Divergent trends in irrigation-water withdrawal and consumption over mainland China

Knowledge of both irrigation-water withdrawal (IWW) and consumption (IWC, i.e. the evapotranspiration loss of applied irrigation water) is critical to sustainable water use and management. However, IWW and IWC are not well differentiated and an integrated analysis of their changes and causes is still lacking. Here we aim to close this gap and investigate the trends and drivers of IWW and IWC over mainland China using the logarithmic mean Divisia index approach and multivariate regression and fixed-effects panel regression models. We find that IWW decreased at a rate of -1.3 km(3) yr(-1) (or -0.4% yr(-1)) while IWC increased at a rate of 2.9 km(3) yr(-1) (or 2.4% yr(-1)) from 1999 to 2013, albeit both showed upward trends from 1982 to 1999. The reduction in IWW was due to the decreased water-withdrawal intensity (WWI) (i.e. IWW per unit area), while the increase in IWC was mainly due to the irrigated area expansion. We find opposite trends in IWW and IWC in about half of the Chinese provinces, with IWW decreasing and IWC increasing in most cases. Changes in irrigation efficiency (IE, defined as the ratio of IWC to IWW) and climatic factors explain a large proportion of the variance in WWI and water-consumption intensity (i.e. IWC per unit area). IE presents a strong negative correlation with WWI but a positive correlation with water-consumption intensity. The improved IE makes a nonnegligible contribution (similar to 20%) to the irrigated area expansion, especially in water-scarce regions. The strong positive linkage between IE and IWC together with the significant rise in IWC with increasing IE suggest that the paradox of IE (i.e. higher IE tends to increase water consumption) has manifested in mainland China. Our findings highlight the importance of considering both IWW and IWC changes as well as farmer's behavior adjustments in water resource management.

Automated summary

This study examines the trends and drivers of irrigation-water withdrawal (IWW) and consumption (IWC) in mainland China. The results show that IWW has decreased while IWC has increased from 1999 to 2013, mainly due to changes in water-withdrawal intensity and irrigated area expansion. Factors such as irrigation efficiency and climatic conditions play a significant role in explaining the variance in water-use intensity.