ENSO-like anomalies alter the diurnal pattern of seasonal rainfall in the Garúa-dominated highlands of the Galápagos archipelago

Small island ecosystems are threatened by climate change in several ways. This includes the Galápagos archipelago in the Tropical Eastern Pacific, where limited freshwater makes the islands dependent on atmospheric supply through precipitation. However, precipitation distribution remains highly uncertain due to the lack of operational observation systems, and it is unclear how climate change will affect availability. Given its location, climate impacts are closely tied to changes in El Niño Southern Oscillation extremes during El Niño and La Niña years. Using a new measurement network incorporating a vertical rain radar profiler, we investigated seasonal rainfall changes (hot and cool) by analyzing El Niño/La Niña-like years, serving as surrogate for a locally warmer and locally cooler world. Our analysis demonstrates that in a locally warmer world, precipitation is increasing in both seasons. Rainfall characteristics and satellite-retrievals convective cloud frequency indicate more convective activity, intensifying heavy rainfall, especially during the hot season. In the cool season, drizzle is replaced by light rain throughout the vertical profile. In a locally cooler world, the hot season's typical midday rainfall maximum is replaced by oscillating, short-wavelength patterns and lower totals. Interestingly, the cool season in a La Niña-dominated world exhibits slightly higher rainfall than a neutral year, likely due to better condensation conditions of the advected moist air at lower air temperatures. Overall, results suggest improved total rainfall supply in a locally warmer world, but torrential rain could endanger the islands in the hot season. Furthermore, cool seasons shift from drizzle to light rain, though totals remain low overall.