How will the “water footprint” of Xinjiang cotton change under climate change?

According to the Sixth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), human activities have significantly intensified global warming, leading to more frequent, intense, and prolonged extreme weather events, which pose a major threat to agricultural production. Xinjiang, as one of the driest regions in China, has an average annual precipitation of less than 270 mm and an evaporation rate exceeding 1000 mm, yet it produces 25% of the world’s cotton, contributing 91.0% of the national cotton production and 35% of farmers’ income. Cotton cultivation in this region heavily relies on irrigation, and climate change is likely to exacerbate aridity in Xinjiang. In this context, how will the water use structure of cotton production in Xinjiang change? How can the water-saving potential of different irrigation technologies be assessed?

A study conducted by Dr. La Zhuo and colleagues from the Institute of Soil and Water Conservation at Northwest A&F University, published in Frontiers of Agricultural Science and Engineering, provides the answers to these questions (DOI: 10.15302/J-FASE-2024585).

This study focuses on the “water footprint” of cotton production in Xinjiang—specifically, the amount of freshwater consumed to produce one ton of cotton, divided into “blue water footprint” (relying on groundwater or surface water) and “green water footprint” (relying on precipitation). Unlike previous studies that primarily focused on food crops or single irrigation methods, this research innovatively simulates three mainstream irrigation technologies—furrow irrigation, micro-irrigation (drip irrigation), and sprinkler irrigation—at a fine grid scale of 5 arcminutes (approximately 9 km × 9 km), analyzing the spatiotemporal changes in cotton’s water footprint under two climate change scenarios for the 2050s and 2090s (SSP2-4.5 moderate emissions and SSP5-8.5 high emissions).

The study first reveals the future climate trends in Xinjiang: compared to the baseline period of 2000–2018 (with a reference crop evapotranspiration ET₀ of 1080 mm), evaporation demand in Xinjiang significantly increases under both scenarios. In the SSP5-8.5 scenario of the 2090s, ET₀ increases by 14.3% annually, with the largest increases occurring in January and November, while the summer increase is only about 8%. Annual precipitation decreases by 15.1% overall, with only July to September slightly exceeding the baseline period. This indicates that Xinjiang will become increasingly arid in the future, and the pressure on agricultural water use may further intensify.

However, a key finding is that the total water footprint of cotton shows a downward trend. The total water footprint for cotton in Xinjiang during the baseline period is 4264 m³·t^-1, of which blue water accounts for 83% (3560 m³·t^-1). By the 2090s, the total water footprint is expected to decrease by 19.3% under the SSP2-4.5 scenario, and by 35.7% under the SSP5-8.5 high emissions scenario. This is mainly attributed to the effects of increased atmospheric CO₂ concentration—under the SSP5-8.5 scenario, CO₂ concentration is significantly higher than under SSP2-4.5, and higher CO₂ levels can enhance the photosynthetic efficiency of cotton while reducing transpiration water loss.

It is noteworthy that the structure of the water footprint is changing: the proportion of blue water in the total water footprint is expected to increase slightly. Although the total amount of blue water is also decreasing—by 16.5% and 33.4% under the SSP2-4.5 and SSP5-8.5 scenarios, respectively—the contribution of green water declines due to reduced precipitation, leading to an increased proportion of blue water. The decline in green water footprint is more pronounced, decreasing by 33.7% and 47.2% under the SSP2-4.5 and SSP5-8.5 scenarios, with only a few areas experiencing slight increases due to minor precipitation increases.

There are significant differences in the water-saving potential of the three irrigation technologies: sprinkler irrigation shows a reduction in water footprint of 24.8% and 40.1% under the SSP2-4.5 and SSP5-8.5 scenarios, respectively, demonstrating the most notable water-saving effects; furrow and micro-irrigation show relatively smaller reductions. This indicates that sprinkler irrigation technology has higher water-saving potential for future cotton cultivation in Xinjiang.

The cotton industry in Xinjiang is crucial for the regional economy, but water resource scarcity is a long-term challenge. This study not only quantifies the dynamic patterns of cotton water consumption under climate change but also clarifies the adaptive differences among various irrigation technologies, providing scientific support for optimizing water resource allocation and promoting water-saving measures. In the future, combined with variety improvement and agronomic upgrades, Xinjiang cotton is expected to achieve more efficient water resource utilization in an increasingly arid environment.