima et al. (2013) , Pandey, Pandey, & Mahanta (2014) , Pereira, Allen, Smith, & Raes (2015) and Widmoser (2009) ). The FAO Irrigation & Drainage Paper No. 56, ( Allen et al., 1998 ), and ASCE Task Committee on Standardized Evapotranspiration Calculations ( ASCE-EWRI, 2005 ) recommended that the FAO56PM method could be used as a standard equation to calculate ET ₀. The FAO56PM method was validated against lysimeter measured data in diverse climatic conditions worldwide and reported the best method for ET ₀ estimation ( Allen et al. (2005) , ASCE-EWRI (2005) , DehghaniSanij, Yamamoto, & Rasiah (2004) , Ghamarnia, Mousabeyg, Amiri, & Amirkhani (2015) , Itenfisu, Elliott, Allen, & Walter (2003) , Jain, Nayak, & Sudheer (2008) , Mohan & Arumugam (1996) and Xu, Peng, Ding, Wei, & Yu (2013) ). Additionally, the FAO56PM now widely used as reference methods in the field of agronomy, irrigation water management, and other related fields for research purpose ( Alexandris, Kerkides, & Liakatas, 2006 ). The FAO56PM accounts for aerodynamic as well as physiological parameters