A bit of background: I live in an old house in Austria and have been following the changes of temperature and relative humidity in our basement (which has two small but permanently open windows).
The temperature has dropped by about 2 degrees Celsius, reflecting the drop in outside temperature. At the same time, the relative humidity has also dropped considerably, by almost 20 percentage points (from 83% to 65%).
My best explanation so far is that a very warm fall weather gave us humid air which cooled in the basement, leading to high relative humidity. But now, with temperatures dropping sharply we get cool air which warms in the basement, leading to a rather lower relative humidity. This would be reassuring to me as it means that the previously high humidity could be prevented by installing airtight windows and I don't have to worry much about humidity coming from the basement walls.
BUT, I was wondering: Obviously, warm air accepts water more readily than cooler air, so the absolute humidity rises faster in warm air than cool air - but is that effect maybe so strong that even the relative humidity rises faster in warm air than in cooler air? Because in that case, my measurements could still be consistent with humid basement walls - the warmer air would just be "drawing out" the moisture more quickly, to the point that the relative humidity is higher than it would be with cooler air.
Is hope my question makes sense and I would appreciate any comments!