The winter storm flood record in Southern California

Why do winter storms drive the flood record here?

The National Weather Service's compilation attributes the flood record of the San Diego region mainly to winter storms, which bring heavy and sustained rain. The most serious events in the record are winter events, and that pattern shapes how the water work is planned.

Winter rain can come in long, wet spells as well as in single heavy bursts. Soil that is already saturated sheds less of the rain, so the water runs off faster into streets, yards and drains. A storm that arrives on wet ground can therefore produce more runoff than the same amount of rain on dry ground.

For a homeowner or a business owner, the pattern means that winter is the season to check the drains, the gutters and the shut-offs before the rain starts. It also means that a winter call often comes at a time when many buildings are wet at once.

What was the wettest season on record?

The compilation lists the 1883-84 season as the wettest on record for the region, at 25.97 inches of rain. That total is the highest in the compilation's record and is the reference point for what a very wet season can bring.

A season total is a broad measure. It does not show how much rain fell in a single day or how fast the water ran off the ground. A season can be wet in many small storms or in a few very heavy ones, and the damage depends on the timing as much as the total.

The 1883-84 figure is an old record. The compilation is a summary of the region's history, and older entries are the ones most likely to need checking against the original data. Read the figure as a sign of what the region has seen, not as a forecast.

What does the 1879 storm tell us about short bursts?

The compilation records a December 1879 storm of 4.23 inches in 48 hours. That is a short-burst event, and it shows how quickly a storm can overwhelm drainage that copes with ordinary rain.

A burst of rain over two days can run through drains and gutters faster than they can carry it away. The water then finds the lowest route into buildings, which is often a garage, a crawl space or a ground-floor room. The pattern matters for planning, because the water arrives quickly and the first hours are the most important.

The date of this storm is flagged for verification in the compilation. The figure is still useful as an example of a short, intense storm, and the scale of the rain is what matters for the planning advice in this guide.

What do the 1937 and 1959 floods show?

The compilation records flooding in 1937 that killed several people, and a 1959 storm with flood and mudslide damage. Both entries show that the region's flood risk includes danger to life as well as to property.

A flood that causes deaths is a reason to treat any warning seriously and to stay out of moving water. The rescue work after a flood of that kind is not the job of a water removal crew, and anyone in danger should call the emergency services first.

A mudslide adds a second kind of damage, because it can bury walls and floors and carry silt into buildings. The 1959 entry is a reminder that a storm can bring more than water, and that the ground and the slopes are part of the risk in a wet season.

How does a winter storm change the water work?

A winter storm usually means more buildings are wet at once, slower drying because the air is cool and damp, and more silt and debris from runoff. The crew plans the visits and the equipment to match those conditions.

The first priority is still to stop the source and remove the standing water. Once the water is out, the drying takes longer in cool, humid conditions, so the readings are watched more closely and the equipment is set to suit.

Storm water often carries silt and debris, and that changes the scope. Silt-laden material is removed where it cannot be cleaned, and the category of the water is recorded on arrival so the decisions can be checked.

What should a household do before the winter season?

Clear the gutters and the drains you can reach safely, test the sump pump if there is one, and know where the main water shut-off and the electrical panel are. Keep the line's number in a place you can reach during a storm.

Look at the ground around the building, and check that water runs away from the walls rather than toward them. A downspout that discharges at the foundation or a planter that holds water against a wall is a common cause of winter damage.

Make a short list of valuables and of what is stored on the floor of a garage or basement. Move the most important items up before a storm, and photograph the rooms so there is a record of what was there.

Test the sump pump, if there is one, by pouring water into its basin until it starts. Check that its discharge runs away from the foundation, and that a battery backup, if fitted, is charged. A pump that works on a dry day can still fail during a storm if its float or its power has not been checked, so a short test before the rains is time well spent.

How should I read a historical flood record?

Read it as a record of what the region has experienced, check the dates in the original source, and remember that a historical record does not predict the next event. The most useful lesson is the range of what has happened.

Some entries in the compilation are old, and the dates and figures of older events may be revised as the sources are checked. The compilation itself flags those entries, and this guide follows the same caution.

A record of past events is a guide to planning, not a forecast. The planning steps are the same whatever the next storm does: know the shut-offs, protect the valuables and call early if water is coming in.

How does a crew read a building after a winter storm?

The crew checks the lowest rooms first, reads the moisture in the floor, the lower walls and the framing, and then works up. It records the readings against each room so that the drying can be measured from the first visit.

Water from a winter storm often finds the lowest route into a building, so the garage, the crawl space and the ground-floor rooms are checked first. The readings are taken on the floor, the bottom plates of the walls, the subfloor and any insulation that can be reached through an opening. A thermal camera helps show cold, wet areas that the eye misses.

The readings are then repeated on each return visit until each material reaches its dry standard. The crew does not treat a winter job as finished because the surface feels dry, since cool air slows the drying and wet framing can hold water for longer than the room above suggests.