California naturally alternates between warm dry summers and wet winters, but in the last few years these have swung wildly from extreme droughts to torrential floods, and this is only going to increase in the near future according to climate scientists.
After a period of drought in a region, there can be a sudden and abundant amount of precipitation that the ground is too dry to absorb, instead generating widespread and often deadly flooding. Scientists call these drastic transitions from one to the other "whiplash" events. In California, these are expected to happen every 200 years but a new study suggests that this will start happening more often.
According to the paper, published in Nature Climate Change, the California wet-dry cycle could become more extreme within the next 70 years. The researchers expect up to a 100 percent increase in extreme precipitation swings. Megafloods could happen every few decades and they would be an enormous challenge for both the state's water storage system and the flood control infrastructure.
Previous research has shown that the average value of precipitation in the Golden State is not expected to change much. But when and how this rain falls, has not been modeled before.
This study shows that more significant precipitation events are on the rise, and this is all down to global warming. A warmer atmosphere can hold on to more water, but sooner or later that water needs to come down. So, the researchers say, the worry is that there are going to be increasing episodes where an unexpected amount of water will be delivered in such a short period of time that neither the ground nor artificial reservoirs can hold it.
The researchers looked at both recent events in California as well as the more distant past to gauge frequency and weather patterns. The state experienced a prolonged multi-year drought between 2012 and 2016, which was challenging for the agriculture industry in the region. After that, the winter of 2016-2017 was suddenly extremely wet, leading to deadly mudslides, a major bridge collapse, and even a failure at the Oroville Dam’s spillway. This and much worse might become the norm rather than the exception.
The touchstone for the extreme events used in the model is the Great Flood of 1862, when California and its neighbors experienced weeks of continuous warm rain after years of drought. The unusually warm period melted the snow in the mountains, aggravating the situation. The Sacramento Valley became an inland-sea and thousands of people died. Many more lost their livelihood due to the flood. This was by far the worst storm in the State's known history. This new research suggests that events like the Great Flood are now three times more likely to occur again in California now.
1