South Africa Wine Research Projects

2. VITICULTURE RESEARCH NEW PROJECT

2.5 TERROIR

GENERATING HIGH RESOLUTION, VINE-SPECIFIC ACTUAL EVAPOTRANSPIRATION MAPS AT DAILY INTERVALS

SU-GEO TS 24-01 Dr Tara Southey, Department of Geography & Environmental Studies, Stellenbosch University Start date: 2024

AIM AND INDUSTRY RELEVANCE: Due to population and economic growth, climate change and the decline in water quality, South Africa faces water scarcity challenges. Accurate estimates of crop water demand through evapotranspiration (ET) modelling are increasingly important to improve irrigation management and maximise water use efficiency. This study aims to develop and demonstrate a methodology for generating high-resolution (10 m), daily, grapevine-specific, actual ET maps. The project has a six-phase work plan approach. 1. Review methods, algorithms and data sources for calculating actual ET (Eta). 2. Hourly Et0 values will be calculated for each weather station point. 3. Images from Sentinel-2 will be sourced and compared to existing crop coefficient (Kc) values using regression analysis. 4. The best-performing vegetation index-based Kc model from Workplan 3 will be combined with the Et0 surfaces from Workplan 2. 5. Inter-row areas with established cover crops (or dense weed populations) can significantly affect the growth and vigour signals received from the satellite. An attempt will be made to quantify this effect by comparing indices derived from 10 m resolution images to those derived from 50 cm resolution images. 6. Using in-field observations by an expert panel, the Eta surfaces from Workplan 4 will be evaluated at key grapevine growth stages and in response to irrigation and/or rainfall events. The project’s final phase involves engaging with industry role players to investigate the potential of integrating the developed method with existing irrigation scheduling tools and determine the appetite for offering ET0 and ETa maps through TerraClim.

SOUTH AFRICA WINE RESEARCH 2024

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