Average annual rainfall patterns of Texas (1991-2020)

How do we determine what is an average climate?

There are often misconceptions when it comes to climate change and what effects that might have on our current & future weather, but we as a whole need to question two things. 1) How many different climatological phases has Earth gone through over 4.6 billion years? 2) Are the weather conditions part of a current pattern, or is this a long-term sustained climate?

Climatologists have concluded that 30 years can determine an average annual climate. The image above shows the change in inches of annual rainfall for the U.S. from the climate period (1991-2020). There has been global warming over the ages and this image shows large portions of the central and eastern United States having seen an increase in annual precipitation from the warming of our planet. What does this mean for our climate in the long run? Specifically for Texas?

A vast majority of the state of Texas has seen increase in average annual rainfall in inches from 1991-2020, with the exception of portions of western Texas. This goes to show you how drastic rainfall patterns are within the state. What is particularly noticeable is the widespread area around the Galveston Bay region where there has been an increase in average rainfall upwards of 4" or greater than the average was for the last 30 year climate period. A couple of catastrophic flood events within the last 5 years have greatly influenced the increase in average rainfall for that region as well.

Hurricane Harvey and Tropical Storm Imelda

Hurricane Harvey

Hurricane Harvey of August 2017 is the largest flood event we have ever seen in U.S. recorded history. Harvey dumped the most rain out of a tropical system to ever hit the U.S. and is the record holder for most rain to fall within the time period that Harvey affected Texas. Almost the entirety of the upper Texas coastline received above 25" of rain, with a majority of the Houston area on southeast and eastward receiving 40-60"+. There are radar estimates that totals may have reached 70 inches of rain over the course of five days. This led to Harvey being the 2nd costliest natural disaster of all time in the U.S.

Is global warming to blame for Harvey?

Studies have shown that a warmer climate supports richer water vapor values in the atmosphere leading to more precipitable water. Harvey could have been directly influenced by a currently warming climate, although Harvey had very little steering currents in the upper atmosphere, which does not seem to be a direct result of climate change and it is not believed that hurricanes will slow down in the future but rather speed up.

Why did the 7th largest U.S. rain event (Tropical Storm Imelda, 2019) occur only two years after the U.S. saw its largest rain and flood event (Harvey) in almost the exact same locations?

Tropical Storm Imelda devastated a large swath of southeast Texas in the same areas that were hit the hardest by Hurricane Harvey 2 years prior. As I mentioned earlier, it is hard to say what climate change truly is especially with weather trends that go back and forth in a short period of time (less than 30 years), but it believed this natural disaster was a direct result of the climate warming. This has been especially impactful on the city of Houston and is certainly alarming to see these trends in the city since 2015. A video is included below talking about what effects climate change, or climate periods may have on Texas, especially the areas that are noticeably getting wetter.

It is clear Southeast Texas has seen an increase in average annual rainfall over the last 30 years. How about other cities throughout the state?

https://www.ncei.noaa.gov/access/us-climate-normals/ is the link to access the new 1991-2020 climate averages. Austin, Texas saw a 0.93" increase in rain from 1981-2010 climate norms to the updated 1991-2020 norms. Waco, Texas saw an increase of 1.71", Dallas, Texas saw an increase of 0.75", and San Marcos, Texas saw an increase of 0.83" of precipitation. You can find these cities on the map below.

As it was seen during the set climatological period of 1991-2020, the rich get richer. The wet have gotten wetter, but what about the drier portions of the state?

El Paso, Texas is located in extreme west Texas and is considered a desert because its average rainfall is below 10" of rain a year. El Paso's average rainfall from the thirty year period (1981-2010) was 9.71". In this latest climate period (1991-2020), the annual rainfall in El Paso fell to 8.78" which is down nearly an inch. Although El Paso isn't considered to be in the areas of Texas that saw a negative change in annual rainfall (see the first map of this webpage), there was certainly a decrease in annual rainfall along with the areas colored in brown in the first map on this website.

