All too often, scrounging up the cash to pay for federal disaster relief has been a haphazard affair. The Federal Emergency Management Agency (FEMA) has a relief fund of about $7 billion or so, but it frequently falls short. That was the case after Hurricane Katrina slammed into New Orleans in 2005, and it happened again this year after tornadoes ripped through Alabama and Mississippi and severe flooding struck Louisiana. Whenever that happens, Congress has to scramble to put together an emergency supplemental. Hence the haphazardness. Last year, FEMA stopped approving rebuilding projects for six months until Congress scraped together an additional $5.1 billion.

This time around, now that Hurricane Irene has chewed up the East Coast and will likely “prove to be one of the 10 costliest catastrophe’s in the nation’s history,” FEMA is short on cash again, and Republicans are basically saying enough is enough. If FEMA wants more money, Congress will have to cut other programs to pay for the emergency supplementals, some say. “Those monies are not unlimited,” said House Majority Leader Eric Cantor on FoxNews, after promising storm relief.

Is there a better way to do things? Possibly. As Slate’s Dave Weigel recently pointed out, tucked deep in the debt-ceiling deal was a little-noticed provision to pre-fund future disaster relief programs. The way this works is that the fund would “be filled up annually with enough cash to pay for disasters, based on an average of what the last 10 years of disasters ended up costing.”

There’s just one problem with that. Disasters seem to be getting more expensive over time. A lot more expensive. Here’s a graph from a study by NOAA’s National Climactic Data Center showing that the number of U.S. weather disasters that cause $1 billion or more in damage has been on an inexorable upward path:

And, of course, climate change may be making disasters worse and worse. True, climate scientists are still debating whether, for instance, global warming is likely to make hurricanes more frequent and fierce. Much less controversial, though, is the idea that a warmer planet will mean more-extreme precipitation events in the Northern Hemisphere, not least because a warmer atmosphere will be able to hold more water. We can also expect a greater prevalence of floods and droughts in certain regions. More wildfires, too. All the sorts of things that frequently get declared federal emergencies.

So we’re quite likely to see weather disasters increase over time—and, no matter what, those disasters will get increasingly expensive. A rainy-day fund that’s based on past events arguably won’t cut it. Which means, unless there’s a better plan in sight, disaster-relief funding is going to keep being a haphazard affair.