Research Projects Major Increases in Storm Frequency and Intensity
A study by researchers from the National Center for Atmospheric Research, published in the journal Nature Climate Change on December 5, shows more frequent intense rainfall events occurring across North America by 2100 if greenhouse gas emissions are not curbed. They project as much as a five-fold increase in storms producing potentially up to 70 percent more precipitation per storm in some places. Even here in the Southwest, where drier conditions are expected because of rising temperatures, an increase in the frequency and intensity of storms is foreseen.
The maps below display the simulated increases in the number of extreme storms by 2100 as compared to the control period, 2001-2013. During December, January, and February (a), the frequency of extremes increased substantially across Canada and the Western US. During June, July and August (b), extremes are shown to intensify in parts of the US Southwest and Mexico, as well as the Gulf Coast and Canadian Northeast.
The Nature Climate Change article, “The future intensification of hourly precipitation extremes,” can be found at http:// www.nature.com/nclimate/journal/vaop/ncurrent/full/ nclimate3168.html.
Experimental Release from Lake Powell Creates 5-day Flood
The Bureau of Reclamation conducted a high flow experiment (HFE) in partnership with National Park Service, U.S. Fish and Wild Service, and the U.S. Geological Survey with the goal of mobilizing and re-distributing sediments in the Colorado River through the Grand Canyon. This is the fourth HFE carried out since 2011. These controlled flood experiments are designed to benefit the Colorado River ecosystem, rebuilding sandbars that support habitat for wildlife and beaches used for recreational purposes. For the experiment to start, optimal sediment load at the Glen Canyon Dam must be reached, which occurs when a Colorado tributary, the Paria River, discharges large amounts of sediment. The HFE in 2016 started on November 7th, when operators opened the bypass tubes at Glen Canyon Dam and began releasing water. The HFE continued with four consecutive days of releases at maximum capacity (36,000 cfs) and ended at 3:00 am on November 12. These experiments do not affect the total annual amount of water delivered from Glen Canyon Dam to Lake Mead. Water releases after the experiment are adjusted in order to compensate the high volume of water released during HFE.
EPA’s CCL4 Released
The Contaminant Candidate List (CCL) is a list of contaminants that are currently not regulated, but there is evidence that they occur in water supply sources and they are suspected of having an adverse effect on human health. The Safe Drinking Water Act requires the Environmental Protection Agency (EPA) to release an updated CCL every five years. To date EPA has published four CCLs since 1998. On November 17, 2016, EPA released the Final CCL 4, which includes 97 chemical or chemical groups and 12 microbial pathogens. Most of the chemicals included in the CCL 4 come from industry and agriculture, as well as cleaning products and pharmaceuticals. After releasing this list, EPA must determine within five years whether or not to regulate at least five of the listed contaminants. To that end, the EPA will collect additional information and conduct research on specific contaminants that present the greatest public health concern. The CCL 4 can be found at https://www.epa.gov/ccl/contaminant-candidate-list-4-ccl-4-0.
New GWAC Committee Looks at Potable Reuse
The Governor’s Water Augmentation Council (GWAC) has formed a reclaimed water committee to help in the process currently underway to revise the water reuse rules. At its October 28 meeting, the GWAC formed a reclaimed water committee that will examine options for statewide standards. John Kmiec, Utilities Director for Marana Water, will chair the committee. Human consumption of reclaimed water is prohibited by rule in Arizona. Part of the new committee’s purpose is consideration of amending state rules to allow for potable re-use. According to Chuck Graf of the Arizona Department of Environmental Quality, Arizona water-treatment facilities produce some of the best-quality reclaimed water in the country, using highly refined and multi-level processes. Regulating potable reuse rather than prohibiting it will receive an added level of scrutiny through the newly formed committee.
Santa Cruz River Could Flow Again
While Tucson is preparing the public for eventual potable reuse of water from the regional wastewater treatment plants, they are making other plans for use of the water. The hope to see the Santa Cruz River flow again after more than 60 years could become a reality. Tucson Water announced the “Agua Dulce” plan (Spanish for sweet water) that would restore the flow in the Santa Cruz River through downtown Tucson using treated wastewater. Existing reclaimed water infrastructure would be used to transport the treated effluent into the Santa Cruz River. Tucson expects to accrue multiple benefits from the plan, which calls for the construction of a river channel feature through the Rio Nuevo development area. Such a project could bring tourism and economic development to the Tucson area by elevating the natural and historical importance of the Santa Cruz in Southern Arizona. In addition, the City would accrue credits from recharge of treated wastewater through the river bed. The City Council can formally consider the proposal once it has gained the support of neighborhood and business leaders, as well as Pima County.
EPA Study Estimates Value of Stormwater Recharge
Green infrastructure (GI) and low-impact development (LID) for urban areas generate multiple benefits including groundwater recharge. The US Environmental Protection Agency (EPA) commissioned a study to estimate the recharge benefits of implementing these practices across the United States for the 20-year period 2021 through 2040. Using a simplified methodology for estimating recharge volume and observed prices of water, the study produced groundwater recharge volume and value estimates for scenarios in which these practices are implemented where stormwater retention is not currently required. The stormwater retention practices were assumed to reduce runoff volumes to pre-development levels, the goal of GI and LID. Because broad assumptions and simplified methods were used, the results reflect the potential range of value for groundwater recharge. Estimates of cumulative volumes of recharge ranged from 6.8 million to 10.8 million acre-feet and cumulative, present monetary values ranged from $0.2 to $4.5 billion.
Although groundwater recharge is just one benefit among many, the study did not directly address the full range of potential benefits of these stormwater retention practices, and in fact covers only a subset of the recharge benefits. An appendix qualitatively discusses the total economic value of groundwater recharge, including potential direct and indirect benefits. The study can be accessed at https://www.epa.gov/green-infrastructure/estimating-monetized-benefits-groundwater-recharge-stormwater-retention.