After more than a decade of construction, project delays and cost escalations, San Mateo’s Clean Water Program is nearly finished but still re…

El Nino warps weather worldwide. Meteorologists say the natural El Nino cycle is both adding to and feeling the heat of a warming world. A new study says a shift from a rare three‑year La Nina to a strong El Nino recently helped trap extra heat in the climate system. Study authors say between warming from greenhouse gases and that La Nina to El Nino change, it explains three-quarters of Earth's energy imbalance, which leads to extra heat. Warmer waters are also causing NOAA to shift how it calculates and labels this cycle, which likely means more La Ninas and fewer El Ninos.

The roughly 40 million Americans who get drinking water from wells are at particular risk when harmful forever chemicals contaminate the supply. Odorless and colorless, the chemicals known collectively as PFAS are linked to increased risk of certain cancers. While water from a utility will be forced to meet federal PFAS limits, those limits won't apply to private wells. And well owners are often the last to learn about contamination. At least 20 states don't test private wells beyond areas where PFAS problems are suspected. When a well is tainted, it can take homeowners years to find a new source of clean water.

Atmospheric rivers are long and relatively narrow bands of water vapor that form over an ocean and flow through the sky. They carry moisture from the tropics to northern and southern latitudes, and can dump heavy rains or snow over land. According to the National Oceanic and Atmospheric Administration, they occur globally but are especially significant on the West Coast of the United States, where they create 30% to 50% of annual precipitation and are vital to water supplies but also can cause storms that produce flooding and mudslides.

Heavy rain and flash flooding have soaked roads in northern California, leading to water rescues and at least one confirmed death. Authorities say police in the city of Redding received numerous calls Sunday from stranded motorists who tried to drive through flooded areas. According to Mayor Mike Littau on Monday, one person died who was pulled out of a vehicle that was flooding. The National Weather Service expects more rain through the Christmas week and warns of potentially flooding, mudslides and rockslides. The flooding in California comes after stubborn atmospheric rivers drenched Washington state earlier this month.