How Climate Change Affects Rainfall

My boyfriend came to visit me for a few days over the holiday. We of course got some outdoor time amid the rainstorms that rolled in off of the Pacific, including walking in the nearby woods here on the farm. While we were walking through the sodden salal and evergreen huckleberry bushes, he remarked on how much rain we were getting, which seemed unusual even for our fall storm season. I shared with him a basic overview of how climate change affects rainfall here throughout the year.

See, it’s not just about the rising global temperatures themselves. Our weather patterns, and the precipitation that results, are heavily influenced by both global and regional/local climate. As the effects of anthropogenic climate change have ramped up in recent decades, we’re seeing definite changes in the amount and rate of precipitation, to include here on the wet side of the Cascades. I moved to this region in 2006, and in those fifteen years I’ve noticed drastic changes that have been corroborated by lifelong residents.

Ways That Climate Change Affects Rainfall

To understand the answer to this, we first have to look at how the change in our global climate affects the hydrological cycle in various places. This is simply the cycle that water takes in moving through air, down to the land, and either across its surface or underneath. You may have learned about a very basic hydrological cycle in elementary school, consisting of evaporation (water on the earth become vapor), condensation (water vapor in the air becomes clouds) and precipitation (water in clouds condenses enough to fall to the earth as rain, snow, etc.) There are many other potential stages that water can visit through this cycle, though, from being locked in ice as part of a glacier, released into the air as volcanic steam, flowing across the land in a river, and even traveling for a time in the body of an animal, plant, or fungus.

However, it’s that basic evaporation-condensation-precipitation cycle that we most need to look at right now. For thousands of years the climate has remained relatively steady, giving living beings in a particular place time to adapt to the hydrological cycle there. That includes being adapted to how much water is available, as well as when it is available, and in what form(s). The animals that live in a desert, for example, can survive on less liquid water than the animals in a rain forest.

The rise in overall temperatures worldwide have caused an upset in hydrological cycles. Warmer average temperatures mean water evaporates at a faster rate, which not only causes many places to dry out more during the dry period of the year, but increased evaporation also causes increasingly intense storms that may happen more frequently.

Too Much Water, Too Little Water

In a soundbite on a news channel, “increasingly intense storms” may not seem like a big deal, especially if you aren’t in a place affected by hurricanes, tornados, or flooding. However, these storms are symptomatic of a bigger problem: increasingly irregular distribution of precipitation.

By that, I mean that the longer we have observed how climate change affects rainfall, the more heavy rainfall periods we’ve recorded. Like here in the Pacific Northwest, our fall, winter, and spring months have frequent rainy days. Usually we get less than an inch of rain in a twenty-four hour period, and even if there are several days of rain in a row it’s not likely to cause flooding. We do traditionally get a few storm systems throughout the rainy season, especially here on the coast, and these may dump a couple of inches of rain at a time. However, most of the time the bulk of the rain falls at a slow enough rate that the soil is able to absorb it like a big sponge, and releases it in a more controlled manner into streams and rivers whose courses have been carved by similar volumes of rain over the years.

What’s happened more recently is a combination of both more precipitation in total, and more severe weather events in which large amounts of precipitation fall in short periods of time. There’s too much for the soil to absorb at once, and more of the rain flows over the surface of the land than is normal, traveling faster than it would otherwise. This overwhelms the streams, rivers, and other catchments, and contributes to markedly increased flooding and erosion; the erosion, of course, means there is less soil to absorb the rain, worsening the problem even more.

Ironically, wetter winters mean drier summers. The precipitation that soaks into the soil and replenishes groundwater reserves is supposed to help plants and other beings survive the dry months. Because more water is flowing off into rivers rather than being retained in the soil, there’s less available for everyone. Moreover, the rain has been ending earlier in the year and starting later, meaning the dry season lasts even longer–making it harder to stretch what water has been saved.

It’s been happening like that not just here in the Pacific Northwest, but in many places globally. And as ecosystems that act as carbon sinks become increasingly damaged by these upset hydrological cycles, climate change is just going to worsen. This is one of the reasons why it is so imperative that we act on stopping and–hopefully–reversing climate change. A future article will focus on some of the concrete things we can do to work against this massive, seemingly overwhelming problem, but for now if you enroll in my Forests, Fire Ecology, and Climate Change class, I do wrap up the class with some of those suggested actions (and a message of hope!)

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2 thoughts on “How Climate Change Affects Rainfall

  1. Martha williams says:

    Thanks Becca- my passion as you know is stopping the climate emergency.
    As Kathryn Hayhoe says, the most important action you can take to stop climate change is to talk about it.

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