Two Faces of Uncertainty: Climate Science and Water Utility Planning Methods

Abstract

Water utilities are increasingly incorporating climate change in their planning activities. A water manager embarking on such a study is often confronted with a large range of climate model projections and the need to incorporate this new source of uncertain information into existing management and operations models. This article discusses these two faces of uncertainty and argues that an increased awareness of both the sources of this uncertainty in climate science and the means to plan for it can help utilities meet this challenge. More specifically, this article investigates the prospects for climate science to provide useful projections, discusses the strategies and challenges faced in translating those projections into effects on water utilities, and presents several decision-support planning methods that are being used or considered for use in several water utilities in the United States. Traditional water utility planning methods are based on an assumption of stationarity—that future hydrology will not significantly deviate from past hydrology. The current scientific understanding of climate change fundamentally challenges this stationarity assumption (Milly et al. 2008). In recognition of the limitations of stationarity, many water utilities are broadening their understanding of climate change and investigating decision-support planning methods to cope with conditions of pervasive climatic uncertainty. Uncertainty in projections of climate change can act as a barrier to the effective use of climate change information. Projections of future climate rely heavily on climate models (also known as general circulation models, or GCMs). On local and regional scales, and for variables such as precipitation and streamflow, the uncertainty in model projections is even greater than for global averages (Hawkins and Sutton 2011), and models may not even agree on the direction of change. Under such conditions, water management and planning must incorporate the new uncertainty of changing climatic conditions, a task for which traditional planning methods are poorly suited. Awater utility’s ability to effectively use this new uncertain scientific information may require adjustments to their management and planning processes, or even the adoption of new approaches. In an important sense, the water resources management community has taken a leadership role in understanding and incorporating climate change into their management, operations, and planning. Much of this effort has occurred at a utility scale, i.e., individual utilities working internally or with an academic and/or consultant partner to investigate the significance of climate change for the resources they manage [East Bay Municipal Utility District (EBMUD) 2009; New York City Department of Environmental Protection (NYCDEP) 2008; Palmer 2007; Palmer and Hahn 2002]. Water resources trade organizations such as the Water Research Foundation (WaterRF), the WateReuse Foundation, and the Water Environment Research Foundation have funded a number of studies investigating the effects of climate change on their member utilities (Miller and Yates 2006; Stratus Consulting and MWH Global 2009; WRF 2010). More recently, some of the largest metropolitan water agencies in the United States formed the Water Utility Climate Alliance (WUCA) to pursue their common objective of understanding and incorporating climate change information into their management, operations, and planning. Water utilities routinely examine the vulnerability of their systems to uncertain factors such as massive supply disruptions, infrastructure failure, potential regulatory requirements, technological changes, and even terrorist attacks. Although climate change may be thought of as simply one more uncertain variable that must be taken into account in water resources management, successfully incorporating this new uncertain information has not proven to be easy, in part because of the assumption of stationary hydrology in existing planning methods. In this article we explore the state of knowledge and practice in several large water utilities in the United States by synthesizing, updating, and greatly condensing the information that the authors developed for four recent studies by the WUCA and the U.S. Environmental Protection Agency (EPA). The first WUCA white paper (Barsugli et al. 2009) focuses on the state of climate modeling, on understanding water utility informational needs and desires, and on assessing which investments in climate science or modeling may yield usability improvements from the perspective of water utilities. The second WUCA white paper (Means et al. 2010) describes five decision-support planning methods that consider multiple future conditions and outcomes to incorporate greater uncertainties into the water planning process.