The dynamics of water in arid cities, Part I: Overview of the central Arizona-Phoenix (CAP) LTER research at the water-climate nexus

Background/Question/Methods:  Over the last 13 years the CAP LTER Program has studied water dynamics in the Phoenix Metropolitan area using interdisciplinary approaches that include ecological, hydrologic, climatological, social, and economic components of the system.  We present a conceptual model of the urban socio-ecological system and an overview of ongoing research projects based on this approach.  In this conceptualization, the function and structure of urban ecosystems are dominated by human actions (e.g., water use) and results of those actions (e.g., the built environment, landscaping choices), respectively.  Both interact with climatic and human inputs of water to control the horizontal and vertical components of the urban water budget.  In Phoenix, stormwater dynamics dominate horizontal water fluxes while evaporation, transpiration, and [largely deliberate] infiltration dominate vertical water fluxes.

Results/Conclusions:  As with all hot, arid cities, the Urban Heat Island (UHI) effect is an important phenomenon in Phoenix.  We are using empirical and modeling approaches to better understand how urban ecosystem structure (the built environment and landscaping) interacts with human decisions about irrigation (part of urban ecosystem function) and regional climate to regulate the UHI and perhaps to create localized Urban Cooling Islands through landscaping choices (transpiration) and water- use decisions (irrigation).  We are parameterizing a well-documented ecohydrology model (TIN-based Real-time Integrated Basin Simulator, or tRIBS) for urban settings to better predict these linkages in a spatially articulate manner. Our results demonstrate its superior efficacy compared with more traditional models, such as the Stormwater Management Model and the HEC Hydrologic Modeling System.  In conjunction with this modeling effort, we have installed micrometeorological towers in 12 suburban yards in the same neighborhood.  We are coupling data from these towers with data on outside water use and landscaping choices, and with information on homeowner perceptions about water use and microclimate.  Finally, CAP LTER coordinates a large stormwater monitoring project in several hierarchically nested watersheds in Scottsdale AZ.  Results from this project will be detailed in two other ESA presentations by L. Turnbull and N. Grimm.  Here, we present results from a detailed land use/land cover analysis of these urban watersheds and we link these spatial data to information on water use based on landscaping type or specific data on the actual use of irrigation water.  Together, these research efforts form the major components of our CAP LTER water-related research, and demonstrate our integrated conceptual approach.