Name: Manuela Brunner 

Talk Title: Time scale determines the spatial patterns and extents of compound hot-dry events: an assessment using a multi-site multi-variable weather generator

Abstract: Compound hot and dry weather and climate events can lead to severe societal impacts across a range of their time scales and spatial extents. Still, these two characteristics have received little attention despite the growing interest in climate change impacts on compound events. Here, we investigate how event time scale relates to spatial patterns of compound hot-dry events, the spatial extent of compound events, and the importance of temperature and precipitation as drivers of compound event occurrence using a gridded data set for the United States. To study such rare spatial and multivariate events, we introduce a multi-site multi-variable weather generator (PRSim.weather), which enables simulation of a large number of spatial compound hot-dry events. PRSim.weather combines an empirical spatio-temporal model based on the wavelet transform and phase randomization with two flexible distributions for temperature and precipitation. Our model evaluation shows that the stochastic model realistically simulates distributional and temporal autocorrelation characteristics of temperature and precipitation at single sites, dependencies between the two variables temperature and precipitation, spatial correlation patterns, and spatial heat and drought indicators and their co-occurrence probabilities. Our compound event analysis demonstrates that (1) compound hot-dry events are most likely in the Northwestern and Southeastern United States independent of the analysis time scale and this likelihood decreases with increasing time scale, (2) the spatial extent and time scale of compound events are strongly related with sub-seasonal events showing the largest extents, and (3) the importance of temperature and precipitation as drivers of compound events varies with the time scale of the analysis, where temperature and precipitation are most important at short and seasonal time scales, respectively. We conclude that time scale is an important choice in compound event assessments and suggest that climate change impact assessments should evaluate joint events using several instead of a single time scale to understand fully how their compound event characteristics may evolve.

This talk is an invited talk at EVA 2021. View the programme here.