Sujoy B. Roy, PhD, a principal engineer in Tetra Tech’s Lafayette, California, office, has more than 25 years of experience in large water-related modeling projects.

“I was drawn to climate change because of the scale and consequences of the problem,” said Dr. Roy. In looking at longer-term infrastructure and future water supply studies, climate considerations are seen less as a separate discipline, and more integrated into ongoing and long-term analyses.

“I was drawn to climate change because of the scale, significance, and consequences of the problem.”

Dr. Roy leads several major interdisciplinary studies related to water resources, water quality, greenhouse gas emissions from water sector projects, and sea level rise impacts, with a particular focus on future growth and climate change. Several of his key studies include climate change impacts on water supplies from Los Angeles Aqueduct, a national study on the role of climate change on future water withdrawals, and an ongoing study on the adaptation of agriculture in San Joaquin Valley, in California, to potential climate change.

Dr. Roy served on the U.S. Environmental Protection Agency’s Science Advisory Board from 2009 to 2015. He also served on National Academy of Sciences panels on Missouri River Basin restoration and on Clean Water Act Implementation across the Mississippi Basin. He holds both a doctorate and master’s degree in civil and environmental engineering from Carnegie Mellon University and a bachelor’s technical degree in civil engineering from the Indian Institute of Technology Delhi.

How did you get involved in modeling related to climate change?

I've been involved in modeling in two ways: looking at it from the cycling of organic carbon in the environment and looking at impacts to human systems and infrastructure. I've been involved in climate-related studies since the mid-1990s. Some of my early work involved looking at carbon cycling on a large scale, and more recently, I've been doing studies looking at impacts to specific areas, like water resources or water quality.

I think climate change has always been a part of projects that are looking at longer-term impacts. For example, how might climate change affect future water supply scenarios? It is quite typical in looking at long-range water quality planning or ecosystem planning to evaluate the impacts of future climate, especially recently. It is seen less as a separate discipline and more as integral to the ongoing, long-term analysis.

What types of questions are you addressing in your more recent modeling focused on the impacts of climate change on water resources?

An area of great interest to me is how extreme behaviors will change in my own area of study related to water. What will happen to long-term droughts? What will happen to extreme high temperature events, and what will happen to extreme precipitation events? Those are the periods when weather effects have a big impact on human and natural systems. As the climate gets warmer, what’s the incidence of extremely hot days or the incidence of extreme rainstorms that could cause flooding?

We are looking at longer-term time horizons for climate change impacts to evaluate the suitability of proposed infrastructure. If you're building a road near the coast, it's important to understand what the flooding or the storm surge will be over the decades to come. You are looking at the specific impacts to your infrastructure and how to make it more resilient to a more variable climate. And it's not just how the averages are changing. People talk about climate change as warmer temperatures, but it’s not just those averages we need to worry about. It’s also the extremes which could be changing, and I think most of the damage to systems happens during those extreme periods. The 100-year flood is of great concern to us. Is there information that suggests that kind of an extreme event is becoming more commonplace? That's the focus of our kind of analysis. That's what my team does at Tetra Tech.

What are the biggest challenges you face when modeling future impacts of climate change on water resources?

Despite a lot of research, we still don't have a good understanding of what's going to happen with something like precipitation in different regions. There could be more extreme wet periods, and we could be worrying about drought at the same time. The challenge is as a society how do we plan for it? If we knew that there would be more droughts, we would be responding a certain way. If we were expecting more floods, we would be responding a different way. I think both of those extremes can happen, and it's the breadth of future scenarios that is the big challenge. For example, looking at California, models suggest that the future climate could be wetter or drier. Depending on which way it goes, we may have to make very different investments.

How do you address the uncertainty involved in predicting future impacts related to climate change and provide meaningful information for your clients?

Presently, the approach we take is to try to communicate that uncertainty. Even though climate change is one of the most actively researched topics today, our confidence in describing conditions 20 to 30 years ahead is quite limited. I think it's an education process. I would like people to be aware of the potential risks for future planning. I recognize there's a wide range of scenarios out there. Some of the needed investments for greater flood protection or enhanced water supplies are huge. Sometimes these climate impacts and investments may span generations. The best recommendation we can provide to our clients is to inform them of the range of possibilities and try to better understand the weak points in their systems so we can focus on the most effective actions.

Has there been advancement in the modeling technology or in data acquisition to feed climate change models?

Absolutely. I think every year—or certainly every few years—the type of data we collect, and the efficiency and cost with how we collect the data, improves. We understand our natural systems much better and the value of that resource becomes more and more apparent to society. The tools we are using for modeling will expand as we get more and more data, especially temporally detailed data on the systems that we're modeling. That improvement is happening because of cheaper technology and the value we're giving to better understand these systems.

What do you think will be potentially the biggest future advancement in the modeling of climate change impacts on water resources?

Society would like us to provide more credible future scenarios to respond to. There was a point when climate change itself was a concept that many people did not agree with or thought it was too far in the future. I think we’re past that and our clients are now trying to make reasonable decisions about long-term infrastructure sustainability. If we acknowledge that climate change will happen, the next question is what we should do about it. I think modeling advancements will provide better insight in years to come. The people making decisions on infrastructure investments should have more confidence in the future conditions they are planning to deal with.