Spatio-temporal Characteristics of Rainfall Frequency Indices over Middle Gujarat and Saurashtra, India

Abstract

Understanding spatiotemporal changes in extreme rainfall is critically important in monsoon-dominated regions. This study investigates trends in heavy (HR), very heavy (VHR), and extremely heavy (EHR) rainfall events across Middle Gujarat and Saurashtra, India, using quality-controlled daily ERA5 reanalysis data for the period 1980–2022. Six climatically diverse districts Ahmedabad, Dahod, Panchmahal, Amreli, Junagadh, and Rajkot — were selected for analysis. Rainfall trends were assessed using linear regression and Sen's slope estimator, with statistical significance evaluated through the non-parametric Mann–Kendall test. Results reveal spatially heterogeneous rainfall behavior across the study region, with weak to moderate increasing tendencies observed in HR events and comparatively clearer increasing trends detected in VHR events at selected stations. EHR events, though rare, exhibit notable episodic increases in recent decades, particularly over urban and semi-arid areas. However, the majority of detected trends do not attain statistical significance at the 95% confidence level, largely attributable to strong interannual variability and the sporadic nature of extreme rainfall occurrences. Despite limited statistical significance, the observed shift toward higher-intensity rainfall events highlights growing hydroclimatic vulnerability across Gujarat, underscoring the urgent need for impact-based risk assessment, improved urban drainage design, and climate-resilient water resource planning strategies.