Influence of local land cover on meteorological conditions in farmlandcase study of a rice paddy field near Tsukuba city, Japan

Abstract

In farmland areas, meteorological conditions affect crop growth and physiology. We examined the influence of seasonal changes in local agricultural land cover on meteorological conditions of farmland in a rural area of Tsukuba City, a medium-sized city in Japan, by comparing conditions in the rural area with those in the urban and suburban areas (horizontal scale ~10 km) of Tsukuba City. The daily mean temperature at a rural farmland site (single cropping system: paddy rice in summer, bare soil in winter) was 0－3 °C lower than that at an urban site (observational field at the Meteorological Research Institute, about 7 km from the farmland site), depending on the season (annual mean 1.07 °C during 2004－2006). The daily mean water vapor pressure deficit at the farmland site was also smaller than that at the urban site across all seasons, and it was markedly lower during the rice-growing period (May to mid-September), resulting in a more humid climate at the farmland site during this period. During the paddy rice-growing period, day-to-day differences in daytime temperature and water vapor pressure between the farmland and urban sites tended to increase with daily solar radiation, and were closely related to the day-to-day difference in daytime sensible and latent heat fluxes between the two sites. During the fallow period (late September to April), the difference in daily minimum temperature between the two sites tended to increase with possible radiative cooling and became larger under weak wind conditions.