摘要
The snow pack of Sierra Nevada, southern Spain, melts during spring and early summer, feeding ancestral irrigation channels in the region known as the Alpujarra. This simulation study compares the traditional irrigation water supply, based on proportional division, with the actual supply, based on up-downstream priority, in one watershed in the Alpujarra. A combination of three models was used for the analysis. Water supply was simulated using the snowmelt-runoff model. The snow cover required by that model was determined using satellite images. A second model simulated the distribution of water based on proportional division and on up-downstream priority. Irrigation requirements and return flows were simulated using a soil–water balance. Proportional division is an inherently equitable mechanism for distributing water, but can lead to water deficits for different crops in a command area. The analysis demonstrated this premise not be true. The superiority of proportional division was magnified in dry years. Because of the internal reuse of return flows, irrigation consumptive use coefficient (the ratio of irrigation water that is evapotranspirated by the crops to the total amount of irrigation water that leaves the area of concern during the period of analysis) at the watershed scale was significantly greater than at the irrigation-channel scale. This result illustrated, based on tradition in ancestral irrigation community, the notion of integrated water resources management.Communicated by E. Bautista.