Farmer response to rationed and uncertain irrigation supplies

It is shown that water scarcity should induce farmers to under-irrigate some crops in relation to full potential evapo-transpirative demand, because reductions in yield may be proportionally less than reductions in water applied. This strategy increases returns to water. However, where water availability (and hence evapo- transpiration) falls below a certain point, the value of the crop can fall to zero -- either because the crop dies or becomes unmarketable. This possibility implies that a strategy of deficit irrigation, when irrigation supplies are uncertain, increases the risk of financial loss. There is thus a theoretical tradeoff between under-irrigation and uncertainty. Field data from northwest India, where irrigation systems were designed and are still operated to ration scarce water among users, confirm the theoretical model, showing that even in very large systems it is possible to encourage individual farmers to maximize returns to water. Field data further confirm that the extent to which farmers pursue this strategy is affected by the reliability of the service they receive. (Author abstract, modified)