Global Croplands and Their Water Use from Remote Sensing and Nonremote Sensing Perspectives
Croplands are the largest user of water worldwide. Much of the water is used for food production, making global croplands and their water use important to world food security. Of all the water used by humans, croplands consume an overwhelming proportion (60%–90%; Thenkabail et al. 2009a; Thenkabail et al. 2009b; Thenkabail et al. 2009c). There are two types of cropland water use (Falkenmark and Rockström 2006): (1) green water use by rain-fed croplands from the unsaturated soil zone and (2) blue water use by irrigated croplands from rivers, reservoirs, lakes, and from saturated zones or groundwater aquifers and rain over irrigated croplands (Hoff et al. 2010; Rockström et al. 2008). However, alternative demands for land water use are increasing steeply due to urbanization (Deyong et al. 2009), industrialization (Liu et al. 2005), environmental flows and ecosystem services (Gordon, Finlayson, and Falkenmark 2009), maintaining water quality (and associated health of the populations), and recreational and other demands (Gordon, Peterson, and Bennett 2008).