Abstract:Evaluating farmland water requirements under different planting structures is an important basis for adjusting the agricultural planting structure and formulating feasible regional irrigation schemes. In order to quantitatively estimate the impact of planting structure changes on agricultural water requirement in the North China Plain (NCP), this paper extracted the main crop types and their planting areas based on MODIS NDVI data and TM/ETM remote sensing images from 2002 and 2012. The water demand of seven main crops in the NCP was calculated based on the crop coefficient method and the influence of planting structure change on crop water requirements in NCP was analyzed. The results showed that firstly:from 2002 to 2012, the main crop planting area decreased by 60.7×10 ⁴hectares. Among them, the planting area of the four crops was significantly reduced:winter wheat-summer maize (-4.318×10 ⁵hm ²), cotton (-3.243×10 ⁵hm ²), rice (-9.3×10 ⁴hm ²), and spring corn (-4.9×10 ⁴hm ²). The crops for which planting area increased were:forest fruit (+1.661×10 ⁵hm ²) and vegetables (+1.26×10 ⁵hm ²). Secondly, from 2002 to 2012, the total water demand for major crops in the NCP decreased from 74.27 billion m ³to 69.55 billion m ³(a decrease of 6.37%). Among this, the types of crop with reduced water demand were as follows:winter wheat-summer maize (-3.54 billion m ³), cotton (-2.43 billion m ³), rice (-0.75 billion m ³), and spring maize (-0.21 billion m ³). On the other hand, fruit trees and vegetables both caused an increase in water demand 1.12 billion m ³and 1.07 billion m ³, respectively. Spatially, crop water demand in the NCP showed an overall decreasing trend, with only the Hebei Plain, northwest Shandong Province, and the coastal plain near the urban periphery displaying increasing water demand. The largest increase in water demand occurred in the coastal plain. Finally, the reduction of crop water demand in the NCP caused by reduction of crop planting area amounted to 4.47 billion m ³, while that caused by planting structure adjustments only amounted to 0.25 billion m ³. Hence, the reduction of the planting scale is the main reason for the decrease in crop water demand in the NCP.