Analyzing the Combined Impact of Hot and Dry Conditions on Vegetation Health in the Southeastern US using Vine Copulas

Abstract Submission: Compound drought events, characterized by simultaneous anomalies in precipitation, temperature, and soil moisture, pose significant threats to agriculture, ecosystems, and society. Soil moisture is an important variable linking meteorological, hydrological, and agricultural droughts. It is influenced by precipitation, temperature, and environmental factors like terrain and soil composition, thereby playing a crucial role in both intensifying and mitigating drought effects. However, soil moisture alone doesn't consistently reflect drought impacts across different vegetation types due to variations in root depths and moisture availability at various soil layers. Therefore, evaluating vegetation health provides a more accurate representation of actual drought conditions. In this study, we examine the combined impact of hot and dry conditions—marked by low precipitation, high temperature, and diminished soil moisture—on vegetation health. To represent these factors, we utilize three indices: the Standardized Precipitation Evapotranspiration Index (SPEI) for precipitation and temperature, Root Zone Soil Moisture (RZSM) for soil moisture levels, and the Normalized Difference Vegetation Index (NDVI) for assessing vegetation health. We use vine copulas to model the three variables and compute the conditional probabilities of observing specific NDVI levels given preceding drought conditions indicated by SPEI and RZSM thresholds which helps us understand the risk that compound events poses the Southeastern US.

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