华北主要作物需水量近50年变化趋势及原因

Trend and causes of water requirement of main crops in North China in recent 50 years

作物需水量是制定灌溉计划和水资源规划的重要依据,了解其历史变化对于掌握未来农业用水走势并据此做出正确决策至关重要.该文利用FAO推荐的作物系数乘以参考作物蒸散量的方法计算了华北地区6个站点近50年主要作物的需水量,并并分析了其变化趋势.结果表明:除北京外,华北冬小麦和夏玉米两大作物需水量均呈下降趋势,每10年分别减少0.9～19.2 mm和8.3～24.3 mm.夏玉米需水量下降幅度超过冬小麦.其中以华北南部的郑州减少最多,下降幅度在19.2～24.3 mm/10年.与日照、降雨、温度、湿度和风速的同步分析表明,需水量变化趋势与日照和风速的下降趋势相-致.由于日照减少造成到达地面的能量减少,风速减小可削弱陆地与大气的水分和能量交换强度,故近50年来华北日照与风速的减小是作物需水量下降的主要原因.

Information of crop water requirement and its historical change are important for irrigation scheduling, water resources planning, and future decision-making. Crop water requirements of winter wheat and summer corn in North China in recent 50 years were calculated by the FAO approach, which equaled to crop coefficient multiplied by reference crop evapotranspiration. Results suggested that water requirements of winter wheat and summer corn in most locations showed a downtrend in the past 50 years except Beijing, which respectively decreased by 0.9-19.2 mm and 8.3-24.3 mm for every 10 years. The decrease for summer corn exceeds that for winter wheat. Zhengzhou, the southern part of North China, ranks the first in terms of decreasing value, 19.2-24.3 mm per 10 year. The correlations among crop water requirement and sunlight, wind speed, temperature, humidity and rainfall revealed that the change of crop water requirement and the downtrend of sunlight and wind speed was coincident. Since decreased sunlight resulted in reduced energy reaching earth, and decreased wind may weaken the water and energy exchange between the earth and atmosphere, the downtrend of crop water requirement in North China mainly attributed to the reduction of sunlight hours and wind speed.