Recent Rapid Change of Water Circulation in the Yellow River and Its Effects on Environment

Fukushima Yoshihiro Tottori University of Environmental Studies (RIHN until March 2008)

A complex set of interacting factors, including natural climate variation, human-caused global warming and changes in land-use, contributed to the 1997 drought crisis in the Yellow River basin. This project evaluated how land use changes affect the water cycle throughout the Yellow River drainage basin and the effect of decreasing groundwater storage on marine environments. This study may prove to be at the forefront of ecological studies of densely-populated coastal zones. In studying the Bohai and Yellow Seas we may also be able to evaluate the effects of Yellow River change on marine products in the Sea of Japan.

Outcome

By implementing our Yellow River Study Project (hereafter referred to as YRiS), we were able to invite young and excellent researchers from Chinese universities and institutes. We were also able to obtain good results from the exchange of information between Japanese and Chinese scientists, and from our analysis based on observations, investigations and inspections in the period of 2003-2007.

We found that reforestation works undertaken by the Institute for Soil and Water Conservation on the Loess Plateau, which occupies almost 40% of the Yellow River Basin, have increased evapo-transpiration and consequently decreased the volume of river water by 15 billion m³. The Chinese Yellow River Conservancy Commission was previously unaware of the link between decreasing river flow and upstream reforestation. Furthermore, regulation governing use of the Yellow River water by surrounding provinces gave each province independent authority. After the severe exsiccation in the Yellow River basin, an improved “water law” was established in 2002. It granted the central government complete authority over river water use and the ability to penalize over-use. Fortunately, there has been a rather large amount of precipitation on the North China Plain since 2000, so there were no instances of the unfair use of river water.

Reforestation has decreased erosion from the Loess Plateau, but the downstream riverbed is still continuing to increase or to maintain the same level despite the completion of the Xiaolandi Dam in 1997 and its important function of flushing out sediment on the riverbed by instigating small flood events. This means that there is increased danger of a flood disaster in an area in which nearly 100 million people live.

The environment of the Bohai Sea has been changed by the shortage of inflow water from the Yellow River. Firstly, the critical condition for primary bio-production has changed from Nitrogen to Phosphorus. Secondly, the exchange of fresh and sea water has decreased remarkably. Thirdly, chlorophyll-a has decreased with the decrease of river water. These findings suggest that primary bio-productivity in the Bohai Sea is decreasing.

How changes in land use affect the atmosphere above the Loess Plateau is still being analyzed. Topographic conditions and the strength of the Asia Monsoon seem to have a larger effect on the atmosphere than do land surface conditions.

It is estimated that almost 10 billion m³ of water is used in upstream irrigation districts such as Qintongxia and Hetao, an amount that has likely remained constant between 1960 and 2000.

Plans for water supply using three routes from the Chang Jiang River to Beijing, Tianjin and the North China Plain may be completed soon. Whether or not water pollution, which is now a serious concern, will be resolved by this project will become a principal issue in the future because of the large cost of addressing such pollution.

Accounts of our study can be found in the YRiS Newsletters 1-8, published from September 1, 2003 to January 31, 2008 (http://www.chikyu.ac.jp/yris/newsletters.html).

Future Issues

Increased demand for food associated with present growth in the human population may lead to expansion of irrigated agricultural fields into areas where climate conditions are rather dry. Efforts to increase the efficiency of water use would appear to be too late to improve agricultural water-use given the rather small amounts of precipitation, and continued decreases in river water volume is likely to lead to salt accumulation in the Yellow River Basin. The supply of water from the Chang Jiang River to Beijing, Tianjin and the North China Plain is to be realized soon. Still many problems can be anticipated because the pollution of the Yellow River water remains unresolved; pollution in the Bohai Sea is likely to worsen.

Fig. Result of model simulation for the Loess Plateau area