Closing Loopholes in Water Rights Systems to Save Water: The Colorado River Basin.

Around the world, water rights systems govern the allocation of water to a multitude of users. Such systems primarily come into play during times of drought, when some users have to be shorted. Yet their management during times of excess can have implications for subsequent drought impacts. This is evident in the State of Colorado, where under "free river conditions" in which there is sufficient water to satisfy all water rights, anyone—including individuals lacking water rights—can divert as much as they want, unconstrained by the limit of their water right. Here, we estimate the amount of excess water used under such conditions within Division five of the Upper Colorado River Basin in the State of Colorado. Comparing the daily water withdrawals of diversion structures along the Colorado River and its tributaries with their (daily) water rights, we find that in 2017, 339 structures report days with excess withdrawals, amounting to 108 million cubic meters (87,577 acer feet). While such excess withdrawal is legal in Colorado, we argue that the free river condition is an antiquated rule that will make much needed reform of water allocation within the water‐stressed Colorado River Basin more difficult. We offer policy suggestions to address it. Plain Language Summary: Challenging water stress situations can be catalysts for reform. The Colorado River Basin is facing such a situation with ongoing drought since the turn of the Century. In the absence of much willingness for change, we propose a pragmatic step toward reform. Within the State of Colorado, when all water users have sufficient water to meet their decreed volumetric water right, the river is said to be in "free river conditions." Under these conditions, anyone—whether or not they own a water right—can divert as much water as they'd like until a senior user downstream makes a "call" on the river because they no longer have enough water to satisfy their right. We estimate that under free river conditions, excess water withdrawals of 108 million cubic meters (87,577 acer feet) is diverted beyond water users' decreed volumetric rights. We argue that such improperly defined water rights stand in the way of longer‐run reforms that seek to bring demand and supply in line in the Colorado River Basin, and propose alternative policies to bank this water to stave off future droughts. Key Points: We quantify the excess water diversions in the Upper Colorado Basin that go beyond diverters' water rightsThe Excess Diversions are a loophole in the Colorado Water System that will impede reformsStemming the Excess diversions will potentially help reduce economic and ecological stress of further depletion of Lake Powell [ABSTRACT FROM AUTHOR]