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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Publications at this Location » Publication #426401
Title: Increased drip irrigation during heatwaves does not alter land surface temperature and evapotranspiration

Author
item GAL, ANDREW - University Of California, Davis
item BAMBACH, NICOLAS - University Of California, Davis
item McElrone, Andrew
item Knipper, Kyle
item BAGSHAW, SOPHIA - University Of California, Davis
item CASTRO-BUSTAMANTE, SEBASTIAN - University Of California, Davis
item EBERT, LOGAN - University Of California, Davis
item GALEANO, MARTINA - University Of California, Davis
item RAAB, NICOLAS - University Of California, Davis
item DOKOOZLIAN, NICK - E & J Gallo Winery
item SANCHEZ, LUIS - E & J Gallo Winery
item FORRESTEL, ELISABETH - University Of California, Davis
item NOCCO, MALLIKA - University Of Wisconsin

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2025
Publication Date: 9/1/2025
Citation: Gal, A., Bambach, N., McElrone, A.J., Knipper, K.R., Bagshaw, S., Castro-Bustamante, S., Ebert, L., Galeano, M., Raab, N., Dokoozlian, N., Sanchez, L., Forrestel, E.J., Nocco, M. 2025. Increased drip irrigation during heatwaves does not alter land surface temperature and evapotranspiration. Agricultural Water Management. Volume 319, 1 October 2025, 109781. https://doi.org/10.1016/j.agwat.2025.109781.
DOI: https://doi.org/10.1016/j.agwat.2025.109781

Interpretive Summary: Heatwave frequency, duration, and intensity are increasing in important agricultural regions and pose issues for winegrape production in California. Growers often utilize supplemental irrigation during these events with the intent of cooling the vines and vineyard, but work is still needed to dial in the exact amounts of water needed to achieve these results. Supplemental water was found to positively impact vine physiology by maintaining higher photosynthesis and transpiration during the heatwave but had little effect on the overall microclimate of the vineyard when measuring whole canopy and soil temperatures with ground based and remotely sensed systems. Delivery of some supplemental water during heatwaves helped vine performance but showed limited impact on temperatures of the vineyard overall.

Technical Abstract: The frequency, duration, and intensity of heatwaves is threatening the stability of perennial crops, including winegrapes. Winegrapes are becoming increasingly irrigated with low-pressure, low-flow micro-irrigation systems (e.g., drip, micro-sprinklers) to address water scarcity. Heatwaves cause both heat and water stress on winegrapes, so many growers commonly increase irrigation to cope with heatwaves. However, the effects of this practice on biometeorological vineyard responses have not been extensively studied. We characterized biometeorological and complementary physiological responses to different drip irrigation treatments surrounding three heatwaves in 2021 from plant to vineyard scale using a combination of remote and proximal sensing approaches – satellite, drone, and tower-based methods – to quantify land surface temperature (LST) and actual evapotranspiration (ETa). We further separated LST into canopy and soil components using a segmentation approach. Additionally, we measured soil water content, leaf-level vine responses including stomatal conductance, net photosynthesis, transpiration, stem and leaf water potentials, and radiometric leaf temperatures. Resembling common viticultural practices, drip irrigation treatments were only implemented surrounding heatwaves and included 60%, 90%, and 120% of the estimated crop evapotranspiration (ETc). Though transpiration, stomatal conductance, CO2 assimilation, and yield increased with moderate increases in drip irrigation, these physiological responses did not translate to differences in radiometric canopy temperature. ETa and LST patterns followed the same ranking by treatment throughout the season, which did not align with or respond to differential drip irrigation treatments. Soil surface temperatures also did not align with or respond to differential drip irrigation treatments. Findings from this study suggest that increased drip irrigation addresses vine water stress and increases leaf transpiration during heatwaves, but does not provide evaporative cooling benefits at larger scales previously demonstrated by high-pressure, high-flow irrigation systems (e.g. center pivot irrigation). Findings from this study can be used to inform optimal irrigation and heat management practices for agriculture production during heatwaves.