Abstract:

The relationship between grain crop harvest and climate change (temperature and precipitation) has been a major topic in the research on social impact of climate change in the past. With 5099 records on poor and bumper autumn harvests kept in historical chorography, annual harvest grade at county scale is quantified using semantic differential method, and the poor/bumper autumn harvest index series in North China from 1739 to 1911 is reconstructed. The variable characteristics of autumn harvest and its relationship with climate change are analyzed, and the reliability and applicability of historical harvest records from chorography are discussed by comparing them with those of the records from official documents in the Qing Dynasty. Results show that, first, the poor harvest records from chorography are more reliable than the bumper ones, and the poor harvest index series can reflect the fluctuation of overall autumn harvest to some extent. At the centennial scale, the autumn harvest markedly turned worse in the 19th century than in the 18th century. Second, the poor harvest index series are significantly and negatively correlated with temperature change at 10- and 5-year scales. Therefore, the poor harvest is sensitive to temperature decline. At an annual scale, the poor harvest is also significantly and negatively correlated with precipitation change, and the correlation coefficient between the poor harvest and drought index is up to 0.71 (p < 0.001). That is, drought is a larger threat to crop production than flood in North China. Third, compared with the harvest records kept in official documents that are reported to the government by local officials, the records from chorography have some advantages in the reconstruction of historical harvest. The records on poor harvest from chorography are more reliable than those from official documents, thereby allowing the index series to describe extreme events of crop production drop exactly. The two historical data sources can be complementary to each other; however, direct interpolation without data rectification may increase the system errors. This study is expected to contribute to the method improvement in the usage of historical documents in reconstructing the social impacts of climate change and the deepening in scientific knowledge on the impact rules of climate change on the agricultural production in the past.

Key words: climate change, social impact, crop harvest, historical chorography, North China