In the gloomiest long-term forecast yet for the drought-stricken Colorado River, a new study warns that lower river basin states including Arizona may have to slash their take from the river up to 40% by the 2050s to keep reservoirs from falling too low. Such a cut would amount to about twice as much as the three Lower Basin states — Arizona, California and Nevada — agreed to absorb under the drought contingency plan they approved in early 2019.