The scoping document could be clearer in distinguishing specific drivers of food security or insecurity. These may influence both rainfed and irrigated production of staples, but may have nothing to do with water per se. Tariff protection for domestic rice production (75% in Uganda at the moment) or rural energy subsidies (South Asia) come to mind, but the paper sometimes asks the questions the wrong way round (e.g "What is the effect of water availability on the international trade of food..").
So some more explicit consideration of the water variable in agricultural production would help (the total factor productivity argument) plus a measured view of how much room for manoeuvre remains through intensification and improving irrigation performance generally. Current trends have already been diagnosed in the 2007 Comprehensive Assessment and then much of the FAO supply-utilization account work is relevant in assessing the prospects for meeting global calorie demand. However real-world water and food security dramas tend to be politicized where access to water for productive uses is captured by a few and compounded by manipulation of food staple prices.
Beyond these general observations the paper could include a contemporary view of environmental pressures arising from agriculture - an issue that easily gets ignored. To this extent, more precision on the hydro- environmental limits of irrigated agriculture in relation to specific national or regional food security goals would be welcome. A draft FAO document produced by the Land and Water Divsion a few years ago is relevant here and is attached [The attachment has been removed. Please refer to the executive summary of the published report, Ed. http://www.fao.org/3/a-i7754e.pdf].
Jacob Burke