jparr said:
Just a personal observation, but it seems that I lose more water during dry windy periods, than during hot, humid, still days.
That makes perfect sense. The formula for evaporation from pools has a factor for wind and another for the difference between the saturation vapor pressure (at water temp) and the actual vapor pressure (at air temp). So there is more evaporation with more wind and with dryer warmer air and with warmer water temperature. The sun does not directly cause evaporation, but it indirectly increases it by warming the temperature of the surface of the water.
Here are some specific examples.
Water Temp: 85ºF
Air Temp: 75ºF
Relative Humidity: 66%
Wind: 0
Evaporation: 0.20 inches/day
Same as above, but with wind of 5 MPH: 0.62 inches/day
Save as above, but with wind of 10 MPH: 1.06 inches/day
NOTE: wind is measured near the water surface so is generally lower than general wind speed
Same as above (no wind), but with relative humidity of 20%: 0.32 inches/day
Same as above, but with water and air temp at 50ºF: 0.04 inches/day
The evaporation rate during the day and at night is actually somewhat similar (assuming the same wind) because the relative humidity rises at night as the temperature cools, basically keeping the same amount of water in the air. You just see the evaporation effects more readily when the air is cooler since its increased saturation means there will be more visible "steam" as the water condenses.