I really depends on what air temperature, wind and humidity you are comparing to from last fall. All 3 can make a major difference in water loss. Take a 5 gallon bucket put some rocks in it and place it in the pond with the rim about 2 inches above the surface. Fill it with water at the same level in the bucket as in the pond. Monitor it for several days and you will see what your actualy leakage rate is compared to evaporation rate.

Bob