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Reclamation’s Modeling and Research in the Colorado Basin

The Bureau of Reclamation plays a critical role in managing the priceless water resources of the Colorado River. Even under ideal circumstances, this monumental task requires technical expertise, accurate information, and experience. This is even more true during a time of drought, like the one the basin has been experiencing since 2000. In this interview, Hydro Leader speaks to Carly Jerla, manager of the modeling and research group of Reclamation’s Lower Colorado Basin Region. Ms. Jerla is stationed at the University of Colorado’s Center for Advanced Decision Support for Water and Environmental Systems (CADSWES), where Reclamation staff play a critical role in the research and modeling work that the agency needs to manage the waters of the Colorado. 

Hydro Leader: Please tell us about your background and how you came to be in your current position. 

Carly Jerla: I am originally from Yellowstone National Park, since my father worked and still works for the National Park Service. I moved to Boulder, Colorado, to pursue graduate studies at the University of Colorado in 2002. I was hired as a research assistant at CADSWES, of which Reclamation was one of the original sponsors. At that time, I was not too familiar with Reclamation. What drew me to CADSWES was the strong linkage between river and reservoir systems modeling and policy development. 

A couple of years later, in 2005, Reclamation hired me through its student program and helped shape my master’s research. I was hired by Dr. Terry Fulp. At that time, things were starting to heat up regarding the development of what would be the 2007 Colorado River interim guidelines. The basin was 6 years into the current drought, and storage in Lakes Powell and Mead had declined from nearly 100 percent capacity at the start of the drought in 2000 to just over 50 percent. In April 2005, concerned with declining elevations in Lake Powell, the upper basin states requested that Secretary of the Interior Gale Norton consider reducing the release from Lake Powell scheduled for that year. This request ultimately kicked off the development of what became the 2007 interim guidelines. 

Dr. Fulp believed that to prepare for the process to develop such guidelines, we needed to start developing modeling tools that would allow for the rapid assessment and screening of different kinds of operational policies. That’s what I ended up focusing my master’s research on. It was exciting research that helped shape the interim guidelines. 

I continue to work for Reclamation and have been involved in many exciting initiatives, including the Colorado River Basin Study; the Tribal Water Study; the Drought Contingency Plans (DCPs); and, currently, the review of the 2007 interim guidelines. I’m still stationed at CADSWES and manage our region’s modeling and research group there. There are eight Reclamation engineers stationed at CADSWES, five from the Lower Colorado Basin Region and three from the Upper Colorado Basin Region. We all work together closely to develop and maintain the modeling tools that are used throughout the basin and to pursue research to support Reclamation’s decisionmaking and operations in the Colorado River basin. 

Hydro Leader: What is the role of modeling and research in the basin? 

Carly Jerla: Modeling and research are critical to managing the Colorado River system. The significance of the Colorado River basin in the West is well known. Modeling and projections of future reservoir conditions are critical for operating Reclamation’s major facilities in the basin. It contributes to our operations on a variety of time scales, including short-term (hourly and daily) scheduling; medium-term operations, which include monthly or yearly reservoir releases; and long-term planning, which involves projections into future years and decades. 

We use the modeling software RiverWare, which was developed and is maintained at CADSWES. For the short and medium terms, we use water supply forecasts provided by the National Oceanic and Atmospheric Administration’s Colorado River Basin River Forecast Center. Looking out further than the next 2–5 years, we collaborate with researchers and incorporate science in developing longer-term water supply projections. 

Because CADSWES is situated within the University of Colorado, we have the opportunity to learn about and work on a lot of exciting and important new research in the field. We also recruit young talent that comes through the university. I believe this was part of Dr. Fulp’s vision. I’m one of a dozen or so students who were hired at Reclamation through CADSWES. 

Hydro Leader: How would you characterize the condition of the Colorado River basin? Is it experiencing a prolonged drought, or is it going through aridification? 

Carly Jerla: There is no question that the drought we’re experiencing is significant. It is the lowest 20‑year period in our measured historical record, which dates back about 100 years. It’s even one of the most significant by paleo standards, although the paleo record does hold some megadroughts that were longer and more dire than the current drought. We know from scientific evidence that the current drought has been exacerbated by a shifting temperature trend. Multiple published research studies state that beginning in the late 1980s, an increased temperature affected runoff efficiency in the basin, resulting in lower average flows for the same amount of precipitation. 

We will need to address and plan for this situation the same way, whether it is labeled prolonged drought or aridification. We need to incorporate assumptions about greater hydrologic variability and the possibility of longer, direr droughts into our planning. We explored this in the Colorado River Basin Study. The DCPs were developed assuming a drier future, more similar to what we have experienced recently than to the norm of the earlier part of the 20th century. Going forward, we need to make sure we understand the wide range of variability that is possible in the basin and build robust policies that can stand up to that variability. 

A night view of Glen Canyon Dam on the Colorado River.

Hydro Leader: What is the current chance of a lower basin shortage? 

Carly Jerla: Lake Mead is currently at about 1,082 feet, which is about 39 percent capacity. It has been hovering in that range for the past 6 years. According to the 2007 interim guidelines, which provide the operational guidelines for Lakes Powell and Mead, a lower basin shortage would be declared if, in August, we project that the elevation of Lake Mead will be at or below 1,075 feet on January 1 of the following year. In August, we projected that the level of Lake Mead would not be below 1,075 feet on January 1, 2021, so there will not be a lower basin shortage in 2021. 

If the dry hydrology we’ve seen in the recent past continues, we see a 32 percent chance of shortage in 2022 and a 42 percent chance in 2025. We expect these percentages to change as we learn more about what type of year 2021 will be hydrologically. 

It is important to note that a large amount of conservation has been undertaken in the lower basin since the implementation of the 2007 interim guidelines. It has been an effective drought-response tool. Since 2007, over 3 million acre-feet of water has been saved in Lake Mead, which has boosted the lake’s elevation by almost 35 feet. If not for that conservation, it is highly likely that a lower basin shortage would have been determined. 

Hydro Leader: What is your message to Colorado River water users and customers? 

Carly Jerla: Colorado River water users know the importance of the Colorado River. It supplies water to over 40 million people; irrigates nearly 5½ million acres of farmland; and supports a wide array of resources, including environmental, recreational, and hydropower uses. It really is the lifeblood of the West. In operating the system reservoirs, Reclamation knows that it is imperative to use the best information available for its short-to long-term operational decisions. In making those decisions, there are two threads: first, the importance of transparency, inclusivity, and collaboration with our partners and stakeholders on those decisions and operations; and second, making use of the best information available. Reclamation’s partnership with CADSWES and its use of the tools developed by CADSWES are instrumental in these areas. 

We’re committed to ensuring that those decisions are made using the best information available in an unbiased, transparent, and inclusive manner. We believe it is important to educate our partners, stakeholders, and the public about the types of information that we can provide. We’re always willing to sit down with people to answer questions and show them the types of information that we have available. 

Carly Jerla leads Reclamation’s Lower Colorado Basin Region modeling and research group. She can be contacted at cjerla@usbr.gov.