Rain is vital to life in the Hawaiian Islands. Hawaiʻi receives rain from trade winds and Kona storms. Cloud formation by trade winds are the most reliable source of rain, and therefore freshwater. In the last 20 years, Hawaiʻi has already seen a reduction in trade wind days and a nearly 15% decrease in rainfall. Drought conditions are only expected to worsen, lessening the amount of freshwater recharge and water in our streams.


Rainfall feeds streams through base flow and storm flow. Stream base flow is supplied by water from underground aquifers and maintains water in streams during periods between rainfall events. Storm flow from heavy, fast rainfall causes stream levels to rise and the amount of water running into the ocean to increase during and immediately after rainfall.

It is predicted that as air temperature rises from climate change, precipitation will decrease in wet areas—reducing freshwater availability, and increase in drier areas not adept to heavy rainfall events—causing flooding.

Stream diversions prevent stream systems from following naturally. During and after a storm, waters can built up in streams not meant for large, quick flows, causing flooding in surrounding areas and harm to residents that live near streams and rivers.


Freshwater resources are already limited in the Hawaiian Islands and will only become more limited as climate change impacts increase. Hawaiʻi’s aquifers hold a lens of freshwater on top of the denser, salt water. Rainfall, fog drip, and surface waters seep into the ground recharging the freshwater lens and displacing the saltwater. However, as sea levels continue to rise and precipitation decreases from climate change, the opposite will occur—saltwater will displace more and more of the freshwater in Hawaiʻi’s aquifers, reducing the quality and quantity of freshwater.

Learn more about Hawaiʻi’s freshwater availability in the face on climate change here.


Our water landscape is changing, ever so quickly. We must protect what water resources we have now to ensure access to quality drinking water for generations to come.