Back to the Future: Innovative Tree Ring Analysis to Reconstruct Paleoclimate and Streamflows for Improved Urban Water Planning Under Climate Change
Project ID: 7855
Principal Investigator: Fred Liljegren
Research Topic: Water Operation Models and Decision Support Systems
Priority Area Assignments: 2011 (Climate Change and Variability Research), 2012 (Climate Change and Variability Research)
Funded Fiscal Years: 2011 and 2012
How can Bureau of Reclamation guided research studies help maintain water supplies for the future existence of the Wasatch Front metropolitan region through planning efforts that are complicated by climate change, increasing temperatures, greater evaporative demand, possible earlier snowmelt and late season shortages, and emergence of cyclic drought?
Can planning for future water supply and demand in a changing climate fraught with the uncertainty of high impacts from droughts be aided by past precipitation and streamflow data re-created from a suite of tree ring chronologies?
Need and Benefit
Maintaining water supplies for the future existence of the Wasatch Front metropolitan region is uncertain. Meeting needs of an increasing population will require balancing reduction in need per capita use demand through conservation with politically adroit increase in supplies. Planning for this balance is complicated by climate change, increasing temperatures that will increase evaporative demand of urban plant water use, while creating earlier snowmelt and late season shortages. Planning for future water supply and demand in a changing climate is fraught with the uncertainty of unforeseen, high impact (but predictable in hindsight) droughts.
The Wasatch Front metropolitan region, from Logan through Ogden, Salt Lake City, and past Provo, Utah, depends on regular input of mountain snow to exist. Approximately 2 million people consume treated, potable water impounded from snow runoff or pumped from percolated ground water for indoor personal use and outdoor irrigation of largely turfgrass landscapes.
Long-term water supplies for the Wasatch Front metro region's future are strained and threatened. Utah has one of the highest population growth rates in the country, nearly 30 percent from 1990-2000, and a similar trajectory since then. High population growth and very high per-capita water use rates will create future demand that is projected to exceed limited existing supplies. Water wholesalers and the Utah State Division of Water Resources are focused on bringing future water demand and supply into balance - water conservation, particularly in irrigated urban landscapes, to reduce demand and limited expansion of water impoundment structures to increase supply.
Balancing future urban water supply and demand is threatened by climate uncertainty. Year-to-year climate variability characterizes northern Utah, including years of below normal snowfall that causes socioeconomic drought, and hotter years that increase evapo-transpiration and, hence, urban water demand.
However, future climate change projections suggest increased demand and reduced supply. Climate models suggest that spring precipitation will increase at mid to higher elevations but decrease at lower elevations (Wang et al. 2010), suggesting drier early growing seasons and increased water demand for irrigated landscapes in the lower elevation urban areas. Increased high elevation precipitation is unlikely to help water supplies because it is predicted to come as rain, rather than snow, due to increased temperatures (Wang et al. 2009). Increased rain will melt the snowpack sooner, reducing late-season urban water supplies for urban areas dependent on historically slow snowmelt that keeps reservoirs full well into the summer. Less late season water stored in reservoirs means less water for urban irrigation and a greater chance of late season water shortages.
Historical climate variability indicating extreme drought also is a significant threat to urban water supplies and may interact with projected climate in unforeseen and potentially worrisome ways. Utah's water wholesalers' drought contingency plans to reduce water demand are based on short-duration dry periods as observed in the recent historical record. However, drought over the past 50 years in northern Utah has been very mild compared to the historical record (Gray et al. 2004). Peering further back in time through dendrochronology shows the potential for severe drought far surpassing that observed in the historical record and shows the potential for "Black Swan Theory" droughts - unforeseen, high impact, but predictable in retrospect. In particular, data suggest droughts appear cyclically, about every 12, 50, and 150 years, that can align harmonically in a megadrought. Future harmonic interaction of drought cycles could interact with projected climate changes to have a particularly negative impact on water supplies and Utah's water wholesalers at several levels.
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