Cheap water, massive federal subsidies and political clout have sustained rice farming in the lower Colorado River basin for decades, but now the industry is in a precarious situation. Drought, population growth upstream and economic boom in Austin are pushing out the practice because of increasing demand for Texas’ scarce water resources. The tightening supply of water raised questions about the sustainability of producing such a water intensive crop in the state. Drought has cut off the cheap water to farmers for three years, and a mobilized coalition of upper river basin interests is calling for a permanent end to subsidized water. It’s increasingly clear that the politics of water in a drought-prone future is likely to side with cities, where voters are heavily concentrated. Rice farmers have scrambled to adapt. Larger rice farms have switched to groundwater. Some farmers have swapped rice for corn, milo or soybeans to keep their income. Crop insurance, which made up for at least 55 percent of the money lost in drought, softened the blow for rice farmers. But revenues in rice-related industries in Wharton, Matagorda and Colorado counties have dropped sharply and some businesses have already packed it in. These new realities cast uncertainties throughout the lower river basin, where locals fear this way of life is disappearing. / text

Between 2000 and 2014, annual Colorado River flows averaged 19% below the 1906-1999 average, the worst 15-year drought on record. At least one-sixth to one-half (average at one-third) of this loss is due to unprecedented temperatures (0.9 degrees C above the 1906-1999 average), confirming model-based analysis that continued warming will likely further reduce flows. Whereas it is virtually certain that warming will continue with additional emissions of greenhouse gases to the atmosphere, there has been no observed trend toward greater precipitation in the Colorado Basin, nor are climate models in agreement that there should be a trend. Moreover, there is a significant risk of decadal and multidecadal drought in the coming century, indicating that any increase in mean precipitation will likely be offset during periods of prolonged drought. Recently published estimates of Colorado River flow sensitivity to temperature combined with a large number of recent climate model-based temperature projections indicate that continued business-as-usual warming will drive temperature-induced declines in river flow, conservatively -20% by midcentury and -35% by end-century, with support for losses exceeding -30% at midcentury and -55% at end-century. Precipitation increases may moderate these declines somewhat, but to date no such increases are evident and there is no model agreement on future precipitation changes. These results, combined with the increasing likelihood of prolonged drought in the river basin, suggest that future climate change impacts on the Colorado River flows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur. Plain Language Summary Between 2000 and 2014, annual Colorado River flows averaged 19% below the 1906-1999 average, the worst 15-year drought on record. Approximately one-third of the flow loss is due to high temperatures now common in the basin, a result of human caused climate change. Previous comparable droughts were caused by a lack of precipitation, not high temperatures. As temperatures increase in the 21st century due to continued human emissions of greenhouse gasses, additional temperature-induced flow losses will occur. These losses may exceed 20% at mid-century and 35% at end-century. Additional precipitation may reduce these temperature-induced losses somewhat, but to date no precipitation increases have been noted and climate models do not agree that such increases will occur. These results suggest that future climate change impacts on the Colorado River will be greater than currently assumed. Reductions in greenhouse gas emissions will lead to lower future temperatures and hence less flow loss.

Salinity issues in the Upper Colorado River Basin have been a serious concern to the western United States and northern Mexico. The Colorado River salinity is mainly come from geologic materials located in the Upper Colorado River Basin. Natural weathering and human activities, such as irrigation, accelerate the dissolution of saline materials. Economic damages due to salinity in the Colorado River Basin are estimated at $295 million in 2010, for example, reduced crop yield, plugging of water pipes and fixtures, and ecological health of rivers. In order to manage salinity in the Upper Colorado River Basin, SPARROW model has been applied to simulate salinity sources and transport. However, the model application discontinued during recent past due to lack of data. Given the motivation and importance of salinity issues in the Colorado River Basin, the overall goal of this research is to develop a decision-making framework for an effective salinity management in the Upper Colorado River Basin. First, this research introduced a methodology for reliable analysis of salinity sources and transport in the Upper Colorado River Basin. However, recent decreasing trend of number of monitoring stations may cause increase of model uncertainty. Therefore, a decision-making methodology for an effective water quality monitoring network was developed. From the results of monitoring network analysis, the redundancy or scarcity of monitoring stations in each watershed can be identified under the given operational costs. Finally, salinity management scenarios considering cost and equity were developed. Management options considering cost only can neglect the fairness in the allocation of salinity control responsibilities among stakeholders. To overcome this limitation in management, the methodology developed in this research considers cost of salinity control, equitable distributions among stakeholders, and cost efficiency. The methodologies developed in this research provide a comprehensive decision-making framework for an effective salinity management in the Upper Colorado River Basin. Moreover, this framework is not limited to the management of salinity in the Upper Colorado River only, but also can be applied to other water quality management problems.

