Reducing Evaporation in Temperate Climates

Temperate reservoirs lose far less water than arid ones — commonly 600–1,200 mm a year, concentrated in summer. That lower loss makes the central question economic rather than technical: does the saving justify the cost? For many temperate sites the answer favours either cheap measures or methods that deliver a second benefit. Warming is shifting the balance, with projections of rising evaporation and falling availability for small reservoirs (Althoff et al., 2020).

What works best here

Multi-benefit and low-cost first. Floating solar is attractive because the power revenue, not the water saving alone, carries the investment. Storage management — consolidating water to reduce exposed surface area — is low-cost and effective. High-coverage modular floating covers make sense where the stored water is genuinely valuable (treated drinking water, industrial process water) or where algae control adds value. Windbreaks are a modest, cheap aid on exposed sites.

What to watch

Run the numbers before committing: with lower annual loss, only methods whose cost clears the saving at your water value will pay back — use the cost-benefit page and a Penman-Monteith loss estimate to check.