evaluating trends in irrigation water requirement per unit are in north region of china, 1960-2005:...
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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
[email protected]@iwhr.com
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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
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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?
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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
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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
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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
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Trends in Irrigation water requirement per unit area in
Northern region of China
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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
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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.
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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
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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.
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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
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Different trends in Ep for stations with different impacts of agriculture land
use over China
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4.1 Data
690 stations over mainland of China
Land use data of 2000
Urban land useCultivated land
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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
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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
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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
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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
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4.3 Temperature Ta
Ta↑→ Ep ↑ Arid/semi-Arid region: increasing effects of Ta on Ep are
weakened for agricultural stations
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4.3 Solar radiation Rs
Rs↓→ Ep↓ Humid/semi-humid region: decreasing effects of Rs on Ep are
strengthen for agricultural stations
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4.3 Relative humidity RH
RH↑→ Ep↓ Arid/semi-Arid region: decreasing effects of RH on Ep are
strengthen for agricultural stations
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4.3 Wind speed u2
u2↓→ Ep↓ Arid/semi-Arid region: decreasing effects of u2 on Ep are
strengthen for agricultural stations
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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
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Thank you for attention!