Climate change likely contributed to Southern California’s record rainfall
Drought-stricken California experienced some desperately-needed rain as the remnants of Hurricane Dolores drew on atmosphere loaded with additional moisture by global warming to drive record-breaking rains. San Diego received over an inch of rain on Saturday, July 18 which not only broke the single day record for July, but also broke the monthly record as July is normally very dry. This means San Diego experienced more rain on July 18, 2015 than it had in any July since record-keeping began. In fact, this combined with the rainfall on Sunday, July 18, San Diego received more than a month’s worth of rain in those two days, more than it has received over the course of every single July in the past 101 years, when record keeping began. Los Angeles also received more rain over the weekend than the record for cumulative July rain. Records tend to be broken whenever natural variation and climate change run in the same direction, in this case towards moister atmospheric conditions.
Global warming contributed to the intensity of the rainfall
The immediate cause of this record rainfall was the remnants of Hurricane Dolores, a Pacific hurricane that pulled tropical moisture into the southwestern United States. Global warming contributed to the intensity of the rainfall by loading the atmosphere with additional moisture. 2015's active hurricane season was likely fueled by record hot ocean waters, which were warmed by a combination of an El Niño and climate change. In June 2015, the global sea surface temperature was 0.74°C (1.33°F) above the 20th century average of 16.4°C (61.5°F), the highest for June on record, surpassing the previous record set last year by 0.06°C (0.11°F).