Vulnerabilities, impacts, adaptation and mitigation
Research theme leaders: J. Ramirez, N. Grigg, and S. Denning
Student programs in this theme area will equip scientists to anticipate the impacts of climate change on water and economic systems and to provide policy and management advice about response and mitigation strategies. For example, climate change in the Colorado River Basin could diminish critical water supply for a large fraction of the US population.
Water management systems are designed for mean climatic conditions and a certain range of variability; however, vulnerabilities are found at climatic extremes (e.g., floods and droughts). Three categories of vulnerabilities can be identified: 1) meteorological and climatological vulnerabilities; 2) hydrologic system and design vulnerabilities; and 3) geographical and societal vulnerabilities. In the context of water resource systems, meteorological vulnerabilities are associated with the magnitude, frequency and timing of storms and with the magnitude, spatial extent, frequency and duration of droughts. Hydrologic system and design vulnerabilities are associated with the physical design, operating rules, and institutional settings. Societal and geographical vulnerabilities are associated with relative levels of demand with respect to supply, water quality, agricultural needs, hydroelectricity, and protection of fragile ecosystems from rapidly changing socio-economic environments.
Later, we explain use of the Cache La Poudre River as a venue to study drought effects on water supply, fisheries, wildlife, ecological integrity, and recreation. This river is a primary source of drinking water and irrigation water and is used widely for recreation. Also, it is amenable to study due to its extensive hydrologic, geomorphic, and ecological data. Other examples of western water problems with similar issues include the Platte River system, the Colorado River endangered species, and the California Bay-Delta water issues. In each of these, there is a convergence of hydrologic and ecological issues with economic and political pressures of scarce water supply, drought, and pressure to use the water resources to meet conflicting demands in the regions.
The overarching objective of this research theme will be a hydrologically and ecologically focused vulnerability analysis. While climate variability and change will affect ecosystems and water quality, human actions to mitigate their consequences are expected to be the primary driver influencing system response. Given the importance of uncertainty and variability in future climate variability and land-use change, a major emphasis will be in designing hydrologic and water resources modeling to allow propagation of these uncertainties through to ecologic modeling and decision making.
Vulnerabilities are found at the extremes of climate. Most natural and human systems are well adapted to or designed for mean climatic conditions and a certain range of variability. With regard to water resources, climate extremes typically are thought of in terms of their manifestations as floods and droughts. An essential task of evaluating regional hydrologic vulnerabilities to floods and droughts is the quantification of the potential changes in the frequency, magnitude and duration of these extreme events as a result of climate variability and change. Of particular importance to this task is the fact, demonstrated by Katz and Brown (1992), that change in the frequency of extreme events is most dependent on the variability rather than the mean of climate parameters.
Hydrologic extreme events span the range of temporal scales, from flash floods to decadal droughts. Consequently, a correspondingly wide range of atmospheric time scales must be modeled if changes in hydrologic extremes are to be captured. Both synoptic weather events and inter-annual variability of climate must be modeled. Previous studies of the ability of GCMs to represent daily to inter-annual variability of precipitation and temperature suggest that they do a mixed job at best (Mearns et al 1990, Rind et al 1989). However, indications are that improvements in the simulation of variability can be achieved with improved representations of atmosphere-ocean and atmosphere-land surface coupling. In particular, the onset, persistence and magnitude of simulated drought are highly sensitive to the representation of ground hydrology (Rind et al 1990, Oglesby 1991).
To fully explore the implications of climate variability to regional hydrologic vulnerability, one must examine how the remaining uncertainty propagates through hydrology to uncertainties in indices of vulnerability of human and natural systems. One such index would be the likelihood of failure of a water resource system, which is an issue of increasing concern for water supply utilities.
Vulnerability of a system is a function of the system’s resilience and robustness with respect to the inherent variability of the main design variables. Thus, in order to address vulnerability issues, it is not sufficient to quantify the potential effects on the mean values of hydrological, ecological, and meteorological variables of interest, but most important, it is necessary to quantify the changes in the inherent variability of those variables. It is not just the changes in the mean that are important but also the changes in the variance. Robustness refers to the relative insensitivity of the system to errors in the estimates of design variables, and is always associated with a given probability level. A system is said to be robust at probability level p if, with probability p, the optimal design, based on erroneous estimates of the design variables, is identical to the optimal design based on the true design variables. Resilience is the ability of a given system to operate under a range of conditions (variability) such that the present value of the cost of failure is low, and expectedly lower than the cost of preventing the failure by modifying the original design.
For any hydrologic, ecologic, or societal system, one can determine a well-defined region, Sus(t), in an n-dimensional space of climatic, hydrologic, ecosystem and economic variables within which the given system is sustainable. At the same time, under the current conditions, one can define a feasible region, Feas(t), in the same n-dimensional space that is feasible under the current conditions. For example, the set of climate variables that is feasible under present conditions. An index of this system’s current vulnerability, V(t), can be defined as the probability that climate will, in any year under the current climate and associated pattern of variability, bring the set of variables defining our n-dimensional space outside of the region of sustainability.
In the context of impacts on hydrological quantities (e.g., water availability) predicted changes in their mean and variance are but imperfect estimates of their true mean and variance under which the given systems will operate in the future. Thus, a major component of vulnerability analysis is the determination of the uncertainty associated with given predictions of changes and associated potential impacts.
