Reconstruction of solar radiation in Tokyo since 1720 based on daily weather records in historical documents

The impact of climate change on human society has been a significant issue in historical studies and is also vital for future adaptation to climate change. To understand climate change before the start of meteorological observations and its devastating impact on societies in the past, the spatial patterns of climate variations must be reconstructed with a higher temporal resolution than those provided by the annual data. Japan has a large volume of records, including those related to daily weather conditions from the 17th to 19th centuries, which can help with this reconstruction.

This study applied the method previously developed by Ichino et al. (2001) for estimating solar radiation from the weather records of the Japan Meteorological Agency (JMA) to those collected from historical diaries. Adjusting the classification of descriptions from historical diaries, which are recorded in various expressions, allowed for their application in the method constructed from the current JMA weather descriptions. We estimated solar radiation for 1720–1912 in Japan based on the weather descriptions recorded in historical diaries from Tokyo, pertaining to the Little Ice Age. We validated the estimation compared to solar radiation estimated from the JMA-observed sunshine duration. The reconstruction was combined with the estimation from sunshine duration and the observed solar radiation to create the solar radiation time series data for 1720–2022.

The method used in this study successfully reconstructed solar radiation data in an adequate manner for all seasons with a higher temporal resolution, compared to other methods, including the use of proxy data for assessing historical climate variation. In addition, solar radiation is a fundamental factor for not only the energy balance of the Earth but also the hydrological cycle and agricultural productivity. Therefore, this extended reconstruction of time series data could contribute towards discussing climate change and its effects on historical societies. Herein, we discuss the long-term variations of the reconstructed solar radiation data since the 18th century, focusing on its particular effects on famine.

Reference

Ichino M, Sakamoto N, Masuda K, Mikami T (2001) The method for estimating global solar radiation based on weather records－toward the climatic reconstruction in the historical period－. Tenki 48:823–830. (in Japanese)

Keywords

Solar radiation, Historical weather descriptions, Historical diaries, Little Ice Age, Climate change, Japan