Effect and side-effect assessment of different agricultural water saving measures in an integrated framework

Water scarcity has always been a serious challenge for agriculture and food security. Hence, different strategies are considered to save more water and increase water productivity. However, the effectiveness of such water saving measures have not been sufficiently evaluated. In addition, they may have side effects like salt accumulation, which will be exacerbated in dry and semi-arid zones. So, any evaluation needs to be done in an integrated framework. Thus, this work aims to evaluate some of the most popular agricultural water management measures from the points of view of real water saving, water productivity, soil salinity and environmental flow. Such an evaluation requires both field- and basin-scale simulations. To this aim, a modelling setup was defined to estimate the components of crop growth (yield, evaporation and transpiration) as well as water and salt budgets, using the SWAT and AquaCrop models. The evaluated measures include: deficit irrigation, replacing surface irrigation with drip irrigation and greenhouse cultivation. The study area of this research work is a part of the Tashk-Bakhtegan Basin, located in the Fars province of Iran. The results show that deficit irrigation can save water up to 12%, but it would also cause up to 94% more salt accumulation than surface irrigation. Notably, implementation of improved irrigation systems like drip irrigation can increase water consumption up to 8% and still have nearly the same problem with salt accumulation. Among the assessed measures, greenhouse cultivation resulted in an up to 24% reduction in water consumption, with no serious salt accumulation. While it was assumed that the rebound effects of measures are controlled, it was seen in the study area that these measures can lead to an illusion of reducing water consumption due to consequent increases in cultivated area or changing to more water consuming crop patterns. This ultimately reduces groundwater recharge or environmental flow that have been traditionally supplied by irrigation return flows.