Effects of “latent waste heat” on the atmospheric moisture field: Fid-Bau Portal

Effects of “latent waste heat” on the atmospheric moisture field

Höschele, K.

AbstractOur knowledge of water vapor or latent heat fluxes and the distribution of humidity in the urban atmosphere is much less complete than that of (sensible) heat transport and the characteristics of the urban temperature field, popularly known as a “heat island”. The reasons for this unequal treatment of interdependent processes may be the different means of measurement for the water vapor content of the air, the influence of temperature on saturation values, and instrumental problems.The mass transport of water vapor is accompanied by a transfer of latent heat, a considerable part of the energy budget at the surface of the earth. Modifications are possible by choosing one of several categories of land use. •— by changing the energy source, the radiation balance, via reflectivity;•— by changing the conditions for heat transfer;•— by changing the availability of water for vaporization;•— by artificial (anthropogenic) heat sources.Of these procedures, all of similar relevance to the urban atmosphere, the last is discussed more thoroughly, with examples of typical investigations and an estimation of water vapor fluxes over urban settlements. As a result the reduced surface evaporation from built up areas is compensated in many cases by artificial sources of water vapor, in combination with waste heat release.