Climate and Population Change Impacts on Dryland Rivers - Integrated Synthesis

The purpose of this blog is to serve as a public documentation outlet for communication within the research group studying semi-arid rivers systems subject to climate and population drivers. We are a group of hydrologists, engineers, ecologists, economists and demographers that are seeking to better understand the interaction of climatic, hydrologic, geomorphic, biological, and social processes that influence how riparian ecosystems will change in response to potential population and climate changes. Ecosystems provide a wide variety of services to human societies. The services from riparian ecosystems in the Southwest United States derive from the presence of water in a dry land and a web of physical, biological and human processes. Southwestern rivers have been significantly altered by human impacts through surface water diversions, damming, groundwater extraction and impacts from land use change. These systems are under continued threat from alterations to groundwater hydrology due to population growth and potential impacts from population change. By necessity human uses of water for economic production are at tension with the water needed to provide ecosystem services for human society. This project seeks to understand how ecosystem services change in response to extraction or addition of water to ecosystems due to population change and climate change (Figure 1). Our work will focus on using the San Pedro and Santa Cruz Rivers as archetypical semi-arid river systems. Existing data from these rivers and a suite of integrated models will be used to understand the incremental effect of water extraction or addition to riparian ecosystems on the physical and biological status of the system and in turn the change in value of ecosystem services derived to human society from these ecosystems (Figure 2). The project will look at how the value of ecosystem services changes in response to decreases in water availability and to increases in water availability to these systems. Investigating both declines and increases in water availability will permit an investigation of different trajectories and thresholds in the value of ecosystems services as water extracted or restored to riparian ecosystems. The standing hypothesis is that once dewatered, restoration of hydrologic conditions will result in a lower level of ecosystem services and value than was originally found in these ecosystems. The utilization of existing data on dewatering and on restoration will provide a robust library of understanding of how the value of ecosystems services in riparian changes in response to hydrologic and biological conditions. This library of knowledge will then be used to understand how these systems might respond to drivers of change in these systems. A set of 3 climate and 3 population scenarios, for both river systems will be developed to understand how population and climate changes might interact in Southwestern river systems.

Few free flowing rivers exist in the Southwest. The San Pedro, one of the study rivers, is among the last. Further understanding of the interaction of physical, biological and economic processes in free flowing river systems will better inform management in more controlled and human affected systems such as dammed rivers or rivers with large amounts of diversion for agriculture. Water scarcity in the semi-arid West is likely to remain a fact. To manage water in the face of scarcity requires understanding tradeoffs between different municipal, agricultural and environmental sector uses of water. Valuing the ecosystem services provided by riparian systems is a key input variable to understanding the tradeoff between water used in the environmental sector versus other sectors of the economy. A particular broad impact of this study will be an incremental understanding of how small changes in water availability will impact the value of ecosystem services. This estimation of the marginal impact will permit more robust understanding of the economic effects of water redistribution among sectors of the economy. Since this project will project the potential effects of future changes in population change and climate change on it is important that these efforts be transferred quickly to the decision-making realm. This project’s team incorporates federal state and local stakeholders. Interaction with these stakeholders will ensure that this research is relevant and can quickly be applied in the real world. This interaction will also expose students and post-doctoral researchers to potential career paths across the earth, ecosystem and economic sciences.