The Cotton Belt refers to a region in the Southern United States where cotton has been grown as the main cash crop from the late 19th century through present day. This region extends from southeastern Virginia to central and southern California and encompasses North Carolina, South Carolina, Georgia, Florida, Alabama, Tennessee, Mississippi, Arkansas, Louisiana, Texas, Oklahoma, Kansas, New Mexico, and Arizona. Temperature is a vital factor in cotton farming throughout the Cotton Belt, as both high and low temperatures can adversely affect growth, yield, and fiber quality (Reddy et al., 2005; Singh et al., 2018). Temperatures above 30°C can lead to heat stress, lower boll retention, and shorter fiber length (Reddy et al., 2005). On the other hand, temperatures below 10°C can hinder crop growth and negatively impact germination and subsequent development (Bradow & Bauer, 2010; Singh et al., 2018).
General Circulation Models (GCMs) predict weather and enable an understanding and forecasting of climate variations (Pierce et al., 2009). GCMs are among the primary tools utilized by researchers to examine past temperature changes and project future temperature alterations. These models replicate the interactions among the atmosphere, terrestrial systems, and oceans, and require some of the world's most powerful supercomputers to produce temperature forecasts. The Coupled Model Intercomparison Project (CMIP) provides a framework for conducting climate model experiments, allowing scientists to evaluate, validate, and consistently improve GCMs (O'Neill et al., 2016). The latest phase of this initiative, CMIP6, provides the most updated global climate model information, which is scientifically sound and forms the basis for the Intergovernmental Panel on Climate Change's Sixth Assessment Report (Kikstra et al., 2022).
This article outlines projections for maximum and minimum air temperatures averaging across nine selected GCMs under four Shared Socioeconomic Pathways (SSP) scenarios: SSP1-2.6 ("Sustainability" pathway with low greenhouse gas emissions), SSP2-4.5 (moderate future warming), SSP3-7.0 (medium to high level of greenhouse gas emissions), and SSP5-8.5 (high greenhouse gas emissions scenario). The projections are provided for five sites across the US Cotton Belt: Maricopa, AZ; Halfway, TX; Chillicothe, TX; Camilla, GA; and Lewiston-Woodville, NC, where key research and extension centers linked with the University of Arizona, Texas A&M University, Texas Tech University, the University of Georgia, and the University of North Carolina, respectively are located.
Climate data processing
The most recent bias-adjusted and spatially refined temperature data from the CMIP6 were obtained from the NASA Center for Climate Simulation (NCCS, accessed on July, 2024) for the five locations (Figure 1) across the Cotton Belt: Halfway, TX (34.18, -101.95), Chillicothe, TX (34.18, -99.51), Maricopa (33.06, -111.97), Camilla (31.28, -84.29), and Lewiston-Woodville (36.13, -77.17). The anticipated temperature data were derived from nine GCMs under four "Tier 1" GHG emission scenarios. The nine GCMs selected for this analysis include ACCESS-CM2, CanESM5, CMCC-ESM2, EC-Earth3, GFDL-ESM4, INM-CM4-8, EC-Earth3-Veg-LR, MPI-ESM1-2-HR, and NorESM2-LM. The chosen GCMs utilize relatively coarse resolution grids of 3.86 square miles or 0.25 degrees x 0.25 degrees. The temperature projections were categorized into four time periods: Historic (1950-2014), Near-future (2015-2040), Mid-century (2041-2070), and Late-century (2071-2100).
Figure 1. Map showing five study sites across the US Cotton Belt, mean annual temperature, and cotton acreages in 2022.
