Under baseline conditions, rice yields will be much lower in the future. Model output shows that salinity is the major reason for this. Although salinity levels in irrigation water are low (0.3 dS/m), this is already sufficient to have salt accumulation in the soil so that crop growth will be hampered and yields will be lower. It might be that the ECHAM4 projections with somewhat more rainfall in the winter would boost leaching and the impact of salinity will be less.

The adaptation strategy in which we assumed that salinity in irrigation water is zero shows that salt is one of the major threats to agriculture in Zayandeh. Rice cultivation in particular is very sensitive to salinity. The second adaptation strategy, where irrigation will be somewhat lower, shows a major drop in yields. Detailed analysis of the impact on irrigation supply and salinity can be found elsewhere (Droogers and Torabi, 2002).

For wheat, the impact of salinity was explored further by including an increased as well as a decreased salinity level. Results show that although salt has an impact on expected yields, this is much lower than for rice. In terms of future projections, climate change will have a positive impact on wheat production in Zayandeh.

It should be emphasized again that results as presented are valid for field-scale analysis, without taking account of basin water resources. For Zayandeh this is essential, since total consumed water will increase for rice as well as for wheat at field level and whether this water is available should be explored at basin level. If not, two options are available to adapt: reduced irrigation depth or reduced cropped area.

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