Estimating future runoff levels for a semi-arid fluvial system in central Arizona, USA

Abstract

We developed a water budget runoff model for the Salt and Verde River basins of central Arizona and used the outputs of 6 global climate models (GCMs) to estimate runoff in the future under assorted emissions scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). We used a statistical downscaling routine to refine the GCM outputs for the 2 basins, and we found that all model-scenario combinations simulate a mean temperature rise in the study area of between 2.4 and 5.6°C, using year 2050 greenhouse gas concentrations. Mean changes in precipitation vary substantially among the models and scenarios, and, as a result, changes in runoff vary from 50 to 127% of historical levels. Assuming equal probabilities associated with each scenario and model run, the overall results suggest that runoff from the Salt and Verde will have an approximately 85% chance of being less strong, the certainty of which is related to consensus on warming in the study area. The large variability among predictions of precipitation trends introduces substantial uncertainty. KEY WORDS: Dryland runoff · Climate change · Water budgetResale or republication not permitted without written consent of the publisher Clim Res 35: 227-239, 2008 change are fully known. And third, if future climate conditions differ substantially from historical conditions, then the political institutions that have allocated water so effectively in the past will need to be reconsidered and revised. Real reductions in water supply, or even the possibility of reductions, will force decision makers to confront previously taboo subjects such as the efficacy of decades-old water pacts and regulations, pricing schemes that rise rapidly after basic needs are met, restrictions on landscaping treatments, and density and growth management.During the last 25 yr there have been at least 6 major studies of the potential impacts of future climate change on runoff within the Colorado River Basin, and all suggest a trend to less runoff in the future. Revelle & Waggoner (1983) used the simple approach of applying temperature and precipitation scenarios for the Upper Basin to a statistical regression equation relating the variables to runoff. Nash & Gleick (1991, 1993 used temperature and precipitation scenarios and more sophisticated GCM output under doubled atmospheric concentrations of CO 2 to run a National Weather Service hydrology model for the Upper Basin. Christensen et al. (2004) used National Center for Atmospheric Research (NCAR) GCM output from a 'business as usual' (BAU) gas emissions scenario as input to the variable infiltration capacity (VIC) hydrological model across the entire Colorado River Basin. Hoerling & Eisched (2007) applied multiple GCM outputs under BAU emissions to the calculation of the Palmer drought severity index (PDSI), which was related to runoff in the upper Colorado Basin using statistical regression. Most recently, Christensen & Lettenmaier (2006) used multiple GCM outputs for 2 emissions scenarios to alter temperatur...

Riparian trees and aridland streams of the southwestern United States: An assessment of the past, present, and future

“…This warming will reduce discharge volume in several southwestern streams, even if amount of precipitation is unaffected (Christensen et al, 2004;Seager et al, 2013). Similar reductions in total discharge have been modeled at the Verde River and Salt River by Ellis et al (2008). Because the climate models we examined do not adequately forecast droughts, which may occur with greater frequency and severity in the Colorado and Rio Grande basins, future decreases in discharge will likely be greater than those projected (Serrat-Capdevila et al, 2013;Gutzler, 2013).…”

“…Managers should therefore anticipate greater change in timing than magnitude for southwestern streams with snowmelt-driven high flows. Among climate change studies, there is less model agreement on changes in amount of rainfall, which has a greater impact on timing and magnitude of peak discharge at the Central Highland streams (Ellis et al, 2008). Greenhouse warming may result in heavier storms occurring during the summer, fall, and winter periods, which would increase variability of peak discharges from year to year, especially at Central Highland streams, which flood readily when heavy rainfall occurs (Hawkins et al, 2015).…”

Decision-Making under Uncertainty for Water Sustainability and Urban Climate Change Adaptation

“…With respect to supplies, scientists attempted to detail the range of likely future climate conditions in the Colorado River Basin and upstream watersheds of the Salt and Verde Rivers (two of Phoenix's three major source regions for water supply) by downscaling global climate model-scenarios combinations to assess their possible effects on local water supplies. A water-budget model for the Salt and Verde River watersheds of central Arizona examined how twenty climate model-emission scenario combinations (i.e., as identified by the Intergovernmental Panel on Climate Change) might affect temperatures, precipitation, and surface runoff for 2050 [51]. All twenty scenarios predicted at least a 2 °C rise in temperatures.…”

“…Figure 2. Twenty model-scenario combinations predicting change in temperature (ΔT), precipitation (ΔP), and runoff (% of historical levels) for 2050 [51].…”

A climate change projection for summer hydrologic conditions in a semiarid watershed of central Arizona

“…This can help improve the reliability of climate simulations in regions with fine-scale features such as rugged terrain, water bodies or land cover differences (Castro et al 2007, leading to more realistic precipitation fields. Similarly, the use of coarse hydrologic models in climate change assessments limits their ability to resolve the finescale meteorological forcing and watershed properties that control hydrologic responses, in particular during the NAM (e.g., Ellis et al 2008;Serrat-Capdevila et al 2013, Robles-Morua et al 2015. Distributed hydrologic models, on the other hand, have a wider appeal for climate change impact studies due to their ability to provide insight on the spatial and temporal details of the rainfall-runoff transformation (e.g., Xu andSingh 2004, Kampf andBurges 2007) In this study, we conduct high resolution (~120 m, hourly) hydrologic projections for summer conditions in a semiarid watershed of central Arizona.…”