Climate change impacts on soybean net irrigation requirements in Maryland: Regional contrasts between Peninsula and Mainland (2006–2100)

Climate change challenges soybean water management in humid temperate regions like Maryland, USA, spanning rainfed and irrigated systems in the vulnerable Coastal Plain Peninsula and inland Mainland. While global projections forecast 20–40% irrigation demand increases by 2100, region-specific, century-scale soybean net irrigation requirements (NIR) remain scarce, particularly disentangling coastal-upland contrasts and multi-decadal acceleration under RCP scenarios. This NA-CORDEX (EC-EARTH/RCA4) study (2006–2100, RCP2.6/4.5/8.5) models daily NIR via FAO-56 water balance, aggregated into 20-year periods with monthly and seasonal NIR-rainfall ratios evaluation, deficit days, regional gaps, decadal trends, and climate correlations. Baseline NIR (May-Sep) averaged 873–950 mm/season (Peninsula) versus 810–916 mm (Mainland); under RCP8.5, Peninsula NIR rose modestly to 945 mm (2040–2060) and 964 mm (2080–2100; +0–2% vs baseline), with Peninsula exceeding Mainland by a stable 50–70 mm across scenarios. July-August NIR exceeding 3–4 times the rainfall, deficit days increase 10–20%, and ET 0 trends drove changes (r = 0.92), explaining 83% NIR variance over weak precipitation changes. Time-resolved projections highlight potential Peninsula aquifer stress by mid-century under moderate emissions, suggesting implications to reform permitting, infrastructure sizing for July-August peaks, and prioritize ET 0 -based scheduling for adaptation. • Quantifies century-scale soybean NIR across Maryland regions using NA-CORDEX CMIP5 daily projections. • Peninsula NIR consistently 50–70 mm/season higher than the Mainland, revealing coastal aquifer vulnerability under all RCP scenarios. • RCP8.5 projects Peninsula NIR reaching 945–964 mm by 2040–2060/2080–2100. • ET 0 trends (r = 0.92) explain 83% NIR variance highlighting mechanistic ET-driven water stress. • Deficit days rise 10–20% late-century, signaling transition from supplemental to essential irrigation in humid temperate agriculture.