The climate of Madras during the eighteenth century

Abstract

Archives of a German–Danish missionary foundation, including two weather diaries for Madras covering the years 1732–1737 and 1789–1791 and annual reports and letters, are used to reconstruct aspects of the climate of the Madras region of SE India during the eighteenth century. Records of rainfall occurrence and diurnal variations in wind direction in the diaries are used to derive the number of raindays and wind direction frequencies at 08:00 and 17:00 h for each month of record. Modern data on rainfall per rainday are used to convert rainday data to estimates of monthly rainfall. Wind direction data at times of land breeze (08:00 h) and sea breeze (17:00 h) are used as indices of the strength of the NE monsoon (in the October–December rainy season) and summer SW monsoon, respectively. Results suggest that annual rainfall in the period 1732–1737 (and probably also the 1720s) was about 27% below the 1813–1991 average, with very low NE monsoon (−41%) but near-average SW monsoon rainfall. The wind direction data suggest that both the SW monsoon and NE monsoon were stronger than normal. In contrast, estimated annual rainfall in 1789–1791 was near-average, but with SW monsoon rain 54% below average and NE monsoon rain 22% above average. This appears to be linked to less strong NE and SW monsoon winds than in 1732–1737. The period 1740–1788 appears to have been considerably wetter than the 1720s and 1730s. Tropical cyclone frequency was low except in the 1740s and 1780s. The 1730s dry period coincided with a period of anomalously warm winters in Europe. Copyright © 1999 Royal Meteorological Society