The next huge natural catastrophe to strike California might not be an earthquake. New research suggests that a major flood could inundate large swaths of California in the next few decades. The last “200-year flood” was more than 150 years ago, and climate change is jacking up the odds of a repeat sooner rather than later. In order to prepare, state water officials must rethink whether big, costly dams really are the best investment of limited resources.