Climate Variations in Tokyo since the Edo Period

Abstract

Climate variations in Tokyo based on reconstructed summer temperatures since the 18th century and instrumental meteorological data from the 19th century to the present are discussed. During the Little Ice Age, especially in the 18th century, remarkably cool episodes occurred in the 1730s, 1780s and 1830s. These cool conditions could be a significant reason for severe famines that occurred during the Edo period. Around the 1840s and 1850s near the end of the Edo period, it was comparatively warm which could correspond to the end of the Little Ice Age in Japan. Although there was a low-temperature period in the 1900s, a long-term warming trend could be seen especially in winter temperatures and daily minimum temperatures throughout the 20th century. While annual precipitation has been increasing during the last 30 years, relative humidity has been decreasing. This could result from a saturated vapor pressure rise due to warming and from a loss of water bodies due to urbanization. During the last century , not only warmer conditions but also wetter conditions in summer and autumn and drier conditions in winter and spring were documented by analyzing hythergraphs. Key words：temperature, precipitation, relative humidity, hythergraph, historical weather record, instrumental meteorological record ：気温降水量相対湿度ハイサーグラフ歴史天候記録気象観測記録