Influence of large-scale teleconnections on annual and seasonal floods in Godavari and Narmada River basins

Abstract

Indian summer monsoon rainfall is strongly influenced by large-scale atmosphere-ocean oscillations including Pacific Decadal Oscillation (PDO), El Niño-Southern Oscillation (ENSO), and Indian Ocean Dipole (IOD). Researchers have shown that the negative phase of PDO or LaNiña episodes of ENSO produce higher magnitude rainfall and hence relatively wetter years. So, it is imperative to have better knowledge of flood characteristics in the Indian watersheds for optimal planning and design of various infrastructure, and for optimal planning and management of reservoir operations. Traditionally, such information is estimated using flood frequency analysis (FFA), however the adequacy of traditionally accepted assumption that the annual peak flows are independent and identically distributed (i.i.d.) is questioned globally. This study evaluates the adequacy of this assumption in Godavari and Narmada River basins and assesses the influence of PDO, ENSO and IOD on flood characteristics. The results indicate that the flood characteristics at the majority of gauges are significantly influenced by these oscillations, higher magnitude floods are associated with negative episodes. A very few gauges are inversely related to these teleconnections, although statistically not significant. Overall, the signal of all the three teleconnections is found in the annual and seasonal floods in the majority of gauging stations.