Projecten - China
Long Term Trends in Agricultural Water Productivity and Intersectoral Water Allocations in Hubei and Henan
Main question
Faced with growing demand for water for non agricultural uses - industry, domestic, and hydropower - China has been adopting a range of water saving irrigation practices. A study has been undertaken in two sites in China to identify the water saving practices and policies and determine the impact on water productivity at farm, system, and district level A first step in this study has been to examine the long term trends in water allocations between agricultural and non-agricultural uses and in crop and water productivity Zhanghe Irrigation System (ZIS) in the Yangtze River Basin, Hubei Province and in Kaifeng City Prefecture, along the Yellow River in Henan Province (Figure 1).
Methodology
The time series on which this paper is based was compiled by ZIS for the period 1966 to 2001 and by Kaifeng City Prefecture for the period 1968 to 2000. The figures in the text show the trends over time. In the text tables, however, mean values are shown for three separate time periods, 1966-78, 1979-88 and 1989-98. This division was made to reflect the very sharp changes that occurred at the end of the first and second time periods Following the end of the Cultural Revolution in the late 1970s, significant reforms took place that affected both irrigation and agricultural production. Introduction of improved varieties and increased use of chemical fertilizers led to a sharp increase in rice yields. In ZIS volumetric pricing was introduced. New pumping stations were built. Medium- and small-size reservoirs were restored or expanded. In Kaifeng Prefecture the Yellow River diversions dropped dramatically.
The end of the 1980s saw further changes. Industrial and municipal demand rose, resulting in an increased competition between water for agriculture and other uses. The introduction of hybrid rice in ZIS gave a further boost to rice yields. In ZIS the installation of two new hydropower plants greatly increased the hydropower capacity. The pressure to save water led to an expansion of AWDI practices at the farm level and to other water-saving practices.
Result and conclusions
In both study areas the water demand for purposes other than irrigation has grown. In Zhanghe Irrigation District this resulted in a sharp reduction of the water availability for irrigation. In Kaifeng City Prefecture the increased demand from other uses could be met by an increase in groundwater extraction without the dramatic cuts in supplies for agriculture as in ZID. However it is not clear how much longer this trend is sustainable. In Zhanghe Irrigation District several water saving practices have been adopted to maintain crop production. The yield per unit area doubled, but production per unit irrigation water supplied almost tripled between the periods 1966-78 and 1989-2001. There are many different factors that may have contributed to the increase in water productivity, including ADWI practices, a changing cropping pattern, development of alternate water sources, volumetric pricing of water and the recapture and reuse of return flows through the network of reservoirs. The relative importance of the different factors contributing to increasing water productivity has yet to be determined and is a major scope for future research. A major objective of this research will be to identify those practices that could be successfully extended to other regions, both inside and outside China.
Figure 1. Allocation for irrigation and other uses in Zhanghe Reservoir, Hubei, China, 1966-2001.
In Kaifeng City Prefecture agricultural production increased substantially since the economic reforms. At the end of the 1970ties agricultural water use declined sharply, primarily due to reduced diversions from the Yellow River, which indicates increased water productivity per unit of land. In the last decade agricultural water use has been essentially constant as has agricultural crop area, but agricultural production has increased substantially. Data indicate that these gains have come from increased yields per unit area. Gains in water productivity in this period are most likely due to improved varieties and increased use of inputs such as fertilizer, not improved water management techniques. The increase in water productivity is, however, impressive, although most of it does not result from reductions in water use due to water saving irrigation techniques.
Figure 2. Water allocation for irrigation and other uses in Kaifeng City Prefecture, Henan, China, 1968-2000
This study illustrates the different stages a basin will experiences under pressure of increased competition of water. In Zhanghe Irrigation District new fresh water sources, i.e. small reservoirs were already exploited and the scope for developing new water sources was limited, resulting in the introduction of water saving policies and practices. But there appears to be little scope for additional water savings and hence any further increase in allocation to non-agricultural uses is likely to result in further reduction in crop production. In Kaifeng City Prefecture there was still an opportunity to exploit new water sources, i.e. groundwater, and till now most of the water productivity increase comes from increased yields. However with an ever increasing competition for water and a limit to the exploitation of groundwater, water saving policies and practices will be needed in the future.
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