Climate Change Makes Rain Shadows Worse
Also, some redistricting thoughts
We talk about climate change in broad strokes: “the world is getting warmer”, “the Western United States is getting drier”, etc. While true, they mask local variations and the complexities of climate. When looking at datasets, it is important to remember that
I have been playing with CHIRPS data for a while now. It is a great dataset for hyperlocal rainfall estimates and it goes back to 1981.1 I am interested in mapping how the rainfall has changed over time. To do this, I made a baseline from all of the years in the 1980s and calculated the change in rainfall compared to the 2010s. I then clipped the data to the area of interest and symbolized it.
The data can be seen below. Please ignore the light-colored striping and tiling. I think it is a product of the process used to calculate the pixel values by the modelers. This artifact of the modeling process might be a reason to discount these numbers, but I am going to sidestep that and just examine the data.
The thing that struck me is how widespread of an area is getting more rain. There is a line that goes from Washington to Califonia right where the mountains start that are getting more rain. Additionally, the high plains of Montana and Wyoming are wetter. On the other hand, some areas are getting less rain. Parts of the Cascades, Sierra Nevada Mountains, Olympic Penisula, and New Mexico are drier. You can see this more in a zoomed-in map of Washington State.
Washington State
From Chelan to Klickitat County there is a defined band of drier areas with a band of wetter areas in front of it. What I think is happening is that the rain shadow is getting worse. A rain shadow happens when clouds with lots of moisture hit a mountain range. As the clouds are forced up to cross the mountain, they get colder and can hold less water vapor. So, it rains. By the time the clouds are on the other side of the mountain, they no longer have much water. This makes that area dry.
One of the data points that helps to confirm my assumption is that when you overlay the physiographic provinces on top of the rain data, you see the front of the Cascades getting more rain and the back of the mountain range getting less. Similarly, the side of the Olympic Peninsula towards the ocean gets more rain in the 2010s than the 1980s, but the side towards Puget Sound receives less rain.
My working hypothesis is that this effect is probably due to climate change. Warmer temperatures mean more evapotranspiration and more water held by clouds. These two factors increase the chances that when a cloud comes into contact with the Cascades, they release all of their rain when crossing the mountain and that the rain is dropped earlier.
California
I honestly have no idea what is going on in California. There are quite a few oddities. There seems to be a massive reduction of rain in the Sierra Nevada mountains near the south of the central valley. The San Fransisco Bay Area also has a large reduction in rain. Ventura and Santa Barbara counties have an uptick in the amount of rain, but it stops abruptly at the county line.
Something is going on, I just can’t pinpoint what it is.
Redistricting
Democratic activists are doubling down on trying to squeeze as many seats out of states that have democratic statehouse majorities. I outlined my opinions on this last month, but in short, I am highly skeptical of any effort to systematically disenfranchise anyone based on their political beliefs. Ilinois looks like it is going to pass a 14D- 3R map, but people are semi-seriously floating 15D - 2R or 17D - 0R maps. The current map is 13D - 5R.
The core problem of this strategy is over-engineering a map. Sure, the map may be great today, but the tides change. Any serious map maker needs to take the red dogs into account. These college-educated suburban voters pulled the lever for Democrats in 2016, 2018, and 2020, but aren’t fully on board with much of the platform. They voted for Romey in 2012, McCain in 2008, and Bush in 2004. I would resist the urge to rest on our laurels and assume these new Democrats are blue for life. A fairly moderate republican could easily woo these voters back, especially in a wave year.
If you want to be technical and annoying it is all precipitation when converted into liquid form, but rain makes more sense in casual conversation