Dust storms that blanketed the Phoenix area in thick haze this week were among the most intense to hit the region in years, scientists said Thursday. “To have Class 5 dust storms occur one right after another a few days apart is unprecedented in our records,” said Randall Cerveny, a professor in the School of Geographical Sciences and Urban Planning at Arizona State. They were only the fifth and sixth dust storms in the last 16 years to reach Category 5, Cerveny told The Associated Press in a phone interview. He noted the Phoenix region has been drier than normal, which can increase the amount of dust that is kicked up. Scientists have said human-caused climate change increases the odds of both severe drought and heavier storms that could set the stage for more intense dust storms in the future.