Meso and microclimate influence on Malbec, Syrah and Bonarda vine physiology and yield during a heatwave in Mendoza, Argentina.

Meso and microclimates (air temperature, radiation and relative humidity, in particular) influence physiological processes, grape ripening, and yield. Heatwave linked to climate change has been increasing both in length and frequency worldwide. In the semi-arid condition of Mendoza viticultural area (33°00'30.2"S), at the foot of the Andes Mountain (430-2.000 m a.s.l.), heatwaves have been intensifying, being necessary to develop mitigation tools to cope with. Overhead spray water treatment (OSWT) in vineyards, is a useful strategy to reduce physiological stress and increase yield. The aims of this work were 1) to calculate meso and microclimate indexes and 2) analyze their links to physiological processes, vine performances and ripening pattern in OSWT during heatwaves. Three cultivars Malbec, Bonarda and Syrah were treated in UNCuyo experimental vineyard, where a weather station allowed to characterize the mesoclimate. Within the canopy (microclimate) iButton temperature sensors were used. One heatwave (8 days-long) was identified during 2024 growing season. Physiological measurements, leaf and berry temperature were registered previous, during and after the heatwave. Four berry samples were collected from veraison to harvest (23 ± 1 Brix) to assess juice technological parameters. Previous to heatwave until harvest, temperature, relative humidity, and solar radiation indexes were calculated at meso scale; a thermal accumulation index was also calculated at micro scale at the same period. Correlation and regression were calculated between climate and physiological variables. OSWT decreased the thermal accumulation and increased the humidity within the canopy, which allowed the vines experience less physiological stress. Ripening patterns and yield were impacted differently by OSWT depending on the length of the varietal growing cycle, being most effective when the heatwave occurred late in the growing season. When it occurs in advance, varieties may show some recovery capacity, also including ripening and yield.