Why extreme rain in Southwest US hasn't fully eliminated the region's megadrought

The record-breaking rain soaking the Southwest U.S. in recent weeks still won't be enough to eliminate the megadrought status in the notoriously arid region completely, according to researchers.

The extra precipitation fueled by several rounds of atmospheric rivers and an El Niño event has improved parched conditions in the Southwest, which was previously suffering from a decadeslong megadrought. The U.S. Drought Monitor is currently indicating no drought throughout the state of California.

At Death Valley National Park, one of the driest places on earth, a temporary lake still remains in Badwater Basin -- a salt flat that once held up to 700 feet of water during the Ice Age. The water, which appeared in August following Hurricane Hilary, has not evaporated due to steady rounds of heavy rain ever since, according to the National Park Service.

However, drought conditions are still persisting in parts of the Southwest, according to maps released by the Drought Monitor.

In addition, the rain has not been enough to increase water availability in the Southwest, especially for major cities such as Los Angeles, Las Vegas and Phoenix, according to experts.

Before the recent years of heavy moisture, the Southwest was experiencing a precipitation deficit of about two decades long, Matthew Lachniet, a professor of geoscience at the University of Nevada, Las Vegas, told ABC News. Therefore, getting back to "normal" would require many more years of above-average rainfall, Lachniet said.

The last truly wet period occurred around 1998 when major reservoirs in the region were close to overflowing, following a very wet decade in the 1980s, Lachniet said.

"Maybe, just maybe, if we had another decade like the 1980s we might get something back to normal," he said.

The bigger problem in the Southwest is how water is distributed and where it comes from. In Los Angeles, most of the rainwater has been washing right to the ocean, which does little to ensure the region's water supply, Alex Hall, director of the Center for Climate Science at the University of California, Los Angeles, told ABC News.

"About 80% of the precipitation falling on the Los Angeles region goes directly to the ocean without being used for human purposes," Hall said.

A large portion of the water that serves Los Angeles, Las Vegas and Phoenix comes from snowmelt that trickles down the Colorado River Basin, which is still partially in drought, data shows.

However, not all of the water from the Colorado River makes its way to these major cities and the surrounding areas. Instead, much of it is rerouted to irrigate agricultural fields.

In California, about 60% of the state's share of water from the Colorado River is allocated for agriculture in the Imperial Valley, Hall said.

Currently, the combined water from Lake Powell and Lake Mead -- the largest reservoirs in the country -- is only about 35% full, according to the U.S. Bureau of Reclamation. An upcoming forecast calls for snowmelt runoff to deliver only 70% of normal water to the reservoirs in the coming months, Paul Miller, service coordination hydrologist for the Colorado Basin River Forecast Center, told ABC News.

In order to completely fill up many of the reservoirs in the West, it would take another six years of normal precipitation combined with a total break from using water from the Colorado River Basin, Miller said.

But not using water from the Colorado River would be impossible for much of the Southwest, which relies heavily on the watershed.

When combining long-term forecasts with a changing climate, the outlook appears grim for the Southwest, which is predicted to get even drier.

Further action and coordination will be needed in the future to continue to supply the region with the water it needs for years to come, the experts said.

ABC News' Stephanie Ebbs, Daniel Peck and Ginger Zee contributed to this report.