Why is the Santa Elena Peninsula much drier than other parts of Ecuador?

The Santa Elena Peninsula is significantly drier than other parts of Ecuador primarily due to the influence of the cold Peru Current (also known as the Humboldt Current) that flows along the coast of South America.12

While most of Ecuador experiences a humid tropical climate, the Santa Elena Peninsula—the northernmost extension of the west-coast desert of South America—is characterized by an arid environment. The cold waters of the Peru Current suppress the development of the moisture-laden air masses that typically bring rainfall to other coastal regions. Consequently, annual precipitation on the peninsula is very low, decreasing from approximately 40 inches (1,000 mm) near Guayaquil to as little as 4 inches (100 mm) at Salinas.312

This arid climate is only interrupted during El Niño events, when warm surface waters replace the cold upwelling associated with the Peru Current, temporarily transforming the coastal climate from arid to wet.12