There’s a lot of debate in the world today about climate change (dun dun dun!) that generally centers around the question: is it real?

YES. IT IS REAL.

Phew. Glad we settled that.

Last time I talked a bit about the water cycle: that wonderful, natural cycle by which the Earth produces the freshwater we all survive on. Today, I want to integrate that discussion of the water cycle with the affects of climate change.

In risk of sounding like a Rubio-robot, let’s dispel of this notion, once and for all, that climate change impacts every region on Earth in the exact same way. Many climate change deniers like to use extreme weather events (i.e. Snowpocolypse) as “evidence” that climate change is not real. Jokes on them, though, because those extreme weather events are exactly what we expect to happen due to global warming. Stick with me, and I’ll explain why.

Temperature

One of the main drivers of global climate change is the warming of the planet.

The video above shows regional temperature changes over the last 130 years (data collected by NASA). To normalize the data (jargon for: to make the data comparable) surface temperatures of a region are compared to the average surface temperature of that region during the base period 1951-1980. In other words, these maps show how much warmer (red) or cooler (blue) a region is compared to the average for that region from 1951-1980.

As you can see, the planet has been warming quite a bit since the late 70s/early 80s. For now, I’m going to side step the question, “What is the cause of this warming?” (its human induced carbon pollution, bee-tee-dubs) and instead ask: So what does that mean? How does this warming of the planet impact everyday peoples’ lives?

Does that mean everywhere is going to turn into the Sahara? Should we expect winter in New York to become more like winter in Phoenix− 70 degrees and sunny all day, everyday? If there is a snow storm that shuts down airports all over Europe, is this indicative that climate change is a hoax?

NO.

Again, let’s dispel, once and for all, this notion that climate change impacts every region on Earth in the exact same way.

Increased global temperatures inherently changes the dynamics of the water cycle for different regions in the world. Global warming meddles with precipitation, runoff, and land surface moisture, all of which inherently change how any particular region interacts with water.

So lets Define the Relationship between Climate Change and the Water Cycle by looking at how global warming impacts precipitation and runoff.

Precipitation

Lets think back to the water cycle.precipitation_intensity_map Recall that as a body of water heats up, water begins to evaporate into the atmosphere. This moisture forms clouds, which precipitate out moisture in the form of rain or snow.

But now, due to the warming planet, the atmosphere is warmer. If the atmosphere is warmer, more water evaporates, resulting in more moisture circulating throughout the lower atmosphere.

Pause to contemplate: if there is more moisture in the atmosphere, do you expect there to be more or less intense precipitation events (i.e. storms)?

More, right? Mo’ moisture, mo’ storms!

However, these storms aren’t going to occur the same amount everywhere because our atmosphere is a complex, ever-moving being. The above map shows estimated changed in precipitation intensity in the 21st century. Blues indicate a predicted increase in precipitation intensity while browns indicate a predicted decrease. You can see that certain parts of the world, especially in the very northern latitudes, there is an expected increase in intense precipitation events, whereas regions along the equator may experience less intense precipitation events.

It’s not just a question of where those perception events occur, its also a question of what kind of precipitation events occur. A warmer atmosphere means that atmospheric moisture wont necessarily be falling as snow. As the globe continues to warm, more of those precipitation events will take the form of rain, not snow, which could pose a serious problem for rivers around the world that depend on spring snowpack melt to fill them with water during the hottest parts of the year.

What this really boils down to is that some regions of the world will see a drastic decrease in the amount of water available, while other regions will experience the opposite. For countries like Saudi Arabia, Yemen, United Arab Emirates, and Iraq (to name only a few) — all of which are already virtually out of water — this means a drastic decrease in the ability to survive and potentially millions of water refugees. So while we in the United States feel confident we can survive these changes to the global climate, remember that there are millions who cannot and will not unless something is done to mitigate the problem.

Climate change is not equal. Let’s dispel, once and for all, this notion that climate change impacts every region on Earth in the exact same way. 

Runoff

The combination of a warmer atmosphere, less intense perception in runoff_map_2084certain regions, and the decrease in snowpack due to more rain events poses some interesting questions about runoff.

Runoff is a term used to describe how much water is flowing down a landscape on hill slopes and in rivers. Remember that in the water cycle, some runoff is due to rain events, meaning the river carrying that water gets most of its precious cargo from rain events like a monsoon season (i.e. the Nile River). However, some rivers get their water from melting snow in the high mountains of their headwaters (i.e. the Colorado River, the Tigris River, the Euphrates River, to name a few). Of course, many rivers get their water from a combination of both rain and snow melt.

Here’s the problem: the warming atmosphere will cause more rain events and fewer snow events, which means less snow in certain mountain ranges. If there is less snow, there is less snow melt, which means there is less water for a particular water system.

On top of that, since the atmosphere is warmer, the winter season may be shorter. A shorter winter season means that the snow that is in the high peaks, will melt earlier in the year. This could cause a whole shift in the hydraulic timing of a river system– peak runoff would be earlier in the year, which would cause less water to be in the system by the hottest portions of summer and fall.

The above maps shows change in runoff expected in the 21st century. Reds indicate apredicted decrease in runoff while blue indicate a predicted increase in runoff. Note that this map combines the concept that precipitation may increase in certain regions with the concept that increases rain events may mean less snow pack in certain ranges.

Let’s look at the southwest United States where there is a predicted -20% runoff over the next century. The pipeline of water in the southwest is the majestic Colorado River, which supplies water to 40 million people in 7 states. Colorado River water is already over allocated, having been originally divvied up in the 1920s using data from the wettest decade in the last 300 hundred years. With populations rising and Big-Agribuisiness producing at an alarming rate in the driest region of the country, the strains on water in the American Southwest don’t need another stressor like climate change to makes things worse.

And yet, climate change exists. If we stay on the path we’re on, warming the globe year after year, less snow is predicted  in the Colorado Rockies — the peaks that feed the headwaters of the Colorado River. With less snow pack, less water will be available to pipe north, south, east and west from the Colorado River to sustain human life in cities like L.A., Phoenix, and Las Vegas.

The Relationship Defined

Climate change causes shifts in the water cycle. Precipitation events and runoff decrease in some regions  while increasing in others, causing a shift in available freshwater. Some parts of the world wont feel the strain, while others will be forced to a breaking point.

Will we, as citizens of Earth, collectively step up and work to mitigate the impending crisis? Or will we be content in letting some countries fall by the wayside, just as we have been content letting our planet fall by the wayside?


Media Sources:

http://earthobservatory.nasa.gov/Features/Water/

 

 

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