This paper applies the principles of water-use accounts, developed in the first of the series, to the Karkheh River basin in Iran. The Karkheh Basin lies primarily in Iran with its extreme downstream discharge into the Hawr Al Azim marshes on the border with Iraq. The northern part of the Basin where the Karkheh and its tributaries rise is mountainous, cooler, and wetter. The River spills out on to the hotter, lower semi-arid plains at its southern end. Near the downstream end of the Karkheh River is a major dam, built recently to supply water for irrigation. Precipitation, mainly in winter, varies from 400-500 mm in the upper part of the Basin falling to about 230 mm in the lower reaches. Rainfall exceeds evaporation only for a few winter months, and only in the upper catchment. Preciptiation varies considerably from year to year.
Net runoff from the basin is less than 2% of total precipitation. Total water use exceeds rainfall by about 14%, the difference is assumed to be largely pumped groundwater in the upper and middle parts of the basin. Grassland is the most extensive land use and uses about 50% of the total available water. Irrigation, although occupying a smaller area, consumes about 28% of the available water followed by rainfed agriculture, which consumes about 20%.
Plausible figures for the effect of the Karkheh Dam suggest that it will reduce flows downstream of the Dam and the inflow into the Hawr Al Azim marshes.
CPWF Working Paper: Basin Focal Projectseries, BFP08. Colombo, Sri Lanka: The CGIAR Challenge Program on Water and Food. 22 pp.