Molly Dolphin grew up in Volcano on Hawaiʻi Island. Since moving back with her own young family, she's noticed changes in her hometown's climate.
"It is much hotter than it was during my childhood — way less rain, way more mosquitoes," she said.
Measurements taken near Hilo International Airport show that the number of days per year with temperatures exceeding 80 degrees Fahrenheit has increased significantly in the last decade.
But data on rising temperatures in Hawaiʻi Island's more rural communities is harder to come by, and measuring temperature alone may not be sufficient to understand how people are actually experiencing heat.
Dolphin, who works for the County of Hawaiʻi Office of Sustainability, Climate, Equity, and Resilience, is part of a project tackling this data deficit.
Last summer, the county partnered with Vibrant Hawaiʻi's islandwide network of resilience hubs to deploy heat and humidity sensors at 12 locations across the island.
Those sensors continuously tracked air temperatures and relative humidity levels for about 12 weeks in six of Hawaiʻi’s nine districts.
Dolphin said that measuring humidity alongside heat is important, as high levels of humidity can make heat more dangerous. When it's humid, sweat doesn't evaporate as quickly, making it harder to cool down.
The National Weather Service's heat index combines air temperature and relative humidity level measurements to approximate how hot a given temperature actually feels to the human body.
At 75%-85% humidity, even temperatures in the mid-80s can put people at risk of heat illness after prolonged exposure or physical activity, according to the NWS heat index.
Average relative humidity levels recorded by the sensors on Hawaiʻi Island ranged between 75% and 90%. Some locations on Hawaiʻi's windward side regularly measured humidity levels upwards of 90%.
Unsurprisingly, sensors in steamy downtown Kailua-Kona tracked consistently high temperatures, with heat indices over 100 degrees. But heat indices also reached concerningly high thresholds in other places, including Nāʻālehu and Pāhoa.
Dolphin pointed out that far fewer households in those communities have air conditioning than in Kailua-Kona, where high temperatures have long been the norm.
"Planning for hot days is easier in a place like Kailua-Kona, where it can be expected," she said. "But what about planning in places where you don't expect that heat?"
While the data collected by the county's resilience hub partners isn't perfect, Dolphin said that establishing these baselines represents a big step in the county's preparation for rising temperatures and major heat events.
"This type of baseline data doesn't exist at all for our island. So just even having that baseline data is such a good starting point to help drive some of the conversations around heat," she said.
The county is preparing a summary report of the data and will redeploy the sensors this summer. It also plans to conduct a community needs assessment to better understand how heat is affecting residents, including vulnerable populations like kūpuna, unhoused people, and outdoor workers.
Vibrant Hawaiʻi Chief Operating Officer Maurice Messina said that the resilience hubs want to continue to serve as a space for local research.
"These resilience hubs are open for any type of collaboration that ultimately will have a benefit for their communities," he said.
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