High-tide flooding is happening across the USA at twice the rate it was just 30 years ago, according to a new report released Wednesday.And this flooding isn’t necessarily caused by a storm, but by rising seas: As ocean levels rise because of global warming, flooding can now occur with high tides in many locations.Also known as “sunny-day,” “clear-sky” or “nuisance” flooding, 27 locations across the nation set or tied records for most days with floods from May 2017 to April 2018, the report said. Cities such as Boston and Atlantic City both had 22 days with high-tide floods.”Due to sea level rise, the national average frequency of high-tide flooding is double what it was 30 years ago,” the report said. William Sweet, a NOAA oceanographer and co-author of the report, said at a press briefing that “what used to be uncommon is now becoming fairly common.” Nationwide, the average of six flood days for each location was the highest on record. Ben Horton. a Rutgers University researcher who was not involved in the study, called it “a warning, a shot across the bow. Across the whole of the U.S. coastline, we are in dire need of action,” he said.The report found tidal flooding was at record levels last year along parts of the southeast Atlantic and eastern Gulf coasts. It examined only coastal flooding, not inundation brought on by sudden, heavy rain or overflowing rivers.”As they examine their risk, communities can use this information to help better mitigate and prepare for high tide flooding from long-term sea-level rise,” according to NOAA. These floods lead to road closures, overwhelmed storm drains and damaged property but are seldom life-threatening. They’re mostly caused by climate-related sea-level rise, NOAA said.