Observations of Changes in Vineyards Using Long-Term MODIS NDVI and LAI around Geothermal Power Plants

Turkey is ranked 4^th worldwide in terms of installed geothermal power plant (GPP) capacity (IRENA, 2023). On the other hand, there are some discussions regarding their impacts on valuable economic agricultural products like figs, olives, and grapes in intense GPP regions. Satellite-based NDVI and LAI data were used in several studies for agricultural vegetation monitoring, management and yield prediction in addition to forest vegetation. FAO (2023) utilizes monthly NDVI anomaly maps to investigate density and health of agricultural vegetation, especially for March-October covering vegetation period and phenological stages of viticulture in the Northern Hemisphere.

MODIS instruments on Terra and Aqua continuously collect NDVI and LAI data every 1-2 days in 36 spectral channels with global coverage. However, they have different spatial and temporal resolutions. Both have been used in several studies regarding vineyards. This study aims to observe changes in satellite-based NDVI and LAI for vineyards around GPPs in Turkey using several statistical analysis methods. Within this scope, the vineyard NDVI and LAI time series were obtained from 250m spatial, 16 days temporal resolutions NDVI and 500m spatial, 4 days temporal resolutions LAI between 2002-2023. All vineyard areas in the study region (AA) were defined using CORINE Land Cover (CLC) data. Three possible impacted (IA1-IA3) and two non-impacted vineyard areas (NIA1-NIA2) were selected considering prevailing wind directions and wind speeds, the capacity of GPPs, and the possible impact distances of emissions from the plants: one of which is the all-impacted area (AIA) consisting of IA1-IA3 within close proximity to GPPs and two of which are NIA1-NIA2. The correlations of NDVI and LAI were analyzed by the areas and each other. According to preliminary results, the 22-year annual profile of NDVI and LAI for AA were between 0.34-0.53 and 0.50-1.07, respectively. Moreover, the NDVI and LAI values vary from 0.26 to 0.63 and 0.30 to 1.48, respectively, between March and October in each year similar to the values found in the literature for the vegetation period for vineyards. The highest NDVI and LAI values were observed in NIA1 and NIA2. The lowest NDVI and LAI values were observed in IA2 and IA3. R (Spearman's correlation coefficients) values for AA are higher between AIA and IA1-IA3 compared to NIA1-NIA2. The lower R values are observed between NIA1 and all other areas.  

The trend, seasonal, and residual components in the NDVI and LAI time series were decomposed with seasonal and trend decomposition using LOESS. Moreover, the observations of NDVI and LAI changes were evaluated with meteorological and GPP-related parameters at phenological stages taking into consideration the pre-and post-GPP installations. The results demonstrate the patterns and changes for vineyards based on seasonality and other reasons, and give insight on whether there are any impacts by GPPs.

Keywords: NDVI, LAI, Vineyards, Geothermal Power Plants

References

Food and Agriculture Organization of the United Nations (FAO) (2023). Earth Observation. https://www.fao.org/home/en/

International Renewable Energy Agency (IRENA) (2023). Renewable Capacity Statistics 2023. https://www.irena.org