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 heig ht of 1.5 m along streets in residential areas. Transects were run on two t ypes of streets: those that opened onto a paddy field, and those that did n ot. Streets opening onto a paddy field, and aligned so the wind moved direc tly from the paddy field down the street, experienced lower air temperature s 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, expe rienced no measured temperature differences. These measurements were compared with the air temperature distribution pred icted by a simple internal boundary layer (LBL) model based on advective ef fects resulting from air movement over a change in underlying surface. The IBL model was able to accurately estimate the air temperatures in all situa tions, with regression coefficients for areas adjacent to large paddy field s of r(2) = 0.93, and for areas adjacent to small paddy fields of r(2) = 0. 83. Standard error of estimate (S.E.E,) values were low at S.E.E. = 0.21-0. 24 degreesC for large paddy fields, and S.E.E. = 0.23 degreesC for small pa ddies. Further work will be needed to test the relationship in other seasons, othe r climatic situations, and other urban settings. However, these results sug gest that there is potential for use of the IBL model in predicting the eff ects of planning and design decisions on air temperature distribution in ur ban areas. (C) 2001 Elsevier Science B.V. All rights reserved.