This is the summer of flooding across the US, and scientists know why

CNN Once synonymous with leisure and reprieve summer has increasingly become a season marked by anxiety and disruption Fossil fuel defilement alongside other compounding factors has transformed these months into a time of mounting peril punctuated by relentless heat waves rampant wildfires and catastrophic flooding This summer in particular has been defined by a tragic surge in deadly flash floods across the United States underscoring the escalating volatility of our warming world It s no accident this is the summer of flooding weather scientists say with -year to -year deluges happening nearly simultaneously in multiple states on multiple days Large parts of the US have seen an unusually humid summer with record amounts of moisture in the air When cold fronts and other weather systems come along that moisture can get wrung out squeezed like a water-laden sponge yielding heavy and often highly localized downpours For much of the summer the atmospheric conditions over the US have funneled humid air north from the unusually warm Gulf and western Atlantic including the Gulf Stream UCLA conditions researcher Daniel Swain stated CNN This has yielded unusually high levels of moisture at all levels of the atmosphere across the US east of the Rockies Swain revealed It has led to record levels of what meteorologists call precipitable water which is the amount of rain that would effect from instantaneously extracting all the water in the air This pattern has led to one flash flood after another First and foremost there was the devastating Texas flood that killed more than people on the night of July But flash flood events have been focused elsewhere as well Three people were killed in a flash flood related to torrential rains falling on a wildfire burn scar in Ruidoso New Mexico on July Certain major roads in Chicago were suddenly under water when a -year rainfall event struck in early July In portions of North Carolina the remnants of Tropical Storm Chantal led to deadly heavy rain and flooding the same weekend as the Texas tragedy In New York City water rushed into the subway tunnels when the city saw its second-heaviest rainfall total in one hour on July with widespread flash flooding lasting into the th And this past week it was Kansas City s turn to flood on July Certain of these floods resulted from rainfall that has a return frequency of about years meaning it has just a chance of occurring in any given year But atmosphere change is loading the dice in favor of extreme precipitation When we talk about e g year events we re talking about the likelihood of these events in the absence of human-caused warming i e how often we would expect them from natural variability alone declared surroundings scientist Michael Mann of the University of Pennsylvania These events are of subject much more frequent because of human-caused warming he commented in an email But his research has identified other factors such as persistent large-scale weather patterns known as atmospheric resonance that can make extreme weather including floods even more likely Just as sound waves or ocean waves can resonate and reinforce each other atmospheric resonance can happen to undulating jet stream patterns in the upper atmosphere resulting in weather systems that stay in place for weeks A up-to-date evaluation Mann worked on identified such weather patterns have tripled in incidence since the mid- th century during the summer months The complication is these patterns are not necessarily well-captured in context models he mentioned This increases uncertainty about future projections for extreme weather trends The influence of situation change on heavy rainfall is the greater part evident when it comes to short duration extreme events like what has happened repeatedly this summer according to Swain It is not average precipitation that really is greater part affected by surroundings change Swain declared It truly is mathematically correct that the more extreme the rain event the clearer the connection to surroundings change is The physics of how global warming affects heavy precipitation events is well known according to circumstances scientist Kate Marvel This is almost a textbook example of circumstances change impacts she informed CNN The science behind it is so basic you can see it in daily life Warm water drives more evaporation the bathroom gets much steamier after a hot bath than a cold one she announced Warm air contains more water vapor a cold beer gets wet on the outside on a hot day because when air comes into contact with the cooler surface it has to condense out its water vapor Marvel announced Warm ground makes it easier for moist air to balloon upwards this is why thunderstorms happen on hot summer afternoons Put these all together and you get the perfect conditions for torrential rain explained Marvel author of the new weather book Human Nature Whether a downpour turns into a catastrophic flood depends on a lot of things how porous the ground is the topography of the area the people and things in harm s way But there is absolutely no doubt that conditions change caused by human emissions of greenhouse gases is making extreme rainfall more extreme