The University of Arizona is recognized nationally and internationally as a leader in the science of adaptation to climate change, and associated research and outreach to understand climate change, its observed and potential impacts, and possible responses.
Climate and Population Change Impacts on Dryland Rivers - Integrated Synthesis
Recent research has revealed the strong dependence of ecosystem services on the physical and biological conditions of riparian areas in the Southwest United States. Nevertheless, it is unclear how ecosystems services change in response to exogenous forcing on the physical and biological state of ecosystems. To address this effectively, an integrated modeling and synthesis approach is needed to quantify how ecosystem services might vary in response to future climate change and population growth. Integrated modeling can predict the space and time scales of exogenous impacts on semiarid riparian areas that may alter their hydrology, ecology and social value. Changes in the water extracted from to ecosystems can have large impacts on the value of ecosystem services provided to society. The differentiation of these impacts will be studied by investigating breakpoints between limited and significant impacts on riparian ecosystem services and their valuation. The interconnected nature of social, ecologic and hydrologic systems requires place-based research using a suite of models integrated across disciplines.
Here, we propose to work on the adjacent (but distinct) San Pedro and Santa Cruz river basins, in southern Arizona. These basins span a gradient in water demand, streamflow regime and ecosystem services and have been studied through multiple projects, including studies on the value of ecosystem services provided by vegetation, birds and species diversity.
To quantify and predict how ecosystems services in semiarid river basins will vary in the face of a changing climate and a changing population, three hypotheses are tested:
1. The value of ecosystem services declines (increases) in non-linear and stepwise fashion as water is extracted (restored) from (to) dryland rivers
2. Hysteretic effects characterize stream re-watering: the trajectories of changes in ecosystem value are reversible, but the absolute magnitude of ecosystem service recovery varies depending on the degree of historic dewatering.
3. Climate change and population growth act together in a synergistic way to decrease the water withdrawal levels at which ecosystem services cross thresholds.
Intellectual Merit: To test these hypotheses, existing scientific and behavioral datasets, will be integrated using a suite of process-based models and linked to a public good market allocation model. First, existing data will be used to develop an understanding of how increasing net water extraction from riparian areas influences ecosystem service valuation endpoints. These systems will then be simulated using a suite of process-based models to understand how increasing the net water extracted from riparian areas decreases the ecosystem services value. Second, several locations where net water extracted from riparian areas has been reversed, either by pumping cessation or wastewater effluent, will be used to identify the effects of riparian restoration on ecosystem services and their value.
These restored rivers will also be simulated to explore a larger range of responses of ecosystem services to restoration. Finally, high-resolution climate and population scenarios will be developed to drive the process-based models. These scenarios will provide a set of alternative futures of ecosystem services in these two river basins. This effort will also address how to couple biophysical and economic valuation models to understand the tensions between human consumption of resources and the ecosystem services they provide.
Broader Impacts: We expect this effort will transform how ecosystem services are valued in the face of future climate and population change. As a result, these efforts need to be transferred quickly to the decision-making realm. To do this, a major target audience will be a group of federal agencies and stakeholders that we are engaging in the project. This interaction will ensure relevancy of our research; introduce our undergraduates, graduate students and post-doctoral researchers to the management community; and benefit agency scientists and managers by transferring new techniques for valuation of riparian systems in the Southwest U.S.