The Phoenix area's single-family home foreclosure rate jumped last month, with 31% of existing-home sales classified as foreclosures, according to a new report from the W.P. Carey School of Business at Arizona State . A month earlier in July, the single-family foreclosure rate in greater Phoenix held steady at 29%. Prior to hitting 29% in July, the foreclosure rate hovered at 43% in January and February, falling all the way down to 29% in July and then ticking back up again last month. "The uptick in foreclosure activity was not entirely unexpected since we’ve seen a pattern of upward movement in this rate in the latter months of a year over the last few years," said the report's author Jay Butler, a professor emeritus at the W.P. Carey School of Business at Arizona State University. "The weak economy and income growth are probably leading to more people giving up on their homes." About 2,900 single-family home foreclosures occurred in Phoenix last month, up from 2,500 in July, but down from 4,000 in August of 2010. Many of the vacant homes are selling to investors outside the market. "Since the start of the housing decline in late 2007, investors, especially foreign investors, have been the dominant buyers of homes to either fix-and-flip or rent out," said Butler. "While the housing market is beginning to produce some positive movement, the surrounding economic environment continues with anemic job and economic growth that’s forestalling consumer confidence and preventing more people from buying homes." Write to: Kerri Panchuk.