Roman Kanivetsky

Water Resources Sustainability Indicator: Application of the Watershed Characteristics Approach

The quantification of the renewable flux (i.e. sustainable limit) of the hydrologic system is the prerequisite for transitioning from unsustainable to sustainable water resources management. The application of the Watershed Characteristics Approach to estimate the renewable flux of the hydrologic system was demonstrated using Minnesota’s (USA) Twin Cities Metropolitan Area (TCMA). The methodology quantified the relationships between landscape properties and water balance characteristics, resulting in the development of functioning hierarchical hydrogeological units with corresponding recharge rates. This renewable flux is a key quantitative characteristic for the assessment of a sustainability indicator. The key indicator of sustainable water use is the ratio of the renewable capacity of the hydrologic system to the water use by humans and the environment. By incorporating water use estimates for the TCMA relative to the calculated recharge rates, sustainability indicators for groundwater and total flux were calculated for the metropolitan area. As far back as the 1890s, declines in TCMA groundwater levels have been observed, which correspond to the unsustainable groundwater extraction estimates identified in the results of this study. The non-stationary characteristics of urban watersheds influenced by ongoing land use/land cover changes as illustrated in this paper, emphasizes the need for conservative hydrologic planning to achieve sustainable water management. This approach can also be applied to other metropolitan areas as a hydrologic tool for decision-makers to design sustainable water policy and prevent the over-extraction of the water flowing through the hydrologic system.

On quantifying freshwater sustainability through multiscale mapping

We agree with Kanivetsky and Shmagin (Eos, 86(50) 2005) that better accounting of flows comprising the hydrologic cycle is needed and that better quantification of recharge (into groundwater) and discharge (i.e.,streamflow) is important from human and environmental perspectives. However, because these authors promote their approach as being useful in assessing “sustainability” we feel compelled to offer words of caution about its applicability. The authors suggest that the ratio of renewable water supply to water use by humans and the environment is a “key indicator” of sustainability. We think that these authors got it half right. The ratio described above is a useful indicator because it quantifies how much strain a natural system may be experiencing. However, all ecosystem water is not equivalent. The river science literature strongly indicates the need for the full range of natural intra-annual and interannual variation of river flows, along with associated characteristics of timing, duration, frequency, and rate of change, to sustain the biotic integrity of aquatic ecosystems [Postel and Richter, 2003]. In this context, only when an adequate assessment of ecosystem needs is performed and compared to net water availability after subtracting human uses will we know if we are truly managing for sustainability.