CE322 Basic Hydrology
Jorge A. Ramirez
Computation of Precipitable Water  Example
Compute the precipitable water for a saturated column of atmosphere extending 10 km up from the ground surface. Assume the surface pressure is 101300 Pa, the surface temperature is 30 C and the ambient lapse rate is 6.5 K/km.
Precipitable water:
The solution is presented in tabular form. The columns of the table are computed as indicated below.
Column 1: Elevation in km
.
Column 2: Linear vertical temperature distribution.
Column 3: Vertical pressure distribution assuming hydrostatic conditions and linear temperature distribution:
Column 4: Saturation vapor pressure:
Column 5: Moist air density
Column 6: Specific humidity
Column 7: Average specific humidity
(1) Elevation 
(2) Temperature 
(3) Pressure 
(4) Vapor Pressure 
(5) Density 
(6) Specific Humidity 
(7) Average Specific Humidity 
(8) Dp/g 
(9) q_{v} Dp/g 

(km) 
C 
K 
Pa 
Pa 
kg/m^{3} 
q_{v} 
kg/m^{2} 

0.00 
30.00 
303.00 
101300.00 
4310.66 
1.15 
0.03 

0.02 
2126.62 
44.05 

2.00 
17.00 
290.00 
80437.86 
1934.12 
0.96 
0.01 

0.01 
1757.16 
20.10 

4.00 
4.00 
277.00 
63200.08 
804.92 
0.79 
0.01 

0.01 
1438.96 
8.50 

6.00 
9.00 
264.00 
49083.90 
307.27 
0.65 
0.00 

0.00 
1166.85 
3.30 

8.00 
22.00 
251.00 
37637.08 
106.16 
0.52 
0.00 

0.00 
935.99 
1.16 

10.00 
35.00 
238.00 
28454.98 
32.66 
0.42 
0.00 

W=77.10 
W = 77.10 kg/m^{2} = 77.10 mm