Bayesian Tail Risk Forecasting with Geopolitical Narratives and Range-Based Volatility
摘要
This study proposes a Bayesian semi-parametric framework for forecasting Value-at-Risk (VaR) and expected shortfall, with emphasis on tail risk dynamics driven by forward-looking geopolitical uncertainty. Narrative-based information is incorporated through the Geopolitical Threats Index (GPT), while market variability is captured using range-based volatility measures that provide stable high-frequency inputs. The model accommodates nonlinear and asymmetric dynamics in both the quantile and expected shortfall processes and introduces a threshold extension to capture regime-dependent tail behavior. Five competing model specifications are estimated within a unified Bayesian setting, enabling full probabilistic inference and coherent uncertainty quantification. Empirical analyses for Bitcoin and Brent crude oil futures evaluate predictive performance using loss-based scoring rules and regulatory backtests. The results show that incorporating geopolitical signals and threshold dynamics leads to substantial improvements in tail risk forecasting.