As others have pointed out, there's no need to store heat for six months. But you bring up a common enough viewpoint, one that I think bears re-examining:

>I'd imagine there's not enough water to do this inland..

We quite often forget that there's no physical limitation on the amount of water available inland. Water is constantly flowing from the oceans onto land, being recycled (mainly by trees pushing it back up into the airstream), and flowing back out and mixing with the ocean.

So the amount of water per square meter of land is limited by only two variables:

* The rate at which fresh water falls on land (liters/hectare/year)

* The time it takes that water to flow to the ocean (years).

The amount of water available on land (liters/hectare) is simply these two quantities divided by each-other.

The flow is fundamentally limited by the energy balance of the sun, so there's not much we can do there. But the time is entirely determined by our ability to design infrastructure and land use patterns that store water on the land in useful catchments instead of draining it off rapidly. Farm-scale dams are one visible way of doing that, but it's much cheaper to store water in the ground via infiltration systems.

The amount of water is inversely proportional to the amount of time it takes water to flow back to the ocean after it falls. So if we want to "wet up" the landscape, we should make it follow a loooong path with a lot of passive friction and storage buffers.

Just to show my math here, in the USA on average there's 715 mm of rainfall per year, which works out to 19,000 gallons for the average 100 m^2 house footprint. And next year you get that much water again.

In extremely arid areas like California it would even be possible to use salt water for thermal storage.

That's true for west coast cities, but not for east coast cities like Boston and New York, which experience terrible temperature extremes.

How much water do we need? I wouldn't try to affect large regions, just specific urban areas. The water doesn't actually have to go anywhere, it just sits around storing heat. All we have to do is bubble a lot of air through it. As a nice side benefit, this should clean the air.

(This is my version of the Reber Plan).

Are you proposing that we capture heat this way to warm houses (in which case it's a terribly ineffective and inefficient system) or to actually raise the outside temperature? If you're proposing the latter, there's just no way. Water might store 400 times as much heat per unit as air, but there's an absurd amount of air hovering around a town and an enormous area that air mixes with constantly.

It's true for Boston and NY as well. Those cities have milder weather than the cities inland of them.