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William Aila remembers seeing streams flowing with water every winter as a teenager growing up in Waianae.

Now, the 56-year-old chairman of the state Board of Land and Natural Resources only sees water in these streams after it’s rained particularly hard. He said this means his grandchildren aren’t able to see oopu, a native fish that lives in streams.

“Climate change is here and we have to deal with it,” Aila said Tuesday at an event discussing the Hawaii and Pacific island portion of the latest national report on global warming.

“If we don’t, our children and grandchildren are going to see less and less of what Hawaii is, less and less of what Hawaii stands for and less and less of what Hawaii needs to be,” Aila said.

Aila’s anecdotal observations are consistent with data scientists present in the National Climate Assessment, which shows average rainfall and stream flows in Hawaii have been declining for nearly a century.

The trend is expected to continue, said University of Hawaii Professor Thomas Giambelluca, one of the scientists who contributed to the report, as drier parts of the state get less rain.

This will boost demand for water as the drier parts of Hawaii are where most people live and grow crops, he said. A growing population will only add to the greater demand for water, he said.

The state’s fresh water supply, meanwhile, will be pressured as sea levels push salt water into aquifers that store the state’s drinking water. A drop in rainfall will also mean less recharging of these aquifers.

This is more of a slow-moving disaster than a dramatic giant storm, said Victoria Keener, a research fellow at the East-West Center who moderated a discussion on the report at the East-West Center in Honolulu.

The report also mentions threats to coral reefs, fisheries, coastal ecosystems and agriculture.

The Pacific tuna fishery is one industry predicted to suffer as temperatures rise.

“What the climate assessment is trying to say is that we have to start taking adaptation action now to be able to combat this so we aren’t too negatively impacted by effects of sea level rise and precipitation changes and storm patterns,” Keener said.

Aila said his department’s push to restore forests by removing invasive weeds and keeping out pigs and other feral animals that dig up plants is one way the state is attempting to deal with the changes that are coming. Healthy forests are critical for water supplies because they soak up and store rain and cloud moisture like sponges.

Efforts to protect coral reefs, meanwhile, he said, would not only help coral and fish but also shield harbors and coastlines from waves. The state is creating a coral nursery to conduct research on corals that might be able to withstand rising temperatures, he said.

Aila hailed a bill the Legislature passed earlier this month giving the department funds to develop strategies for coping with coastal erosion and changing coastlines.

He said the state needs to be ready to “run with” innovative programs.