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Better Safe than sorry

Better Safe than sorry

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    San Francisco's sewer system master plan is being designed to protect the city's sewer system against the rising tides of the next 30 years. One short-term option is to retrofit outfalls with duckbill valves that protect against backflow. Photo: Tideflex Technologies

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    Carollo Engineers examined local surface water supplies, irrigation demands, and sea-level rise as part of Santa Barbara, Calif.'s water supply planning study. The study looked at precipitation trends to determine whether to modify surface water supply management to accommodate increased variability brought by climate change. At this time, Santa Barbara will continue current operations management while tracking precipitation patterns for future planning. Photo: City of Santa Barbara, Calif.

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    San Francisco flooding on the riseThis chart maps historical monthly mean higher high water (MHHW) levels relative to the San Francisco city datum and estimated 2001 Intergovernmental Panel on Climate Change (IPCC) projections of future high tides. Long before the projections of even higher tides exceed the weir levels, flooding will occur. For a larger version of this graph, visit the “article links” page under “resources” at www.pwmag.com. Source: Carollo Engineers

Web Extra

For information on climate change and what can be done to prepare for it, visit the “article links” page under “resources” at www.pwmag.com.

Not everybody is sold on the concept of global warming and climate change. Yet scientific evidence is mounting. Carbon dioxide levels in the atmosphere are at their highest in 800,000 years, and the average global surface air temperature has risen at a rate of 0.23°F each decade over the last 50 years. By 2100, it is anticipated to be between 3° to 7° F warmer, according to projections by the United Nations-endorsed Intergovernmental Panel on Climate Change (IPCC).

Future climate change could overwhelm current U.S. water, stormwater, and wastewater infrastructure, due to such factors as more frequent and intense storm events, rising mountainous snowlines, earlier spring runoff from snowmelt, increased melting of land ice (specifically in Greenland and Antarctica), and thermal expansion of the marine mixed layer in oceans.

Given the long lead times required to plan for and build water infrastructure, it is critical that water utilities include climate-change mitigation and adaptation strategies into their planning scenarios now.

MITIGATION: PREVENTION THROUGH EMISSIONS REDUCTION

The IPCC publishes assessment reports that help evaluate potential impacts on climate change. These reports consider various scenarios as a basis for estimating the rate of change in atmospheric concentrations of greenhouse gases (GHGs). Some show that by reducing GHG emissions, we can slow or prevent future climate change.

A mitigative planning strategy incorporates GHG reduction measures to prevent future climate change in long-term planning and designs for infrastructure and water management. Such strategies include, but are not limited to:

  • Increasing energy efficiency of facility pumps and treatment processes
  • Reducing truck transport of materials, e.g., chemicals and solids
  • Implementing renewable energy use (onsite production or purchasing).

While GHG legislation has been developing abroad over the last couple of decades, California adopted the United States' first GHG regulation in September 2006. The state's Global Warming Solutions Act regulates GHG emissions from both public and private agencies to reach 1990 levels by 2020 and 80% below 1990 levels by 2050 (see January 2009 issue, “Emission remission,” page 37).

The regulation, however, does not mandate publicly owned water and wastewater treatment works unless they (1) generate more than 1 MW of power and emit more than 2,500 metric tons of carbon dioxide equivalent (CO2e) emissions or (2) have stationary combustion sources that emit more than 25,000 metric tons of CO2e combined.

The U.S. EPA is following this lead and in March 2009 proposed a mandatory GHG reporting rule using the same emission threshold for stationary combustion sources. Approximately 13,000 entities nationwide would be affected by this rule, comprising 85% to 90% of annual GHG emissions.

It is likely that, in the near future, wastewater treatment plants will be mandated to report and reduce emissions.

ADAPTATION: PLANNING FOR CLIMATE CHANGE

In some regions, adaptation may be more urgent than mitigation. Adaptation includes incorporating current and predicted regional and local climate change impacts into planning for water systems. Some climate changes have already happened:

Annual precipitation. A recent study led by the Climate Research Division of Environment Canada looked at two data sets of global rainfall from 1925 through 1999, which showed increased average annual precipitation in temperate regions of the U.S. Northern Hemisphere. Since about 1970 through 2000, the average tended to remain above the 20th-century mean and about 5% more than the previous 70 years. In the Western mountains, approximately 74% of weather stations showed an increase in annual precipitation falling as rain rather than snow from 1949 through 2004.

Projected changes in total annual precipitation have varied widely across models and emissions scenarios. Therefore, long-term planning should be based on current precipitation trends analyzed on a monthly basis. Monthly trending is important for evaluating water supply in terms of precipitation falling as rain versus snow, as well as observing the timing of precipitation events throughout the year.