Cotton production in the Texas High Plains can survive expected climate changes, especially if water is available to compensate for higher temperatures, and increased atmospheric carbon dioxide concentrations can mitigate yield loss in the dry years.
That was the conclusion of a Texas A&M AgriLife Research study, “Simulating future climate change impacts on seed cotton yield in the Texas High Plains using the CSM-CROPGRO-Cotton model,” recently published in the Agricultural Water Management journal.
“We believe cotton production in the Texas High Plains can withstand the effects of future climate variability under moderate increases in carbon dioxide levels,” said Dr. Srinivasulu Ale, AgriLife Research geospatial hydrologist in Vernon. “But our study shows that maintaining high yield levels will still require greater than 80 percent of current irrigation levels, even when increased carbon dioxide levels are accounted for.”
Joining Ale on the modeling study was Dr. Pradip Adhikari, AgriLife Research post-doctoral research associate in Vernon, and Jim Bordovsky, AgriLife Research senior research scientist and agricultural engineer in Lubbock/Halfway, among others.
The overall study was funded by Cotton Incorporated with model calibration partially supported by a Texas A&M Water Seed Grant.
Dwindling groundwater resources in the underlying Ogallala Aquifer, future climate variability and frequent occurrences of droughts are major concerns for cotton production in this region, Ale said.
Cotton growing under various levels of water stress due to irrigation quantity and timing treatments at the Texas A&M AgriLife Research Center at Halfway. (Texas A&M AgriLife Research photo by James Bordovsky)
He said it is known that climate change can affect agriculture both positively and negatively. Increases in carbon dioxide concentration due to climate change are positive for plant growth. Previous research reported elevated carbon dioxide levels could enhance crop growth and yield by increasing photosynthesis and decreasing stomatal conductance. As a result, transpiration per unit leaf area is reduced and overall water-use efficiency is improved.
“We know this region is predicted to have warmer summers and reductions in annual precipitation in the future,” Ale said. “Such trends would necessitate larger groundwater withdrawals to meet the higher evapotranspiration needs of cotton and prevent yield loss.”
That is why it is important to begin assessing the impacts of climate change on cotton production now to enable the development and evaluation of irrigation strategies for efficient utilization of groundwater resources in this region in the future, he said.
“Our study showed it may still be possible to produce cotton yields of 1,000 pounds of fiber per acre even under high deficit – 60 percent – irrigation,” Ale said.
In this study, the CROPGRO-Cotton model was evaluated for the Texas High Plains region using 27 treatments of measured data from cotton water-use efficiency experiments conducted from 2010-2013.
The measured data came from Bordovsky’s work at the Texas A&M AgriLife Research Center at Halfway and the impacts of future climate variability and change on irrigated cotton yield were assessed at Halfway and four other locations: Bushland, Lockney, Lubbock and Lamesa.
The future climate data used in this study was taken from research conducted by Dr. Naga Modala, also a co-author on the paper, while he was a graduate student in Ale’s program.
The evaluated CROPGRO-Cotton module withing the Cropping System Model was used to simulate the irrigated seed cotton yield under historic, 1971-2000, and future, 2041-2070, climate scenarios projected by three climate models, Adhikari said.
Simulated seed cotton yield matched closely with observed yield during model calibration and validation, he said. The evaluated model was able to accurately simulate seed cotton yield under various irrigation strategies over the four growing seasons.
The scenario examined the changes from 380 parts per million of carbon dioxide currently experienced to increasing levels of 493 parts per million in the year 2041 to 635 parts per million by 2070, which is the Intergovernmental Panel on Climate Change A2 emission scenario.
Also modeled in this study were the effects of reducing irrigation due to declining water levels, Ale said.
On an average, when compared to historic yields, simulated future yields across the Texas High Plains decreased within a range of 4-17 percent due to the combined effect of the increase in temperature and decrease in rainfall when carbon dioxide concentration was assumed to remain at the current level of 380 parts per million under three climatic model scenarios.
When the carbon dioxide concentration was assumed to increase from 493 parts per million in year 2041 to 635 parts per million in 2070, the simulated irrigated yields increased within a range of 14-29 percent as compared to historic average yield.
At the same time, when irrigation was reduced by 40 percent, the average 2041-2070 yields under the constant carbon dioxide concentration and the increasing concentration scenario decreased by 37 percent and 39 percent, respectively.
In general, average seed cotton yields under changing carbon dioxide concentration were higher by 11-15 percent when compared to constant carbon dioxide concentration among different irrigation levels. However, this trend varied among wet, normal and dry years, Adhikari said.
The percentage change in average seed cotton yield due to changing carbon dioxide concentration ranged between -9 percent at a 60 percent irrigation level and 7-8 percent at 100 percent irrigation level for the wet and normal years. It changed 30 percent and 98 percent at the respective irrigation levels for the dry years.
“These results imply that cotton is sensitive to atmospheric carbon dioxide concentrations, especially in dry years,” Ale said.