Space-time variation and regionalization of seasonal and monthly summer monsoon rainfall of the sub-Himalayan region and Gangetic plains of India

Abstract

The present study analyses space-time variation of the seasonal and monthly monsoon rainfall of the sub-Himalayan region and Gangetic plains of India by using rainfall data of 90 well-distributed stations for a period of 114 yr (1871 to 1984). Principal components (PCs) and varimaxrotated principal components (RPCs) are computed from the interstation similarity matrix. The 4 leading PCs explaining 52 to 61 % of the variance respectively for seasonal and monthly rainfall are found to be statistically significant. When rotated by the varimax method these 4 PCs provide 4 distinct areas of homogeneous rainfall variability for both time scales. The most coherent region is located along the central longitude of the study area, with another coherent region over the extreme western parts. The area east of 81° E is divided into 2 coherent zones roughly along the 22° N parallel. It is noted that the regions thus identified will be useful in understanding climate variability and in weather prediction research.