Reply on RC1

Abstract

The water footprint (WF) concept is a generally accepted tool introduced in 2002. Many studies applied water footprinting, indicating impacts of human consumption on freshwater, especially from agriculture. Although the WF includes supply chains, presently it excludes irrigation supply chains and non-beneficial evapotranspiration, and calculations for agriculture start from crop water requirements. We present a conceptual framework distinguishing between traditional (net) WFs and proposed gross WFs, defined as the sum of net WFs and irrigation supply chain related blue WFs and as the sum of green WFs and green WFs of weeds. Many water management studies focused on blue water supply efficiency, assessing water losses in supply chain links. The WF concept, however, excludes water flows to stocks where water remains available and recoverable, e.g. to usable groundwater, in contrast to many water management approaches. Also, many studies focused on irrigation technology improvement to save water. We argue that not only irrigation technology should be considered, but whole water supply chains, also distinguishing between surface and groundwater, to improve efficient blue water use in agriculture. This framework is applied to the Pakistani part of the Indus basin that includes the largest man-made irrigation network in the world. The gross blue WF is 1.6 times the net blue WF leading to a K value (ratio of gross and net blue WF) of 0.6. Surface water losses vary between 45 and 49 %, groundwater losses between 18 and 21 %. Presently, efficient irrigation receives much attention. However, it is important to take irrigation supply chains into account to improve irrigation efficiency. Earlier WF studies showing water scarcity in many regions underestimate agricultural water consumption if supply chains are neglected. More water efficient agriculture should take supply chain losses into account probably requiring water management adaptations, which is more a policy than an agriculture task.