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Land use and cover change detection and modelling for North Ningxia, China1
- Two kinds of mutation of water-body were distinguished in the Yinchuan Plain. One is 'land to water-body', meaning that land changed into waterlogged depressions or fish ponds. This mutation is linked with the agriculture output increase (R2 = 0.743). That is to say, the activities of rural people in food production, fish farming, etc, which compose partially the agricultural output, are the main cause of this change. Their relationship is presented below:
[Land to water-body] = 0.3965 + 0.0448 [Agriculture output increase]
.
.
(6)
The other change is 'water-body to land', representing water-body drying or having converted into land, partially farmland. Panel analysis shows that this change is associated with the sown area increase (R2 = 0.867). It is reasonable that people need more water for irrigation with the increase of the cultivated land. If the water-body has been poorly recharged, it can be easily dried. Additionally, the dried water depression can be cultivated and become farmland (e.g., Gaomiao Lake in Huinong county). These might be the reasons that the 'water-body to land' is related to the sown area increase:
[Water-body to land] = -2.0059 + 1.6716 [Sown area increase]
.
...(7)
Therefore, water-body changes seem to have some transversal mobility which is related to the agricultural activities: in some places, waterlogged depression extended or land turned into water depressions or fish ponds while such depressions converted to land elsewhere. But totally, the surface of the water-body in these counties has an increase of about 49 km2 at an increment rate of 4.07km2/yr or 0.998%. Then where does the water come from when the climate gets dryer and warmer ?
- The Yellow River has been largely narrowed in the extent of North Ningxia (by 83.83 km2). This decrease would be probably due to the following reasons: (1) local climate warming and precipitation decrease and (2) overuse, even waste of water in agriculture in the Yinchuan Plain.
At a reduction rate of 6.99km2/yr or 6.10%, the present Yellow River (with a surface of 81.3km2, Wu et al, 2002) would be wholly dry in 2010. This means that the river, which has been the cradle of the 7000-years' Chinese civilisation, would not exist any longer in ten years!
Acknowledgement
The authors want to thank first the Federal Office for the Scientific, Technical and Cultural Affairs (OSTC) of Belgium Government for funding our research of the Sino-Belgian Co-operation Project on Northwest China. We would also like to thank our Chinese partner, the United Remote Sensing Centre of Northwest China, especially, Ningxia Remote Sensing Centre, for their reception during our field verification and for their provision of the necessary maps and socio-economic data so that our research could be achieved smoothly. We would too thank Prof. Hiroyuki Yoshida and Fukui Research Group, Keio University, Japan, for their permission to access the Landsat TM data (1987). Here a special thank will go to Mr. ZHANG Wenfeng for his first arrangement of the county-level socio-economic data during his stay in Belgium for the co-operation research.
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