URBAN EFFECTS ON ' IATE 



needed to model the urban-weather 

 system. However, this will require 

 three-dimensional, mesoscale numeri- 

 cal models (not currently available) 

 and computers (soon to be available) 

 with the capacity to handle them. 



Practical Implications of 

 Urban-Induced Weather Change 



Regional Planning — The factors 

 that produce undesirable weather 

 changes clearly need to be assessed, 

 and hopefully minimized, in planning 

 and building new urban areas and 

 redeveloping old ones. For instance, 

 the ability of large urban-industrial 

 complexes to produce thunderstorms, 

 heavy rains, and hailstorms in and 

 downwind of the complexes has par- 

 ticular importance in hydrologic de- 

 sign for urban storm drainage and 

 in agricultural planning. 



Pollution — Knowledge of the 

 urban-induced wind and rainfall 

 changes apt to occur with various 

 weather conditions is also required 

 for determining whether these 

 changes will materially affect pollu- 

 tion levels. The generally expected 

 decrease in winds and poorer ventila- 

 tion are certainly undesirable, but ur- 

 ban-increased rainfall is beneficial in 

 this connection. Such knowledge 

 would also help in improving local 

 forecasting, thus enabling man to do 

 better planning of his outdoor ac- 

 tivities. 



Weather Modification — Study of 

 the exact causes of various urban- 

 produced weather changes can also 

 be expected to help man in his efforts 

 to modify weather intentionally. In 

 particular, the study of the conditions 

 whereby urban complexes affect pre- 

 cipitation processes could generate 

 needed information about the weather 

 conditions appropriate for seeding, 

 the types and concentrations of ef- 

 fective seeding materials, and poten- 

 tial rainfall changes expected beyond 

 the areas of known urban-related 

 increases. Continuing disagreements 

 over evaluation of man-made changes 



and the types of physical techniques 

 and chemical agents of modification 

 reveal the need for proper study of 

 these aspects during urban field in- 

 vestigations and analyses. 



The economic aspects of this prob- 

 lem are hard to assess but are surely 

 significant. Reduced visibility, more 

 fog, and added snowfall directly and 

 indirectly restrict human activity. 

 The damages to health, property, and 

 crops resulting from added contami- 

 nants, less sunshine, higher tempera- 

 tures, and less ventilation can be 

 serious. National economic losses at- 

 tributable to urban-induced weather 

 changes are inestimable. 



Requirements for Scientific 

 Activity 



The interactions of urban-produced 

 weather changes with such matters as 

 agriculture and hydrology, and with 

 ecology, are only partly understood, 

 since the inadvertent aberrations are 

 frequently within the limits of natural 

 variability of weather. For instance, 

 the increase in crop yields resulting 

 from urban-increased rainfall could 

 be easily and accurately assessed, 

 whereas the effect on crop yields of 

 increased deposition of urban con- 

 taminants into soils cannot currently 

 be assessed without special studies. 

 Our knowledge and understanding of 

 the interactions of weather changes 

 with man and society are almost 

 totally lacking. The legal and social 

 ramifications are barely understood, 

 although the threats of damage to 

 property, crops, health, and safety 

 from such changes as increased con- 

 taminants, more fog, less sunshine, 

 and higher temperatures are now 

 clear. Certainly, the responses to 

 inadvertent weather changes provide 

 an opportunity to study and assess 

 potential human reaction to planned 

 weather modification. The only 

 means of fully assessing the urban- 

 modification effect of each weather 

 element in a given locale, however, 

 is to measure all elements in three 

 dimensions. 



Adequate measurement and under- 

 standing of the interactions between 

 urban factors and atmospheric con- 

 ditions that produce, for example, a 

 10 percent rainfall increase in one 

 urban complex should lead to rea- 

 sonably accurate predictions of the 

 precipitation changes in most com- 

 parable cities where routine measure- 

 ments of the urban factors exist or 

 could easily be performed. Indeed, 

 major projects to study the urban 

 conditions that change weather ele- 

 ments are sorely needed at several 

 cities, each of which should be repre- 

 sentative of basically different North 

 American climates and urban com- 

 plexes so that the results could be 

 extrapolated to other cities. A min- 

 imum national effort would consist 

 of a thorough field project in one 

 city that is representative in size and 

 climate of several others. 



Such a project would be more 

 meaningful if relevant interdiscipli- 

 nary projects involving the physical 

 and social sciences were conducted 

 simultaneously. 



To achieve meaningful, three- 

 dimensional measurements of weather 

 and urban conditions will require 

 marshalling of instrumentation and 

 scientific effort to create dense net- 

 works of surface instruments heavily 

 supplemented by vertical measure- 

 ments obtained by aircraft, balloons, 

 and remote probing devices. The 

 scientific skills, personnel, and fa- 

 cilities necessary to explain and pre- 

 dict most facets of this topic exist, 

 but they have yet to be focused on 

 it. Answers exist in relation to sev- 

 eral basic questions concerning the 

 urban-weather topic, but more con- 

 centrated study is needed in the next 

 five years. No serious effort has 

 been made to describe the interac- 

 tion between urban-induced weather 

 changes and man, and this, too, is 

 urgently needed. If performed, these 

 studies should provide information 

 adequate to modify some of the un- 

 desirable weather changes within ten 

 years. 



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