Pecos River Basin Study Examines Water Supply Under Various Climate Change Scenarios
As climate change affects the water supply in the southwest, farmers in the Pecos River Basin could face challenges.
The United States Bureau of Reclamation on October 12 released a study on the impact of climate change and agriculture on the Pecos River basin under five different scenarios.
Reclamation study director Dagmar Llewellyn said the challenges are significant as the basin is arid with a limited and highly variable water supply. During a webinar on Wednesday, she said the Pecos River Basin is already seeing less snowfall in its headwaters. These springs are located in the Sangre de Cristo mountain range northeast of Santa Fe. She said winter precipitation increasingly comes in the form of rain rather than snow. This is important because the snowpack feeds the spring runoff. At the same time, the demand for water for irrigation is increasing.
The study aimed to answer four questions: what are the current and forecast hydrological and meteorological trends in the basin, how these trends affect irrigation water supplies and demands, what infrastructural or operational changes might be made, and how Modeled water management strategies could mitigate changes in water supply.
Since the future impacts of climate change remain unknown, the authors developed various scenarios to analyze potential water supplies and demand under low and high emission scenarios.
The basin includes three irrigation districts (Fort Sumner Irrigation District, Pecos Valley Artesian Conservation District, and Carlsbad Irrigation District). Of these three, the Carlsbad Irrigation District will likely be the most affected by the increase in temperature and decrease in precipitation. Indeed, the Carlsbad irrigation district depends on surface water and is located further downstream than the others.
USBR has partnered with the Water Smart Study with non-federal agencies to assess the future of water in the basin, including supply and demand projects. Non-federal agencies include the New Mexico Interstate Stream Commission and the three irrigation districts.
The study focused primarily on agriculture and not on municipal or industrial uses such as oil and gas extraction. The main use of water in the Pecos River basin is agricultural and more than 80 percent of the water is for irrigation and agricultural needs, according to Llewellyn.
The researchers developed scenarios based on the amount of anthropogenic emissions that will occur in the future. The amount of emissions from human activity will determine the extent of global warming.
In a high emissions scenario, they add three different possibilities. The first possibility was moderate impacts, which would lead to a slight drying out of the Pecos river basin. Under this scenario, the temperature would rise by almost nine degrees Fahrenheit and precipitation would decrease by 3.6 inches. The model also shows a decrease in runoff of over 60,000 acre-feet.
The second scenario they looked at included much drier conditions with less water available for storage, irrigation, and compact compliance. Under this scenario, the temperature would increase by more than 13 degrees Fahrenheit, precipitation would decrease by 8.37 inches, and runoff would decrease by more than 140,000 acre-feet.
The final scenario was based on low levels of winter precipitation and high intensity monsoon storms. Under this scenario, temperatures would rise by more than 12 degrees Fahrenheit. Unlike the other two scenarios in the high emissions scenario, this one would see an increase in both precipitation and runoff. The models show nearly two inches of increased precipitation and over 81,000 acre-feet of increased runoff.
Meanwhile, under the low-emissions scenario, the researchers evaluated two scenarios. The first scenario examined what would happen if there were an increase in monsoons and a modest decrease in snowpack during the winter. Under this scenario, temperatures would rise by more than four degrees Fahrenheit. Precipitation would increase by 3.15 inches and there would be over 36,000 acre-feet of increased runoff.
The second focused on a slight increase in winter precipitation and a decrease in precipitation in other seasons. This scenario saw an increase in temperature of about two and a half degrees Fahrenheit. Precipitation would decrease by less than an inch and there would be a decrease of about 26,000 acre-feet of runoff.
Some of the strategies examined include decreasing the use of irrigation water and increasing efficiency improvements on farms. In terms of decreasing the use of water for irrigation, Llewellyn said that “is not saying that irrigation districts have to reduce their irrigated area or that their production could certainly be achieved by changing the types of crop methods. irrigation or installing greenhouses, there are many different ways to implement them.
If high emissions do occur, there is little that these management strategies could do to address the water shortages that would occur.
However, the study found that some steps can still be taken. This includes improving the efficiency of transportation. This would require the rehabilitation or replacement of the canals and the control of works and diversion works. This would lead to a reduction in water loss during water transport. By reducing the amount of water lost, more water will be available for irrigation. Water loss can also be reduced by controlling invasive species like the tamarisk and Russian olive tree.
Another action that can be taken is to modify reservoir operations to more effectively capture water from monsoon storms.
One of the other stages identified in the study is the maintenance of the canals on the main course of the Pecos river and in the watersheds.
And irrigation districts are already taking steps to address some of the challenges, such as implementing real-time flow metering devices and automatic valves in the Fort Sumner Irrigation District.