Andrea CITRINI, Matteo SANGIORGIO, Lorenzo ROSA (2025)
The study quantifies how unsustainable irrigation water consumption (UIWC)—the share of irrigation use exceeding locally renewable blue-water supplies—may evolve globally through 2100 under two CMIP6 pathways (SSP1-2.6 and SSP5-8.5). Decade-by-decade projections at ~50 km resolution are aggregated across 329 irrigation regions, showing a general increase in irrigation pressure, particularly in South Asia and the Mediterranean, with higher magnitudes and uncertainties under high emissions.
∇ – Methods
UIWC is defined monthly at 30-arcminute resolution (~50 km ate the equator) as the exceedance of total water consumption over renewable blue-water availability after reserving environmental flows.
Grid results are aggregated into 329 irrigation regions mapped from the 2015 irrigated-area dataset and refined with hydrologic basin boundaries.
Future trajectories are generated with a delta-change approach: for each of 5 CMIP6 GCMs × 2 hydrologic models (H08, WaterGAP2-2e) under SSP1-2.6 and SSP5-8.5, monthly anomalies are added to baseline (2001–2010) fields to produce decadal UIWC series to 2100; irrigation consumption varies with climate deltas, while other sectoral uses are held at baseline.
∇ – Main Results
Baseline UIWC is ~458 km³/yr. By 2100 it edges up under SSP1-2.6 (458–546 km³/yr) and climbs further under SSP5-8.5 (456–638 km³/yr), with the high-emissions ensemble showing the widest spread. Hotspots include the Ganges, Sabarmati, Indus, Lower Tigris–Euphrates, and Nile Delta; per-area pressure surpasses 50 mm/yr in South Asia and the Nile Delta. Regions such as the Ganges, Indus, and US High Plains strengthen upward trends—strongest under SSP5-8.5—while relative surges reach +117% (Lower Yangtze) and +80% (Godavari) by late century.
∇ – Conclusion
UIWC rises globally, with bigger and more uncertain increases under high emissions. The picture is heterogeneous: absolute volumes grow in major Asian and American breadbaskets, and per-area pressure concentrates in South Asia and the Mediterranean. The decadal, multi-model framing points toward targeted adaptation (efficiency, conjunctive surface-groundwater use, reuse, diversified supplies) and ensemble-based planning to manage risk across irrigation regions.
∇ – Resources
Citrini, A., Sangiorgio, M., & Rosa, L. (2025). Global multi-model trends of unsustainable irrigation under climate change scenarios. Environmental Research Letters, 20, 104011.
∇ - The Water Table 
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