Loosely coupled SaltMod for simulating groundwater and salt dynamics under well-canal conjunctive irrigation in semi-arid areas

Abstract

Long-term predictions of regional groundwater and salt dynamics are important for maintaining agricultural sustainability in semi-arid areas where the conjunctive irrigation of groundwater and surface water is used. In this study, the mass balance model, SaltMod, is loosely coupled for simulating groundwater and salt dynamics under complex conditions of the well-canal conjunctive irrigation. In the loosely coupled model, two SaltMod models are used to simulate the canal- and well-irrigated areas separately, and an exchange flux is used as an additional mass balance term for calculating the mass balance of the canal- and well-irrigated areas. This makes it possible to use SaltMod (without modifying its source codes) for simulating well-canal conjunctive irrigation with multiple irrigation sources and different groundwater levels in the groundwater aquifer. The loosely coupled SaltMod is applied to simulate the flow of irrigation water and the salt transport at the Longsheng well-canal irrigated area in Hetao Irrigation District, Inner Mongolia, China. Measurements of soil salinity and groundwater level are used to calibrate SaltMod model parameters, and the calibrated model is used to predict groundwater level and soil salinity for the next 100 years under the current climate and irrigation conditions. The predictions indicate a slight salinization trend in the root zone of the well-irrigated area and a slight desalinization trend in the root zone of the canal-irrigated area, and salt accumulation mainly occurs in the aquifers of the well- and canal-irrigated areas. However, the amount of salt accumulated in the root zone of the well-irrigated area is small enough not to impact agricultural production. Therefore, the Longsheng well-canal irrigated area can sustain a long-term development under the present irrigation practice. Increasing the autumn irrigation water amount or decreasing the groundwater level in the future in the well-irrigated area can slightly alleviate the soil salinity, but cannot change the salinization trend in the root zone of the well-irrigated area.