Beyond the Gini Index: A Multi-Metric Approach to Precipitation Concentration in Chile

Precipitation concentration is an important component of hydroclimatic variability, but its interpretation depends on the metric selected and the treatment of dry days. This study assesses precipitation concentration across continental Chile using daily precipitation records for 1980–2024 and four complementary metrics: the Gini index (GI), Palma index (PI), normalized Shannon entropy (H), and Precipitation Concentration Index (PCI). Daily indices were evaluated using all valid observations or wet-day samples, as appropriate, with wet-day thresholds of ≥0.1 mm and ≥1 mm. Temporal trends were assessed using the Mann–Kendall test with Benjamini–Hochberg false discovery rate correction, requiring at least 30 valid annual index values per station. The indices revealed marked geographical differences, with the greatest concentration generally occurring between approximately 27° and 45° S. GI values decreased from approximately 0.7–1.0 when dry days were included to 0.4–0.6 when restricted to precipitation ≥0.1 mm, illustrating the distinction between rainfall intermittency and wet-day inequality, partly inherent in the index’s definition. GI and H exhibited an inverse association, while wet-day GI was significantly associated with PI. No significant PCI trends were detected, suggesting that daily precipitation redistribution may occur without detectable changes in monthly seasonality. Bootstrap analysis indicated lower PI instability with the ≥1 mm threshold. By integrating complementary metrics and distinguishing all-day from wet-day inequality, this study extends previous Chilean assessments and supports indicator selection for hydroclimatic monitoring, drought preparedness, water storage, agriculture, and flood and erosion management.