Rice production in Walawe will benefit substantially from climate change and increases in yield are expected to be about 45% and 20% at the end of this century for A2 and B2 scenarios, respectively. Only a small decrease in annual variation can be expected and also the increase in water consumption is less than 10%. Precipitation will also be about 10% higher, which will keep the water balance similar. However, it is expected that more water will be required for domestic, industrial and service-oriented activities, which will result in less water available to irrigation. One adaptation strategy was rice cultivation with less irrigation water (adaptation strategy 2) and results indicate that yields will be lower even with a small decrease in irrigation. A detailed study on this adaptation strategy, where field and basin water resources were linked, showed a strong reduction in yields under lower irrigation intensities.

The other adaptation strategy (adaptation strategy 1) explored whether a shorter season would be worth implementing. According to the simulations, such an approach is indeed an option and, although rice yields will be somewhat lower, water productivity will increase. It was assumed here that the appropriate rice variety would exist.

The second crop considered is referred to as vegetables. Although a wide variety of vegetables exist, each with its own characteristics, we have used here a kind of reference vegetable crop. One of the most striking results is that an enormous increase in variation in yields is to be expected in the future. A closer look at the model results shows that this variation was mainly due to water surplus instead of water shortage. The soils considered are not well drained, which is an advantage for rice, and combined with the expected increase in variation in rain will result in soil moisture conditions that are too wet for vegetables during some years. The two adaptation strategies, less irrigation and short season, have the same impact on vegetables as on rice: yields will be lower but also variation in yields will reduce. The short season option is also beneficial in terms of water productivity.

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