Introduction
Between December 2022 and early January 2023, several atmospheric rivers (ARs) drenched California, which caused major floods, road closures, power loss, and in addition, partially resupplied the state's reservoirs (Fox Weather). According to the National Oceanic and Atmospheric Administration (NOAA), downtown San Francisco received 17.64 inches of rain, and the town of Honeydew in Humboldt County recorded the state's highest total, 47.74 inches of rain, from Dec. 26, 2022, to Jan. 17, 2023. In comparison, the 1981 to 2010 average annual rainfall for California was about 22 inches, and the average December rainfall was about 3.75 inches according to NOAA and the Western Regional Climate Center.
Using SMAP to Measure Coastal Storm Rain Runoff
Heavy precipitation and flooding on land can have an impact on the coastal ocean via runoff. The unusually large amount of freshwater discharged into the ocean can form a plume that can be traced using satellite measurements of Sea Surface Salinity (SSS). For example, the NASA Soil Moisture Active Passive (SMAP) instrument was used to detect the unusually fresh SSS associated with the atmospheric rivers that affected the western part of the U.S. in December 2022 and January 2023.
Major Findings
The visualization above shows the persistence of fresh anomalies (deviation from normal) along the western coast of the U.S. a few days to few weeks following the atmospheric river storms. The unusual presence of fresh waters — highly concentrated in terrestrial organic and inorganic matter — can have a detrimental impact on ocean ecosystems due to the significant perturbation of salinity and the terrestrial matter intrusion carried from land via runoff that can threaten marine life. Therefore, impacts of runoff from heavy land precipitation into the ocean should be monitored.
The end of February 2023 is seeing another pulse of heavy rainfall from a cold northern system with downtown Los Angeles receiving 4.49 inches of rain and the mountain communities measuring up to 93 inches of new snow (NOAA).
Related Links
- IMERG precipitation data used in the animation
- Notebook tutorial to recreate the animation shown above, and explore the datasets