N˚

Climatic zone

Average annual rainfall P, mm

Parameters

β

n

λ

I

humid

≥900 mm

0.0025

0.80

0.6

II

Subhumid

900 - 400 mm

0.0103

0.50

0.9

III

semi-arid and arid

≤400 mm

0.1440

0.25

1