Impact of climate change on the water requirement of summer maize in the Huang-Huai-Hai farming region

Crop water requirement and the temporal and spatial changes of this important characteristic provide key information for irrigation scheduling, water resource planning, and future decision-making. In the Huang-Huai-Hai (HHH) farming region in north China, both crop evapotranspiration (ETc) and evapotranspiration of the applied water (ETaw) in the growing season of summer maize during 1960–2009 were calculated using the SIMETAW (simulation of evapotranspiration of applied water) model and the daily weather data. Inverse distance weighted interpolation (IDW) was used to interpret spatial distribution of ETc and ETaw. Results showed that: (1) During 1960–2009 in the HHH farming region, ETc of summer maize during the growing season showed a significant downward trend; the average ETc decreased from 335.6 mm/decade in the period 1960–1969 to 311.4 mm/decade in the period 2000–2009. The variation of ETaw of summer maize during the growing season did not drop significantly due to yearly fluctuation of the effective rainfall (Re) in the growing season, and the improvement of irrigation efficiency and cultivation management measures. Although the descent of ETc might mitigate the agricultural water stress in this area to some extent, the variation of ETaw still depended on the effective rainfall. (2) The average ETc values per decade presented higher in the eastern and lower in the western regions; inter-regional differences were observed for ETaw, and the highest ETaw value of about 109.6 mm was found in the western regions of the Shandong and Hebei Provinces. Adjusting irrigation system and adopting the different irrigation systems in different region should be taken into consideration to guarantee the maize yield in this area. (3) During 1960–2009, a significant overall increase in temperature, a significant decrease in wind speed, humidity, and solar radiation, and a slight decrease in precipitation were observed. The solar radiation decrease contributed most to the summer maize ETc decrease, while relative humidity and precipitation were negatively correlated with ETc.