CHINA CROP WATER REQUIREMENT EVAPOTRASPIRATION. A New Approach to Water Use Efficiency Development LIPING JIANG WORLD BANK OFFICE BEIJING

Transcription

1 CHINA CROP WATER REQUIREMENT EVAPOTRASPIRATION A New Approach to Water Use Efficiency Development LIPING JIANG WORLD BANK OFFICE BEIJING

2 Conventional Approach to Irrigated Agricultural Water Savings Improve the way it is delivered by lining irrigation canals, laying pipes or installing sprinkler or drip irrigation to reduce the water that is lost by seeping into aquifers; Increase water use efficiency to save water and then use saved water to expand irrigated area or other uses, e.g. urban water supply; Believe that it would save 30% of extra water resources if water use efficiency is raised by 30%.

3 CHENGAN COUNTY (HEBEI) CHINA Using Sprinklers

4 CHENGAN COUNTY (HEBEI) CHINA lining of canals and ditches Part A / 6-3

5 Questions on Conventional Approach Improved water use efficiency makes 30% of reduction in water delivery from a reservoir. Does the reservoir can supply all savings to other water users? Improved water use efficiency makes a famer be able to irrigate more land. Any problems with that? Statistics show that over the past 30 years China s effective irrigated area has increased by about 8 million hectares, while the total use or drawing of water has remained much the same. Guess what s happened? Annual over-exploitation of groundwater has reached up to 22 billion cubic meters! Why s that?

6 Types of Water Scarcity Areas Economic water scarcity area - where there are relatively abundant water sources and water scarcity occurs when there is a lack of investment in water infrastructure or a lack of human, institutional and/or financial capacity to satisfy demand; Physical water scarcity area - where surface and groundwater resources have already been overused and water scarcity occurs when there are insufficient water resources available to meet all water demands; and Mixed types of water scarcity areas where it s not possible to build infrastructure in the near future. What s the strategic focus to combat the water scarcity in different types? Are they the same?

7 Strategic Focus for Different Type of Water Scarcities Economic water scarcity area - to increase water use efficiency by adopting engineering type solutions combined with agronomic measures to increase farmer incomes with more consumptive use of water; Physical water scarcity area to reduce total water consumption while increasing farmers incomes, by increasing the value of their agricultural production per unit of water consumed; and Mixed types of water scarcity areas where the above measures would need to be applied in conjunction.

8 Why important to reduce consumptive use of water in physical scarcity areas? Experiences and lessons from China and other countries suggest that limiting the use or drawing of water, or increasing water-use efficiency may increase rather than reduce the consumptive use of water, particularly in physical water-scarce areas; Saving water under the traditional concept is to reduce supply and application losses, however, such water is not all lost: much of it returns to the aquifers below, from where it can be pumped up again. The only water truly lost in a hydrologic system is through evapotranspiration (ET), since no one can make further use of it once it is in the atmosphere.

9 What is the Genuine Water Savings? It s Reduction of ET!!! Simple Water Balance P ET = CS CS=0 ET = P

10 How Can We Obtain ET? Experimental Method for North China Single Crop ETi Average Crop ETac= wi ETi Comprehensive ETc = w ETac where: a=area of total crop land; ai=area of single crop land; wi=ai/a; w=a/a +0.6 (1- a/a); A=area of total land.

11 How Can We Obtain ET? Remote Sensing (RS) Method

12 Why RS-based ET Measurement Useful? Remote sensing by satellites can provide ET readings for areas of 30 by 30 meters. This tells farmers how much water they can consume without adversely affecting the ecosystems around them; ET information can be correlated with data on production and the value of production to develop spectrums that show the range of water productivities (WPs) for different crops in terms of Yield/ET and $/ET; It is then possible to identify irrigation, cultivation, and general management practices with low, average, and high WPs and to train farmers with low WPs in the practices of the high-wp farmers; and Water User Associations (WUAs) established under the project are key to success in this.

13 ET Changes in Different Counties in China

14 ET in TongZhou District of Beijing, China Before Project After Project

15 Zhang-Jia-Wan Township in Tongzhou District of Being, China Before Project After Project

16 Zhang-Jia-Wan Township Tongzhou District of Being, China Before Project After Project o o o Flooding irrigation before project; Low-pressure pipe irrigation after project; The red dot in the middle is a fish pond so no change of ET.

17 CHENGAN COUNTY (HEBEI) - CHINA real water savings placard Part B / 7-7

18 Thanks Welcome Questions 12