An ARkStorm (for atmospheric river 1,000 storm) is a hypothetical but scientifically realistic "megastorm" scenario developed and published by the Multi Hazards Demonstration Project (MHDP) of the United States Geological Survey, based on historical occurrences. It describes an extreme storm that could devastate much of California, causing up to $725 billion in losses (mostly due to flooding), and affect a quarter of California's homes. The event would be similar to exceptionally intense California storms that occurred between December 1861 and January 1862, which dumped nearly 10 feet of rain in parts of California, over a period of 43 days. The name "ARkStorm" means "atmospheric river (AR) 1,000 (k)" as the storm was originally projected as a 1-in-1000-year event.