The Relationship between Urban-Rural Water Vapor Pressure Differences and the Population Sizes of Settlements in Saku, Nagano, Japan

Abstract

This paper presents the relationship between urban-rural vapor pressure differences and population size for six settlements in Saku, Nagano Prefecture, Japan, from April 1998 to March 1999. Data were collected using a circuit-type, automobile-based travel method. The water vapor pressure in urban areas was less than that in rural areas almost year-round. The mean value of urban-rural vapor pressure differences was -1.4 hPa on fine days, which was twice larger than values for cloudy and fine nights. The regression line of mean urban-rural vapor pressure differences to settlement population size for cloudy nights was similar to that for fine nights. The mean value of the urban-rural water vapor pressure difference in summer was -1.7 hPa, a value nearly twice that in winter. Mean urban-rural water vapor pressure differences for fine days, fine nights, and cloudy nights related to the logarithm of the settlement population size. Regression line slopes for cloudy and fine nights showed no differences. However, the slope for fine days was twice that of fine and cloudy nights. Finally, the relationship between the annual maximum urban-rural water vapor pressure difference and the logarithm of population size was remarkably steady with R2 > 0.77.