Abstract
The downstream plain of the Yellow River is experiencing some of the most severe groundwater depletion in China. Although the Chinese government has issued policies to ensure that the Yellow River can provide enough irrigation waters for this region, groundwater levels continue to decrease. Yucheng City was selected as a case study. A new method was designed to classify the cropland into various irrigated cropland. Subsequently, we analyzed data regarding these irrigated-cropland categories, irrigation norms, and the minimum amount of irrigation water being applied to cropland. The results showed that 91.5% of farmland can be classified as double irrigated (by both canal/river and well water), while 8.5% of farmland can be classified as well irrigated. During the irrigation season, the sediments brought in by the river have blocked portions of the canals. This has led to 23% of the double-irrigated cropland being irrigated by groundwater, and it is thus a main factor causing reductions in groundwater supply. These blocked canals should be dredged by local governments to mitigate local groundwater depletion. The method for classifying irrigated cropland from high-resolution images is valid and it can be used in other irrigated areas with a declining groundwater table for the sustainable use of groundwater resources.
Highlights
The downstream plain of the Yellow River is one of the most important irrigated regions in China
Based on our classification methods, 91.5% of farmland in the region is classified as double irrigation and 8.5% of farmland is classified as well irrigation (Table 3 and Figure 3)
The density of canals in this region is very high for northern China, as this area is located in the Yellow River watershed and it is well-known for its saline and alkaline lands in eastern China
Summary
Previous studies have indicated that the shallow groundwater table has descended at a rate of 0.46 ± 0.37 m/year, while the deep groundwater table has declined at a rate of 1.14 ± 0.58 m/year [1,2]. The waters of the area are mainly used for the irrigation of agricultural lands and the over-exploration of groundwater for irrigation is considered to be the primary factor driving groundwater depletion. It should serve as an effective way to resolve the declining levels of groundwater in the region by increasing the use of canal irrigation while decreasing groundwater irrigation
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