abstract: Rapid urbanization and population growth occurring in the cities of South Western United States have led to significant modifications in its environment at local and regional scales. Both local and regional climate changes are expected to have massive impacts on the hydrology of Colorado River Basin (CRB), thereby accentuating the need of study of hydro-climatic impacts on water resource management in this region. This thesis is devoted to understanding the impact of land use and land cover (LULC) changes on the local and regional hydroclimate, with the goal to address urban planning issues and provide guidance for sustainable development. In this study, three densely populated urban areas, viz. Phoenix, Las Vegas and Denver in the CRB are selected to capture the various dimensions of the impacts of land use changes on the regional hydroclimate in the entire CRB. Weather Research and Forecast (WRF) model, incorporating the latest urban modeling system, is adopted for regional climate modeling. Two major types of urban LULC changes are studied in this Thesis: (1) incorporation of urban trees with their radiative cooling effect, tested in Phoenix metropolitan, and (2) projected urban expansion in 2100 obtained from Integrated Climate and Land Use Scenarios (ICLUS) developed by the US Environmental Protection Agency for all three cities. The results demonstrated prominent nocturnal cooling effect of due to radiative shading effect of the urban trees for Phoenix reducing urban surface and air temperature by about 2~9 °C and 1~5 °C respectively and increasing relative humidity by 10~20% during an mean diurnal cycle. The simulations of urban growth in CRB demonstratedii nocturnal warming of about 0.36 °C, 1.07 °C, and 0.94 °C 2m-air temperature and comparatively insignificant change in daytime temperature, with the thermal environment of Denver being the most sensitive the urban growth. The urban hydroclimatic study carried out in the thesis assists in identifying both context specific and generalizable relationships, patterns among the cities, and is expected to facilitate urban planning and management in local (cities) and regional scales. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2017

Changes in climate influence agricultural production. This study looks at the impacts of climate variability in the Utah regions of the Upper Colorado River Basin by combining regression techniques with interview data to explore how climate variability affects agricultural production and how the farmers are adapting their practices to these changes. The results show that climate does not have any significant impact on cattle and hay production in the study area on a decadal scale. However, on an annual basis temperature seems to have more impact than precipitation. Among non-climatic variables, commodity prices and their regulations by the government are the most important factors that influence the year-to-year production. Farmers are well-aware of these impacts and have adapted significantly to the changes that occur on a year-to-year basis.

Colorado River cutthroat trout, Oncorhyncus clarki pleuriticus , occupy less than 12% of their historic range. Restoration and conservation of this species are currently under way across the upper Colorado River basin, but guidance to inform management decisions related to the impacts of climate change on cutthroat is lacking. Shifts in the thermal distribution of freshwater fish have been documented, and will continue to occur as cold water habitat is threatened by warming water temperatures. Coupled air and water temperature data allow for an estimation of potential resistance and resilience to warming, determining the effect that local air has on stream temperature. The United States Forest Service, cooperating with federal agencies, state agencies and private landowners, placed temperature loggers in the water and two air locations at 50 sites. To select a representative subset of sites, six habitat characteristics of each Colorado River cutthroat trout core conservation population were considered. These characteristics include solar input, elevation, watershed area, riparian vegetation, groundwater input, and the 30-year mean maximum July air temperature. Results from coupled temperature loggers indicate that the relationship between air and water temperature in the upper Colorado River basin is neither linear, nor one-to-one. Using Mohseni's (2003) equation, the relationship between air and water temperature was fit to a nonlinear regression curve. Analysis shows that the median rise in daily maximum water temperature is only 0.41°C for a 1.0°C increase in the median daily maximum air temperature. Air temperature exerts the most influence over water temperature; however, these results indicate that there are other characteristics that influence stream temperature. To determine these characteristics, analysis of the six habitat characteristics used for site selection in addition to aspect, slope, and latitude were used to model multiple temperature metrics. The best model, nonlinear water to air temperature relationship, had an R2 between actual and predicted values of 0.71. It also became clear that using multi-metric analysis would provide a much more robust indicator of resistance. This work will allow managers to consider potential climate change resistance or resilience in project prioritization, by understanding potential habitat characteristics to buffer stream warming.

