If typical desert communities show ranges in the evapo-transpiration deficit which exceed the estimated water stress imposed by the receiving antenna, then locating a receiving antenna in such a community is not likely to disrupt it excessively. The result may be a slight change in the composition of the local community in the direction of similar communities in slightly drier climes. Such a shift would probably be observable only to an expert, if at all. Table 28 shows that this is the case. The water budget components for representative vegetation in the western United States are tabulated. The ranges of these components for communities in the northeastern (colder) and southwestern (dryer and hotter) regions are shown. The evapo-transpiration deficit for the year is shown in the second column from the right. Deficits characteristic of these desert communities vary from 142 mm of water for a sagebrush community in Utah to 1328 mm of water for an alkali sink community in California. The range of deficits observed for each type of community is large, varying from about 140 for the sagebrush to about 350 mm for one type of creosote bush community found in parts of California and Nevada. Since these total deficits and ranges of deficits are large compared to the estimated 10 to 65 mm load imposed by the receiving antenna mean heat losses, we may conclude that the effects on such communities will be small. Thev will resemble the natural effects due to local variations in topography, and be almost undiscernible. e. Environmental Effects of Local Heat Losses The primary environmental effects of heat losses are modifications to local climate caused by changes in the sensible or latent heat transferred to the atmosphere which, in turn, cause the air to rise, and/or, change its moisture regime. Such heat may also cause modifications in rainfall patterns in the local environment. Some effects attributed to cities may also be due to the emission of condensation nuclei and to changes in the surface roughness, which also affect turbulent motions of the air. These have been reviewed by Landsberg (52). Although many studies have indicated generally drier and hotter air near cities, other effects such as modifications of rainfall patterns are more difficult to discern reliably, and have not been extensively studied. (See, for example, Huff and Chagnon (53). The possibly deleterious effects of receiving antenna heat losses can be indicated by comparing them to the heat losses characteristic of cities in which urban heat island effects have been observed or suspected. The latter may be determined by examining the total energy consumption (in terms of fuel use) of selected cities or large, densely populated megalapoli as a function of area. Table 29 lists the relevant factors for several regions of the globe, together with the mean annual net radiation at those points. This table shows that many regions reach or exceed the estimated maximum receiving antenna heat loss of 50 W/m2, including Manhattan, (with 630 W/m2) and Moscow (with 127 W/m2). We may conclude from this table that the receiving antenna by itself will have no heat island effect, although sites of energy use may.
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