Diverging monthly rainfall trends in south peninsular India and their association with global climate indices

With the frequent recurrence of hydroclimatic hazards, such as rainfall-induced floods and landslides, it is essential to look at the spatio-temporal evolution of rainfall trends and teleconnections of regional rainfall with global climatic indices. The present study is carried out in two climatologically contrasting terrains, the humid regions in the western side of South-Peninsular India (SPI-W) and semi-arid to arid regions in the eastern side of South-Peninsular India (SPI-E). Trends in the rainfall were studied over a long-term (1901-2020) gridded rainfall data, and change points were detected using the Pettitt's test. An expanding-sliding window trend analysis based on Kendall's Taub was carried out to decode the time evolution of rainfall trends and to differentiate consistent gradual monotonic trends from step changes. Two distinct change points were observed in the rainfall, the first in the 1960s and second in 1990s. SPI-E manifested a strong positive trend in the monsoon rainfall after 1990's while SPI-W demonstrated a weakening in rainfall after 1960's. The regionally diverse trends during the recent epochs are evaluated along with IOD (Indian Ocean Dipole) and it was observed that there is a significant increase in co-occurrence of positive rainfall anomaly, positive IOD and positive ENSO (El Nino Southern Oscillation) events after 1990. Increase in positive IOD events could be associated with the changes in the regional rainfall during these recent epochs. The trends in monthly and annual rainfall showed high sensitivity to data periods and data lengths, highlighting the need to perform such comprehensive analysis for the planning of reservoir operations, water management and agricultural activities.