Summer Climate Change in Osaka City since Late 19th Century

Climate change in urban areas is affected by global trends such as global warming and by local trends such as heatisland phenomenon. Heat islands are formed in urban areas by urbanization. This paper analyzed summer (August) climate change in Osaka City, central Japan, during the period from 1883 (or 1890) to 2006 using the monthly means or totals of six climate parameters. During these 124 (or 117) years, the monthly means of daily mean, maximum and minimum air temperature increased by 2.0°C, 1.5°C, and 2.7°C, respectively, while the relative humidity and the duration of sunshine decreased by 11% and 33 hours, respectively. Rainfall showed a stable trend with large fluctuations. Relative humidity decreased at a very low rate (2.7%/100 years) in 1883-1950, but at a higher rate (13%/100 years) in 1951-2006. Regression of the three temperature parameters and relative humidity to rainfall and sunshine values suggested that the trend difference in temperature and humidity change from the middle of the 20th century cannot be explained by only local natural factors such as rainfall and sunshine, but is mainly due to