Local Sea Surface Temperatures Modulate the Occurrence of Heavy Rainfall Events in the Galápagos Archipelago

Climate change is expected to increase the frequency and intensity of heavy rainfall events (HRE) globally. In the Galápagos Islands, HREs have caused severe impacts such as infrastructure loss and ecosystem damage, yet their occurrence remains poorly understood. This study identifies 137 HREs between 1985 and 2024 and demonstrates that local sea surface temperatures (SST) from a new regional SST index, called the Galápagos Regional Niño Index (GReNI), correlate more strongly with HREs than widely used large-scale El Niño-Southern Oscillation indices. We analyzed the rainfall and 10 m wind fields from the Galápagos Archipelago Refined Analysis data set and find that while HREs occur outside Pacific-wide El Niño events, they are generally strongest during local GReNI El Niño-like phases. These findings highlight how local SST anomalies influence mesoscale rainfall, suggesting local rather than large-scale SST are significant HRE modulators.