Experts on Camera

Dr. Amir AghaKouchak: Drought in the southwestern United States

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SciLine Interviewed: Dr. Amir AghaKouchak, a professor of civil and environmental engineering at the University of California, Irvine. See the footage and transcript from the interview below, or select ‘Contents’ on the left to skip to specific questions.

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Interview with SciLine

‪How is human activity contributing to the drought in the western United States?


AMIR AGHAKOUCHAK: It is really hard to say how human activity has changed the likelihood or severity of one specific event, but we can confidently say that there is human footprint in almost all events that we observe from two different perspectives. We call them bottom-up and top-down. Top-down, we mean events that we don’t have much control on – for example, rainfall patterns, snow pattern. Anthropogenic emissions may change rainfall, snow and other climatic processes, leading to intensification of drought or more frequent drought events. But there is a more local and bottom-up dimension as well, and that’s our local water use. Over the years, our water use has increased, meaning we need more and more water for our daily lives. So if this same drought that happened, let’s say, 30 years ago happens today – the same severity, the same event – the impact will probably be more extreme because there are more people, more need for water. And just because of that, the impact will – probably will be more severe. But this is a whole different dimension. The bottom-up part is what we have more control on. We have control on our demand, on how we use water, and we have more flexibility to modify, change – make changes and prepare for – better prepare for drought events.

What is “anthropogenic drought,” and why are some places now experiencing non-stop drought regardless of weather?


AMIR AGHAKOUCHAK: Anthropogenic drought refers to events that are caused or intensified by human activities. Let’s think about Southern California. This area is developed so much that we need to bring water from other places. Even if we have an extremely wet year with a lot of rain, still, that won’t be sufficient to satisfy the water demand in Southern California. This means regardless of the local meteorological situation, you need to bring water from other places. That’s kind of like perpetual drought. You’re in drought all the time.

What is “snow drought,” and is the western United States experiencing one this year?


AMIR AGHAKOUCHAK: Snow drought refers to deficits in snow storage or the situation that you have snow, but snow melts quickly because of warm temperatures, and eventually, most of that drains into the ocean. This is broadly called snow drought. And yes, this year, we are in deep in snow drought. If you look at the Sierra Nevada, snow is somewhere between 40 to 50% of the average – the southern part of Sierra around 45% of average and northern part maybe around 60 to 70% of the average. So yes, we are in snow drought this year, and we will see the impact of snow droughts later in spring and summer low flows.

How could the snow drought affect the risk for flooding in the spring, and wildfires in the summer?


AMIR AGHAKOUCHAK: Snow drought definitely means drier environment, less surface water, surface runoff, dry vegetation and fuel for wildfire. Also, if you look at historical records, we see that fires are happening at higher and higher elevations – in fact, even above snow line. This means that fire and snow interact with each other. How? In many different ways. If you have a burned environment and snow falls, there is no canopy and vegetation to protect snow. Snow is more exposed. There is higher chance of rapid snow melt, even flooding early in spring and dry conditions later in the summer. So both flood and drought impacts kind of what you can expect from the interactions between snow and fire.

How could the snow drought affect agriculture?


AMIR AGHAKOUCHAK: Our agricultural industry in California relies on snow, and snow deficit definitely impacts water availability for agriculture industry. If there is a drought situation, then we need to pump more and more groundwater to sustain agriculture. This means impacts at the groundwater level, more energy consumption and more expensive production.

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