Estimation of evapotranspiration in agricultural areas of Pakistan based on the METRIC model

Water depletion in irrigated agriculture is recognized as an important cause of water scarcity. For agricultural water resource management, precisely measuring field evapotranspiration is critical since it plays a critical role in both the energy and water cycles. Being one of the major irrigation regions in the world, Pakistan’s agricultural region necessitates accurate calculation of actual evapotranspiration through the use of remote sensing technology for more advanced agricultural water resource management. This study estimated the real evapotranspiration in Pakistan’s agricultural region for the years 2019–2020 using MODIS data, meteorological data, and DEM data using the METRIC model. The study conducted an analysis of the spatiotemporal distribution patterns of evapotranspiration throughout several crop growth stages with the objective of presenting empirical evidence supporting the prudent use of agricultural water resources in Pakistan. 1) Using lysimeters to compare the METRIC estimation results with data from agricultural stations, the correlation coefficients were 0.65 and 0.84 for daily and monthly scales, respectively, indicating root mean square errors of 1.16 mm/day and 25 mm/month. Comparing METRIC estimation findings with ETMonitor products at the spatial scale showed that the former were more accurate. 2) In Pakistan’s agricultural region, the planting structure was directly associated with the spatial distribution of evapotranspiration, which decreased progressively from north to south. For wheat, cotton, rice, and sugarcane, the evapotranspiration was 392 mm, 652 mm, 745 mm, and 1224 mm for the whole growth period. The rate of evapotranspiration in Punjab province is higher than in Sindh province for the same crop during the growth phase. 3) Throughout the growing season, wheat showed a pattern of monthly evapotranspiration that first decreased, then increased, and finally decreased. The growth period observed in cotton in Sindh province showed a "bimodal" monthly evapotranspiration pattern, whereas cotton in Punjab region had a "unimodal" monthly evapotranspiration pattern. During the growth era, the monthly evapotranspiration patterns of rice and sugarcane were "unimodal". In addition to providing a methodology for crop-scale or regional evapotranspiration estimation based on remote sensing, this study realizes the parametric application and applicability analysis of the METRIC model in Pakistani agricultural areas. This is significant because it reveals the spatial and temporal characteristics of evapotranspiration and water consumption of various crops and helps manage regional agricultural water resources.