Managing diversions in unregulated streams using a modified percent-of-flow approach

In Mediterranean-type river systems stream flows are naturally low in summer and autumn. This pattern is often exacerbated by over-exploitation of water resources during the dry season, which has implications for managing flows for both environmental and human needs. Mediterranean systems are characterised by strong inter- and intra-annual variability with almost all precipitation occurring in winter months followed by summer droughts with little or no rainfall, and extreme year-to-year variation ranging from intense winter storms to year-round drought (Gasith & Resh, 1999; Power, Kupferberg, Cooper, & Deas, 2015; Power, Parker, & Dietrich, 2008). The seasonal pattern of precipitation in Mediterranean climatic regions results in water availability and demand being out-of-phase; precipitation and runoff occur (almost exclusively) in winter when human demands are lowest, and precipitation is virtually non-existent in summer months when human demand is greatest (Kondolf & Batalla, 2005; Merenlender & Matella, 2013). As a result, rivers in Mediterranean climates tend to have a high degree of alteration with streamsdiverted and dammed to provide scarce water for human use (Kondolf, Podolak, & Grantham, 2013; Marr et al., 2009; Moyle, 2013). While the biophysical responses to alterations of land use, vegetation and hydrology are similar in Mediterranean and other climatic regions, the magnitude of responses tends to be intensified in Mediterranean systems. For example prolonged dry season flows may result in lower dissolved oxygen, higher temperatures and concentration of contaminants among other impacts (Cooper, Lake, Sabater, Melack, & Sabo, 2013). Climate change and increasing frequency and severity of drought promise to increase the conflict between human needs and ecological needs over time (Arthington, 2012).