Climate change impacts assessments and mitigation strategies for sustainable water and agricultural management in the Prince Edward Island

Prince Edward Island (PEI) has abundant water resources and rainfed agriculture and is the largest producer of potatoes in Canada. However, the sustainability of these natural resources is at stake due to environmental changes for which science-based information was lacking; the project filled the research and knowledge gaps. The changes and impacts on temperature, precipitation, streamflows, groundwater recharge, potential evapotranspiration (PET), potatoes' water requirements (CWR), supplemental irrigation requirements (SIR), and sustainable water availability (SWA) were analyzed. The analyses were spatially segregated into eastern, central, and western PEI; and temporally into climate normals (continuous 30-year period) for the longest 150 years (1931–2080). Daily observed climatic data and validated modeled data of Pacific Climate Impacts Consortium (PCIC) etcetera were used. Rational methods, like Probability of Exceedance (PoE), Intensity-Duration-Frequency (IDF), and World Meteorological Organization’s (WMO) guidelines for computation of climatic-normal averages, were used etcetera. Hydrological modeling of the western (Mill and Wilmot rivers), central (West and Winter rivers), and eastern Bear river watersheds was performed using the Soil and Water Assessment Tool (SWAT). Statistical significance of the temporal changes in the parameters among the climatic normals and scenarios were determined using Analysis of Variance (ANOVA). The Island underwent statistically significant warming as the historical (1961–1990) average annual temperatures increased by +1.14°C in the east to +0.75°C in the west during 1991–2020. The trend will likely continue with a further rise of 3–5°C in the next 30–60 years. Historical warming was uniformly distributed throughout the year; however, prospectively, it would be more concentrated during January–July, which would moderate cold intensity. The warming would cause annual PET of 1.95–2 mm/day to insignificantly increase 3–6% during the next 30–60 years, with a 2–4 times increase in colder months (January–April) and reductions during August–December due to coastal climate. Therefore, the historical CWR of potatoes ~425 mm would decrease by 5–9%. That, and changes in effective rainfall, would cause potatoes' SIR (July–September) in normal years to fall up to 50–90 mm, which, however, be 2–3 times more during dry years, with almost no SIR in wet years. Annual precipitations increased by 6% in the east and decreased by 5% and 8% in the central and western parts, respectively, from 1961–1991 to 1991–2020, along with a significant snowfall reduction in the west (-20%). While rainfall intensities in the central and western parts significantly increased by 5–32% in recent years (2004–2017) than 1961–1990. Prospective precipitations (2021–2080) would not change significantly and would range ~1150–1200 mm/year. Nevertheless, in western PEI, precipitations would be 17% higher than that during 1991–2020. The interannual precipitation uncertainty between wet and dry years would reduce to ~300 mm/year from the current ~400 mm/year but will remain a water management challenge. Streamflows among the modeled watersheds ranged from 565–811 mm/year during 1991–2020. Streamflows are highly contributed by groundwater, up to ~70%. Therefore, pumping in the populous Winter river (191 mm/year) and Wilmot river (16 mm/year) watersheds has almost equally reduced streamflows to 565 mm/year and 652 mm/year respectively, against a weighted average of ~688 mm/year for all the five watersheds. Groundwater recharges in PEI are relatively higher (~35% of precipitation), the highest in the eastern (~600 mm/year), lesser in the western (~330 mm/year), and moderate in the central watersheds (~450 mm/year). Temporally, March–May produce the highest streamflows, whereas recharge is maximum during April–July, which underscores strong surfacewater-groundwater interactions. Climate change and an increase in pumping would further reduce streamflows and recharges, and significantly change its intra-annual distribution. More attenuation is likely with higher quantities in late winter and early spring and somewhat lesser during summers. Groundwater fulfills 100% water needs of the Island; wherein existing water policy allows pumping up to 20% of yearly recharges (annual-SWA) but not exceeding 35% of summers' stream-baseflows. The policy ensures sustainability if implemented at the watershed scale. Despite insignificant reductions in the annual-SWA (3–17%) in the next 30–60 years, summer-SWA would significantly reduce by 38–50% due to its intraannual redistribution. Groundwater pumping for irrigation to satisfy normal years' SIRs would consume: 5–6%, 27–37%, and 63–79% of annual-SWA in the eastern, central, and western watersheds, respectively but it would surpass summer-SWA at some places. Extension of sprinkler irrigation to meet SIR is challenging on economic and technical grounds, though groundwater is mostly available. Extension of streamflow and groundwater monitoring network, integrated hydrological modeling, watershed scaled \ninvestigations, and continuous policy review and adaptations are required for sustainable water and agricultural management in PEI.

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