Environmental costs (IMAGE)
Caption
Environmental effects of national cropland redistribution on irrigation water use and soil erosion by wind. (A) Spatial distribution of water demand deficit. (B) Cropland area and proportion of different water demand deficit levels, and the irrigation water use increase resulting from cropland gain in each zone. (C) Spatial distribution of average wind erosion modules. (D) Effect of cropland gain on soil erosion by wind in each zone. (E) Spatial distribution of average fertilizer use per crop yield. (F) The increase of fertilizer use resulting from cropland gain in each zone. Cropland redistribution to NE and NW China since 2000 has resulted in serious environmental costs and aggravated the local ecological vulnerability. The newly cultivated croplands in NE and NW China increased wind erosion (+3.47%), irrigation water consumption (+34.42%), fertilizer use (+20.02%), and decreased natural habitats (-3.11%). The croplands converted from grasslands or oases in NW China were primarily located in arid and semi-arid areas with mean annual precipitation less than 200 mm yr-1. The precipitation can meet only 18.7% to ~54.0% of crop water demand in NW China, resulting in an increase in irrigation water use by 278.65×108 m3 yr-1. Since more than half of the croplands in NW China (55.4%) were located in water demand deficit areas after redistribution, extracting groundwater for irrigation caused continuous groundwater depletion. The environmental costs in water use and black soil degradation were also high in NE China, due to the local precipitation can only meet about 60% of crop water demand.
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