Temperature, relative humidity, amount of direct sun light and wind as well as aeration can all impact evaporation rates. I know here we went about 6 weeks with little to no rain and the week before the rain finally came we were at 90 degree days for a week. That week we lost about 6 inches but all the weeks before we lost much less (inch or 2 per week). Having a bog area behind our pond appears to act as a reserve to slow down level drop and also slow up replenishment when it finally starts raining again.
