Unconventional monetary policy and debt sustainability in Japan

We adapt to the Japanese case a model of stochastic debt sustainability within a monetary policymaking framework. The model incorporates the effects of unconventional monetary policy and its potential unwinding on sovereign debt dynamics. A scenario tree represents stochastic and correlated macroeconomic and fiscal variables, and a coherent risk measure allows to draw probabilistic inferences on sustainability. We calibrate the model to the Quantitative and Qualitative Easing (QQE) that Bank of Japan launched in 2013. Using a retrospective analysis, we find a large favourable effect of the QQE on sovereign debt dynamics. Forward-looking simulations under different exit strategies show that the termination and unwinding of the QQE could raise debt sustainability concerns. A sharp tightening of global financial conditions could have a similar negative impact on debt dynamics, requiring a fiscal adjustment to keep debt sustainable.