Covering drastic rainfall differences throughout Texas

It is a large misconception to many outside of Texas that the entire state is a desert. People have to consider how large Texas truly is, in fact the largest state of the lower 48. Well, extreme western Texas is classified as a desert, influenced by the dry southerly winds of the Mexican desert. However, central Texas is influenced by a mix of the dry air from Mexico and the warm-humid air from the Gulf of Mexico, leading to a large portion of the central part of the state to get more abundance in rainfall which is around the United States' average rainfall (about 35"). The upper Texas coast into eastern and southeast Texas are by far the wettest areas in the state, dominated yearlong by the humid air from the Gulf of Mexico, leading to these areas of the state to qualify among some of the wettest in the United States annually.

Just how much rain falls in the wettest parts of Texas, and where does that qualify amongst the wettest portions of the United States?

As it has been known by now, eastern Texas has seen an increase in annual rainfall over the past 30 years. As a direct result of extreme rainfall from tropical cyclones, and several other major mesoscale flood events, southeast Texas in particular has seen a pretty note-worthy increase in the average rainfall. Much of southeast Texas averages 50-65" of rain annually, with some isolated spots receiving near 70" (1991-2020). Here below are some station examples with their average rainfall from 1991-2020:

Houston NWSO (located in Dickinson, Tx off of 646) : 60.20"

Baytown, Tx : 64.73"

Houston Heights : 60.49

Beaumont, Tx : 65.07

Bridge City, Tx : 70.45

Source: NCEI data 1991-2020 climate norms

It widely depends on how you view annual rainfall data to determine just where these cities stack up amongst others, and here's why.. some only consider the lower 48 to measure rainfall data, other do not take in account enhanced rainfall in mountainous regions of the United States, and it is also difficult to get a mean of the Globe's average rainfall and could have leeway one direction or another, but GIS has helped map Global rainfall data and has created an average. According to Britinnica, Earth, including all land and oceans, averages about 39" of rainfall a year. If we are talking only landforms, then the average is about 29". Here in the United States, the average yearly rainfall ranges from 30-35". This ought to put some perspective on just how high the annual rainfall totals for these cities out of Texas, listed above, truly are. It is hard to say what threshold truly determines how wet a U.S. city is on average, but it appears that 45" of rain yearly is the threshold used by NOAA-NCDC to outline the wettest places in the United States. The eastern half of Texas blow these numbers out the water, no pun, leading to a conclusion that this geographic area of Texas certainly qualifies as one of the wettest areas in the United States.

How will climate change affect Texas in the future?

What will updated 1991-2020 annual precipitation maps look like for Texas?

Frankly, we're still early in the game. With these 30 year norms coming out only a year and a half ago, it'll take some time to get some in depth isohyets on a new map. What I can tell you, however, is to expect more isohyets and a larger scale on the legend with higher average annual rainfall values for Texas. Below I placed the 1981-2010 average annual rainfall map of Texas, and will update this with a side by side view of the new 1991-2020 annual rainfall map as soon as it comes out.

1981-2010 average annual rainfall map of Texas

What we can take away from this data

Although we do not have in depth isohyet rainfall analysis maps of Texas from 1991-2020 quite yet, it is still suggested by the new NCEI 1991-2020 annual climate values of individual cities, and recently published rainfall percentage maps of surplus or deficiency showing a rather large percentage of increase in rainfall throughout the state. Over 90% of Texas is getting wetter, y'all! But it is important to understand the vast differences in annual rainfall throughout the state. A slight increase in average annual rainfall would mainly have benefits for those areas of desert in extreme western Texas, and those areas that have been drought stricken for years in the panhandle on throughout west-central Texas, but the problems come as you progress on eastward throughout Texas. Central, northern, eastern, and especially southeastern Texas have been ravaged by floods from major rainfall events in the last 30 years, and have seemingly become more common within the last decade. It is hard to say whether or not the floods of the last decade are a direct result of climate change considering a norm is classified as a 30 year period by climatologists, but it is an alarming trend that we will need to monitor over the next 10 to 20 years as it is possible that freak rain events will become more common during this time span and these areas as the climate warms, which could also lead to another increase in average annual precipitation come the next climatological time period.