Century-Scale Assessment of Compound Dry-Hot Extremes across Space and Time

Abstract:

Droughts and hot extremes can occur concurrently, exacerbating their societal and environmental impacts. While one of these drivers may not necessarily be extreme by itself, the combination of multiple hazards (e.g., moderate drought and extreme temperatures) can lead to a so-called compound event. Using over a century of ground-based observations of precipitation and temperature from the United States Climate Divisional Database through the National Oceanic and Atmospheric Administration (NOAA) and a unique multivariate model, this study shows that compound dry and hot extremes have increased significantly in the past decades, a trend that is expected to continue under current global warming projections. Our results indicate that the area impacted by concurrent extremes has also increased significantly over the contiguous United States. Further, for the first time, the homogeneity (i.e., connectedness) of dry-hot extremes across space is explored. Findings suggest that dry-hot extremes have homogeneously enlarged over the last 122 years, pointing to increased probability of continental scale concurrence of extreme dryness and heat. Using a type of multivariate copula models known as “AND” scenario, the joint return periods of compound dry-hot extremes were derived. Results indicate alarming increases in very rare dry-hot extremes (i.e., joint return period of 75 years). Finally, the results show an interesting shift between the main drivers of dry-hot extremes over time. While a continental scale severe drought was the main driver of the dry-hot events in the 1930s, the observed warming trend has become the dominant driver in recent decades. These results provide extended understanding of spatiotemporal variation of compound dry-hot extremes which is critical for social-environmental adaptation planning as our planet continues to warm.