Estimation of crop water requirement of rice using CROPWAT model in Ramganga river sub basin, India

Water scarcity is one of the issues that today’s agriculture is facing thus requires use of the technologies and strategies for water resource management. The water requirement of crops varies widely during various growth stages of the crop, which necessitates proper irrigation scheduling to maximize water use efficiency. Therefore, this study estimates the crop water requirement (ET_c) of rice in the Ramganga river sub-basin using the CROPWAT model. The study area is comprised of the Nainital and Udham Singh Nagar districts of Uttarakhand and the Rampur and Bareilly districts of Uttar Pradesh under Ramganga River sub-basin, India with a humid sub-tropical climate with rice being the main crop. Meteorological data from 14 weather stations during 1996-2019 were used to estimate reference crop evapotranspiration (ET_o) by the Penman-Monteith model that was subsequently adjusted for crop specific parameters to express rice crop evapotranspiration (ET_c). Effective rainfall (ER) and net irrigation requirements (IR) were also computed for each station. The crop water demand differed substantially among stations from 482 mm to 633.2 mm. The highest crop water requirement was observed in Bareilly district (503-543 mm), whereas the lowest in Nainital district (418.5-496 mm). Using an application efficiency of irrigation water about 60%, the irrigation water requirements across these responses ranged between 455.5 mm and 612.8 mm and suggested a scenario with high spatial variability with respect to both water availability and climate conditions. This research gives essential knowledge on the irrigation requirements for rice and underlines that the sustainability of agricultural production in water-limited areas depends on water management practices.