Response to Mac's question: Why do we need this?

As always, Mac poses some good, tough questions. The main one is probably this: Why is Water Productivity Plus needed?

I know David is away from his desk at the moment, so let me take the opportunity to offer my perspective. He can correct me later

Firstly, there's a need to consolidate the concept, taking account of new observations from BFPs, sometimes over very large areas. Insights of large-scale variation of water productivity from the Andes, Nile and Mekong provides a wealth of new observations that deserve review.
Secondly, there's a need to explain how to take a broader view, where this is necessary to relate water productivity of the whole system as is supports livelihoods. For example, the Nile, Karkheh and Niger BFPs are producing observations that suggest that concepts of crop water productivity (which has been the main focus so far) may need to be expanded to take account of livestock systems. In the Mekong, aquatic systems are very important. To date, these concepts have been dealt with somewhat independently. I think it woudl be helpful to bring them together.
Thirdly, I sense there's a need to consolidate the analytical framework of water productivity to account for 'multiple water productivities' and how these contribute together to well-being. Without losing sight of the value of simple measures such as kg/m, I feel it may be time to look at further valuation of water-using systems, if that can be done.