Alberta's water balance reveals a critical relationship between measured precipitation and evapotranspiration losses that has significant implications for water availability across the province. The data shows that actual evapotranspiration consumes approximately 78% of Alberta's annual precipitation, leaving only 22% available for runoff and groundwater recharge.alberta+1

Provincial Water Balance Overview

Alberta receives an average of 467 mm of precipitation annually based on long-term data from 1950-2019. However, this precipitation faces substantial losses through evapotranspiration processes, with actual evapotranspiration averaging 364 mm per year—equivalent to 74% of the total precipitation received. This leaves approximately 103 mm per year available for surface runoff and groundwater recharge.alberta+1

Alberta's water balance: Annual precipitation compared with actual evapotranspiration and potential evaporation (provincial averages in mm/year)

The province's potential evaporation capacity significantly exceeds actual precipitation, with shallow lake evaporation rates averaging 677 mm annually—145% of the provincial precipitation average. This indicates that Alberta operates under moisture-limited conditions where water availability, rather than energy availability, constrains evapotranspiration rates.agriculture.alberta

Regional Variations and Climate Patterns

Precipitation varies dramatically across Alberta's diverse landscape. Southeastern Alberta receives less than 350 mm annually, while northwestern regions exceed 450 mm per year. The Rocky Mountain foothills can receive over 600 mm annually, creating the headwater sources for Alberta's major river systems.alberta+1

Recent monitoring shows concerning trends. Alberta's total annual precipitation has decreased by 4.77 mm per decade from 1950-2019, representing approximately a 10% reduction over the 70-year period. This decline is primarily driven by significant decreases in winter precipitation of 4.42 mm per decade, which reduces snowpack accumulation critical for spring and summer water supplies.alberta

Recent Precipitation Patterns and Drought Conditions

The period from 2020-2025 demonstrates the high variability in Alberta's precipitation patterns. Calgary's data illustrates this variability clearly:

Alberta precipitation trends 2020-2025: Calgary annual totals compared to provincial and local averages (mm/year)

2023 was particularly severe, with Calgary receiving only 274 mm of precipitation—well below both the local normal (419 mm) and provincial average. This contributed to drought conditions that affected 83% of Prairie agricultural lands by 2025.calgaryherald+2

However, 2024 and 2025 showed recovery, with Calgary receiving 547.8 mm in 2024 and tracking toward above-normal precipitation in 2025. Notably, Calgary received 222.7 mm between June 20 and July 22, 2025 alone—representing nearly half the annual average in just over one month.calgary.weatherstats+1

Evapotranspiration Patterns and Water Loss

Evapotranspiration rates vary regionally based on temperature, vegetation, and available moisture. The Morton Method calculations used by Alberta Environment indicate that shallow lake evaporation ranges from 575-850 mm annually across different regions of the province.agriculture.alberta+1

Actual evapotranspiration is consistently lower than potential rates due to moisture limitations. Provincial data shows that actual ET averages 364 mm annually, confirming that water availability rather than atmospheric demand limits evapotranspiration across most of Alberta.agriculture.alberta

For wetlands specifically, research indicates that 87% of Alberta's open water wetlands lose water through a combination of evaporation and surface/groundwater outflow, while 13% (mainly in prairie regions) lose water primarily through evaporation.wetland-report.abmi

Regional Water Balance Assessment

The provincial water balance varies significantly by region:

alberta_regional_water_balance.csv

Generated File

Southeast Alberta operates at a significant water deficit of approximately 90 mm annually, with precipitation (350 mm) insufficient to meet evapotranspiration demands. This region experiences the most severe and persistent drought conditions.waterportal

Central Alberta regions including Calgary and Edmonton areas maintain slight water surpluses of 99-108 mm annually, though these can quickly shift to deficit conditions during dry periods.currentresults+1

Northwestern Alberta and the Rocky Mountain foothills maintain the most reliable water surpluses of 120-150 mm annually, serving as the primary source regions for the province's major watersheds.alberta+1

Long-term Trends and Climate Implications

The data reveals several concerning long-term trends. Winter precipitation has declined significantly across all natural regions, with decreases ranging from 3.48 to 11.91 mm per decade. The Rocky Mountain and Parkland regions show statistically significant decreases in total annual precipitation, which is particularly concerning since the Rocky Mountains serve as headwater regions for Alberta's major river systems.alberta

22.2% of the province shows significant decreasing precipitation trends, while only 2.6% shows increasing trends. This pattern suggests that drought conditions may become more frequent and severe in many regions.alberta

Current research indicates that actual evapotranspiration represents about 74% of Alberta's total precipitation, but this proportion may increase with rising temperatures and changing vegetation patterns associated with climate change.agriculture.alberta+2

Water Management Implications

Alberta's water balance demonstrates that the province operates close to hydrological limits in many regions. With 143 billion cubic metres of nonsaline water available annually, but significant regional disparities, water management becomes increasingly critical during drought periods.waterportal+1

The data shows that potential evaporation exceeds precipitation by 210 mm annually (45%) on a provincial basis, indicating that Alberta's semi-arid climate creates substantial evaporative demand that consistently exceeds water supply in many areas.agriculture.alberta

This analysis reveals that Alberta's water security depends heavily on precipitation timing, regional distribution, and the critical balance between water inputs and evapotranspiration losses. The recent patterns of extreme variability—from severe drought in 2023 to excessive precipitation in parts of 2025—highlight the challenges of managing water resources in a province where evapotranspiration consumes the majority of available precipitation.

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Monday, September 8, 2025

Alberta's Water Balance: Precipitation vs. Evapotranspiration in Recent Years