## M. AYDIN, S. F. KEÇECİOĞLU

2} 2i_{fc }

#

2} 2i_{ad }

#

i_{fc }

i_{fc }

}

=-

(i_{fc }- i_{ad})

i_{ad }

i_{ad }

}

=

(i_{fc }- i_{ad})

c)

S

_{ifc }=d)

S

_{iad }=

e) S_{a }=

2} 2a

#

a }

=-1

For |ψ_{ad}|, Kelvin’s equation can be employed (Brown and Oosterhuis 1992; Aydın 2008):

}_{ad }=

R_{g}T mg

lnH_{r }

(4)

where ψ_{ad }is the water potential for air-dry conditions (cm of water), T is the absolute temperature (K), g is the acceleration due to gravity (981 cm s^{−2}), m is the molecular weight of water (0.01802 kg mol^{−1}), H_{r }is t h e r e l a t i v e h u m i d i t y o f t h e a i r ( f r a c t i o n ) , a n d R g i s t h e u n i v e r s a l g a s c o n s t a n t ( 8 . 3 1 4 3 × 1 0 4 k g c m 2 s − 2 K^{−1}). m o l −1

Climate data and soil properties

The climate data were obtained from Adana Meteorological Station (Turkey) for the study year of 2006 (Table 1). The soil properties used in the model were as described by Aydın (2008). The soil texture is fine with sand of 331, silt 122, and clay 547 g kg^{−1 }of soil mass at the layer of 0-40 cm. Dry bulk density varies between 1.20 and 1.27 g cm^{–3}. On average, volumetric water content at field capacity is 0.35 cm cm^{−3}. In this study, albedo of the bare soil was assumed to be 0.15 (van Dam et al. 1997; Ács 2003). I n t h e c a l c u l a t i o n s o f s o i l w a t e r p o t e n t i a l , t o r t u o s i t y p a r a m e t e r ( α ) , w h i c h c a n b e d e f i n e d a s t h e a c t u a l round about flow path, for the clay soil was taken as 1.1 cm. The volumetric water content at air-dry condition and hydraulic diffusivity were assumed to be 0.05 cm^{3 }cm^{−3 }and 95 cm^{2 }day^{−1}, respectively. As suggested by Aydın (2008), ψ_{tp }for the clay soil was taken as 60.0 cm of water. 3

# Computation of relative sensitivity coefficients

The relative sensitivity of |ψ_{ad}| to input variables in Equation (4) are as follows:

a) S_{T }=

2}_{ad }2T

#

T }_{ad }

=1

b) S_{Hr }=

2}_{ad }

# 2H_{r }

#

H } r ad

=

1 lnH_{r }

In the simplest form, a first-order Taylor series approximation requires computing the model output at a single point and determining the derivative (van Griensven et al. 2006). Therefore, the daily model outputs were calculated by using measured climatic data and soil properties for the entire year of 2006. Then the relative sensitivity coefficients for the selected variables were determined based on partial

January

8.8

62.9

4.4

1.6

36.3

February

10.5

63

3.4

1.6

131.6

March

14.1

76.4

5.1

1.3

46.2

April

18.5

76.2

4.3

1.2

9.3

May

22.4

69

10.4

1.1

19.7

June

26

73.2

10.6

1.2

4.5

July

27.9

78.8

10

1.1

41.3

August

29.1

78.9

9.5

1.1

5.7

September

26.2

67.7

8.7

1

37.4

October

21.5

70.8

6.7

0.9

156.3

November

13.2

65.1

6.5

0.9

91.5

December

9.3

57.7

6.9

1.2

0

501

Mean

Mean relative

Mean duration

Mean wind

Rainfall

temperature

humidity

of sunshine

speed

(mm)

(°C)

(%)

(h day^{-1})

(m s^{-1})

## Month

Table

1. Some monthly climatic

data of Adana for the study

year of 2006.