Projected changes in temperature
Maricopa, Arizona
At Maricopa, the average historical annual maximum and minimum temperatures were 37°C (98.6°F) and 21°C (69.8°F), respectively (Figures 2 and 3). Under the SSP1-2.6 scenario, the maximum air temperature is expected to rise by as much as 2°C (35.6°F) by the middle of the century, with no further changes anticipated in the later century, which reflects the outcomes of adopting a sustainabilityfocused growth and equality pathway (Figure 2). In contrast, the maximum temperature is projected to show a steady increase over future time frames under other SSPs, with the greatest rise of 5.3°C (41.5°F) predicted for the late century under SSP5-8.5 (Figure 2). For all SSPs, the projected average annual maximum temperature is set to increase by 1.5-3.8°C (34.7-38.8°F) in future time frames compared to the historical period (Figure 2). Projected trends indicate a rise of 1.4-4.0 °C (34.5-39.2°F) in minimum temperatures for future time frames compared to the historical period (Figure 3).
Halfway, Texas
At Halfway, the average annual maximum temperature for the historical period was 30.8°C (87.4°F), while the minimum temperature was 16.7°C (62.1°F) (Figures 2 and 3). Under the SSP1-2.6 scenario, the maximum air temperature is expected to increase by up to 3°C by mid-century, followed by a slight decline in the latecentury period. This reflects the implications of adopting a sustainability-focused growth and equality pathway (Figure 2). In contrast, under the other SSPs, a gradual increase in temperature is projected over the coming decades, with the highest average maximum temperature of 37.2°C (98.9°F) anticipated in the late-century period under SSP5-8.5 (Figure 2). Overall, across all SSPs, the average annual maximum temperature is expected to rise by 2-5°C (35.6-41°F) in future periods compared to the historical period (Figure 2). Similarly, future projections indicated that minimum temperature could increase by 2.3-5.1°C (36.1-41.1°F) across SSPs compared to the historical period (Figure 3).
Chillicothe, Texas
The Chillicothe, TX location was approximately 3°C (37.4°F) warmer than Halfway, TX during the historical period. The average annual maximum and minimum temperatures during the historical period were recorded at 33.5°C (92.3°F) and 19.7°C (67.5°F), respectively (Figures 2 and 3). Future projections for air temperature trends in Chillicothe mirrored those of Halfway (Figure 2). The projected average maximum temperature was forecasted to reach its peak at 36.2°C (97.2°F) in the midcentury under SSP1-2.6 (Figure 2). In contrast to SSP1-2.6, the temperature was predicted to rise steadily over the future periods, with the largest increase of 6.0°C (42.8°F) anticipated in the late century under SSP5-8.5 (Figure 2). Throughout the SSPs, the air temperature was expected to rise by 2.1-4.4°C (35.7-39.92°F) in future periods when compared to the historical period. In a similar manner, it was projected that the minimum temperature would rise by 2.1-4.7°C (35.7-40.5°F) across various SSPs in upcoming periods when compared to the historical data (Figure 3).
Camilla, Georgia
The average annual maximum temperature at Camilla, GA was 32.7°C (90.8°F) during the historical period, while the minimum averaged at 20.0°C (68°F) (Figures 2 and 3). Future projections indicate a continuous increase in the average maximum temperature, with the highest expected rise of 4.9°C (40.8°F) by the late century under the SSP5-8.5 scenario (Figure 2). Across various SSPs, the air temperature is anticipated to increase by 1.3°C to 3.4°C (34.3 to 38.1°F) in the future compared to the historical period. It was projected that the minimum temperature will increase by 1.7 to 3.9°C (35.1 to 39°F) across SSPs in future periods when compared to historical data (Figure 3).
Woodville, North Carolina
At Woodville, the average annual maximum and minimum temperatures for the historical period were recorded at 30.5°C (86.5°F) and 18.8°C (65.8°F), respectively (Figures 2 and 3). Under the SSP1-2.6 scenario, maximum air temperature is expected to rise by as much as 2°C (35.6°F) by the middle of the century, with no additional increase projected for the late-century period, highlighting the effects of selecting a sustainability-oriented growth and equality pathway (Figure 2). For the other SSPs, a steady rise in temperature was forecasted over future time frames, with the highest average maximum temperature of 35.3°C (95.5°F) anticipated in the late-century period under SSP5-8.5 (Figure 2). Among all SSPs, the projected increase in average annual maximum temperature in future periods compared to the historical period is estimated to be between 1.3°C (34.3°F) and 3.3°C (37.9°F). Future projections indicate that minimum temperatures are expected to rise by 1.7 to 3.9°C (35-39°F) when compared to historical averages (Figure 3).
