And the young who left with a few seeds in each pocket,
Their belts tightened on the fifth notch of hunger—
Under the sky that deafened from listening for rain.
--Gary Soto, from The Drought, ©1978
Water has always been precious in the southwest, but climate change is likely to make it worth its weight in platinum. As part of the Secure Water Act, the Department of Interior's Bureau of Reclamation has begun to explore the water management challenges posed by climate change over the 21st century. The initial report examines surface water availability for key river basins in the western United States. Across a wide range of modeled conditions, two consistent trends emerge for the coming century. Water levels will likely substantially decrease in river basins in the lower southwest and increase in the upper northwest.
Specific projections include:
-a temperature increase of 5-7 degrees Fahrenheit;
-a precipitation increase over the northwestern and north-central portions of the western United States and a decrease over the southwestern and south-central areas;
-a decrease for almost all of the April 1st snowpack, a standard benchmark measurement used to project river basin runoff; and
-an 8 to 20 percent decrease in average annual stream flow in several river basins, including the Colorado, the Rio Grande, and the San Joaquin.
The projections are based on an ensemble of 112 models that incorporate soil, terrain, seasonal, historical, hydrological, and climate data. The basic idea is to incorporate what we know about how a particular basin has behaved in the past and estimate what effects future temperature and precipitation projections on the basin. By taking the mid-range of predictions, the agency can begin to look at the most likely water management scenarios from 2020 to 2099.
These figures show predictions for expected temperature and precipitation rate changes across the western United States from 1950-1979 levels. The largest increase in average temperatures occurs in Utah, eastern Nevada, and western Colorado. Precipitation levels are expected to fall most dramatically in southern California and Arizona. These changes to the semi-arid and arid conditions of the southwest will mean severe stress on water resources in the future. Given the rapid population growth in these areas in recent decades, the need for ramping up efforts to improve conservation and reclamation should be apparent.
Much of the available freshwater supplies in the southwest come from the flow through large river basins. The largest increases in temperature and decreases in precipitation are expected to pose significant water management problems for the San Joaquin, Rio Grande, and lower Colorado River basins.
Here is a summary for each of those 3 southwestern basins (from full report pdf):
a) San Joaquin
Temperature is projected to increase by roughly 5-6 °F during the 21st century, with precipitation slightly increasing in the northern Central Valley and slightly decreasing in the southern Central Valley. The projections also suggest annual precipitation in the Sacramento and San Joaquin River Basins will remain quite variable over the next century with a slight increase of 0.6% over the Sacramento River Basin and a decrease of from 4.2 to 5.3% over the San Joaquin River Basin by 2050.
The basin's annual runoff is projected to increase very slightly during the first half of the 21st century and slightly decline in the latter half of the century.
Mean annual runoff is projected to increase as much as 2.5% in the Sacramento River Basin and decrease by 8.7% in the San Joaquin River Basin by 2050.
Moisture falling as rain instead of snow at lower elevations will increase wintertime runoff and decrease summertime runoff.
b. Rio Grande
Climate projections suggest that temperatures throughout the Rio Grande are projected to increase by roughly 5–6 °F during the 21st century.
The projections also suggest that annual precipitation in the Rio Grande Basin will remain quite variable over the next century with a decrease of from 2.3 to 2.5% by 2050.
Mean annual runoff is projected to decrease by from 7.3 to 14.4% by 2050.
Moisture falling as rain instead of snow at lower elevations will increase the wintertime runoff and decrease runoff during the summer.
c. Colorado
On average, Colorado River Basin temperature is projected to increase by 5–6 °F during the 21st century, with slightly larger increases projected in the upper Colorado Basin.
Precipitation is projected to increase by 2.1% in the upper basin while declining by 1.6% in the lower basin by 2050.
Mean annual runoff is projected to decrease by 8.5% by 2050.
Warmer conditions will likely transition snowfall to rainfall, producing more December–March runoff and less April–July runoff.
The flow through these river basins is expected to be substantially lower than current levels, particularly during the spring-summer season when water is critical for agricultural demands. These changes will have a profound impact on the human population, economic viability, and ecology of the area. The bottom line is simple. Without careful management of water resources, these areas are at high risk for desertification.
Of particular concern is that these predictions are based on the mid-range climate models, which assume stabilization of global carbon dioxide emissions at around 550 parts per million. I see no reason to believe that optimistic scenario will take place. Given current inaction and zombification of the political landscape in the United States, stabilization of greenhouse gas emissions over this century is much more likely to take place much closer to 1000 parts per million than 500.
Texas has recently experienced a small taste of what the future is likely to bring to the southwest. Wildfires have burned over a million acres in Texas during the past two months, but the real story is drought. Drought conditions in the state rivals any on record since 1895, most reservoirs are below 30% of capacity, and agricultural production is down by 50% for most non-irrigated crops. Suffice it to say that people in Texas have water on their mind and with very good reason.
NASA's Terra satellite provided a glimpse at surface temperature conditions during early April as the wildfires began to break out in Texas. Precipitation across the area has been extremely low since late autumn. High temperatures further dried out vegetation and dropped soil moisture levels to create a readily combustible environment.
The top image shows ground temperatures for April 7 to April 14 compared to long-term average for the week. The red tones indicate that most of Texas was much warmer than average, further drying out the abundant grasses, shrubs, and trees already suffering from a lack of rain.
In essence, the conditions that are producing wildfires, crop losses, dust-bowl conditions, and water shortages in west Texas are likely to become the norm for this area by 2050. Unfortunately, the national media has not paid much attention to the drought until the wildfires broke out. I guess images of fires are more dramatic and strike some primordial psychological chord in us than images of dust, parched ground, and wilted vegetation. Here is a slideshow of images from the wildfire outbreak. (I found the images to be compelling but the soundtrack annoying so I would suggest muting the video.)
Disclose.tv - texas wildfires Video
Update: Here is a sobering reminder of the potential costs of water management in arid and semi-arid environments from Australia.
That’s why we should pay attention to the lessons of Perth. It took water professionals and elected officials years to realize that water availability was changing. Once the problem really sank in, it was a crisis, and leaders had to scramble--water became a hot political issue, and smart decisions got hard to make. (One candidate for state premier suggested building a canal to supply water to Perth that would have been the equivalent of supplying water to Las Vegas by building a canal from Niagara Falls.)
In just the last five years, relative to population, Australians have had to spend the equivalent of half of President Obama’s stimulus program, just on water and water systems. The cost of the desalination plants alone comes to $14 billion--$646 for every man, woman and child of Australia, just on desal plants.