Tom Cheesewright, author of The Book of The Future, will make the claims at the annual charities event The Gathering in Glasgow this week.
He says many lower-level white collar jobs are destined for redundancy, leaving the natural supporters of many charities short of cash to help fund their work.
Meanwhile the 'buzz' of altruism which motivates charity volunteers, fundraisers and benefactors may be increasingly available through one-click online charity campaigns, depleting real-world organisations of time and money, he warned.
The futurologist, whose consultancy has provided advice on long-term planning to councils, health boards and housing bodies, will speak at the event run by the Scottish Council for Voluntary Organisations on Wednesday at the SECC.
However, he said he would avoid discussion of the independence referendum, despite its prominence in the minds of many charities, to concentrate on technology-related vulnerabilities.
He said: "There are other issues which are more dramatic and pressing, which are not being addressed, and to which charities ought to be preparing a response ."
One of the key changes which could affect charity campaigning is the effect of the internet, Mr Cheesewright will warn.
The proliferation of online campaigning sites, such as Change.org, Avaaz and SumOfUs, is a significant threat, he fears.
He said: "These sites have used the internet to build enormous memberships, backing campaigns which are chosen for their likely success. But we know there are chemical effects which happen when you give. We are chemically rewarded for engaging in society.
"If you can get an equal dopamine high for giving just one click, rather than giving an hour of your time or cash, that will raise serious questions."
He also claims automation, which has already affected many manual and production-line jobs, will increasingly affect non-manual workers. This could lead to the loss or reduction of large numbers of middle income jobs.
He said: "Technology is going to drive even more change. The Institute of Chartered Accountants is currently going through a huge futurism exercise, and is predicting great chunks of what accountants currently do will soon be automated.
"The same will happen to lawyers, finance and HR departments. Over the next few years, huge swathes of the lower end of middle class jobs are being chopped out of the sector.
"The middle-classes are a big constituency for charities. If they are becoming less wealthy and less secure in their income, that affects an important source of funding. On the other hand, people may have time freed up to volunteer or be carers, if part-time work becomes more common."
His talk on Wednesday will be followed by sessions in which charity leaders will be invited to brainstorm solutions.
John Downie, director of public affairs, SCVO said: "The latest UK Giving report in 2012 found a 20% drop in donations to charities in real terms. Despite remaining very supportive of charities' work, people are seeing their disposable incomes fall as the cost of living rises and salaries fail to keep up.
"Should this trend continue, it could be particularly worrying for smaller charities, which tend to rely more on donations from the general public."