Non-linear Fiscal Effects of Uranium Price Shocks in Namibia

The analysis focuses on three fiscal outcome indicators, each representing a distinct transmission channel through which critical mineral price shocks influence public finances (Table 1). The mining revenue share (LMRSH), measured as the natural logarithm of mining revenue relative to total government revenue, and the overall fiscal balance (FBAL), expressed as a percentage of GDP, are flow-based indicators that contemporaneously respond to commodity price movements. Therefore, these variables capture fiscal stability channels, reflecting short-run budgetary pressure and revenue volatility. By contrast, the public debt-to-GDP ratio (LDEBT), expressed in natural logarithms, is a stock variable that evolves cumulatively and reflects the government’s capacity to meet its debt obligations without an unsustainable fiscal adjustment. Thus, we interpret LDEBT as a fiscal sustainability indicator that captures the long-term consequences of asymmetric commodity price shocks.

To ensure consistency across the model specifications, a common set of explanatory variables was included in all the estimations (Table 1). These include real GDP growth (GDPG), consumer price inflation (INF), the natural logarithm of mining value-added as a share of GDP (LMVA), the natural logarithm of the real effective exchange rate (LREER), and the natural logarithm of the real uranium price (LUP), which is deflated using the US CPI. In addition, a policy dummy variable (POLICY) is introduced, taking a value of one from 2021 onward to capture the implementation period of Namibia’s Minerals Beneficiation Strategy and zero otherwise.

本分析聚焦于三类财政结果指标，每类指标均代表关键矿产价格冲击影响公共财政的独特传导渠道（见表1）。采矿收入份额（LMRSH）以采矿收入占政府总收入的自然对数衡量；财政总余额（FBAL）以国内生产总值（GDP）的百分比表示，二者均为流量型指标，可对大宗商品价格波动做出即期响应。因此，这两类变量刻画了财政稳定渠道，反映短期预算压力与收入波动性。与之相对，公共债务占GDP比重（LDEBT）以自然对数形式表示，属于累积演化的存量变量，体现政府在无需实施不可持续财政调整的前提下履行债务偿付义务的能力。据此，我们将公共债务占GDP比重（LDEBT）视为财政可持续性指标，用以捕捉不对称大宗商品价格冲击的长期影响。

为确保不同模型设定的一致性，所有估计均纳入了统一的解释变量集合（见表1）。这些变量包括：实际GDP增长率（GDPG）、消费者物价通胀率（INF）、采矿增加值占GDP比重的自然对数（LMVA）、实际有效汇率（LREER）的自然对数，以及以美国消费者物价指数平减后的实际铀价（LUP）的自然对数。此外，还引入了政策虚拟变量（POLICY）：2021年及以后取值为1，用以捕捉纳米比亚《矿产加工增值战略》的实施周期，其余时期取值为0。