Considerable rainfall occurs in India during the post-monsoon period from October to December, particularly over north-eastern, eastern and southern regions, and this is of great significance in agricultural and allied sectors. For the first time, we have attempted to provide detailed information on the variability and predictability of the post-monsoon rainfall (PMR) of the country. Details on the summer monsoon rainfall from June to September are extensively documented. This study comprises four sections: (i) examination of large-scale rainfall features; (ii) examination of small-scale (or regional) rainfall features; (iii) diagnostic study in order to identify possible regional forcings and global teleconnections; and (iv) modelling long-period rainfall series and extrapolation of future trends for the next 10 years.
To understand large-scale features from year-to-year, expansion/contraction of the wet area (October -December rainfall ] 200 mm) was examined, involving data from 306 well-separated locations spanning 114 years (1871 -1984). The post-monsoon wet area (PMWA) series (1871-1984) is homogeneous, but its interannual variations are quite large. In the low-frequency mode fluctuations however, some distinct wet/dry epochs can be identified that are broadly consistent with the wet/dry epochs of summer monsoon fluctuations, implying that the same forcing factors affect the large-scale rainfall activities of both periods. Variations in the regional rainfall were studied in order to provide some useful information for practical purposes. The longest-possible instrumental period from the October to December rainfall series for each of the six zones of the country was reconstructed by applying the objective optimization technique to the limited observations available. Rainfall series were produced for the following regions of India, the reference period of reconstruction being 1871-