VP THE FUTURE OF ARID LANDS 
TABLE 1 
: F Height of Pan Diameter Evaporation 
L : 
Station ocation (ft) (ft) (in.) 
Tower 1 1500 ft inland Ground 2 164.50 
Tower I 1500 ft inland 40 2 193.44 
Tower 2 500 ft at sea 2 4 108.65 
Tower 2 500 ft at sea 45 4 137-75 
Tower 4 7500 ft at sea 2 4 106.45 
Tower 4 7500 ft at sea 45 4 140.02 
measuring inflow, outflow, and change in water level. The results 
for three years are as follows: 
Period Evaporation (in.) 
June 1, 1907—May 31, 1908 51 
June 1, 1908-May 31, 1909 59 
June 1, 1909—May 31, Ig10 69 
The average annual evaporation for the 3-year period was about 
60 inches. 
The evaporation from the inland ground pan was more than 
two and one-half times that from the sea and that from the two 
pans mounted 2 feet above the sea surface, 80% greater than 
from the sea. The similar evaporation from comparable pans on 
towers 2 and 4 indicates that the rate of evaporation from the 
sea is nearly uniform, beginning a short distance from the shore. 
The much smaller evaporation from the 45-foot high pans over 
the water than from the 40-foot pan over the land proves the 
existence of a ‘“‘vapor blanket’ over the water and shows the 
strong reciprocal relation between the moisture structure of the 
air and the evaporation. 
The evaporation from Lake Okeechobee in the humid climate 
of Florida has been determined by careful measurement of pre- 
cipitation, surface inflow, and outflow (3). Inseepage and out- 
seepage were not measured but are believed to be small. The lake 
is 600 to 800 square miles in area. At the same time, the Weather 
Bureau has maintained a standard 4-foot evaporation pan at 
Belle Glade, on the south shore of the lake (6). The comparative 
mean monthly evaporation in inches is as follows: 
J 1 AMIE NET] i BS O INP = ID Yieate 
Dake 254) 2586" 4.20) 666, 5.98 5-360 16.045 263) 14-155 990 02 7 Ee ge 
Pan ~ 322) 4-05 (15-79) 6264.77.25, (6.28 16.32. (6-36) 5533) 5-03) 6 3-77eg Oo lOR EOS 
