Evaluating trends in irrigation water requirement per unit are in north region

of China, 1960-2005: should stations being classified according to land use?

Songjun Han Songjun Han

Shaoli WangShaoli WangDepartment of Irrigation and Drainage Department of Irrigation and Drainage

China Institute of Water Resources and Hydropower ResearchChina Institute of Water Resources and Hydropower Research

hansj@iwhr.comhansj@iwhr.com

Outlines

1 Background2 Data and Methods3 Trends in Irrigation water requirement

per unit area and the influencing factors4 Different trends in Ep for stations with

different impacts of agriculture land use over China

5 Conclusions

1 Background

In north region of China, with an average annual precipitation less than 800 mm, irrigation is the most important practice to ensure food security.

Knowledge on how irrigation water requirements changes may have great significance in the future agricultural water management (Döll and Siebert, 2002).

Obvious changes in precipitation and potential evapotranspiration in past 50 years were reported

Meteorological stations are surrounded with different land use types, is there any influences?

690 stations over mainland of China

5 large basins in the north region of China, 347 stations with monthly climate data

2.1 Study area and data

2.2 Methods: Net irrigation requirement (Nir)

Nir: net irrigation requirement

ETc: the crop water requirement

Pe: fraction of the total precipitation

if

0 if m cm e cm e

m cm e

Nir ET P ET P

Nir ET P

0c cET K ET＝

0

0.2

0.4

0.6

0.8

1

1.2

1.4

15-M

ar

29-M

ar

12-A

pr

26-A

pr

10-M

ay

24-M

ay

7-Ju

n

21-J

un

5-Ju

l

19-J

ul

2-A

ug

16-A

ug

30-A

ug

13-S

ep

Kc Wheat

Maize

*

0

9000.408 ( )

2731 0.34

n a aR G u e eTET

u

2.3 Methods: Trend analyses

( ),

( )j iX X

median i jj i

2)Significance non-parametric Mann-Kendall test Mann 1945; Kendall 1975

Burn & Hag Elnur 2002

3) trend-free, pre-whitening method Yue et al. 2002, 2003, 2004

1)Trends

Trends in Irrigation water requirement per unit area in

Northern region of China

3.1 Trends in P and ET0

y = -4.5826x + 1360.2

R2 = 0.4841000

1100

1200

1300

1400

1500

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

ET

c (m

m)

y = -1.148x + 414.87

R2 = 0.1401

0

100

200

300

400

500

600

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

P (

mm

)

ET0: -46.0 mm/decade P: -11.2 mm/decade

P and ET0 Trends in different basins

0

100

200

300

400

500

600

700

800

900

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

P (m

m)Songhuaj i angLi aoheNorthwestHai heYel l ow Ri ver

600

800

1000

1200

1400

1600

1800

2000

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

ET

c (m

m)

Songhuajiang

Liaohe

Northwest

Haihe

Yellow River

Songhuajiang Liaohe Northwest Haihe Yellow River

P -8.0 -32.6** 6.6** -32.1** -21.5**

ET0 -21.26** -48.6** -48.5** -62.2** -49.1**

NirWheat -19.2** -23.7** -34.0** -35.3** -11.6*

NirMaize -7.5 -16.7** -25.2** -26.5** -18.9** * Significant at the 95% confidence level; ** Significant at the 99% confidence level.

3.2 Trends in Nir

y = - 1. 9068x + 248. 96R2 = 0. 2689

y = - 2. 3121x + 529. 88R2 = 0. 3234

0

100

200

300

400

500

600

700

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Nir

(mm)

WheatMai ze

(Mai ze)线性 (Wheat )线性

Average value of all the 347 stations Nir decreased significantly, Wheat: -24.2 mm/decade, Maize: -18.9 mm/decade

Nir Trends in different basins

0

100

200

300

400

500

600

700

800

900

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Nir

(mm)

Songhuaj i angLi aoheNorthwestHai heYel l ow Ri ver

0

100

200

300

400

500

600

700

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Nir

(mm)

Songhuaj i angLi aoheNorthwestHai heYel l ow Ri ver

Songhuajiang Liaohe Northwest Haihe Yellow River

P -8.0 -32.6** 6.6** -32.1** -21.5**

ET0 -21.26** -48.6** -48.5** -62.2** -49.1**

NirWheat -19.2** -23.7** -34.0** -35.3** -11.6*

NirMaize -7.5 -16.7** -25.2** -26.5** -18.9** * Significant at the 95% confidence level; ** Significant at the 99% confidence level.