Figure 2: Projected differences in the annual average maximum temperature between future periods and the historical period under four SSP scenarios at five study sites. The horizontal lines represent annual averages of maximum temperatures for the historic period.
Figure 3: Projected differences in the annual average minimum temperature between future periods and the historical period under four SSP scenarios at five study sites. The horizontal lines represent annual averages of minimum temperatures for the historic period.
Summary
Historically, Maricopa and Chillicothe sites have been among the warmer areas, while Halfway and Woodville have been relatively cooler among five locations across U.S. Cotton Belt. All study locations are expected to experience temperature increases under the higher SSP scenarios throughout the late century. Future projections indicated that, by mid-century, temperatures could rise under the SSP1-2.6 scenario. The projected maximum temperature increase was the highest at Halfway, with a rise of 6.4°C (43.5°F), followed by Chillicothe at 6.0°C (42.8°F) and Maricopa at 5.4°C (41.7°F) under SSP5-8.5 and late-century (Figure 2). The smallest projected increase in maximum temperatures was 4.8°C (40.6°F) for both Camilla and Woodville. The highest projected increase in minimum temperature was 6.8°C (44.2°F) for Halfway, followed by 6.5°C (43.7°F) for Chillicothe, 5.4°C (41.7°F) for Maricopa, and 5.2°C (41.3°F) for Woodville, with Camilla again having the lowest increase at 4.8°C.(40.6°F) Overall, the projections indicate that the increase in minimum (nighttime) temperatures exceeds the increase in maximum (daytime) temperatures for each location.
The research findings regarding projected temperature increases at study sites offer essential insights for researchers aiming to tailor site-specific adaptation strategies that address the challenges posed by rising temperatures. One practical measure might involve adjusting planting dates to circumvent the peak heat periods that coincide with critical growth phases, particularly during flowering and boll development— stages that are notably sensitive to heat stress. Adopting wider spacing when planting cotton could significantly enhance airflow within the crop canopy, leading to a reduction in canopy temperature and alleviating water stress. Additionally, a lower plant density may minimize competition among plants for limited water resources, further supporting optimal growth conditions. Implementing cultural practices such as intercropping and cover cropping can help buffer soil temperatures, decrease evaporation rates, and create more favorable microclimate conditions within the agricultural environment. As the climate challenges intensify, cotton breeders should prioritize developing new varieties that exhibit early maturity, possess robust root systems, and can efficiently cool their canopies. Traits such as enhanced pollen viability and improved boll retention in high-temperature (especially nighttime temperatures) scenarios are also crucial. Moreover, advancements in genetic engineering that target genes related to antioxidant pathways could significantly boost cotton plant resilience to heat stress. Timely irrigation practices are essential to maintaining plant turgor during critical growth phases, such as flowering and boll formation, thereby mitigating the adverse effects of heat stress. The implementation of efficient irrigation systems, such as drip irrigation combined with fertigation, would optimize water use efficiency and promote cooling within the root zone. Soil management practices, including conservation tillage and the application of soil amendments, can enhance the soil's capacity to retain moisture and moderate temperature fluctuations. Additionally, utilizing plant physiological tools could determine the physiological adaptations of cotton, such as increasing the levels of photoprotective pigment antioxidants, which can strengthen the cotton’s ability to withstand high temperatures. Furthermore, employing crop simulation models such as Decision Support System for Agrotechnology Transfer (DSSAT) or AquaCrop can facilitate the assessment of heat impacts on cotton growth and development, enabling farmers and agronomists to make informed management decisions that enhance their resilience to projected heat stress.
Acknowledgements
We are grateful to Cotton Incorporated for funding this project.
Disclaimer
This publication provides an objective summary of projected temperature increase across the cotton belt region of the United States and does not endorse or promote any particular brand, product, or trademark. Any references to product names, trademarks, or companies are included for informational purposes only.
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