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It's winter and the rain falls none stop. Although you're dry and warm inside, your roof is redirecting lots of rainwater. For a 1000 square foot roof and 1 inch of rain, the roof will run off around 620 gallons of water! And if that water isn't properly redirected away from your house, water takes the path of least resistance and can end up in your crawlspace. Water in your crawlspace is not good.
Clear Roof gutters and downspouts
Most buildings already have gutter with downspouts. And since the goal of the gutters is to prevent the rainwater from rolling off the edge of the roof, make sure the gutters are clear of leaves and other debris that may have cluttered it up during the fall season. Luckily, I don't have any large trees on or near my property that drop any leaves, but I have been in other homes where leaves are a big problem. In that case, we've used gutter guards that prevent leaves from clogging up the downspouts.
Redirect Downspout as far away as possible
Once the gutters and downspouts are clear allowing water to properly draining, the next step is to drain the water as far away from the house as possible. In the front of the house where it meets the street, both the downspouts connect to underground drain pipes that lead rainwater to the curb into the storm drains which lead to the bay. But in the backyard, access to the street isn't as easy and the houses are pinned by neighbors. Also, both of the my backyard downspouts were not extended anywhere, so I had to purchase a downspout adapter and expandable drain pipes to direct it as far away from my foundation as possible (also being mindful my neighbors).
I've considered purchasing a simple splash block that moves the water away maybe 2-3 feet away from the downspout. A splash block could be permanently setup whereas the expandable drain pipe needs to be setup and taken down once each season. But I wanted better performance and found the expandable drain pipe to be the better solution.
I'll be the first to admit that having expandable drain pipes laying around the backyard isn't very pretty, but I only leave these out during the rainy season and tuck it away during non-rainy seasons.
My Experience
When I first moved into my home, the first rainy season was terrible. The entire backyard was flooded with water. To make matters worse, there was a layer of water that completely covered the crawlspace (mine is very low, I can literally barely crawl through, with a dirt bottom). Though I couldn't tell, the professionals could immediately identify a problem with the grading around my home. Once I hired professionals to install paver stones in the backyard, that solved much of the backyard flooding. What it didn't solve was the water under the crawlspace. Once I realized it was the downspouts, I DIY purchased home hardware parts I needed to drain the water as far from the house as I could. Fitting the pieces together takes no more than 5 minutes and I do check before any major storms.
Now, the dirt in the crawlspace of my house is only noticeably damp, but free of major puddling. If it holds up the entire rainy season, I'll considering adding a vapor barrier to further control moisture in the vented crawlspace.