abstract: Water resource systems have provided vital support to transformative growth in the Southwest United States; and for more than a century the Salt River Project (SRP) has served as a model of success among multipurpose federal reclamation projects, currently delivering approximately 40% of water demand in the metropolitan Phoenix area. Drought concerns have sensitized water management to risks posed by natural variability and forthcoming climate change. Full simulations originating in climate modeling have been the conventional approach to impacts assessment. But, once debatable climate projections are applied to hydrologic models challenged to accurately represent the region’s arid hydrology, the range of possible scenarios enlarges as uncertainties propagate through sequential levels of modeling complexity. Numerous issues render future projections frustratingly uncertain, leading many researchers to conclude it will be some decades before hydroclimatic modeling can provide specific and useful information to water management. Alternatively, this research investigation inverts the standard approach to vulnerability assessment and begins with characterization of the threatened system, proceeding backwards to the uncertain climate future. Thorough statistical analysis of historical watershed climate and runoff enabled development of (a) a stochastic simulation methodology for net basin supply (NBS) that renders the entire range of droughts, and (b) hydrologic sensitivities to temperature and precipitation changes. An operations simulation model was developed for assessing the SRP reservoir system’s cumulative response to inflow variability and change. After analysis of the current system’s drought response, a set of climate change forecasts for the balance of this century were developed and translated through hydrologic sensitivities to drive alternative NBS time series assessed by reservoir operations modeling. Statistically significant changes in key metrics were found for climate change forecasts, but the risk of reservoir depletion was found to remain zero. System outcomes fall within ranges to which water management is capable of responding. Actions taken to address natural variability are likely to be the same considered for climate change adaptation. This research approach provides specific risk assessments per unambiguous methods grounded in observational evidence in contrast to the uncertain projections thus far prepared for the region. / Dissertation/Thesis / Doctoral Dissertation Geography 2016

abstract: The Colorado River Basin (CRB) is the primary source of water in the southwestern United States. A key step to reduce the uncertainty of future streamflow projections in the CRB is to evaluate the performance of historical simulations of General Circulation Models (GCMs). In this study, this challenge is addressed by evaluating the ability of nineteen GCMs from the Coupled Model Intercomparison Project Phase Five (CMIP5) and four nested Regional Climate Models (RCMs) in reproducing the statistical properties of the hydrologic cycle and temperature in the CRB. To capture the transition from snow-dominated to semiarid regions, analyses are conducted by spatially averaging the climate variables in four nested sub-basins. Most models overestimate the mean annual precipitation (P) and underestimate the mean annual temperature (T) at all locations. While a group of models capture the mean annual runoff at all sub-basins with different strengths of the hydrological cycle, another set of models overestimate the mean annual runoff, due to a weak cycle in the evaporation channel. An abrupt increase in the mean annual T in observed and most of the simulated time series (~0.8 °C) is detected at all locations despite the lack of any statistically significant monotonic trends for both P and T. While all models simulate the seasonality of T quite well, the phasing of the seasonal cycle of P is fairly reproduced in just the upper, snow-dominated sub-basin. Model performances degrade in the larger sub-basins that include semiarid areas, because several GCMs are not able to capture the effect of the North American monsoon. Finally, the relative performances of the climate models in reproducing the climatologies of P and T are quantified to support future impact studies in the basin. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2018

This research presents the Colorado River basin as a social-ecological system. Utilizing event data on cooperative and conflictive interactions over fresh water, the system is decomposed to look for evidence of outcomes of resilience enhancement. The Animas-La Plata Project in the upper San Juan basin is presented as a case study, and qualitative methods are used to analyze interactions that led to its construction in order to assess social-ecological outcomes. In the upper San Juan basin, cooperative interactions over fresh water outnumbered conflictive ones. Interactions over water rights and infrastructure were most common, and the most cooperative interactions focused on these issue types. Many of these interactions focused on the Animas-La Plata Project compromise, which ultimately enhances social-ecological resilience in the Colorado River basin. / Graduation date: 2012

From the Proceedings of the 1971 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 22-23, 1971, Tempe, Arizona / The Colorado River is the only major stream in the U.S. whose water supply is fully utilized. This distinction has brought the Colorado more than its share of controversy, within states, between states and between nations. The Colorado River compact, whose purpose was to equitably apportion the waters between the upper and lower basins and to provide protection for the upper basin through water reservation, was ratified by all states except Arizona, in 1923. Arizona finally ratified it in 1944. The history of controversies and negotiation concerning the compact are outlined through the supreme court decision on march 9, 1964, which entitled California to 4.4 maf, Nevada to 0.3 maf and Arizona to 2.8 maf, of the first 7.5 maf available in the lower Colorado. Unfortunately, the court did not attempt to establish priorities in the event of shortage. The problem is complicated by an international treaty of 1944, guaranteeing Mexico 1.5 maf annually, except in years of unusual circumstances. Because Senator Connally of Texas was then chairman of the senate foreign relations committee and because the treaty allocated twice as much Colorado River water to Mexico as it was then using, it was argued that this treaty represented a tradeoff to Mexico, giving it less water from the Rio Grande in exchange for more water from the overburdened Colorado. Problems of inter-basin water transfer studies, uniform Colorado basin water quality standards and central Arizona project planning are discussed.