Monitoring regional agricultural water use efficiency for Hebei Province on the North China Plain

Increasing competition for water in China, due to industrialisation of its economy and urbanisation of its population, has led to the introduction of water-saving agricultural practices in an attempt to increase agricultural water use efficiency (Ag WUE). This study was conducted to assess whether changes in management practices have increased regional Ag WUE for a focus area covering 20% of the 300 000 km(2) North China Plain (NCP). An 'input-output' definition of regional Ag WUE was used, where 'input' is the water available over the crop growing season and 'output' is grain yield. Regional databases of precipitation, irrigation, and yield from 1984 to 1996 were established in a Geographic Information System (GIS) to calculate winter wheat and summer corn Ag WUE on a county basis. For wheat, the average Ag WUE was 7.0 kg/ha. mm in 1984, whereas in 1996 it was 14.3 kg/ha. mm. For corn, Ag WUE increased from 9.0 kg/ha. mm in 1984 to 10.1 kg/ha. mm in 1996, although values >11.5 kg/ha. mm were obtained for both 1991 and 1992. Time series plots of the resulting Ag WUE, and its components, were generated to reveal spatial and temporal variability. Counties with a relatively high mean Ag WUE in combination with low year-to-year consistency have been identified as those with the highest potential for improving Ag WUE management. Total county water resources (WR) were also calculated for the time series, and county-basis normalisation of Ag WUE and WR also showed that there have been recent improvements in Ag WUE. For some counties in wet years, there may be an opportunity to plant larger areas of crop to increase county level Ag WUE. For the focus study site (and for the time series data available), it is most likely that recently introduced water-saving agricultural practices in the NCP are associated with improvements to Ag WUE.