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  • By Mar-Vic Cagurangan

Report: Climate change to take its toll on Guam's freshwater resources

Climate change threatens to bring more scorching days to Guam in a scenario that will compromise the island’s freshwater resources, according to a new report released this week by the East West Center.

The center’s report said Guam typically gets 35 days with temperatures above 88℉ per year. But recent air temperature measurements at Antonio Won Pat International Airport show an increasing trend in the annual number of hot days over 90℉ since 1999.

“The number of hotter days over 90℉ in Guam is projected to increase to 257 days per year under a high scenario by the end of the century,” the report states. “In other words, more than 70 percent of days in the years are projected to experience temperatures over 90℉.”

The report titled, "Climate Change in Guam: Indicators and Considerations for Key Sectors," provides guidance for decision-makers seeking to better understand how climate variability and change impact Guam and its communities. It is the latest in a series of report for the Pacific Islands Regional Climate Assessment.

The report warned that climate change is expected to disrupt many aspects of life in Guam and those who are already vulnerable “are harmed more than others by extreme weather and climate shifts.”

Guam’s water resources, the study said, are among the areas that will be severely impacted by climate change. It will bring blistering hot weather that is predicted to result in an increased water demand and a decrease in available surface fresh water fresh water.

The report noted southern Guam’s dependence on surface water supplied from rivers and Fena Valley Reservoirs. “Streamflow in southern Guam and Fena Reservoir water volume decreased below usable level during long severe droughts,” the report said.

“Rising temperature will increase evapotranspiration (about 14 percent higher and up to 29 percent higher in some locations) affecting both the amount of fresh water availability and human population’s demand for water.”

Guam is also expected to face more frequent droughts under a high emission scenario, in which average islandwide annual rainfall will decrease about 7 percent over all by the end of the 21st century.

“The aquifers are likely now more vulnerable to drought-linked depletion than in the past,” the report said. “During droughts depleted water surface water sources can increase dependence on well water.”

In the northern part of Guam, the study projected the lens aquifer to decrease by about 19 percent later this century. “The combined effects of higher demand and the need to increase pumping, more frequent drought and sea level rise could bring salt water closer to wells that supply drinking water,” the report said.

It noted that many of northern Guam wells have already been showing increased saltwater contamination. "Water conservation particularly during dry spells may be necessary more often in the future,” the report said.

Besides risks to freshwater resources, droughts are also likely to cause increased wildfires, and the potential for damage to infrastructure caused by future sea level rise and stronger typhoons.

Along with frequent droughts, Guam is also predicted to experience a higher number of extreme rainfall events annually. “Heavy rainfall events will result in increased runoff and increased potential for flowing and erosion,” the report said.

The sea level around Guam continues to rise and such patterns will accelerate in the future. "For Guam and tropical Pacific islands which are far away from the decreasing gravitational attraction of melting land ice, sea level rise is expected to be higher than the global average," the report said.

“Guam’s tide gauge for measuring long term sea level trends recorded an average rise of 0.13 inches per year since 1993,” the report said.

Guam is expected to see 1.2 feet of sea level rise. With 3.3 feet of global mean sea level rise relative to historical levels (considered likely by 2100 under a high scenario) Guam is expected to see a 3.9 feet of rise by 2100. It is possible that sea level rise may exceed these levels.

Sea level rise threatens infrastructure, including housing and transportation, as well as ecosystems and cultural sites, according to the report. It cited a 2019 vulnerability assessment, which forecast that rising sea levels will expose at least 58 percent of Guam’s infrastructure to periodic flooding during this century.

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