Ichino et al. (2025) Reconstruction of solar radiation for Tokyo since 1720 using weather descriptions from historical diaries

Identification

• Journal: Climatic Change
• Year: 2025
• Date: 2025-12-01
• Authors: Mika Ichino, Kooiti Masuda, Takehiko MIKAMI
• DOI: 10.1007/s10584-025-04036-w

Research Groups

• Center for Open Data in the Humanities, Joint Support-Center for Data Science Research, Research Organization of Information and Systems, Japan
• Faculty of Geo-Environmental Science, Rissho University, Japan
• Tokyo Metropolitan University, Japan

Short Summary

This study reconstructs daily solar radiation for Tokyo from 1720 to 1912 using qualitative weather descriptions from historical diaries, validating the method against modern observations and sunshine duration records. The reconstruction reveals significant low-insolation episodes coinciding with cool summers and famine events during the 18th and 19th centuries, demonstrating the feasibility of converting qualitative historical data into quantitative climate records.

Objective

• To reconstruct a continuous, long-term record of solar radiation for Tokyo from 1720 to 1912 using daily weather descriptions from historical diaries.
• To validate the reconstruction method against modern meteorological observations and sunshine duration records.
• To explore the implications of long-term solar radiation variations for past climate and society in Japan, particularly in relation to famine events during the Little Ice Age.

Study Configuration

• Spatial Scale: Tokyo, Japan (specifically Hachiōji for historical diaries and Otemachi for Japan Meteorological Agency observations).
• Temporal Scale: Reconstruction from 1720 to 1912. Combined with sunshine-duration-based estimates (1896–1985) and direct observations (1961–2022) to form a continuous record from 1720 to 2022.

Methodology and Data

• Models used:
  • A method for estimating solar radiation by converting daily weather descriptions, adapted from Ichino et al. (2001).
  • Normalized daily solar radiation (q) calculated as the ratio of daily total solar radiation (S) to daily insolation at the top of the atmosphere (STOA).
  • Historical solar radiation (Sej) estimated using Sej = qmean(k) * STOA, where qmean(k) is a conversion parameter based on cumulative monthly mean values for each weather level (k).
  • Three-level classification systems: Type HD for historical diaries and Type TG for Japan Meteorological Agency (JMA) weather condition records.
• Data sources:
  • Historical diaries: Ishikawa family diaries (1720–1912) from Hachiōji, Tokyo, providing daily qualitative weather descriptions.
  • Modern JMA records:
    • Daily weather overviews ("Tenki-gaikyo") from Tokyo observatory (1979–2010) for calculating conversion parameters.
    • Daily total solar radiation observations from Tokyo observatory (1981–2010 for parameters, 1961–2022 for long-term series).
    • Sunshine duration records from Tokyo observatory (1896–1986) for validation and extending the dataset.
  • Orbital parameters: Used to calculate S_TOA, with a total solar irradiance value of 1.365 × 10³ W/m².

Main Results

• The method successfully reconstructed monthly mean solar radiation for Tokyo from 1720 to 1912.
• Validation of the method using JMA data (1981–1985) showed high accuracy: correlation coefficient (r) of 0.977, root mean square error (RMSE) of 7.99 W/m², mean absolute error (MAE) of 6.25 W/m², bias of 0.51 W/m², and relative RMSE of 5.92% for monthly scale.
• Comparison of reconstructed monthly solar radiation from Ishikawa Diaries (1896–1912) with estimates from sunshine duration showed a high correlation coefficient of 0.95 and a root mean square difference of 13.3 W/m².
• The reconstructed data revealed significant low-insolation episodes coinciding with cool summers and severe famines in the 18th and 19th centuries, specifically during the Tenmei famine (1783) and Tenpō famine (1836).
• The 11-year running mean of August solar radiation showed periods of low insolation in the 1780s, 1810s, and around 1840, and high insolation around the 1800s, 1880, and 1905.

Contributions

• Demonstrates a robust method for converting qualitative historical weather descriptions from diaries into quantitative daily solar radiation data, extending climate reconstructions to periods before widespread instrumental observations (since 1720).
• Provides a unique, high-temporal-resolution (monthly) long-term record of solar radiation for Tokyo, offering valuable insights into pre-20th-century climate variability.
• Establishes a framework for future spatiotemporal expansions of solar radiation reconstruction using similar historical documents from other regions and for deeper investigations into the linkages between climate variation and societal impacts, such as agricultural productivity and famine events.
• Mitigates uncertainties associated with subjective historical records through a carefully developed classification approach, yielding reliable monthly-scale solar radiation fluctuations consistent with sunshine duration data.

Funding

• JSPS KAKENHI (grant numbers 17540410, 18H03794, 20K01152, 21H03776, 22H04938, 25K04619)
• ROIS-DS-JOINT (grant numbers 032RP2020, 027RP2021, 031RP2021, 041RP2022, 043RP2022, 044RP2023, 060RP2023)

Citation

@article{Ichino2025Reconstruction,
  author = {Ichino, Mika and Masuda, Kooiti and MIKAMI, Takehiko},
  title = {Reconstruction of solar radiation for Tokyo since 1720 using weather descriptions from historical diaries},
  journal = {Climatic Change},
  year = {2025},
  doi = {10.1007/s10584-025-04036-w},
  url = {https://doi.org/10.1007/s10584-025-04036-w}
}