Monitoring Agricultural Drought in Mainland Portugal - Monitoring and Predicting Agricultural Drought: A Global Study - page 190

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Table 14.1 Palmer drought severity index
values for Beja, Portugal, during three drought
spells (Pires, 2003)

Year Month PDSI

1991 Sept. -2.17

1991 Oct. -1.98

1991 Nov. -2.64

1991 Dec. -3.56

1992 Jan. -4.11

1992 Feb. -4.28

1992 March -4.80

1992 Apr. -4.13

1992 May -3.62

1994 Sept. -2.20

[190

1994 Oct. -2.50

1994 Nov. -3.22

1994 Dec. -4.31

1995 Jan. -4.51

Line
——
4.4
——
Norm
PgEn

1995 Feb. -4.02

1995 March -4.37

1995 Apr. -4.29

1995 May -4.65

1995 June -4.91

1995 July -4.76

1995 Aug. -4.15

1995 Sept. -3.40

1995 Oct. -4.59

[190

1997 Feb. -1.67

1997 March -3.97

1997 Apr. -3.75

additional information on surface conditions. These channels are used to
estimate mass and energy fluxes between the surface and the atmosphere
(Cooper et al., 1989). The difference between surface temperature ( T s ) and
atmospheric temperature ( T a ) is a decreasing function of the plant's real
evapotranspiration (Jackson et al., 1977).
Taking into account this relationship, another index, the forest fire index
(FFRI), is computed at the IM on an operational basis:
FFRI T a )/ [ R g ( NDVI max ) ] [14.1]

where k is a constant, R g is the global radiation, and NDVI max is 10-day
maximum NDVI value. The above index is calculated on a daily basis; T s is
calculated using AVHRR data, and T a and R g are collected from the IM's
meteorological stations. The surface temperature, T s , is calculated using a
split window method (Melia et al., 1991) as expressed by equation 14.2:
T s =

=

k ( T s

−

T 4 + [1 . 31 + 0 . 27 ( T 4 − T 5 ) ] ( T 4 − T 5 ) + 1 . 16 [14.2]

where T 4 and T 5 are the brightness temperatures of respectively channel