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Hawaiʻi’s freshwater resources are intricately linked to rainfall patterns. (Photo credit: DLNR)

El Niño events have long been perceived as a driver for low rainfall in the winter and spring in Hawaiʻi, creating a six-month wet-season drought. However, the connection between Hawaiʻi winter rainfall and El Niño is not as straightforward as previously thought, according to a recent study by researchers in the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology (SOEST).

Studies in the past decade suggested that there are at least two types of El Niño: the Eastern Pacific and Central Pacific, when the warmest pool of water is located in the eastern or central portions of the ocean basin, respectively. El Niño events usually begin in summer and last for about one year.

Atmospheric scientists at UH Mānoa analyzed data on the large-scale circulation patterns over the eastern and central Pacific to find that Hawaiʻi drought is only associated with the Eastern Pacific El Niño. For the Central Pacific El Niño events, deficient rainfall in Hawaiʻi occurred only 60% of the time. Therefore, a winter drought is not guaranteed following a Central Pacific El Niño.

people working outside
Hawaiʻi agriculture is dependent on ample rainfall in the region. (Photo credit: Corey Rothwell)

Critical for planning and water resource management

The differences in how the Eastern and Central Pacific El Niño affect rainfall can be critical for proper planning and water resource management.

“This new result is a boon for many agencies in Hawaiʻi, for example, the Board of Water Supply, Hawaiʻi Department of Land and Natural Resources, and Hawaiʻi Department of Agriculture,” said Pao-Shin Chu, a SOEST professor, Hawaiʻi state climatologist and co-author of the study. “Beyond these agencies, ranchers, flower growers and other stakeholders that are concerned with the relationship between El Niño and water supply in Hawaiʻi may also benefit from the new findings.”

Given that El Niño is a recurring phenomenon, knowing the type of El Niño that occurs will allow researchers and resource managers to more easily evaluate and prepare for Hawaiian regional climate in winter.

For more information see SOEST’s website.

–By Marcie Grabowski

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