As mentioned before, categories of vulnerabilities of water resource systems can be identified as:
Taking these into account, measures or indices of vulnerability can be defined that are functions of:
Our perceptions of droughts and the tools available to predict their severity and reliability are rapidly evolving. A growing body of evidence from tree ring studies in the Colorado River and other Western U.S. river basins suggests that much more serious droughts than any found in the modern records occurred during earlier centuries (e.g., Young 1995). Similarly, models accounting for the effects of non-stationarity and persistence on drought risk estimation provide improved estimates of return period and failure risk (Douglas et al. 2002, Chen and Rao 2002). As new data and models become available, strategies for managing and mitigating drought impacts are simultaneously evolving from a reactive, crisis management approach to more proactive risk management approaches. At the same time, an emphasis on drought as a “socio-economic” phenomenon underscores a number of important concerns such as (a) changing social environments because of urbanization, sprawl, increasing densities or changing economic activities that contribute to increasing vulnerability to drought of larger segments of population; (b) increasingly complex responses to drought as more interdependent systems are affected and the calls for more integrated, long-range planning are becoming more vocal; and (c) responses to drought which also require broader mobilization of institutions and people in order to accommodate adaptive policies for resource scarcities, climatic vagaries, and the uncertainty of future environments.
We suggest that there is now an unprecedented opportunity to integrate detailed drought scenarios developed through advanced hydrologic and ecological modeling with risk-based decision tools to explore coupling among key stakeholder groups and aquatic systems during extended ‘dry spells.’ We propose to assess responses to scenario-based modeling of environmental consequences associated with water allocation choices in decision-makers and non-technical stakeholders in the South Platte River Basin with a focus on the Cache La Poudre River watershed. The Cache La Poudre is a regulated river system with an array of competing demands from agricultural uses, a rapidly growing urban population, a large number of diverse recreational users, and environmental organizations concerned with alterations to the natural flow regime (sensu Poff et al. 1997). The Cache La Poudre originates in largely pristine alpine headwaters and experiences numerous diversions as it traverses National Forest, rangelands, broad glacial valleys, canyons, and ultimately the eastern plains. In many ways the Cache La Poudre is a microcosm that typifies the complex constraints and vulnerabilities facing scores of river systems in the western US. The Cache La Poudre watershed is an ideal context for the proposed research given that it is: (1) a primary source of drinking water for the City of Fort Collins and Greeley (and proposed transbasin diversion to Denver area) and irrigation water for the eastern plains of north central Colorado, (2) home to commercial recreational companies with whom we are collaborating and widely valued for its fishery and diverse recreational opportunities, (3) characterized in an existing water allocation decision support system, and (4) a system where the PIs have compiled extensive base of hydrologic, climatic, geomorphic, and ecological data.
The conceptual approach entails generating a variety of drought descriptors and a spectrum of realistic drought scenarios with linked outcomes, and exploring how key sectors respond to different types of information, the responses of other sectors (agricultural, urban, environment, recreational industry), and ecological consequences. Key goals of this research are to: (1) use the best-available forecasting tools to simulate drought impacts and consequences including environmental, ecological, social, and economic aspects, and (2) explore the socio-political, economic, and technological interactions involved in risk management tools that place greater emphasis on anticipatory and participatory drought preparedness, planning, and mitigation. The research will focus on analysis and mitigation of drought effects on the quantity and quality of water with implications for drinking water supply, fisheries, wildlife, ecological integrity, recreation, and tourism industries in the Cache La Poudre River watershed. We will also examine how stakeholder perceptions of nature as resilient, random, ephemeral, or constant (Holling 1995) affect coping mechanisms and responses to the various drought-outcome scenarios. For example, some stakeholders recognize that ecological processes in rivers are controlled by flow variability and low flows are an inherent part of the pattern of variability. While extreme conditions may cause high mortality rates among plant and animal species, such periods are nevertheless recognized as one of the components controlling the long-term functioning of river systems. Other sectors value constancy (e.g. consistently large populations of legal-sized fish) which can result in ‘anti-drought’ conditions: the augmentation of flows in regulated rivers at times when the rivers would naturally experience low or no flow (McMahon and Finlayson 2003). Ultimately we intend to identify opportunities for and mechanisms leading to agricultural-urban-recreational-environmental collaboration, appropriate institutional mobilization, responding to socio-economic challenges, restoring nature flow regime variability, and working towards an integrated framework of drought planning and management.
Drought scenarios will be linked to specific economic and ecological outcomes that are contingent on the spatial and temporal allocation decisions of individual and multiple sectors. Mock drought scenarios will facilitate stakeholder envisioning of likely impacts on agricultural production, municipal water supply, the recreational industry (whitewater boating, fishing, tourism), instream flows, and ecological processes resulting from sector decisions.
We will use different types of drought characterization information, and the assistance of local collaborating agencies to identify the response to drought in the Cache La Poudre watershed for each sector. This analysis will identify decisions, concerns, preferred information type(s), and causal linkages controlling sector response for each drought scenario. We will then identify relationships between and among each sector, observe how stakeholders make choices, and ask why they made them. This approach will identify cause-effect relationships among sectors and reveal the sensitivity, vulnerability, and potential dominance of disparate sectors in each drought scenario. Furthermore, we will identify which ecological outcomes most influence decisions of the various sectors and how stakeholders’ views of nature and their understanding of drought as a natural part of system variability affect responses to these outcomes.
We will examine how adaptive responses cluster and translate to other sectors and elucidate the complex set of coping mechanisms that exists within and among sectors. Identification of response spectra and causal linkages will lead to an assessment of adaptive potential in the watershed system. Feedback from this process will be used to develop innovative and generalized tools for improved characterization, interpretation, and mitigation of potential drought impacts. These tools will include development of an “impact matrix” approach that is akin to a payoff matrix from financial risk (Hoag et al. 2002).
The primary mission of I-WATER is to prepare Ph.D. students to work in an interdisciplinary team-based activity. Our research themes involve interacting teams of hydrologists, meteorologists, ecologists, and management experts. I-WATER features problem-focused research to bridge basic and applied science by combining fundamental research on scientific problems with application of scientific knowledge to actual resource issues.
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