Integrating field measurements, novel modeling, and remote sensing datasets for crop coefficient and evapotranspiration calculations in thermo-limited region of the High Plains

The declining water resources from Ogallala Aquifer and strong climate warming trends provide opportunities for planting alternative crops that reduce irrigation water needs, are tolerant to higher temperatures, and provide comparable yields. For example, cotton, a drought-tolerant crop that meet these requirements, has experienced a rapid growth in planting in Kansas from 6,500 ha in 2015 to 79,000 ha in 2020. As expansion of cotton and other drought tolerant crops intensifies, a thorough examination of evapotranspiration, water use, and irrigation strategies is merited for development of sustainable crop production. In this study, we developed an approach to evaluate crop coefficient and evapotranspiration fluxes using continuous field measurements of various physical variables, aerial imagery, remote sensing datasets of vegetation growth, and maximum entropy production (MEP) model. The MEP model is based on non-equilibrium thermodynamics and allows the partition of surface radiative fluxes into (turbulent and/or conductive) heat fluxes as functions of field collected surface net radiation, temperature, humidity, and ground heat fluxes, thus making the estimates less sensitive to the uncertainty of the input data and model parameters. Comparison of actual ET from MEP model and crop ET and reference ET from Penman-Monteith model yielded derivation of crop coefficient functions for corn and cotton in thermo-limited climate of High Plains of the United States. Two flux towers with near surface and subsurface measuring devices were instrumented on two irrigated fields of cotton and corn in Southwestern Kansas, and the approach was tested on collected data from 2020 and 2021. Remote sensing data from Sentinel-2 and drone aerial imagery were used to evaluate the crop growth factors at the two fields. The results showed cottons higher tolerance to heat, lower water demand, and lower ET rates making cotton a viable option for integration in sustainable crop production practices under changing climate in semi-arid regions.