Songjun Han Shaoli Wang Department of Irrigation and Drainage

1. 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 Shaoli Wang Department of Irrigation and Drainage China Institute of Water Resources and Hydropower Research hansj@iwhr.com

2. Outlines 1 Background 2 Data and Methods 3 Trends in Irrigation water requirement per unit area and the influencing factors 4 Different trends in Ep for stations with different impacts of agriculture land use over China 5 Conclusions

3. 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?

4. 2.1 Study area and data • 690 stations over mainland of China • 5 large basins in the north region of China, 347 stations with monthly climate data

5. 2.2 Methods: Net irrigation requirement (Nir) Nir: net irrigation requirement ETc: the crop water requirement Pe: fraction of the total precipitation

6. 2.3 Methods: Trend analyses 1)Trends Burn & Hag Elnur 2002 2)Significance non-parametric Mann-Kendall test Mann 1945; Kendall 1975 3) trend-free, pre-whitening method Yue et al. 2002, 2003, 2004

7. Trends in Irrigation water requirement per unit area in Northern region of China

8. 3.1 Trends in P and ET0 • ET0: -46.0 mm/decade • P: -11.2 mm/decade

9. P and ET0 Trends in different basins

10. 3.2 Trends in Nir • Average value of all the 347 stations • Nir decreased significantly, Wheat: -24.2 mm/decade, Maize: -18.9 mm/decade

11. Nir Trends in different basins

12. 3.3 Discussions • Nir decreased with the decreasing ET0 • Changes of ET0 or Epshould be evaluated All the stations are mathematically averaged to evaluate the regional changes Are they have similar trends? Should they be evaluated equally? Are there any local climate effect on Ep? Stations surrounded with cultivated land Stations surrounded with natural land

13. Different trends in Ep for stations with different impacts of agriculture land use over China

14. Cultivated land Urban land use 4.1 Data • 690 stations over mainland of China • Land use data of 2000

15. 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.

16. 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

17. 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

18. 4.3 Trends of meteorological factors and their influences • Arid/semi-Arid region：Agricultural stations: u↓RH↑ • Humid： Agricultural stations: Rs↓ • Method：regression

19. 4.3 Temperature Ta • Ta↑→ Ep ↑ • Arid/semi-Arid region: increasing effects of Ta on Ep are weakened for agricultural stations

20. 4.3 Solar radiation Rs • Rs↓→ Ep↓ • Humid/semi-humid region: decreasing effects of Rs on Ep are strengthen for agricultural stations

21. 4.3 Relative humidity RH • RH↑→ Ep↓ • Arid/semi-Arid region: decreasing effects of RH on Ep are strengthen for agricultural stations

22. 4.3 Wind speed u2 • u2↓→ Ep↓ • Arid/semi-Arid region: decreasing effects of u2 on Ep are strengthen for agricultural stations

23. 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

24. Thank you for attention!