Abstract

Rainfed agriculture in Prince Edward Island is affected by climatic changes like warming, seasonal shifts, varying precipitations, and reduced water availabilities; all questioning its sustainability. Projecting future scenarios was critically important. Therefore spatiotemporal variations in Potential Evapotranspiration (PET), Crop Water Requirements (CWR), Effective Rainfall (ER), Supplemental Irrigation Requirements (SIR), and Sustainable Water Availabilities (SWA) were analyzed. Average annual PET was predicted to insignificantly increase (3–6%) under RCP4.5 during the next 30–60 years, with a 2–4 times increase in colder months (January–April) and a significant reduction during August–December. Accordingly, the historical CWR of potatoes (currently ~425 mm) would decrease by 5-9%, except for the least likely RCP8.5 scenario, which projects a ~10% increase in 2051–2080. That, and changes in ER, would cause SIR to decrease to 50–90 mm in normal years but 2–3 times higher during dry years and almost no SIR in wet years. Spatially, SIR increases by ~40 mm from east to west and is expected to be higher in 2021–2050 than in 2051–2080. Monthly SIR ranges in normal years would be July: 02–36 mm, August: 31–48 mm, and September 04–20 mm. The existing water policy allows pumping up to 20% of yearly recharges (annual-SWA) and up to 35% of summer’s stream baseflows (summer-SWA). Despite insignificant reductions in annual-SWA (3-17%) for the next 30-60 years, summer-SWA may be reduced by 38-50% due to temporal redistribution. Even in dry years, the reduced amounts would still be sufficient to fulfill SIR in the eastern forest-dominated Bear River watershed and SIR in normal years in the central zone; however, they would not be enough to enable the entire cultivated area of the western zone. In normal years, SIR would consume 5-6%, 27-37%, and 63-79% of annual-SWA in the eastern, central, and western zones, respectively. Sprinkler irrigation to meet SIR is challenging, and more economic evaluations and policy adaptations are needed for sustainable agricultural management.