Climate constraints and maximum attainable yield of rain-fed wheat in the Upper Blue Nile Basin under climate change

Abstract

Rain-fed agriculture in Ethiopia is highly vulnerable to climate change. However, the future viability of wheat—a staple crop providing 14% of national caloric intake—remains poorly quantified under emerging climate scenarios. This study assesses the spatiotemporal evolution of production constraints and maximum attainable yields for rain-fed wheat in the Upper Blue Nile Basin (UBNB). The assessment covers the period from the 2020s to the 2080s. We used two Shared Socioeconomic Pathways (SSP3-7.0 and SSP5-8.5) to capture a range of future climate conditions. We applied the FAO Global Agro-Ecological Zones (GAEZ v4.0) framework with bias-corrected CMIP6 climate projections. We quantified climate-related constraints (CRC), agro-climatic constraints (AgCC), multi-cropping potential and attainable yield ceilings. CRC dominates production limits across all scenarios. The southern UBNB faces severe vulnerability by the 2080s under SSP5-8.5, with CRC values falling below 5,000. This implies potential yield losses exceeding 50%. Multi-cropping potential contracts substantially. Under SSP5-8.5, double-cropping area declines by 58.4% by the 2080s, while single cropping expands to 87.9% of the basin. This contraction is driven by increased rainfall variability and shortened growing periods. In contrast, the northern highlands retain resilience. Attainable yields there exceed 9,000 kg ha⁻ 1 under high-input systems. The area with yields below 3,000 kg ha⁻ 1 expands dramatically. It increases from 1.2 to 23.4% of the basin by the 2080s under SSP5-8.5. This represents a 19-fold expansion of marginal wheat-growing areas. Sustainable intensification of rain-fed wheat in the UBNB requires spatially explicit adaptation strategies. Vulnerable lowlands should diversify toward heat- and drought-tolerant crops such as sorghum and millet. Highland refugia should promote climate-resilient, fast-maturing wheat varieties combined with water conservation measures including terracing and conservation tillage. This integrated constraint-based assessment provides policymakers with an evidence-based blueprint. It helps prioritize agricultural investments and safeguard food security in a critically important region for Ethiopia's wheat production.