To understand climate change impacts on Prince Edward Island (PEI), Canada, historical daily precipitation and temperature of the island was investigated between the periods: 1931–60 (1940s), 1961–90 (1970s), and 1991–2020 (2000s) in its eastern, central, and western parts. Observed climatic data were utilized, augmented by some validated modeled data of Pacific Climate Impact Consortium (PCIC) for missing years. Statistically significant warming of the island was found ranging from 1.14°C in the east to 0.75°C in the west from the 1970s to 2000s. The warming trend during the period was distributed throughout the year including winters. In the east, mean monthly temperature significantly increased in all the months except for January, March, and June. Significant increase in temperature was found solely during August (+0.80°C) in central, and for August (+0.64°C), September (+0.99°C), and October (+0.73°C) in western parts. Proportionate increase in annual minimum temperature was greater than the maximum, particularly in eastern (+1.57°C) and central (+0.75°C) parts and thus indicated moderated cold there. Over the same 30‐year period, annual precipitation increased 6 percent in the east but decreased 5 and 8 percent in the central and the western PEI, respectively. The changes in precipitation were not statistically significant, except snowfall reduction (−20%) in the west, which was a statistically significant change. Interannual precipitation variations during wet and dry years having 20 and 80 percent probabilities of exceedance, respectively, ranged 350–470 mm/year during 1991–2020. Rainfall intensities, measured by hourly data, increased from 1.15 to 2.24 mm/hr, on average in central and western parts, respectively, in 2004–17 compared to 1970s. Impacts of the rising temperatures, decreasing precipitation, and uneven and intense rainfalls patterns on water resources and rainfed agriculture need further investigations. Climate change adaptations be included in existing water policies to mitigate the impacts.

Prince Edward Island (PEI), Canada, entirely depends on groundwater for freshwater supplies, which also highly feeds streamflows. In a few watersheds, pumping has had disturbed steady‐state conditions and reduced streamflows. Spatiotemporal hydrological analysis of streamflows and recharges was performed in its scattered watersheds. Mill, Wilmot, West, Winter, and Bear River watersheds were modeled by the Soil and Water Assessment Tool (SWAT) under the shallow water‐table conditions, besides other analyses. The model was calibrated against 120 observed mean monthly flows (1995–2004) and validated for another 120 observations (2005–2014), with Nash–Sutcliffe efficiency (NSE) as the major performance assessment parameter. The model accurately simulated mean monthly flows for all watersheds during 1995–2014, except Winter River watershed (NSE = 0.02–0.33), wherein it overpredicted by 31%–52% and 5–12% in Wilmot River (NSE = 0.28–0.64). Streamflows were found highly dependent on groundwater; therefore, pumpings of 6.92 and 0.73 million cubic meters (MCM)/year caused the overpredictions in Winter and Wilmot watersheds, as SWAT cannot account pumping. In the rest three watersheds with negligible pumping, 4%–18% underprediction was due to multisite calibration. Spatially, streamflows randomly varied between 555 and 811 mm/year across watersheds, whereas thick and highly permeable sandstone produced higher recharges, the maximum ~600 mm/year in the eastern forest‐dominated Bear River watershed, lesser in western ~330 mm/year, and moderate ~450 mm/year in central watersheds. Temporally, March–May are the months of highest streamflows, whereas recharge is maximum during April–July. The succession trend justified strong surface water–groundwater interactions. Existing Water Extraction Permitting Policy ensures sustainability at the island scale. It sets pumping limit at 20% of recharge, that is, 0.48 km3/year altogether, against the present pumping of ~0.04 km3/year, yet a few watersheds are somewhat water‐stressed due to population and pumping concentration. Expansion of streamflow and groundwater monitoring, promoting population and pumping in rural areas, and more scrutiny for further pumping permits in water‐stressed watersheds are quite important for sustainable water management in PEI.

