The difference of water footprint and availability as a physical metric for sustainable water use and management.

This paper presents a physical metric that is defined as 'difference of water footprint and availability in a given region' during either normal or dry periods, based on blue and green water concepts. Proposed metric quickly highlights water‐stressed regions and directly provides volume of water surplus/deficit in the region of interest. Evaluated green water surplus/deficit for agricultural areas can be applied to assess optimum irrigation water requirement while blue water surplus/deficit can be used to assess potential growth of agricultural‐based economy and sustainable water use and allocation within a watershed. We assessed surplus/deficit volumes of blue and green waters for three watersheds of Karaj, Latian and Mamlu dams located in Tehran and Alborz Provinces of Iran. Blue and green water resources are quantified using well‐calibrated hydrologic model of the Soil and Water Assessment Tool during the period 1995–2013. Results denote that minimum and maximum water deficit occur during wet and dry seasons, respectively. Study area does not experience green water deficit during normal periods, but a few regions encounter green water deficit during droughts. Annual blue water metrics show that one (Subbasin 7) and three subbasins (Subbasins 5–7) are ecological hotspots during normal and dry periods, respectively. Results also indicate that farmers should reduce applied irrigation water from 4.86 to 3.165 (−35%) and 3.4 (−30%) m3/s during normal and dry periods, respectively, while cultivated area (agricultural production) in Karaj, Latian and Mamlu watersheds can, respectively, be increased by 31 (46.5×106 kg), 52 (65.6×106 kg) and 31.4 km2 (47.6×106 kg) during droughts. [ABSTRACT FROM AUTHOR]