Charitable giving in the U.S. totaled $323.9 billion in 2010, up 6.6 percent from 2009, says a newly released report from the Atlas of Giving.

The 2010 figure is particularly meaningful given the fact that 2009 saw an unprecedented decline in donations to American nonprofits of 5.7 percent.

The growth in giving was fueled primarily by robust stock market performance. The S&P index gained more than 15 percent for the year.

Charitable giving results varied considerably by organization. Nonprofits that derive significant income from major gifts, corporate giving, foundation grants, and bequests did better than those relying on smaller gifts from individuals. Donor-advised funds had a record year in additional contributions, new accounts, and distributed gifts. Online giving was exceptionally strong in 2010.

The rebound, while welcomed, was limited by factors, including high unemployment and economic fallout from the BP gulf oil spill.

"The impact of unemployment on giving is far reaching and long lasting," says Rob Mitchell, former president of the American Cancer Society Foundation and now CEO of Philanthromax, which publishes the Atlas of Giving. "In addition to the obvious limitations associated with loss of income, once individuals again become employed there are typically accumulated financial responsibilities, such as credit card debt and essential purchases that have been deferred due to job loss."

While the environmental damage of the BP spill on the gulf failed to meet initial estimates, the impact on the regional economy was nothing short of devastating. Charities and churches in Louisiana, Mississippi, and Alabama saw dramatic declines in giving as local economies contracted in the wake of the spill, the study showed. Several nonprofits have subsequently filed suits against BP in hopes of recovering lost revenue.

Giving in response to the Haitian Earthquake was modest in comparison to similar disasters in previous years. As a result, disaster-related giving had only a minor additive impact in 2010, the report said.

The Atlas of Giving touts itself as the definitive measurement of charitable giving in the U.S. It is a precise mathematical algorithm that relies on specific, defined economic and demographic input factors. The formula accurately matches published giving data from Giving USA for the last 42 years. Its coefficient of correlation to past published data is 99.5 percent accurate, Atlas says. Because the factors included in the algorithm are documented and reported monthly, the Atlas of Giving is able to use that data to measure charitable giving monthly and doesn't need to rely on surveys or delayed segment reporting data. The Atlas of Giving contends it takes into account the entire giving universe and is the precise measurement of total annual giving in the U.S.

The algorithm accurately accounts for changing economic conditions, demographic trends, natural disasters, and significant national and world events, Atlas of Giving asserts.

The Atlas algorithms can be used to create customized charitable giving measurement and forecasting for giving sectors such as health and education. Custom versions can also be created for individual nonprofits.

The Atlas of Giving was created by a team of 25 mathematicians, analysts, and statisticians who evaluated more than 50 possible variables over four decades to establish the model.

The Atlas of Giving is a free service and combines a rolling 12-month forecast with reports of monthly, quarterly, and annual aggregate giving. The no-cost subscription includes monthly updates, trend reports, and analysis.

Those on the cutting edge of nonprofit management have been quick to embrace what the new technology represents, Atlas of Giving claims.

"What the Atlas of Giving has accomplished in terms of providing charitable giving data to charities in real time represents a major innovation," says Stephen Nill, Founder and CEO of CharityChannel.com, an online resource for nonprofit professionals, with over 30,000 members. "The Atlas is a game-changer for nonprofits in terms of the management of operations related to gift income."