Climate change is impacting different parts of Canada in a diverse manner. Impacts on temperature, precipitation, and stream flows have been reviewed and discussed region and province-wise. The average warming in Canada was 1.6 °C during the 20th century, which is 0.6 °C above the global average. Spatially, southern and western parts got warmer than others, and temporally winters got warmer than summers. Explicit implications include loss of Arctic ice @ 12.8% per decade, retreat of British Columbian glaciers @ 40–70 giga-tons/year, and sea level rise of 32 cm/20th century on the east coast, etc. The average precipitation increased since 1950s from under 500 to around 600 mm/year, with up to a 10% reduction in Prairies and up to a 35% increase in northern and southern parts. Precipitation patterns exhibited short-intense trends, due to which urban drainage and other hydraulic structures may require re-designing. Streamflow patterns exhibited stability overall with a temporal re-distribution and intense peaks. However, surface water withdrawals were well under sustainable limits. For agriculture, the rainfed and semi-arid regions may require supplemental irrigation during summers. Availability of water is mostly not a limitation, but the raised energy demands thereof are. Supplemental irrigation by water and energy-efficient systems, adaptation, and regulation can ensure sustainability under the changing climate.

Climate change impacts on temperatures, precipitations, streamflows, and recharges were studied across eastern, central, and western Prince Edward Island (PEI) between climate normals in 1991–2020, 2021–2050, and 2051–2080 using observed and projected data, and SWAT modeling. Average annual temperature can significantly rise from the existing 5.90–6.86 °C to 8.26–11.09 °C in different parts during the next 30–60 years under different RCP scenarios. Average annual precipitations would not significantly change except in western PEI where a 17% likely increase would offset further warming impact; therefore, current streamflows (~650 mm/year) and recharges (~320 mm/year) would not be much affected there. However, warming and increased pumping together in its Wilmot River watershed could reduce streamflows up to 9%, and 13% during 2021–2050, and 2051–2080, respectively. In the eastern forest-dominated Bear River watershed, no significant reductions in current streamflows (~692 mm/year) or recharges (~597 mm/year) are expected. Nevertheless, near constant precipitation and warming could cumulatively reduce streamflows/recharges up to 8% there, as pumping will be negligible. In the central zone, precipitation could insignificantly increase up to 5%, but current streamflows (~737 mm/year) and recharges (~446 mm/year) would not be significantly affected, except for RCP8.5 under which streamflows could reduce by ~16% during 2051–2080. Overall, more attenuated streamflows and recharges are likely with higher quantities in late winter and early spring, and somewhat lesser ones in summer, which could reduce water supplies during the growing season. Besides, precipitation uncertainty of ~300 mm/year between dry and wet years continues to be a major water management challenge. Adapting policies and regulations to the changing environment would ensure sustainable water management in PEI.

Groundwater availability, utilization, sustainability, and climate change implications were assessed at regional and provincial scales of Canada. It remains an unexplored resource, estimated to be renewing between 380 and 625 km3/year. However, the provinces have initiated developing their quantitative and qualitative databases for their accurate inventory. Sustainable groundwater availability at the national scale was estimated as 19,832 m3/person/year (750 km3/year), with high regional variations ranging from 3949 in the densely populated Prince Edward Island (PEI) province to 87,899 in the thinly populated Newfoundland and Labrador (NFL). It fulfills 82%, 43%, and 14% of water requirements of the rural population, irrigation, and industry, respectively. It is the potable water source for more than 9 million people countrywide (24% of the population), and provinces of Quebec, and Ontario (1.3 million people), and PEI (0.15 million people) particularly depend on it. It is mostly a free or nominally charged commodity, but its utilization was found to be well under sustainable limits (40% of recharge) at the provincial scales, i.e., under 4% for all the provinces except New Brunswick (NB), which also had just 8% extraction of sustainable availability. Nevertheless, localized issues of quantitative depletion and qualitative degradation were found at scattered places, particularly in Ontario and Quebec. Climate change impacts of warming and changing precipitations on groundwater underscored its stability with some temporal shifts in recharge patterns. In general, increased recharge in late winters and springs was observed due to reduced frost and more infiltration, and was somewhat decreasing in summers due to more intense rainfall events.