In India, the agricultural economy with large growing population is closely linked with the performance of its two monsoon systems, namely southwest monsoon (SWM) active during June to September and northeast monsoon (NEM) during October to December, confined to south peninsular India. While SWM accounts for most of the annual rainfall over a large part of India, the southeast peninsular Indian region falls under a rain-shadow area during this season. Therefore, this region critically depends on NEM to supplement the inadequate SWM rainfall. Indeed, in Tamil Nadu state that is at the core of the NEM region of India, nearly 50% of the annual rainfall is received during the NEM season. The interannual variability of NEM rainfall is very high, which significantly affects the agricultural activities and other water-based enterprises in the region. Therefore, more concentrated research efforts are required to understand the variability and predictability of NEM rainfall over south peninsular India. Also it is required to identify the teleconnections with the regional and global circulation parameters, with the primary aim of developing suitable forecasting strategies of NEM rainfall at least a season in advance. Seasonal prediction of NEM rainfall, particularly over the core regions of Tamilnadu and Kerala, has considerable application for decision making.
Scope of the study
The interannual variability of NEM rainfall occasionally leads to large-scale droughts and floods over different parts of the NEM region. However, not much attention has so far been given to examine the interannual variability of NEM and to explore its predictive potential. An attempt is made in the present thesis to study rainfall variability over south peninsular India on subdivision scale in detail. The overarching objective of the thesis is to document the detailed characteristics of the interannual variability of NEM rainfall, identify regional/global teleconnections and reliable precursors that can be exploited for empirical seasonal prediction, and to develop a suitable prediction scheme. The thesis also examines the issues of global warming and climate change relevant to the region. The following are the major components of the targeted output related to NEM rainfall:
Homogeneous rainfall time series of NEM.
Teleconnection patterns.
A set of Predictors.
Seasonal prediction schemes.
Regional climate change scenarios for NEM region.