Climate experts say the floods that sent rivers of mud tearing through towns in Italy’s northeast this week are the result of extreme weather phenomena that are becoming increasingly frequent around the world. That includes prolonged periods of drought punctuated by intense periods of rain that can’t be absorbed by the parched ground. That's what happened in hard-hit Emilia-Romagna, where rivers burst their banks to drench towns in mud. At least 13 people were killed and billions of euros in damage was done. Italy is far from alone in lurching from dry to deluge. California and the United States West sloshed its way from a record-setting megadrought to at least a dozen atmospheric rivers dousing the state with so much rain that a long-dormant lake reappeared.