The number of people giving online has fallen by almost 28 per cent in 18 months, according to a new report.
About 1.8 million people donated to charity online in the year to autumn 2006, down from 2.3 million in the year to spring 2005, according to Continental Research.
The market research company's Internet: The Autumn 2006 Report, one of a series published biannually, tracks online spending activity.
"Charities received a huge boost from the December 2004 tsunami appeal, which demonstrates the benefit of the internet in a time of crisis," said a spokeswoman for Continental.
Megan Pacey, director of policy and campaigns at the Institute of Fundraising, said the report's findings were unsurprising. "It's not just the tsunami effect," she said.
"Last year there were other high-profile appeals, most notably after Hurricane Katrina and the Pakistani earthquake."
Brendan Gormley, chief executive of the Disasters Emergency Committee, said his organisation had noticed an increase in online giving with each emergency appeal it launched in 2005.
The DEC received about 15 per cent of donations for its tsunami appeal online. Twenty-three per cent of donations for its later Asian earthquake appeal were made online.
Other online transactions, such as music downloads, have increased over the same period.