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Expect to see more floods and droughts this spring and summer

Angie Pendergrass is a climate scientist at the National Center for Atmospheric Research in Boulder, Colorado. She studies precipitation, evaporation, thermal energy emissions, and more. One focus of her studies is global warming and the effect of greenhouse gasses on precipitation.

SF: What do your studies show?

AP: Globally, we expect to see a small increase in average precipitation. We also expect to see that precipitation falling in heavier, but fewer, events. One thing that’s difficult to sort out is how much is climate change and how much is just weather variability. Those two things are happening together.

One of the scary things we see in model projections is that as the planet warms you have more water vapor, but a decrease in the number of events. This means an increase in floods and droughts.

To get a flood, you have a heavy rain event that’s hitting saturated ground or it’s happening so fast that there’s a lot of runoff. These heavier precipitation events have been occurring more frequently since 2011.

More variability of precipitation also means longer periods of dryness. If it doesn’t rain for weeks and it’s not a crucial time of year for farmers, then maybe that’s fine.

SF: What tools provide the best weather predictions?

AP: Rain gauges tell you exactly how much precipitation is in a specific spot. With summer thunderstorms, there can be different things happening a few miles apart. We would like to have rain gauges in a dense network.

The National Weather Service runs ground weather radars. Those are useful for knowing what’s happening in a specific storm, but there is a lot of variation. We don’t have a dense network of those radars.

Satellites are another tool. There’s a cool satellite that went up in 2014 called the Global Precipitation Measurement Mission. It’s actually a constellation of satellites with radar.

Satellites allow you to see storms, but they’re only passing over a couple of times a day. They give you a picture of what’s happening throughout the vertical column of the atmosphere, but they don’t tell you exactly what’s happening on the ground. So if you have evaporation of rainfall in the lowest part of the atmosphere, that can be hard to pick up from satellites.

It’s really important to have rain gauges on the ground. They take a lot of effort and cost to maintain, but they’re worth it.

SF: Everyone used to have a rain gauge in the backyard.

AP: One thing we’ve seen around the globe since the year 2000 is a decrease in the number of rain gauges. That’s a trend I don’t like. It’s important that we actively measure how much precipitation there is. 

SF: What else are you watching?

AP: There is a satellite put up by a European consortium that looks in great detail at emissions from methane. Methane has the second-largest radiative impact in terms of greenhouse gas emissions after carbon dioxide. With carbon dioxide, we can look at the isotopes of carbon and oxygen and understand whether it’s coming from the burning of fossil fuel or respiration of plants. We can get ice cores and see how that’s changed.

Methane is a much harder problem, because there are a lot more sources. Gas from animals is one of the contributing factors, but there are many factors to this complicated problem.

SF: Can plants adapt to the climate changes?

AP: This is a hot topic in drought research right now. Changes can take place in plant stomata openings for evaporation. Plants can use water more efficiently. They can still get the carbon dioxide that they need without having to evaporate away as much water.

With the increase in temperature, we expect to see an increase in evaporative demand. That’s how thirsty the atmosphere is. We expect the overall thirst of the atmosphere to increase, and that’s another factor that could increase drought. We hope that plants can modulate some of that.

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