Date of Award

1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geography and Anthropology

First Advisor

Keith G. Henderson

Abstract

Of the many weather conditions influenced by urban areas, precipitation is one of the most controversial and unsolved elements in characterizing the urban climate. The purpose of this dissertation was to identify anomalies in precipitation totals and frequencies due to urban effects and to evaluate whether certain meteorological conditions or seasons have more apparent effects. The five largest cities in the south-central United States were selected: Houston; Dallas; San Antonio; New Orleans; and Memphis. It was assumed that simple spatial analysis can detect urban effects on precipitation over and downwind of the city with a localized maximum. Trend surface analysis was used to evaluate a natural precipitation gradient over the study area. Residual maps were used to detect whether a maximum in the simple spatial analysis is present after eliminating the regional effect. To evaluate the magnitude of precipitation enhancements, differences between the city (or downwind) and the upwind control areas were calculated. This research showed that Houston revealed the most distinct precipitation enhancement due to urban effects in summer with a 15.5% increase during the 1961-1990 period when examining precipitation totals. Dallas had a 5% increase of precipitation totals in spring and a 7% increase in summer. Precipitation frequencies showed more apparent enhancements than precipitation totals with a higher magnitude of enhancements. Houston showed distinct urban effects on extreme rainfall events producing 1-inch or higher rainfall in summer (23%) while the other four cities revealed apparent increases on the light precipitation-days in the colder seasons (20-60%). Rainfall frequency relations of extreme 24-hour rainfall did not show apparent precipitation enhancements due to urban effects because the magnitude of storms was too large. Airmass type storms showed more apparent precipitation enhancements due to urban effects than the other types and the three Texas cities showed more distinct effects than New Orleans and Memphis. The magnitude of precipitation enhancements might be closely related to the size of the city.

ISBN

9780591766585

Pages

149

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