3.3 Discussions

Nir decreased with the decreasing ET0

Changes of ET0 or Ep should be evaluated

Stations surrounded with cultivated land

Stations surrounded with natural land

Are they have similar trends?

Should they be evaluated equally?

Are there any local climate effect on Ep?

All the stations are mathematically averaged to evaluate the regional changes

Different trends in Ep for stations with different impacts of agriculture land

use over China

4.1 Data

690 stations over mainland of China

Land use data of 2000

Urban land useCultivated land

4.2 Trends in Ep influenced by land use?

Plot of trends in Ep vs. the cultivated land ratio within the R km radius of each station

Stations with larger cultivated land ratios show more significant decreasing trends in Ep

During the growing season, the correlations are most significant when R=5km.

R

4.2 Station classification Agricultural stations (A): Cultivated land ratio > 50%, 244 Natural stations (N): Sum of cultivated and urban land ratio <

30% ：

Agricultural stations ： urbanization influence can be ignored Natural stations ： ignoring agricultural and urbanization influences

4.2 Different trends in Ep for agricultural and natural stations

Agricultural stations ： 79.4%, 78.1%, 83.1% decreased with larger slopes Natural stations ： 59.7%, 50%, and 64.2% decreased

4.3 Trends of meteorological factors and their influences

Arid/semi-Arid region ： Agricultural stations: u↓RH↑ Humid ： Agricultural stations: Rs↓

Method ： regression

Arid/semi-arid Semi-humid Humid China as a whole Item

Na Aa N A N A N A

Trend of average 0.29 0.36 0.16 0.19 0.24 0.11 0.12 0.17 Ta

Average trend 0.34 0.29 0.22 0.24 0.13 0.13 0.24 0.23 Trend of average -0.61 -0.31* 0.27* -2.20 -0.93 -2.77 -0.29 -1.52

Rs Average trend -0.79 -0.29 -0.72 -2.40 -1.88 -2.64 -1.06 -1.79 Trend of average 0.03* 0.44 -0.01* -0.21* -0.03* -0.19 -0.22 -0.17*

RH Average trend 0.04 0.35 0.22 -0.11 -0.01 -0.21 0.09 0.01 Trend of average -0.11 -0.20 -0.11 -0.12 -0.15 -0.11 -0.12 -0.15

u2 Average trend -0.14 -0.21 -0.08 -0.14 -0.11 -0.12 -0.11 -0.16 Trend of average 3.4 0.5* -5.1* -12.2* 3.5* 2.4* -10.9 -11.1

P Average trend 3.6 4.7 -0.2 -11.7 2.8 6.3 2.1 -2.3

1

1 2 3 4 2p a sE a T a R a RH a u b

1 2 3 4 2p a sE a T a R a RH a u

4.3 Temperature Ta

Ta↑→ Ep ↑ Arid/semi-Arid region: increasing effects of Ta on Ep are

weakened for agricultural stations

4.3 Solar radiation Rs

Rs↓→ Ep↓ Humid/semi-humid region: decreasing effects of Rs on Ep are

strengthen for agricultural stations

4.3 Relative humidity RH

RH↑→ Ep↓ Arid/semi-Arid region: decreasing effects of RH on Ep are

strengthen for agricultural stations

4.3 Wind speed u2

u2↓→ Ep↓ Arid/semi-Arid region: decreasing effects of u2 on Ep are

strengthen for agricultural stations

5 Conclusions

Using wheat and maize as examples, the trends in Nir in the north region of China were evaluated.

Nir decreased in all the five large basins with the significantly decreasing ET0

More obvious decreasing trends in Ep are observed for the agricultural stations than for the natural stations.

In the arid/semi-arid region, the more significant decrease in Ep for the agricultural stations is attributed to the more significant ↓u2, more significant ↑RH, and smaller increase in ↑Ta compared with the natural stations.

The land use around the stations should be considered when evaluation climate change effects of a whole region

Thank you for attention!