Evaporation at High Altitude & in Cold Climates
Thin air, intense UV and low humidity keep evaporation high at altitude even when it's cold. What that means for choosing a suppression method.
Altitude defies intuition: it can be cold yet still lose water quickly. Two effects keep evaporation high. First, low atmospheric pressure lets molecules escape the surface more easily — roughly +3% per 1,000 m of elevation, a correction built into FAO-56. Second, high-altitude air is typically dry and intensely sunlit (strong UV), keeping the vapour-pressure deficit large. The result is significant loss for the temperature.
What works best here
Durable high-coverage physical options lead: modular floating covers and geomembrane covers seal the surface and block the intense UV, and load-bearing or insulating designs help where snow load and ice are concerns. Floating solar benefits from strong high-altitude irradiance, with cold-climate engineering. Storage management reduces exposed surface area in the harshest season.
What to watch
Materials take a beating: intense UV, freeze-thaw cycles and snow load all shorten the life of thin or unrated products, so favour UV-stabilised, temperature-rated covers with strong warranties. Account for the pressure effect when estimating loss with Penman-Monteith, and check that the saving justifies the (often higher) cost of cold-rated equipment on the cost-benefit page.