Rainfall Variability and Drought Characterisation Using SPI and Rainfall Deviation in Tirupur District, India (1991–2023)

Abstract

Drought remains a critical hazard in semi-arid agro-climatic zones, with substantial effects on agricultural productivity and regional water resources. This study characterises rainfall variability and evaluates meteorological drought dynamics in Tirupur district, Tamil Nadu, India, over the 33-year period from 1991 to 2023. Daily rainfall data from 16 rain-gauge stations were analysed using Rainfall Deviation (RD), based on India Meteorological Department classifications, together with the Standardised Precipitation Index (SPI) at 1-, 3-, 6-, 12-, 24-, and 48-month timescales. Spatial analysis of annual rainfall indicates a distinct west–east gradient: western blocks receive more than 800 mm, whereas eastern blocks consistently receive less than 500 mm and show coefficients of variation exceeding 40%. Although normal-rainfall years accounted for 63.6% of the study period, the region exhibited high interannual variability, including severe deficit years (1991, 2012, and 2016) and marked excess years (2004 and 2019). Multi-timescale SPI analysis indicates that near-normal conditions generally predominated, although recurrent moisture stress occurred. Short-term indices captured transient meteorological droughts, medium-term indices identified sustained seasonal water stress that peaked during 2013–2014, and long-term indices identified multi-year hydrological drought cycles during 2003–2005 and 2013–2016. Spatial drought-severity mapping identified Palladam, Avinashi, and Kangeyam in the eastern and north-eastern parts of the district as persistent drought hotspots. The combined use of RD and multi-timescale SPI provides an integrated framework for regional drought monitoring and may inform groundwater management, drought-resilient crop planning, and climate-adaptation strategies in hydro-climatically sensitive regions.