Improving efficiency to meet agricultural water demand

Water security is under threat worldwide and effective, long-term water management strategies are urgently needed. The IIASA Water Future and Solutions Initiative aims to establish a comprehensive water assessment framework which covers agricultural, industrial, and domestic sectors [1]. In a recent study for the initiative, researchers projected the future trajectories of the key drivers of agricultural water demand: crop and irrigation area, and irrigation efficiency.

As a basis for the modeling the authors used three Shared Socioeconomic Pathways, which describe possible paths human societies could follow over the next century, along with the Representative Concentration Pathways, which are greenhouse gas concentration trajectories. Together, these pathways are used as the foundation for much of the world’s global change modeling.

As food demand rises, crop area and irrigation area are both expected to expand, causing an increase in agricultural water demand. The IIASA Global Agro-ecological Zones system (GAEZ) provides projections of the spatial patterns that crop and irrigation areas will follow [2]. These projections take into account different climate scenarios; demographic and socioeconomic factors; production; consumption; and world food trade.

Although water demand is rising, economic and technological progress has the potential to improve water use efficiency. For this work researchers examined irrigation efficiency at a country level, considering all possible combinations of five crop types and three irrigation systems (gravity, sprinkler, and drip irrigation).

Efficiency increases when an existing irrigation system is replaced with an improved irrigation system of the same type, or another higher efficiency system, or when new areas are fitted with a high efficiency system. For this study, therefore, irrigation efficiency was defined as a function of replacement speed and irrigation area, and the researchers assumed that irrigation efficiency would increase with socioeconomic growth.

The GAEZ results indicate that the global area of irrigated land will be 10-15% larger by 2050. Under the sustainability scenario the area of land under irrigation would peak and decline after 2050, but the irrigated area is expected to keep expanding in the other two socioeconomic scenarios (Figure 1).

Irrigation efficiency is expected to steadily improve in all countries because of their economic growth. The biggest improvements were in China (0.6-1.5% efficiency gains per year), India (1.8-2.8% per year), Pakistan (2-3.4% per year), and the USA (0.6-1.7% per year). The results demonstrate that increased irrigation efficiency can cancel out the impact of irrigation area expansion on water demand (Figure 2).