Implications of rainfall variability on groundwater recharge and sustainable management in South Asian capitals: An in-depth analysis using Mann Kendall tests, continuous wavelet coherence, and innovative trend analysis

Abstract

Groundwater resources, a critical component of hydrogeological systems, are under increasing pressure due to climate change and anthropogenic activities. South Asia, a region highly vulnerable to climate shocks, has seen over half of its population affected by climate-related disasters in the past two decades. These climate changes, characterized by intensifying heat waves, cyclones, droughts, and flooding, pose significant risks to groundwater resources management. This study aimed to address the recent variability, intensity, and depth of rainfall patterns in the capitals of south Asian countries on a daily, monthly, and annual basis. Mann-Kendal tests (MKT), Innovative Trend Analysis (ITA), and Continuous Wavelet Coherence were conducted to identify trend patterns. The Gumbel distribution of Intensity Depth Frequency (IDF) analysis was performed to analyze the depth and intensity of rainfall patterns for rainfall durations of 5, 10, 15, 30 min, 1–hr, 2–hr, 12–hr and 24–hr for 2, 5, 10, 25, 50, 75 and 100 years return periods. Results of ITA and MKT showed similar trend results for all cities and time scales. Findings suggest that Kotte receives the highest annual rainfall of 1745.28 mm and Kabul the lowest (380.76 mm). MKT showed both positive and negative monthly trends in most of the months, while annual rainfall exhibited positive trends in all cities with a change rate between +0.56 and + 2.34 mm/year. Seasonal trend analysis confirms positive trends for all seasons, except in Delhi, Malé, and Kathmandu in winter. IDF analysis reveals that current rainfall trends will slightly affect the depth and intensity of rainfall events for the various return periods. The study provides valuable insights into the water-energy-food nexus and contributes to the broader discourse on water policy and social aspects of groundwater in the face of climate change.