11. Reduction of Water Losses by Use of Alternative Irrigation Techniques in the Aral Sea Drainage Basin

The Aral Sea drainage basin (ASDB) in Central Asia is a region under severe water stress. Its population depends to a large extent economically on irrigated agriculture, which consumes over 90% of the withdrawn freshwater in the drainage basin. There is thus a strong need to increase the water productivity, i.e. the ratio between crop production and water use. We analyse impacts on water use of possible large-scale implementations of alternative irrigation techniques, replacing traditional furrow irrigation on cotton fields in the ASDB. We base our quantifications on experimental field comparisons of yield and water use between traditional furrow irrigation and alternative irrigation techniques (drip irrigation, alternate furrow irrigation, surge flow irrigation and surge flow irrigation on alternate furrows). All alternative methods, except drip irrigation, are associated with lower cotton yields than the traditional furrow irrigation. In order to keep the cotton production unchanged when yields are lower, extended irrigation areas are needed, over which non-negligible additional water volumes will be lost. We show that despite such negative feedback effects, the irrigation water use on cotton fields in the ASDB could decrease by as much as 10 km³/year, if the traditional furrow irrigation were to be replaced by one of the investigated alternative methods. Such decreases in water use can considerably influence the hydrological conditions in the entire basin. In particular, by reducing the severe water stress in the lower ASDB, which suffers from elevated groundwater tables, and high soil and groundwater salinity.