Evaluating the sensitivity of vegetation and water indices to monitor drought for three Mediterranean crops

Authors: YILDIRIM, TUGBA - Ege University; ZHOU, YUTING - Oklahoma State University; Flynn, Kyle; Gowda, Prasanna; MA, SHENGFANG - Independent Ecological Researcher; Moriasi, Daniel

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2020
Publication Date: 1/12/2021
Citation: Yildirim, T., Zhou, Y., Flynn, K.C., Gowda, P.H., Ma, S., Moriasi, D.N. 2021. Evaluating the sensitivity of vegetation and water indices to monitor drought for three Mediterranean crops. Agronomy Journal. 113:123-134. https://doi.org/10.1002/agj2.20475.
DOI: https://doi.org/10.1002/agj2.20475

Interpretive Summary: Understanding drought effects on health of crops within important producing locations, such as the Seferihisar-Kavakdere region, is vital for crop/field management. Therefore, this study aimed to utilize satellite-based vegetation indices, specifically Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), and Land Surface Water Index (LSWI), to evaluate the performance of three major crops (citrus, grape, and olive) under dry (2008), wet (2010), and normal (2015) climatic conditions. Results showed that all three crops were affected by drought despite two (citrus and grape) being irrigated. However, grape and olive were more affected by drought than citrus. More severe drought occurred during September and October because of a lack of precipitation and irrigation, as irrigation in these months is not a common practice in this region. Therefore, this study aimed to utilize and compare drought sensitivities of satellite-based vegetation indices. We calculated the relationships between different indices. All studied indices were closely related for citrus, grape and olive. The results showed that different vegetation indices are needed to detect drought from one crop to another under different climatic conditions. Our findings indicate that the irrigation applications in the drought year (2008) were not sufficient to alleviate the severe drought stress experienced throughout the winter and growing seasons.

Technical Abstract: Understanding drought effects on vegetative health for crop producing locations, such as the Seferihisar-Kavakdere region, is vital for management. Therefore, this study aimed to utilize Landsat-derived spectral vegetation indices, specifically Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), and Land Surface Water Index (LSWI), to evaluate the performance of three major crops (citrus, grape, and olive) under dry (2008), wet (2010), and normal (2015) climatic conditions. Results showed that all three crops were affected by drought despite two (citrus and grape) being irrigated. However, grape and olive were more affected by drought than citrus. More severe drought occurred during September and October because of a lack of precipitation and irrigation, as irrigation in these months is not a common practice in this region. Therefore, this study aimed to utilize and compare drought sensitivities of Landsat-derived spectral vegetation indices. We calculated the relationships between different indices with coefficient of determination (R2). All studied indices were closely related (0.48=R2=0.98) for citrus, grape and olive. EVI and LSWI were greater than NDVI when NDVI values were greater than 0.65 for citrus and LSWI values were larger than NDVI when NDVI values were greater than 0.6 for grape and olive during the wet year. The results showed that different VIs are needed to detect drought from one crop to another under different climatic conditions. Our findings indicate that the irrigation applications in the drought year (2008) were not sufficient to alleviate the severe drought stress experienced throughout the winter and growing seasons.