First Advisor

Daniel M. Johnson

Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Geography






Portland (Or.) -- Climate



Physical Description

1 online resource (119 p.)


This study examines the spatial and temporal characteristics of the surface air temperature in Portland, Oregon. Spatial temperature patterns indicate that the dominant control factors on seasonal temperature distribution are local topography, elevation, and urban-rural differences in surface structure. A heat island exists in the Portland area; the intensity of the heat island rang€s from 4° to 10° F, and varies throughout the year. The strongest heat island is found in the July minimum temperature. Temperature distribution in Portland and the adjacent area is affected by winds and rainy conditions, but less influenced under overcast skies. The long-term temperature over the last century shows that Portland's mean annual temperature trends are 0.057° F/yr and 0.052° F/yr in the two warming periods 1900-1940 and 1961-1984, respectively, and these warming trends are largely due to warming in spring and early summer as well as in winter months except January. Comparisons between Portland and other local non-urban climatic stations show a general warming trend in Portland since the end of the last century, which is 0.028° F/yr in the mean annual temperature, and 0.017° F/yr in maximum temperature after the regional trends are removed. Monthly mean temperature in July and January demonstrate a warming by 0.023° F/yr and 0.015° F/yr at Portland, respectively. All these warming trends are due mainly to the impact of urbanization. It is found that the cooling effect on the northern Willamette Valley due to the presence of the Columbia Gorge is most noticeable in the daytime and in January.


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