Soil-climate impacts on water cycling at the patch level

Statement of the problem

These numerical experiments investigate the impacts of climate and soil physical properties including soil texture and soil depth on the cycling of water, mainly on soil water, soil tension, volumetric soil water, outflow, and leaf area index for evergreen needle-leaf forest in Chapel Hill Area.

Experimental setup

(1) Dependent variables: soil water, soil tension, volumetric soil water, outflow, and leaf area index.

(2) Treatments: There are six treatments in total, including two soil depths and three soil textures. For the soil depth, topsoil (0-30cm) and root-distributed profile (0-100m) are considered. For the soil textures, Sandy/silt/clay loams are considered respectively

Table 1 Treatments for Soil-climate impact on water cycling in Chapel Hill

Tr. Soil Texture

Depth(m)

Sand(%)

Silt(%)

Clay(%)

Typical Soil Types in Chapel Hill

Ch1 sandy loam 1 60 30 10 Appling sandy loam

Ch2 silt loam 1 35 50 15 Georgeville silt loam

Ch3 clay loam 1 30 30 40 Hiwassee clay loam

Ch4 sandy loam 0.3 60 30 10 Appling sandy loam

Ch5 silt loam 0.3 35 50 15 Georgeville silt loam

Ch6 clay loam 0.3 30 30 40 Hiwassee clay loam

(3) Other model simulation control information in the initiation file

• Climate data years: 1980-2004; 25 years in total, beginning with 1980.

• Forest type: enf (Evergreen needle-leaf forest)• To write a restart worksheet: set up sim_type=1;

read restart worksheet: false; and write restart worksheet: true

• To run daily or annual simulation: use normal simulation(sim_type=0); read restart worksheet: true; and write restart worksheet: false

Results

1. Effect of climate and soil texture on the annual total water outflow

climate data

0

20

40

60

80

100

120

140

160

180

19801982 19841986 19881990 19921994 19961998 20002002 2004

Pre

cip

13

13.5

14

14.5

15

15.5

16

16.5

17

Precip (Cm yr-1)

Average Temp (deg C)

The wet years in Chapel Hill were 1989 and 1999, and the dry years were 1988 and 2001.

• The maximum water outflow was occurred in 1999, which is also the wettest year in Chapel Hill

• There was no obvious difference in outflow between different soil textures. But soil depth affected the outflow greatly. The water outflow in top soil (0-30cm) is 0.9-22.4 cm yr-1 more than those for one meter soil depth.

• For leaf area index, it is higher in 1m profile than 0-30 profile

Outflow

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

ch1

ch2

ch3

ch4

ch5

ch6

max LAI

3.0

3.3

3.6

3.9

4.2

ch1

ch2

ch3

ch4

ch5

ch6

Other related simulated annual results

Evapotranspiration

80.0

90.0

100.0

110.0

120.0

130.0

140.0

150.0

160.0

year

ch1

ch2

ch3

ch4

ch5

ch6

NPP

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

ch1

ch2

ch3

ch4

ch5

ch6

MR

1100.0

1200.0

1300.0

1400.0

1500.0

1600.0

1700.0

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

ch1

ch2

ch3

ch4

ch5

ch6

GPP

1500.0

1800.0

2100.0

2400.0

2700.0

3000.0

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

ch1

ch2

ch3

ch4

ch5

ch6

2. Effect of climate and soil texture on the daily water cycling

• Simulate data of 1999-2004 were used to analyze the effect of climate and soil physical parameters on daily water cycling, which concluded both the wet and dry years.

• Correlation analysis indicated that there was no significant relation between precipitation and water cycling parameters such as soil water, outflow and LAI.

• Soil textures affect the water cycling greatly. For soil water and volumetric soil water, the results showed that sandy rich soil < silt rich soil < clay rich soil. But for the leaf area index (LAI) presented the reversed order, i.e. sandy rich soil > silt rich soil > clay rich soil. For the soil tension and water outflow, the result was more complex.

• Soil depths also have great effects on water cycling parameters. In the 0-100cm soil profile, the values of soil water, soil tension and LAI is greater than those in the top soil (0-30cm). But it has no significant effect on volumetric soil water. While the outflow in top soil was much greater than that in 0-100cm profile.

Soi l Water

0

100

200

300

400

500

1 237 473 709 945 1181 1417 1653 1889 2125

ch1

ch2

ch3

ch4

ch5

ch6

SOI LVWC

0

0. 2

0. 4

0. 6

0. 8

1

1. 2

1 217 433 649 865 108112971513172919452161

CH1CH2CH3CH4CH5CH6

Outfl ow

02040

6080

100120

140160180

1 225 449 673 897 11211345156917932017

ch1ch2ch3ch4ch5ch6

Soi l PSI

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

01 205 409 613 817 10211225142916331837 2041

ch1ch2ch3ch4ch5ch6

LAI

2. 5

2. 7

2. 9

3. 1

3. 3

3. 5

3. 7

3. 9

1 219 437 655 873 109113091527174519632181

ch1ch2ch3ch4ch5ch6

Conclusions• There was no significant relationship between climate

data and water cycling outputs while the highest outflow occurred in the wettest year. Water cycling parameters were affected not only by precipitation, air temperature, but also by vegetation, soil physical characters, managements and other factors;

• The content of sand, silt, and clay affects the physical behavior of a soil. Compared with sandy rich soil, soil water is higher in the more clay rich soils. The amount of clay affect the ability of the soil to retain moisture;

• Soil depths also affect the water cycling. Outflow mainly occurred in top soil.

What have I learned by this exercise?

• prepare the ini files and run the model;• write a restart worksheet;• what the parameters in the models means;• how to obtain a daily or annual output; • how to solve scientific problems using the model