Spatiotemporal patterns of water consumption and irrigation requirements of wheat-maize in the Huang-Huai-Hai Plain, China and options of their reduction

Severe water shortages threaten the sustainability of agriculture in the Huang-Huai-Hai Plain (3HP), China. This study investigated spatiotemporal variations in crop water consumption (evapotranspiration, ET) and irrigation water requirements (IWR) under existing winter wheat-summer maize (WWSM) cropping system in the 3HP, and tested alternatives of their reduction that may require less irrigation, i.e., wheat-maize-wheat-fallow (WMWF), wheat-maize-fallow-maize (WMFM), wheat-maize-fallow-spring maize (WMFSM), and fallow-spring maize-fallow-spring maize (FSMFSM). The results showed that the annual ET indicated no significant change from 2001 to 2018, which decreased from southeast to northwest and ranged from 700 mm to 900 mm. In the winter wheat (WW) season, ET increased significantly at the junction of Hebei and Shandong provinces, while it decreased in western Hebei during the summer maize (SM) period. Moreover, ET for WW decreased from dry to normal and wet years (433, 413, and 373, mm), while it increased in SM season (377, 392, and 396, mm). IWR showed great interannual variability. Anhui, central and southern Henan, and southwestern Shandong presented annual IWR below 200 mm, with 100-300 mm in the WW period, and -300 (0) - 100 mm in the SM period (negative IWR means rainfall surplus and no real irrigation). The north of the 3HP required considerable irrigation in the WW season, especially in western Hebei and northwestern Shandong (over 300 mm in dry years and 200 mm in wet years), with IWR ranging from -100-100 mm in the SM period. The 18-year average IWR of WWSM, WMWF, WMFM, WMFSM, and FSMFSM was 344, 321, 211, 240, and 119 mm, respectively, from 2001 to 2018 (Luancheng as example, same below). Reducing irrigation by 32%, 44%, and 64%, WMFSM, WMFM and FSMFSM showed the greatest potential for reducing IWR, but food security should also be considered when adjustments are made.