Creeks, rivers and lakes that are fed by melting snow across the U.S. West are already running low as of mid-July 2021, much to the worry of farmers, biologists and snow hydrologists like me. This is not surprising in California, where snow levels over the previous winter were well below normal. But it is also true across Colorado and the Rocky Mountains, which in general received a normal amount of snow. You’d think if there was normal amount of snow you’d have plenty of water downstream, right? … But another less studied way moisture can be lost is by evaporating straight into the atmosphere.