We know California is very, very dry, right now, but just how dry? Dry enough that the “rain debt” the state has been steadily stacking up in the past three years is now equal to a full year of average rainfall.

NASA Goddard put together a survey of the last 36 years of California rainfall and found that the “rain debt” now came in at a full 20 inches—or the average rainfall the state receives in a year.

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It’s a sign of just how deep the drought has gotten, but it’s also a good reminder of why—when we’re talking about ending a drought—we’re not just talking about the amount of water, we’re also talking about the timescale it comes in.

Drought has a stacking effect with the drought of one year building off the drought of the year prior. To some degree, drier and wetter years tend to even out over time, but the longer the drought goes on and the bigger that rain debt becomes, the harder it is to ever catch back up to that equilibrium.

Image: California Department of Water Resources

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