The cooling effect of paddy fields on summertime air temperature in residential Tokyo, Japan

A study was undertaken to measure and estimate summertime air temperatures in suburban Tokyo, Japan. Air temperatures were measured at a standard height of 1.5 m along streets in residential areas. Transects were run on two types of streets: those that opened onto a paddy field, and those that did not. Streets opening onto a paddy field, and aligned so the wind moved directly from the paddy field down the street, experienced lower air temperatures to a distance of approximately 150 m into the neighborhood. Streets that did not open onto a paddy field, and ran normal to the wind direction, experienced no measured temperature differences. These measurements were compared with the air temperature distribution predicted by a simple internal boundary layer (IBL) model based on advective effects resulting from air movement over a change in underlying surface. The IBL model was able to accurately estimate the air temperatures in all situations, with regression coefficients for areas adjacent to large paddy fields of r2=0.93, and for areas adjacent to small paddy fields of r2=0.83. Standard error of estimate (S.E.E.) values were low at S.E.E.=0.21–0.24°C for large paddy fields, and S.E.E.=0.23°C for small paddies. Further work will be needed to test the relationship in other seasons, other climatic situations, and other urban settings. However, these results suggest that there is potential for use of the IBL model in predicting the effects of planning and design decisions on air temperature distribution in urban areas.