The Yellow River basin in China – Part 1
Following my scene-setting yesterday, this is the first of four posts presenting my case-study of the challenges posed by ongoing climate change in the Yellow River basin of northern China. All references cited will be listed in Part 4 on Friday.
The problematisation of water resources in the Yellow River basin
The Yellow River is the second-longest river in China (after the Yangtze River) and, at 5,463km, the seventh-longest in the world. In China, the Yellow River (Huang He) is known as the “Mother River of China” because it is considered by many to be the birthplace of Chinese civilization.
It is called the Yellow River because huge amounts of loess sediment turn the water that colour in its lower reaches. Here, the average annual sediment flow is 1.6 billion tonnes with a sediment content of 35kg/m3. An average of 400 million tonnes of sediment is deposited every year; resulting in an increase in the elevation of the river bed of 10cm/year (Yellow River conservancy Commission[YRCC], 2007a).
The source of the Yellow River (in Qinghai Province) is located in the rain shadow of the Himalayas; within the high altitude Tibet-Qinghai plateau (greater than 4000 m above sea level (ASL). This forms the first of three distinct topographical areas through which the Yellow River flows; the other two being the Loess Plateau (1000-2000 mASL); and the North China Plain.
After this section and the two that follow (regarding human geography and hydrogeology respectively), this threefold geographical division of the Yellow River basin will be used to structure the discussion of groundwater resources; followed by a multi-faceted assessment of the water resources (i.e. surface water and groundwater) of the river basin (i.e. its surface water catchment area) as a whole; and the presentation of conclusions drawn from all of the above.
Within the Tibetan Plateau, the Yellow River valley floor is at 4800-3700 mASL. The Yinchuan and Hubao Plains (the main parts of the Loess Plateau) are at 1200-1100 mASL. The Taiyuan and Guangzhong basins (incised into the Loess Plateau) are 830-735 mASL and 800-320 mASL respectively. The lower reaches of the Yellow River are below 100 mASL; and the river delta below 15mASL.
Because of this large change in elevation over its vast length, the Yellow River basin encompasses a wide range of vegetation types and climatic zones. However, most of the basin – below approximately 3000 mASL – has been classified as having a mid-temperate to warm-temperate climate; but is bounded by the aridity of Inner Mongolia to the north; and the humidity of the Yangtze basin to the south. The Yellow River basin has an average annual precipitation of 479 mm; the distribution of which is very uneven in both space and time. Between 58% and 77% of all rainfall occurs between June and September.
With reference to WEN et al Figure 3, it may be seen that there is a wide range of total precipitation; with over 1000 mm/yr in areas bordering the Yangtze catchment to the south. However, the majority of the Yellow River Basin (south of 35°N in the west and south of 38°N in the east) receives at least 750 mm/yr.
The average annual runoff into the Yellow River from its catchment area is in excess of 57 billion cubic metres per annum. However, because of its seasonal nature – and as a result of over-abstraction (for industrial and agricultural use) – the lowest reaches of the Yellow River dried up completely in 22 out of 29 years between 1972 and 1999. However, since 1999, better centralised regulation of abstraction may have prevented any drying-up of the river between 2000 and (at least) 2006 (WEN et al.2009: 13).
WEN et al Figure 3.
The silt load of the Yellow River is the highest for any river in the world, but is highly seasonal – with 85% being carried between June and September. As with rainfall, the distribution of this sediment load is therefore uneven in space as well as time; with sediment input being particularly high where rainfall is low and evaporation is high.
Today, the human population living within the catchment is in excess of 110 million, and the area of land under cultivation is in excess of 12 million hectares. With regard to its economic importance to China, the Yellow River basin is home to less than 8% of the total Chinese population but it contains greater than 12% of Chinese land under cultivation. Furthermore, the basin is also the source of greater than 25% of China’s oil and greater than 50% its coal. The Yellow River basin contains 8 provincial capitals and 36 other cities above prefecture level. As a consequence of this activity, the total demand for water supply in 2005 was 46.5 billion cubic metres; with usage being 70% agricultural, 14% industrial, and 6% domestic (WEN et al. 2009: 14).
Chinese Ministry of Water Resources data (circa 2005) suggest that there was a 10% reduction in total water supply volume between 1998 and 2005; which may be due to climate change. This is giving cause for concern because any significant increase in demand will not be sustainable (WEN et al. 2009: 15-16).
As with all other countries in the world, China has found it very hard to achieve continuous economic development without causing ongoing environmental degradation. This subject is addressed in detail in the Overall Resource Assessment towards the end of this essay.
ZHANG et al Figure 1 (below) presents a simplified geology map of the Yellow River Basin. The Yellow River basin contains a relatively complete set of geological strata ranging from the Archaean to the Cenozoic in age (i.e. from greater than 2500 to less than 65 million years old). The former are mainly represented coarse-grained metamorphic rock (gneiss) generally exposed at the margins of the river basin (i.e. at altitudes in excess of 2500mASL), whereas the latter form the surface of much of both the Loess Plateau and the North China Plain; with a wide variety of water-bearing lithologies present (including aeolian and alluvial deposits). In between these two, there are generally very significant thicknesses of both Palaeozoic and Mesozoic strata; with a variety of lithologies present, although limestone (both karstic and non-karstic) is the most regionally-important aquifer type (ZHANG et al. 2009: 19-21).
ZHANG et al Figure 1.
As described above, tomorrow I will look in detail at the hydrogeology (i.e. aquifers, groundwater chemistry, circulation, and the balance between supply and demand [such as it may be]) within each of the three main geographic areas making up the surface water catchment.