Less & Heavy Rain


Hawai‘i is getting drier. Rainfall has declined significantly over the past 30 years, with widely varying rainfall patterns on each island. This means some areas are flooding and others are too dry. Since 2008, overall, the islands have been drier, and when it does finally rain, it rains a lot.

Coffee berries in Kona, Hawai‘i Island. These crops are increasingly threatened by unusually dry summers, and in turn economic loss threatens the agriculture industry, Photo by Robert Cowlishaw, Flickr Commons


PARTS OF HAWAIʻI ARE GETTING DRIER. Average yearly rainfall is declining across all the islands. The Big Island is experiencing more prolonged dry spells than ever. Coffee farmers, who normally rely on rainfall to water their crops, have started buying public water, drawn from groundwater, for irrigation. But they are still experiencing overall crop losses.

WHEN WE DO GET RAIN, WE GET IT ALL AT ONCE. And that means more landslides, runoff, algae blooms, erosion, and flooding. Remember the “rain bomb” on Kaua‘i in April 2018, where 50 inches of rain fell in 24 hours and cut off a whole community for months?  

FLOODS ARE CREATING ECONOMIC AND PUBLIC HEALTH RISKS. The number of floods per year has increased sharply since the 1960s and is expected to keep rising.  In Honolulu alone, high tide flooding has increased from 6 days per year to 11! Floods cause water contamination, damage to infrastructure, and put people and their houses at risk.


More El Niño (ENSO) years caused by warming seas will bring more intense periods of drought and heavy tropical storms. Less rainfall will put our drinking water supply at risk. This means less groundwater, more risk of drought, and increased risk of wildfires. For example, 80% of Maui’s drinking water comes from the Na Wai Eha watershed, which is experiencing significant decreases in average annual rainfall. More ENSO years and extreme weather events will threaten the reliability of aquifers on all islands. Droughts will cause water shortages to become more common, with some islands expected to enter extreme droughts and accompanying water shortages within the next 5 years. As populations increase across islands, economic instability, a crippled municipal water system, degrading agriculture, and decreased tourism caused by ecosystem loss could become serious threats to our well being.