Recent Global Cropland Water Consumption Constrained by Observations

Under current global warming and accelerated population growth scenarios, cropland irrigation water consumption has become a central issue limiting the sustainability of coupled human-natural systems. This study proposes a new estimate of recent global cropland water consumption constrained by observations and provides attributions for its recent trend. By incorporating observations, including extracted cropland leaf area index and irrigation threshold data, this study provides improved estimates of recent global cropland evapotranspiration and transpiration as well as irrigation water consumption and withdrawal. The global annual consumption and withdrawal of irrigation water are estimated to be approximately 874 and 1,867 km(3) (in 2005), respectively. From 2000 to 2014, a rapid increase in cropland irrigation was detected, especially in water-deficient areas (i.e., hyperarid, arid, and semiarid regions). Climate change, which mainly consists of rising temperature and reduced moisture conditions, is usually distinguished as the major driving factor. Human-induced increases in crop canopy cover have also contributed to more irrigation in hyperarid and arid regions. This study also provides suggestions for water-savings-targeted cropland management in water-deficient areas based on the transpiration ratio (i.e., ratio of transpiration to evapotranspiration).