Abstract
The structure, function, and services of urban ecosystems evolve over time scales from seconds to centuries as Earth’s population grows, infrastructure ages, and sociopolitical values alter them. In order to systematically study changes over time, the concept of “urban evolution” was proposed. It allows urban planning, management, and restoration to move beyond reactive management to predictive management based on past observations of consistent patterns. Here, we define and review a glossary of core concepts for studying urban evolution, which includes the mechanisms of urban selective pressure and urban adaptation. Urban selective pressure is an environmental or societal driver contributing to urban adaptation. Urban adaptation is the sequential process by which an urban structure, function, or services becomes more fitted to its changing environment or human choices. The role of water is vital to driving urban evolution as demonstrated by historical changes in drainage, sewage flows, hydrologic pulses, and long-term chemistry. In the current paper, we show how hydrologic traits evolve across successive generations of urban ecosystems via shifts in selective pressures and adaptations over time. We explore multiple empirical examples including evolving: (1) urban drainage from stream burial to stormwater management; (2) sewage flows and water quality in response to wastewater treatment; (3) amplification of hydrologic pulses due to the interaction between urbanization and climate variability; and (4) salinization and alkalinization of fresh water due to human inputs and accelerated weathering. Finally, we propose a new conceptual model for the evolution of urban waters from the Industrial Revolution to the present day based on empirical trends and historical information. Ultimately, we propose that water itself is a critical driver of urban evolution that forces urban adaptation, which transforms the structure, function, and services of urban landscapes, waterways, and civilizations over time.
Highlights
Over half of the Earth’s population currently lives in urban areas and this number is projected to increase in the future [1]
Urban Adaptation: Urban adaptation is the sequential process by which an urban ecosystem and its structure, function, or ecosystem services becomes more fitted to its changing environment or human choices over time
We suggest that the metabolism of urban systems evolves over time in response to urban selective pressures through the process of urban adaptation (Figure 4)
Summary
Over half of the Earth’s population currently lives in urban areas and this number is projected to increase in the future [1]. Understanding the evolution of how humans have interacted with urban waters is important for guiding innovations for future water management [9] It is important for improving our scientific understanding of how urban water systems evolve over time scales from seconds to centuries as Earth’s population grows, infrastructure ages, and sociopolitical values alter them. A transition in the structure, function, and services from the Industrial City to the “Sanitary City” was driven by the need for clean drinking water and centralized sewage infrastructure [14]. We suggest that the concept of urban evolution is critical for elucidating the role of urbanization during the Anthopocene, an epoch when human activities have had a significant global impact on the Earth’s ecosystems including water [24,25]. Site during 2009 (POBR is a forested stream, BARN is a stream draining forest/residential land use, GFVN is a stream draining suburban/urban land use, and GFCP drains urban land use); error bars denote standard error (b)
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