As we prepare to enter an era of increased water scarcity, a premium must be placed on understanding the factors controlling urban water demand to protect human and ecosystem water security. In this vein, a variety of studies have explored drivers of demand, including meteorological, socioeconomic, and other variables related to water policy, and water use behavior. Much of this work has utilized traditional multivariate and timeseries approaches for evaluating relationships between demand and its drivers. However, more recently, wavelet analysis has been promoted as a means for assessing these relationships. A key advantage of wavelets is that they allow for identification of transient relationships between variables at multiple frequencies and times, whereas most other methods assume stationarity. Here we use wavelet analysis to explore how and why rates of response to drought in two different drought prone cities (Melbourne, Australia and Los Angeles, California) change over time (the so-called “evolutionary trajectory” of water demand). Specifically, the rate of change of a wavelet-based water demand ratio (e.g., decadal to annual demand) is used to identify 1) possible regime shifts in water demand management associated with drought events (e.g., reddening of the afore-mentioned demand ratio), and 2) how rates of response to and relaxation from those drought events change over time. In the case of Melbourne, we observe the city transition from a reactive water user (fast, reversible changes in water use with limited staying power), to an adaptive water user (lasting behavioral change or technological innovation in the face of water stress). The story in Los Angeles, however is less clear cut. No obvious trend was observed in rates of drought response over time, but rates did differ among groups of water users (e.g., multi-family residential, commercial, and industrial &gt; single family residential and governmental). These findings illustrate that drought response varies both within cities over time and between different cities with similar drought histories. Furthermore, they suggest that urban water use optimization will require water demand management reforms that target those specific groups of water users (e.g., single family residential and governmental water users in Los Angeles) that are the least responsive to drought.

Evolutionary trajectories of urban water demand and the journey towards the water sensitive city

255th National Meeting (2018)

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