Evaluation of Bowen's Ratio and the Climate-moderating Index on Agricultural Land in Clear Summer Days

Abstract

The climate-moderating function of agricultural land has been attracting attention from the viewpoints of global warming and environmentally conscious agriculture. In this study, we observed Bowen's ratio in rural and urban areas on clear summer days in daylight, using the prototype of a portable Bowen's ratio measuring device. We continued this observation for three years from 2004 to 2006, and analyzed 18 full clear days. It was found emerged that Bowen's ratio in the daylight varies slightly over a range of approximately ±2, and the mean value for each land-use type was 0.65 in urban areas, -0.029 in sweet potato fields, and -0.059 in rice paddy fields respectively. These values were compared with previous ones. Urban areas and rice paddy fields showed almost the same values as the previous values, however, crop fields showed smaller values, suggesting that they were in a singular condition in which the oasis effect was excellent. Next, we surveyed the relation between Bowen's ratio and the mean temperature, and observed a relation expressed by a hyperbolic functions. When this relation is applied, for example, if rice paddy fields are converted to urban areas, the mean temperature increases by approximately 3°C because Bowen's ratio rises by approximately 0.86 on clear days in summertime. This rise is estimated to lead to an approximate 148.5 yen increase in daily electric costs for artificial cooling. Based on these considerations, it was clarified that Bowen's ratio depends on the degree of humidity (wetness) of land types, which is effective as an index of climate moderation and a climatologic evaluation method.