Developing Tailored Climate Change Information for Strategic Water Supply Planning at a North Carolina Utility

The impacts of climate change on water resources are frequently measured by driving hydrologic models with projections from general circulation models (GCM). Often, though, water resource managers do not find this approach useful because of uncertainty associated with model projections, or a lack of specificity or fit with relevant concerns. Thus, new approaches have emerged, centering on an analysis of a system's or decision's vulnerability to future changes in climate, and identifying actions that work well over a wide range of futures. Also referred to as ‘bottom-up' or ‘vulnerability-based' assessments, these are generally expected to have enhanced relevance to decision making by requiring engagement with decision makers and being inherently context-specific - two of the few key factors recognized as important in providing effective climate-related decision support (National Research Council, 2009). While such approaches are being increasingly applied, there has been limited focus on documenting specifically how the information production process was informed by the decision making context (Dilling et al., 2015) and the extent to which the resulting information is ultimately incorporated into decision making.

Researchers at Carolinas Integrated Sciences and Assessments (CISA) are working with representatives from a public water utility in North Carolina and their engineering consulting firm to assess the implications of climate change on the long-term dependability of their raw water supply. The utility periodically updates their strategic plan to ensure that they meet projected future demands. Much of the analysis for planning is done by using a yield metric based on the historical records of flows into the reservoirs and the resulting availability of water during the single most extreme drought event. For future long-term updates, the resource managers would also like to consider changes in climate in addition to customer demands. Hence, the goal of this assessment is to produce climate change information that fits within the existing, traditional planning context of the utility.

Based on preliminary communication with utility personnel, we closely follow a bottom-up approach known as ‘Decision Scaling' (Brown et al., 2011) which emphasizes a systematic evaluation of the water system's vulnerability, in terms of decision-relevant metrics, to changes in climate prior to utilizing GCM-based projections. Another key aspect of the assessment is the use of thresholds critical for decision-making to identify the extent of changes in climate required for alternative actions, and, to summarize the spread of potential changes under climate change projections in the form of relative likelihoods of threshold exceedance.

After a brief introduction to the Decision Scaling approach, our presentation will focus on those aspects of the utility's planning context that informed some of the analytical choices in this study, such as, the general bottom-up framework, time-horizons, the scale and type of planning-relevant metrics of system performance, and the level of complexity chosen for modeling their response to climate changes. We will also discuss the suitability of the yield metric (currently used in planning) for a climate change assessment. Lastly, we will show preliminary findings about relative likelihood of critical changes in water supply's dependability under climate change.

References: Brown, C., Werick, W., Leger, W., & Fay, D. (2011). A Decision‐Analytic approach to managing climate risks: Application to the upper great Lakes. JAWRA Journal of the American Water Resources Association, 47(3), 524-534

Dilling, L., Lackstrom, K., Haywood, B., Dow, K., Lemos, M. C., Berggren, J., & Kalafatis, S. (2015). What Stakeholder Needs Tell Us about Enabling Adaptive Capacity: The Intersection of Context and Information Provision across Regions in the United States. Weather, Climate, and Society, 7(1), 5-17.

National Research Council (2009). Informing Decisions in a Changing Climate. Panel on strategies and methods for climate-related decision support, Committee on the Human Dimensions of Global Climate Change, Division of Behavioral and Social Sciences on Education, National Research Council. National Academies Press, Washington, DC, p188