Wetlands are cool places

Posted on December 18, 2015

A largely overlooked ecosystem service provided by wetlands is the cooling of surrounding landscapes. Most of the solar energy that strikes a wetland is used to evaporate water, a process that doesn’t increase the ambient temperature because energy is “hidden” as latent heat in the kinetic movement of water vapour molecules. The water vapour then moves to cooler parts of the atmosphere, where it condenses and releases its latent heat. In this way, wetlands, and to a lesser extent green cropland, help to equalise temperatures and moderate local climate extremes. Czech scientists set out to quantify this process by monitoring four different sites (a wet sedgy meadow, a pasture dominated by herbs, a winter barley field and a concrete surface) for a year. Analysis of meteorological data for the May-August period showed that in the wet meadow 90% of net radiation was converted to latent heat through evapotranspiration. Corresponding values for the pasture, field and concrete sites were lower (79, 75 and 26% respectively). The elevated value for the wetland site was due to its high moisture availability and the low surface resistance to evaporation. On average, each square metre of agricultural land near the wetland was cooled by the evaporation of around 500 litres of water per year. Based on the costs of alternative methods of air-conditioning, the value of this ecosystem service was estimated at $US 70 / m2.

Reference: Huryna, H. et al. 2014. The importance of wetlands in the energy balance of an agricultural landscape. Wetlands Ecology & Management 22, 363–381. http://www.researchgate.net/publication/260005675_The_importance_of_wetlands_in_the_energy_balance_of_an_agricultural_landscape