All of this is happening against the backdrop of more frequent flooding. Between 1861 and 1943, Criss said, the river near St. Louis topped 38 feet only once. Since 2013, it topped 40 feet four times. Flooding like that experienced in the Midwest this spring is occurring with increased regularity, and scientists say the frequency of heavy rains is skyrocketing. After a reprieve over the past two weeks, more rain is in the forecast in the next few days, reigniting concerns that the river may once again test the limits of the levees and the river valley towns from the Quad Cities to St. Louis.