A new study by NASA scientists says California took on a “rain debt” of 20 inches between 2012 and 2015. On average, that’s about the same amount of rainfall the state gets in a full year. The researchers suspect a high-pressure system over the Pacific Ocean is preventing the formation of what they call “atmospheric rivers,” or air currents heavy with water vapor, from hitting the coast. These rivers aren’t frequent, but when they do come, they bring a lot of rain with them. For instance, the state received three inches when two rivers hit last December (one is shown above, with the rain in red and yellow).
Unfortunately, since 2011, these extreme rainfall events, which typically account for 20 percent to 50 percent of the state’s annual precipitation, have become in even more infrequent. And from the ground, the impact of this liquid debt has been all too obvious. Just take a bird’s-eye look at its reservoirs, shown below.
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