Evidence of higher evapotranspiration in croplands than in forestlands in four Mississippi watersheds over the past decade

Authors: OUYANG, YING - Us Forest Service (FS); YANG, JIA - Oklahoma State University; Huang, Yanbo; LEININGER, THEODOR - Us Forest Service (FS); Chastain, Daryl

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2024
Publication Date: 8/7/2024
Citation: Ouyang, Y., Yang, J., Huang, Y., Leininger, T.D., Chastain, D.R. 2024. Evidence of higher evapotranspiration in croplands than in forestlands in four Mississippi watersheds over the past decade. Agricultural Water Management. 302(108992):1-8. https://doi.org/10.1016/j.agwat.2024.108992.
DOI: https://doi.org/10.1016/j.agwat.2024.108992

Interpretive Summary: Evapotranspiration (ET) contributes the largest amount of water loss from vegetated terrestrial surfaces and plays a critical role in the hydrological cycle and water resource management. Historically, forestlands have been widely recognized to lose more water through ET than croplands, particularly in semi-arid and arid regions. This study, using satellite remote sensing ET data product from MODIS (Moderate Resolution Imaging Spectroradiometer), compared the annual ET between two croplands (watersheds) and two forestlands (watersheds) in the Yazoo River basin (YRB), a humid subtropical region in Mississippi, USA, over a 21-year period from 2001 to 2021. The results indicated that the croplands had 19% higher annual ET than that of the forestlands in the recent 11 years, which occurred maybe because of the increase in irrigated cropland areas in the YRB during this period, providing more water for ET. The finding that croplands lost more water than forestlands through ET challenges the traditional understanding of how forests and crops influence ET in the humid subtropical region, which may need more scientific research to prove.

Technical Abstract: Evapotranspiration (ET) contributes the largest amount of water loss from vegetated terrestrial surfaces and plays a critical role in the hydrological cycle and water resource management. Historically, forestlands have been widely recognized to lose more water through ET than croplands, particularly in semi-arid and arid regions. Using remote sensing data from MODIS (Moderate Resolution Imaging Spectroradiometer) with an 8-day temporal and 500m spatial resolution, we compared the annual ET between two croplands (watersheds) and two forestlands (watersheds) in the Yazoo River basin (YRB), a humid subtropical region in Mississippi, USA, over a 21-year period from 2001 to 2021. Based on the Mann-Kendall test, there were very significant (t = 0.44 and p = 0.006) increasing trends in annual ET for the croplands over the 21-year period, but no such trends were observed for the forestlands during the same period. According to Pettitt’s test, there was an abrupt change (or turning point) in annual ET starting in 2011 for the croplands. Using the time at this turning point (i.e., 2011) along with the Kolmogorov-Smirnov test, we found that there was a very significant difference (a = 0.05) in annual ET between the croplands and the forestlands over the 11-year period from 2011 to 2021, while no such difference occurred between the croplands and forestlands over the 21-year period from 2001 to 2021. The results demonstrate that the croplands had 19% higher annual ET than that of the forestlands in the recent 11 years, which occurred because of the increase in irrigated cropland areas in the YRB during this period, providing more water for ET. The research finding that croplands lost more water than forestlands through ET challenges our traditional understanding of how forests and crops influence ET in the humid subtropical region.