Resource information
Energy fluxes, including net radiation, latent heat flux and sensible heat flux were determined on clear days during the vegetative period in four types of land cover: wet meadow, pasture, arable field, and an artificial concrete surface. The average net radiation ranged between 123� W� m⁻² at the concrete surface and 164� W� m⁻² at the wet meadow. The mean maximum daytime latent heat ranged between 500 and 600� W� m⁻², which corresponds to an evapotranspiration rate of about 0.2� g� m⁻²� s⁻¹ under the prevailing conditions of the wet meadow. The results demonstrated that the wet meadow dissipated about 30� % more energy through evapotranspiration than the field or the pasture, and up to 70� % more energy than the concrete surface. The evaporative fraction indicated that more than 100� % of the energy released by the wet meadow was dissipated through evapotranspiration; this was attributed to local heat advection. Wetland evapotranspiration thus contributes significantly to the cooling of agricultural landscapes; the energy released can reach several 100� MW� km⁻². Wetland evapotranspiration has a double ‘air conditioning’ effect through which it equalises temperature differences: (1) surplus solar energy is bound into water vapour as latent heat; (2) The vapour moves towards cooler portions of the atmosphere where the energy is released. The air-conditioning effect of wetlands plays an important role in mitigating local climate extremes; this ecosystem service tends to be disregarded in relation to other better-known wetland functions such as nutrient retention and provision of high biodiversity.
