Reservoirs across the country are dealing with some of the same problems those in the west have been facing. According to a new study, there are longer periods of unusually low storage in many of the nation’s reservoirs, and that storage has become less reliable.
With me to explain what’s happening is Caelan Simeone, a hydrologist with the U.S. Geological Survey, worked on the study and joined The Show to explain what is happening.
Full conversation
MARK BRODIE: What to you are the key takeaways from this research?
CAELAN SIMEONE: Yes, absolutely. The key takeaways that we have are that this study highlights the changes that are occurring in reservoirs across the U.S. and the value of continued investigation both at national scales like this study and at local and regional scales on helping to improve and understand reservoir dynamics under changing conditions, especially hydro chromatic extremes.
In this paper, we see longer periods of low storage in recent years in some regions, which suggests decreased reservoir reliability or at least the possibility for that in a changing hydro climate. And we also see maximum annual storage declining in many reservoirs across the country, suggesting that there are some changes that are impacting a wide number of reservoirs across the U.S.
BRODIE: Is there one reason why you're seeing lower storage in reservoirs across the country or is it more regional or even local than that?
SIMEONE: We think that there are likely a number of different causes. And again, we didn't investigate every possible cause, but we think that likely the two leading contributors to these changes are climate change and sedimentation. But other factors such as changing reservoir management could be at play as well.
And for climate change, for example, bringing warm temperatures and changing precipitation regimes can impact reservoirs in a number of ways, including making things like snowpack less reliable or changing the timing of stream flow or snow melt.
BRODIE: When you talk about sedimentation, what do you mean there?
SIMEONE: Yeah. So sedimentation is the process where reservoirs accumulate incoming sediment from rivers and this causes storage losses as that segment builds up behind a reservoir, replacing water that you or replacing space that used to be used by water. And so this process is called sedimentation. And it's something that most reservoirs plan for over their lifespan, but is something that sort of changes the usable water storage throughout the lifetime of a reservoir.
BRODIE: OK. So in reading through some of the data, like it doesn't seem like much of a surprise that reservoirs in the West are dealing with, you know, lower storage and lower levels. I'm wondering if it was surprising to you at all that reservoirs in other parts of the country are seemingly dealing with some of these same issues.
SIMEONE: Yeah, I agree. I think that, you know, we expected, especially places like the Southwest which have had ongoing droughts for a lot of the last couple of decades to have sort of changes in their reservoir dynamics, something that I'm sure your listeners are familiar with.
But other regions of the West, including sort of the central plains Texas through the Dakotas and the Pacific Northwest, we saw similar declines. However, in the northern Rocky Mountains, we actually saw declining low storage anomalies in comparison to the rest of the western U.S. And we were really surprised, though, to see that. In addition to those changes in low storages, we saw declines in maximum storages at many reservoirs across the country.
BRODIE: Meaning that fewer reservoirs are holding as much water as they can.
SIMEONE: Yes, specifically, we looked at trends in the maximum annual storage to the highest level that each reservoir reaches in any given year.
BRODIE: So do you think that this all means that there needs to be a different storage system for water, like our reservoirs still the best way to be storing water?
SIMEONE: I think this study doesn't look into policy solutions for addressing this and doesn't sort of investigate, you know, how reservoirs should be operated in the future only. It mostly looks at how reservoirs have been operated in the past and looking at trends and trying to interpret what that might mean for the future.
But I think it does highlight that the current climate conditions that we're experiencing and the conditions moving into the future are likely changing away from the conditions that many of these reservoirs were built and designed for. And that this may create additional challenges that water managers might need to respond to in order to keep the reservoirs operating in an optimal fashion.
BRODIE: Again, understanding that you didn't really look into to policy changes here, I'm wondering if you have a sense of where this information, where this data fits into the overall discussion about water shortages, especially in the West and and how people use water and how much and in what capacity like, do you see this fitting into that conversation in a specific way?
SIMEONE: Yes, I do think that this research highlights the importance of sort of a conversation at the national level of how reservoirs are changing. And that ideally we'd have research that's pairing sort of a national scale, look at what's going on across many different reservoirs with more specific local or regional studies at specific reservoirs or specific basins in order to best understand how reservoirs are being impacted by climate change and what options there are to mitigate those challenges.
And reservoirs specifically are something that people should care about because they're one of the main ways that water managers have to be able to impact the hydrologic cycle and where water is going and when it's going there and millions of people have drinking water supplied from reservoirs or from the river systems managed by these reservoirs.
And many more than that eat food that at some level is produced with water that is impacted by the reservoir. And so understanding reservoirs is really critical to understanding the ways that we can influence the hydrologic cycle and be able to best manage that for potential future challenges.
BRODIE: When you look at the data for some of the reservoirs in the West and the Southwest, did it kind of match what you had seen in, in other data or you know, some of the reports that we've heard about the status of a place like Lake Mead, for example, like did, did you find anything surprising there or did it kind of confirm what you had already thought?
SIMEONE: I think yes, for certain reservoirs like Lake Mead and Lake Powell, it wasn't a surprise to see that most anomalies have increased through time. But I think we were surprised to see some of the outliers, like I personally was surprised to see that the reservoirs in the northern Rocky Mountains sort of again, Montana, Idaho, Wyoming didn't have those same declines as well as was sort of surprised by some of the declines in some of the northern central plains where in some recent studies on stream flow, they have not seen those same declines or same increases in streamflow drought.
