I studied the Wikipedia formulas and they are beyond my knowledge. Can one figure evaporation from a fish pond with just this information? Copy paste of Historical for August:
High: Low: Average:
Temperature: 93.1 °F 38.3 °F 69.5 °F
Dew Point: 47.1 °F 25.8 °F 36.0 °F
Humidity: 71.0% 12.0% 33.0%
Pressure: 29.91in 29.66in -
Precipitation: 0.00in
Lat: N 39 ° 11 ’ 36 ‘’ ( 39.194 ° )
Lon: W 119 ° 45 ’ 53 ‘’ ( -119.765 ° )
Elevation (ft): 4723
I’m sure someone else can come up with the right equation, but I’m also sure they’re going to need at least two more bits of information: 1) water temperature and 2) surface area.
Pond plants and muddy shores can also contribute to evaporation. So can waterfalls or other water features that create spray.
At noon today the water temperature was 69F and the air was 81F. The area is 129 square feet.
I don’t know how to figure it out but you will certainly need to know the wind speed as well.
Here you go.
That’s a Desert Research Institute report on evaporation from open water surfaces in northern Nevada, including Carson City. Page 21 of that pdf file gives estimates of monthly evaporation from a number of local reservoirs, and Figure 5 shows the different reservoirs over the course of the year. A fish pond will mix pretty well and doesn’t have a lot of thermal inertia, so you’re going to be closer to the Boca pan evaporation rate (the heavy black line in Fig. 5) than any of the reservoirs. In a typical August, you’re probably losing about 7 in/month (5-6 mm/day) of water due to surface evaporation.
There are references in the back of the report if you really want to dig into the equations, but if you’re just looking for a number that should get you going.