Question: I visited Lake Mead, Nevada recently and it was far below normal. How much rain would it take to refill?

Answer: Calculating a specific rainfall amount is difficult because of the large, complex watersheds that feed into the lake. However, it has recently dropped to levels that put it about 9 trillion gallons below normal. Rainfall and snowpack in the region have finally recovered some this year, which should help. The lake has been lower than it is now twice since 1940, taking one and ten years to refill.