华北平原种植结构变化对农业需水的影响

不同种植结构下的农田需水研究是调整农业种植结构、制定切实可行的区域灌溉方案的重要依据。为了定量估算华北平原种植结构变化对农业需水的影响,本文基于MODIS NDVI数据和TM/ETM遥感影像提取了2002年和2012年华北平原主要作物类型及其种植面积,同时基于作物系数法计算了华北平原7种主要作物需水量,分析了华北平原种植结构变化对作物需水的影响。结果表明:2002—2012年,主要作物种植面积减少60.7万hm~2。其中,种植面积明显减少的作物分别为冬小麦-夏玉米(-43.18万hm~2)、棉花(-32.43万hm~2)、水稻(-9.3万hm~2)和春玉米(-4.9万hm~2),种植面积增加的作物主要是林果(+16.61万hm~2)和蔬菜(+12.6万hm~2)。2002—2012年,华北平原主要作物的总需水量从742.7亿m~3下降至695.5亿m~3,共下降6.37%。其中,需水量减少的作物类型为冬小麦-夏玉米(-35.41亿m~3)、棉花(-24.31亿m~3)、水稻(-7.48亿m~3)和春玉米(-2.1亿m~3),需水量增加的为林果(+11.24亿m~3)和蔬菜(+10.71亿m~3)。从空间分布来看,华北平原作物需水量整体呈减少趋势,仅在河北平原、鲁西北以及滨海平原靠近城市周边的区域呈增加趋势,其中滨海平原需水增加量最大。华北平原由于作物种植面积减小引起的作物需水减少量达44.7亿m~3;由作物种植结构调整引起的作物需水减少量为2.5亿m~3。种植规模的减小是华北平原作物需水量减少的主要原因。

Impact of planting structure changes on agricultural water requirement in North China Plain

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 60.7×10⁴ hectares. Among them, the planting area of the four crops was significantly reduced:winter wheat-summer maize (-4.318×10⁵ hm²), cotton (-3.243×10⁵ hm²), rice (-9.3×10⁴ hm²), and spring corn (-4.9×10⁴ hm²). The crops for which planting area increased were:forest fruit (+1.661×10⁵ hm²) and vegetables (+1.26×10⁵ hm²). Secondly, from 2002 to 2012, the total water demand for major crops in the NCP decreased from 74.27 billion m³ to 69.55 billion m³ (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 m³), cotton (-2.43 billion m³), rice (-0.75 billion m³), and spring maize (-0.21 billion m³). On the other hand, fruit trees and vegetables both caused an increase in water demand 1.12 billion m³ and 1.07 billion m³, 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 m³, while that caused by planting structure adjustments only amounted to 0.25 billion m³. Hence, the reduction of the planting scale is the main reason for the decrease in crop water demand in the NCP.