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Government, North America, United States, Water
Climate Change and Water Supply
Preparing for the Future
Melting glaciers, extreme snow storms, flash floods and hot summers—people are constantly looking to climate change to explain abnormal weather and environmental trends. Water supply planners are also considering the effects of climate change as they prepare to meet demands. Traditionally, planners have estimated available water supplies and projected future demands. Today, they are also analyzing how changing climate variables—such as precipitation, temperature and evaporation could influence the ability to meet those water demands.
With precipitation and temperature predictions from global circulation models (GCMs)—mathematical models used to forecast the weather, understand climate and predict climate change on a global scale for the next 100 years—planners and decision makers are able to assess the long-term impacts of climate change on water supplies and future reliability.
Choosing a Model
In the state of Texas, USA, population growth is rapid and water supply is declining. CDM Smith is working with the Texas Water Development Board to select a GCM that is best suited to the region and can be used in the state’s conservation and water management strategy. Multiple GCMs exist with varying output, so selecting the right one is instrumental. Spandana Tummuri, CDM Smith water resources engineer, developed comparison methodology that will ensure that the most appropriate selection is made.
“Factors that change the climate—or climate forcings—are represented in GCMs by a suite of greenhouse gas emission scenarios that are determined by social, economic, demographic and ecological practices. The first step in our process is to choose one or more GCMs from a total of 23 that best represent the global-scale climate of Texas,” explains Tummuri.
Incorporating climate change into the decision-making process is essential ... this information will assist policymakers in prioritizing adaptation techniques to manage water supplies in a time of uncertainty.
Downscaling Data
After selecting the best GCM(s) for Texas, the state may downscale the model’s data. Once the data is downscaled, predictions of sea level rise, humidity, precipitation and temperature may be run through hydrologic models to help predict naturalized stream flows, groundwater availability and, ultimately, future water supplies.
“Incorporating climate change into the decision-making process is essential. As Texas develops a 5-year water supply plan, this information will assist policymakers in prioritizing adaptation techniques to manage water supplies in a time of uncertainty,” says Tummuri.
Relying on Reservoirs
In Santa Fe, New Mexico, USA, a different method to assess climate change impacts was applied to understand the future of the area’s water resources. Here, CDM Smith conducted a research study to assess how climate change could affect urban stream flows, as well as water supply. According to Enrique Lopez Calva, CDM Smith principal water resources engineer, “There have been a great number of studies related to climate change and water resources, but until now, very little quantitative research was available. As part of CDM Smith’s research and development program, we have standardized methodologies to probabilistically estimate climate change impacts on water resources.”
Natural urban streams provide important environmental, aesthetic and recreational benefits. The city of Santa Fe depends on reservoir water for summer river flows through the downtown area—an important feature to the community. Given that the city also relies on the McClure and Nichols reservoirs as water supply sources, understanding the effects of climate change has particular importance.
“We wanted to develop and apply a methodology for translating GCM output data into stream flows, particularly for areas where flows are driven by snow pack,” explains Lopez Calva. “If snowfall amounts decrease, or if temperatures increase, making the snow melt earlier, the amount of water flowing into the reservoirs will be less. We know that intuitively, but now we have quantified the impacts probabilistically, by applying our methodology.”
Comparing Results
The CDM Smith team used downscaled temperature and precipitation data from several GCMs specific to the Santa Fe region. This data was applied to two different hydrologic modeling tools to forecast water flowing into the city’s reservoirs, with a 2060 planning horizon. “Both approaches indicated an overall reduction in supply from the city’s local reservoirs and a clear shift in the seasonal pattern of stream flows, as snow starts to melt earlier each year,” notes Lopez Calva.
Having already developed a water supply planning model for Santa Fe, CDM Smith was able to compare the results of simulations that did not incorporate the impacts of climate change with those that did—highlighting the importance of how predicted climate variables can enhance planning studies.
Planning for the Future
According to Claudia Borchert, water resources coordinator for Santa Fe’s municipal water utility, “To plan for a reliable and sustainable water supply for our region, we need to understand how the predictions from GCMs are projected to affect the availability of our local water resources. The research that CDM Smith has conducted provides valuable information to assist us in planning for the future.”
