Modeling the large scale water balance impact of different irrigation systems.

In this study, two parameterizations for different irrigation techniques have been implemented in a regional climate model. These implementations allow for a comparative study of water use and land–atmosphere interactions associated with traditional flood irrigation—a widespread but highly water-inefficient practice—and water-conserving drip irrigation. Both parameterizations yield realistic results for coupled climate simulations, and do so without the need to reproduce an entire crop model within the climate model. Simulations with drip irrigation exhibit ∼30% less irrigation season evapotranspiration and ∼60% less water demand overall relative to simulations with flood irrigation. Examination of the water balance for various irrigation zones in Syria and Turkey demonstrates that planned Syrian irrigation expansion in the Euphrates watershed is only feasible if accompanied by modernization. Even then, planned expansion in the Khabur watershed, a major tributary of the Euphrates, would only reach sustainability if there is significant irrigation water runoff into Syria from Turkey. Thus Syria has a window of opportunity within which it can reap the benefits of investing in modernization and expansion of irrigation. That window begins now, with the Syrian governments recent commitment to modernize its irrigation infrastructure, and in the absence of an international water-sharing agreement, ends when increased water demand and/or decreased precipitation causes the Turkish government to invest in modernizing its own irrigation systems. Such a precipitation decrease is predicted to occur in the Middle East by mid-century if greenhouse gas emissions are not curbed substantially.

Figure 3: Mean difference in latent heat at 1200 local time (FLOOD – DRIP).