Temperature Difference between Meteorological Station and Nearby Farmland –Case Study for Kumagaya City in Japan–

The seasonal (monthly) variation in temperature difference between a meteorological station in an urban-area and nearby farmland in Kumagaya City was examined over 2010-2012. Kumagaya, one of the hottest cities in Japan, has an urban area of about 5 x 5 km and is surrounded by farmland. The daily mean, maximum, and minimum temperatures (T-mean, T-max, and T-min) routinely observed at the meteorological station (urban site) were higher than at the nearby farmland site across all seasons. Differences in the monthly temperatures between the two sites were 0.17-0.90 degrees C (T-mean), 0.55-1.63 degrees C (T-max), and 0.20-0.62 degrees C (T-min), and the maximum differences were in August (T-mean and T-max) and April (T-min). Large temperature differences (> 1 degrees C) for T-max were observed during the paddy rice-growing season in farmland from July to September. Differences in daily T-max and T-mean between the two sites were found to increase with daily solar radiation Sd. The sensitivities of these temperature differences to Sd were larger from July to September. The number of "extremely hot days" (T-max >= 35 degrees C) at the farmland site was only 36% of the number at the urban site, while the relative proportion of "sultry nights" (T-min >= 25 degrees C) was 62%.