Envisioning resilient futures for urban water and wastes
Most cities lack resilience and would be severely disrupted if environmental perturbations were to occur. By “disruption” I mean outcomes like illness and death, economic downturns, and emigration. In this presentation I focus on two likely perturbations: drought and depletion of phosphate rock (P).
A severe drought can permanently debilitate a city, yet we not know makes a city resilient to drought. This is an important problem: the conflation of climate warming, rapid urbanization, increasing wealth (resulting in greater per capita water consumption), and weak governance may lead to disastrous droughts, especially in the global south. Drought can be conceptualized as a socio-ecological phenomenon (SE drought), because the actions of social systems determine the impact of a hydrologic drought. In this view, a given hydrologic drought may devastate one city, but another might survive intact.
The second perturbation is supply of P. Most P enters human ecosystems via farms, which ship food to cities. We are probably at the beginning of an era of P scarcity; we know that U.S. production will decline quickly, and that prices are increasing. Yet, a “brown devolution” does not have to occur, if we learn how to utilize P efficiently, with minimal losses.
Using Phoenix as a case study, the importance of antecedent conditions has emerged. In our studies, we have shown that the aquifer is contaminated by nitrate (from prior agriculture) and salts (from evapoconcentration), and urban soils have high salinity levels, increasing irrigation requirements. Moreover, during a drought – usually also a period of high temperature – water use would increase, especially for power generation and plant irrigation. For cities of the global south, pollution problems are far worse; moreover, inefficient governments and poverty limit the capacity to adapt.
Regarding P, we are modeling a “circular economy” for P in the Twin Cities region, connecting the urban region to the state’s agricultural system, which supplies 80% of the urban food P. High production agricultural systems in the state are approaching 100% P use efficiency (whole system), but the city is an inefficient P user: 64% of input P is stored (mostly landfills) and only 4% is recycled; in a “modest” conservation scenario 68% of input P was recycled and only 22% was stored. Ongoing study will examine the barriers toward recycling P. These include, among others, low adoption of food waste recycling and transportation costs for moving P-rich biosolids to agricultural land.