Confronted with an unprecedented string of tornadoes, floods and wildfires, the American Red Cross and other relief groups are scrambling to raise money fast enough to meet the demand for help.

“The disasters just keep coming,” said Red Cross spokesman Roger Lowe, reporting that the organization has spent $41 million thus far responding to the seven-week onslaught while raising $33.6 million to cover the costs.

Those figures were tallied before the latest violent storm system rampaged through a wide swath of the Midwest starting late Tuesday.

No single one of the recent disasters — not even the cataclysmic tornado in Joplin, Mo., on Sunday — poses a challenge on the scale that the Red Cross confronted after Hurricane Katrina in 2005. However, Red Cross officials said the period that began March 31 is unique in their memory for the sheer number of major natural disasters in such a short span.

During that period, the Red Cross has launched 29 separate relief operations in 22 states, responding to wildfires in Texas, flooding along swollen rivers, and the rash of tornadoes that have killed more than 500 people. More than 9,200 Red Cross disaster-responders have been deployed; they’ve served more than 2.1 million meals and snacks and opened more than 200 shelters.

Lowe said costs are running high in part because of the long-term effects of many of these home-destroying disasters. For example, he said 93 people were still living in Red Cross shelters in Alabama, where tornadoes wrecked their homes a month ago.

“The public truly has been very generous, but the series of tornadoes and floods is really stretching our resources,” Lowe said. “The fundraising is not keeping up with our extended needs, and we don’t know how long we need to be providing shelter, food, mental health assistance.”

So far, Lowe said, the Red Cross has been able to meet essential needs despite the gap between expenses and fundraising. One reason is the charity’s Annual Disaster Giving Program, involving 28 companies that collectively donate more than $15 million a year so that the money is in place for immediate disaster response.

Aside from government entities, the Red Cross is by far the largest U.S. disaster-relief organization, but many other national and local groups also are facing fundraising challenges as they respond to the recent calamities.

“We are really struggling,” said Roger Conner, spokesman for Catholic Charities USA. “We’ve not seen this number and extent of spring storms in 40 years … and we just don’t have the outpouring of donations we would like. The need is huge.”

Through mid-May — before the Joplin tornado — Catholic Charities had received about $300,000 for the spring disasters, which Conner described as very low. He noted that the charity raised $2 million in the same timespan after hurricanes Gustav and Ike in 2008.

The Salvation Army said it raised $7.7 million in response to the tornadoes in the South in April but doesn’t have an updated figure to account for this month’s disasters. By comparison, it raised $382 million for Katrina relief efforts.

The Southern Baptist Convention’s North American Mission Board, which engages in disaster relief, said it has raised only about $100,000 thus far for tornado relief work in a half-dozen states.