For 27 years, the American Southwest has been gripped by a historic megadrought. A controversial new hypothesis says it may be here to stay. The current megadrought in the American Southwest is the driest 27-year period in the past 1,200 years, according to soil moisture anomalies derived from tree ring data and modern observations. Data: Park Williams/UCLA Kearny, Ariz., is a town on the brink. Located at the foot of the Dripping Spring Mountains in eastern Arizona, this small community of 2,000 people sources its water from the Gila River, a verdant waterway that snakes by the southern edge of town. …