Impact Assessment of Hydrologic Attributes and Slope Instability - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 99

The following equations and constants were summarized from the Jensen et al.
( 1990 )

i. Slope of the saturation vapor pressure curve:
Values for the can be obtained from,

Δ

7

D ¼ : ð : þ : Þ : ð 3 : 2 Þ

0 20 0 00738T 0 8072 0 000116

where,
T temperature in ° C.

ii. Determination of the psychrometric constant (in kPa/ ° C):

c ¼

: =k ð 3 : 3 Þ

0 00163 P

iii. Determination of estimated atmospheric pressure:

P ¼ 101.3 0.01055 (EL) ð 3 : 4 Þ

iv. Determination of the latent heat of vaporization:

k ¼ 2 : 501 0 : 002361 T ð 3 : 5 Þ

where,
P estimated atmospheric pressure in kPa,

EL elevation in m,

λ

latent heat of vaporization of water in MJ/kg.

v. The Calculation of net radiation (R n ):
The net radiation (R n ) can be calculated from,

h i 0

T 4
a

0 : 5

R n ¼ ð 1 a Þ R s r 0 : 34 0 : 139 e ðÞ ð : 1 þ 0 : 9 n/N Þ ð 3 : 6 Þ

where,
R n

s surface in MJ m − 2 day − 1 ,

the solar radiation received at the earth '

ʱ the radiation reflection coef cient or albedo with values near 0.25 for

green crops,

10 − 9 MJ m − 2 day − 1 k − 4 ).

˃ Stefan Boltzmann Constant (4.903 × °

T a C +273),

n/N ratio of actual to possible hours of sunshine.

absolute air temperature in ° k( °