New research: Hawaii dramatically drier over past 40 years

 Hawaii has grown drier and browner over the last 40 years.

This won’t be a big surprise to land managers who have faced repeated droughts, more wildfires and lower streamflows. But now there’s data to back up their observations.

A new study in the journal Environmental Management confirms that reduced rainfall has had significant impacts across the state.

That translates to less green, more brown.

The paper, which was published in November 2022, has the title: “A Near Four-Decade Time Series Shows the Hawaiian Islands Have Been Browning Since the 1980s.” 

The lead author, Austin Madson, is with Wyoming Geographic Information Science Center, University of Wyoming. Co-authors, several from Hawai’i, include Monica Dimson, Lucas Berio Fortini, Kapua Kawelo, Tamara Ticktin, Matt Keir, Chunyu Dong, Zhimin Ma, David W. Beilman, Kelly Kay, Jonathan Pando Ocón, Erica Gallerani, Stephanie Pau and Thomas W. Gillespie.

They used satellite measurements to show that Hawai’i’s environment is going in the opposite direction of most of the planet.

“Globally there has been a significant increase in … greenness due to climate warming,” they wrote.

The researchers looked at all eight major Hawaiian Islands, using a system called the Normalized Difference Vegetation Index or NVDI.

Their findings: “Overall, there has been a significant decline in NDVI (i.e., browning) in the Hawaiian Islands from 1984 to 2019.”

Ni’ihau and Kaho’olawe, already the driest of the islands, did not see significant changes, but all the other islands “experienced significant declines,” they wrote.

Kaua’i was a little better off, but the problem was worse on O’ahu and Molokai, and worst of all on Lana’i and Hawai’i.

Native forests, generally in the uplands, suffered some if the worst declines: “Native ecosystems on O’ahu (56%), Moloka’i (70%), and Hawai’i (57%) decreased the most in NDVI from 1984 to 2019.”

That translates, they said, into reduced productivity and reduced biodiversity.

“In the future, if the drying and warming of the climate on the leeward slope of the island of Hawai’i continue, native ecosystems may become increasingly vulnerable to fire and succumb to the expansion of invasive species.”

Whether the drying trend will continue isn’t known, but it’s a worrisome trajectory.

© Jan TenBruggencate 2023