Future climate change could reduce irrigated and rainfed wheat water footprint in arid environments

The concept of water footprint (WF) has been used to manage freshwater resources for the past two decades and is considered as indicator of the sustainability of agricultural systems. Accordingly, the current study aimed to quantify WF and its components in the future climate for rainfed and irrigated wheat agro-ecosystems in 17 provinces of Iran located in arid or semi-arid environments. The provinces were divided into five climate classes. The simulations were conducted under current (1980-2010) and future climate (2040-2070) using the Agricultural Production Systems sIMulator (APSIM) crop model, following the Agricultural Model Intercomparison and Improvement Project (AgMIP) protocol. Baseline simulations indicated that the total WF, averaged across all climate classes, was 1148 m³ t^-1 for irrigated and 1155 m³ t^-1 for rainfed wheat. WF was projected to decline in the future compared to baseline in both irrigated and rainfed systems mostly because of increases in yield of +9% in rainfed systems and 3.5% in irrigated systems, and decreases in water consumption by -5.4% and -10.1%, respectively. However, the share of gray water footprint (WF_gray) was projected to increase in the near future for both rainfed (+5.4%) and irrigated (+6.9%) systems. These findings suggest that cleaner and more sustainable production (i.e. obtaining grain yield under optimal water and nitrogen consumption) could be achieved in irrigated and rainfed wheat ago-ecosystems if optimal N fertilizer management is adopted. Additionally, rainfed cultivation can be further expanded in some areas which is expected to result in a substantial reduction in blue water (i.e. less irrigation), especially in sub-humid and semi-arid cool areas.