Reading San Diego Rainfall Data Correctly
Most people look at annual rainfall numbers and think they understand what happened during a given season. They don't. The raw totals are only half the story. The other half is how those totals distributed across months, intensity events, and whether they came from Pacific storm tracks or monsoonal moisture. I've spent years pulling NOAA data, cross-referencing CoCoRaHS station reports, and trying to make sense of what "normal" actually means for a city that gets roughly 10.6 inches of rain annually on average. The 2023-2024 season is one of those years that looks fine on the surface and tells a different story underneath.San Diego Rain Totals How The 20232024 Season Compares To Historical Averages And Drought Records
The 2023-2024 rainy season ran roughly October through March. San Diego International Airport recorded about 11.8 inches during that window, which puts it slightly above the long-term average of 10.6 inches. On paper that sounds like a near-normal year. It wasn't. Here's what the aggregate number hides: the first four months delivered maybe 3 inches total. Then a single atmospheric river event in mid-January dumped over 3 inches in 24 hours. The rest of the season was mostly dry spits and light drizzle. So you had one massive event and a lot of nothing, which is the opposite of the steady widespread rain pattern that actually recharges aquifers and fills reservoirs. For context, the 2022-2023 season had been severely below normal at around 6.5 inches at the airport station, cementing multi-year drought conditions that had been building since 2020. The 2023-2024 season wasn't a recovery. It was a blip above average that didn't change the broader trajectory.
Where The Data Comes From And What To Trust
There are three main sources for San Diego rain totals. The National Weather Service maintains the official cooperative observer network at Lindbergh Field. CoCoRaHS runs a citizen science network of thousands of volunteer rain gauges across the county. And the Southwest Climate Hub publishes seasonal drought summaries through the U.S. Drought Monitor. Each source has a different failure mode. The NWS station at the airport sits at sea level in an urban environment. It systematically under-reports rainfall compared to higher-elevation stations by roughly 10 to 15 percent because of wind shadow and evaporation. Hillcrest and Mount Soledad will consistently log higher totals than the airport for the same storm. If you're comparing the airport number to historical averages from the same station, you're fine. If you're comparing it to a gauge in the Cleveland National Forest, the numbers won't match and you'll draw wrong conclusions. I ran into this exact problem when a local water district asked me to verify whether the 2023-2024 season had meaningfully improved groundwater recharge in the eastern part of the county. The airport data said above average. The CoCoRaHS stations in the mountains said near normal to slightly below. I ended up using a weighted average based on catchment area—airport for coastal, a handful of eastern CoCoRaHS gauges for the rest—and that gave a more useful picture. The eastern slopes got maybe 8 to 9 inches that season, which is close to their local average of 12 to 14 inches but not by much.
What Above-Average Actually Means For Drought
This is where most people get tripped up. Being 1.2 inches above the annual average does not cancel out two years of severe deficit. Let me walk through the math briefly. The 2021-2022 season at the airport was roughly 8.5 inches. The 2022-2023 season was about 6.5 inches. That's a combined two-year shortfall of roughly 8 inches below what would have been normal. The 2023-2024 season added about 1.2 inches above normal. So you've recovered maybe 15 percent of the two-year deficit in a single season. The ground is still dry. Reservoirs are still below median. The drought classification from the U.S. Drought Monitor for San Diego County shifted from D2 (severe drought) to D1 (moderate drought) in early 2024, but that's a category improvement, not a resolution. Another thing nobody talks about: soil moisture saturation. A heavy single-event rain like the January 2024 atmospheric river runs off quickly on dry, crusted soil. A lot of that water went straight into the ocean rather than infiltrating. Years of gentle, widespread rain soak in differently. The total accumulation can be the same but the hydrological impact is completely different.
Get the Full Details
How To Look At This Yourself
Go to the NOAA Climate Data Online portal. Search for San Diego International Airport, select daily precipitation from October 2023 through March 2024. Sum the values. Compare to the normal period 1991-2020, which is the current NOAA standard climate normal. The airport's October-to-March normal is approximately 8.2 inches, which means the 11.8-inch total was notably wet for the core rainy season. For drought context, pull the U.S. Drought Monitor archive. It updates weekly and goes back to 2000. You'll see San Diego County was in D1-D2 territory for most of late 2022 and early 2023, briefly dipped to D0 in early 2024, and then drifted back toward D1 as the spring dried things out. The Drought Monitor is a composite index—it factors rainfall, soil moisture, streamflow, and snowpack, not just rain gauges. That's why it's more useful than raw precipitation data alone.
Limitations You Should Know About
Raw rain totals are a blunt instrument for understanding drought. They don't tell you about evapotranspiration rates, which were running above normal in 2023-2024 due to warmer-than-average temperatures. They don't capture spatial variability—San Diego County spans from coastal desert to alpine conditions in under 60 miles. They don't account for the fact that the heaviest rain fell in January when demand is lower but also when evaporation losses are higher due to wind and sun between events. If you want a better picture, pair precipitation data with SAC-SMO soil moisture models from the Pitman Center or streamflow data from USGS gages on the San Diego River and Santa Maria River. Those give you actual water movement through the system, which is what drought is really about. Rain totals alone will mislead you every time.
