I've been playing around with google trends, and i see for many keywords that the searchvolume has increased dramatically in the last months.. I see this with english and spanish keywords... any explanation? Casa: http://www.google.com/trends?q=casa&ctab=0&geo=all&date=all&sort=0 House: http://www.google.com/trends?q=house&ctab=0&geo=all&date=all&sort=0
Google trends shows relative trends as far as I can tell. That means that any keyword that shows an increase does so at the expense of some keyword that shows a decrease. In other words: it's a pure coincidence that the keywords you tested show increases. And the examples you give are in the housing market (casa and house): since there has been a lot of press around that market recently, I'm not surprised there's an increase in search volume for those words.