Threshold-based influence of currency devaluation on external debt sustainability: Insights from smooth transition regression and multiple thresholds nonlinear ARDL approaches

This study offers unique insights into the threshold-based influence of currency devaluation (CD) on external debt sustainability (EDS) in designated Sub-Saharan African (SSA) countries. The absence of evidence from this viewpoint, particularly in SSA, inspires this new assessment. On this premise, the study utilizes two innovative estimation procedures: smooth transition regression (STR) and multiple thresholds nonlinear ARDL (MTNARDL) to estimate the sign-based and magnitude-based asymmetric influence of CD on EDS. The outcomes indicate that first, an average CD threshold of 21.1% is consistent with EDS in the designated nations; second, a small CD significantly reduces the external debt–GDP ratio and improves sustainability, while a very high CD largely worsens the EDS problem; third, in the CD regime, devaluation has more detrimental effects on external debt burden; fourth, exceedingly large changes in exchange rate (whether positive or negative) essentially affect the countries’ EDS negatively; and fifth, the adverse effect of large depreciation on EDS is greater than that of large appreciation. The study recommends, amongst others, that heavily indebted countries with sizeable external debt denominated in foreign currency should, as a matter of urgency, avoid excessive and escalated large percentages of devaluation or exchange rate depreciation.