HKMA Stress Testing Scenario Design for Banks: Macroeconomic Variable Assumptions

The Hong Kong Monetary Authority (HKMA) published its updated Supervisory Policy Manual module on stress testing in October 2024, requiring all authorised institutions to recalibrate their scenario design frameworks by the first quarter of 2025. This directive follows a series of macroeconomic shocks—the rapid interest rate normalisation cycle of 2023-2024, the prolonged property market correction in Hong Kong, and the ongoing geopolitical fragmentation affecting trade finance flows. Banks that fail to embed realistic, severe, and institution-specific macroeconomic variable assumptions into their stress tests now face not only supervisory scrutiny but also potential capital add-ons under Pillar 2 of the Basel framework. The HKMA’s 2024 Annual Report explicitly noted that “the macroeconomic environment remains highly uncertain, and the resilience of the banking sector must be tested against plausible yet severe downside scenarios.” For compliance officers and risk managers, the core challenge is no longer whether to run stress tests, but how to design scenario narratives and variable assumptions that satisfy both the letter and the spirit of the HKMA’s expectations. This article sets out the regulatory framework, the approved methodology for macroeconomic variable selection, and the practical steps for constructing scenarios that will pass HKMA review.

The Regulatory Framework for Stress Testing Under HKMA Supervision

The HKMA’s Supervisory Policy Manual module SA-2, “Stress Testing,” provides the primary regulatory foundation. This module requires all authorised institutions to maintain a stress testing programme that covers credit risk, market risk, liquidity risk, and concentration risk. The legislation provides that the HKMA may, under Section 63A of the Banking Ordinance (Cap. 155), direct an institution to conduct additional stress tests if the authority considers the institution’s own scenarios insufficiently severe.

Step 1: Identify the Mandatory Scenario Categories

The HKMA requires banks to run at least three distinct scenario types: a baseline scenario reflecting the institution’s central forecast, an adverse scenario representing a moderate downturn, and a severely adverse scenario capturing a tail-risk event. The October 2024 circular introduced a fourth category: a “Hong Kong-specific stress scenario” that must reflect domestic vulnerabilities, including the property market correction and the interest rate sensitivity of mortgage portfolios.

The HKMA does not prescribe specific variable values for these scenarios. Instead, it requires each institution to justify its assumptions through a documented methodology that links macroeconomic variables to the institution’s own exposure profile. The authority’s 2023 Thematic Review on Stress Testing found that 14 of the 27 reviewed institutions had used variable assumptions that were “insufficiently differentiated” between the adverse and severely adverse scenarios, leading to a false sense of resilience.

Step 2: Select the Relevant Macroeconomic Variables

The HKMA expects institutions to include a minimum set of macroeconomic variables in their stress test models. These variables must cover three domains: domestic economic activity, external economic conditions, and financial market variables.

For domestic economic activity, the required variables include Hong Kong’s Gross Domestic Product (GDP) growth rate, the unemployment rate, and the Composite Consumer Price Index (CCPI) inflation rate. For external conditions, the HKMA expects institutions to model Mainland China’s GDP growth, the US federal funds rate, and the trade-weighted exchange rate of the Hong Kong dollar. Financial market variables must include the Hang Seng Index, the three-month Hong Kong Interbank Offered Rate (HIBOR), and residential property price indices.

The critical regulatory requirement is that these variables must move together in a coherent narrative. The HKMA’s 2024 guidance states that “scenarios must be internally consistent, meaning that the assumed paths of macroeconomic variables should reflect a plausible economic story.” A scenario that assumes a sharp rise in HIBOR alongside a booming property market, for example, would fail this consistency test.

Designing the Scenario Narrative and Calibrating Variable Paths

Once the variable set is defined, the institution must construct a narrative that explains how the economy arrives at the assumed stress conditions. The HKMA’s supervisory practice treats the narrative as a substantive requirement, not a procedural formality. During the 2024 annual stress test exercise, the HKMA requested written narratives from all major institutions and rejected three submissions where the narrative contradicted the variable assumptions.

Step 3: Build the Narrative Around Recognised Risk Drivers

The HKMA’s preferred approach is to anchor scenarios to recognised risk drivers that appear in its own Financial Stability Reports. The October 2024 Financial Stability Report identified four primary risk drivers for Hong Kong’s banking sector: a sharper-than-expected economic slowdown in Mainland China, a disorderly repricing of global risk premia, a prolonged downturn in the Hong Kong property market, and an escalation of geopolitical tensions affecting trade and capital flows.

A compliant narrative should select one or two of these drivers as the primary shock and then trace the transmission mechanism through the selected variables. For example, a severely adverse scenario might begin with a Mainland China GDP growth rate falling to 2.5% (the HKMA’s severely adverse assumption in its 2024 industry-wide stress test), which then depresses Hong Kong’s exports, raises the unemployment rate to 6.5%, and triggers a 25% decline in residential property prices over two years.

The HKMA does not require institutions to use the exact figures from its own stress tests. However, the authority’s 2023 Thematic Review noted that institutions whose assumptions were “materially less severe than the HKMA’s own severely adverse scenario” were required to provide additional capital planning documentation. The practical implication is clear: the severely adverse scenario should be at least as severe as the HKMA’s published scenario, and preferably more severe for institution-specific risk concentrations.

Step 4: Calibrate Variable Paths Using Historical Benchmarks and Forward-Looking Data

The HKMA expects institutions to use a combination of historical stress periods and forward-looking projections when calibrating variable paths. The historical benchmark most commonly referenced in HKMA publications is the 1997-2003 Asian Financial Crisis and SARS period, during which Hong Kong’s GDP contracted by 5.9% in 1998, unemployment peaked at 7.9% in 2003, and residential property prices fell by approximately 65% from their 1997 peak to their 2003 trough.

For the current cycle, the HKMA’s 2024 industry-wide stress test assumed a Mainland China GDP growth rate of 2.5%, a Hong Kong GDP contraction of 4.5%, an unemployment rate of 6.5%, and a property price decline of 25%. Institutions should note that these are aggregate assumptions. The HKMA’s approach is to set the severity at a level that would deplete the banking sector’s Common Equity Tier 1 (CET1) ratio by approximately 300 to 400 basis points over a two-year horizon.

The legislation provides that institutions must also consider institution-specific factors. A bank with a large mortgage portfolio concentrated in the New Territories, where property prices have fallen 18% from the 2021 peak according to the Rating and Valuation Department’s February 2025 data, should assume a steeper property price decline in its own scenarios than a bank with a diversified loan book.

Documentation, Validation, and Supervisory Review

The HKMA’s supervisory process places heavy emphasis on the documentation trail. The 2024 circular requires institutions to maintain a complete record of the scenario design process, including the rationale for variable selection, the sources of data, the methodology for calibration, and the results of any sensitivity analysis.

Step 5: Document the Assumption Justification

Each macroeconomic variable assumption must be supported by a written justification that references either historical data, published forecasts from recognised sources such as the Hong Kong Monetary Authority, the International Monetary Fund, or the Hong Kong Census and Statistics Department, or the institution’s own econometric modelling. The HKMA’s 2023 Thematic Review cited one institution for failing to document why it assumed a 0% decline in the Hang Seng Index in its severely adverse scenario, when the index had fallen 28% during the 2020 COVID-19 shock.

The documentation should also include a sensitivity analysis showing how changes in individual variable assumptions affect the institution’s capital ratios. The HKMA expects institutions to identify which variables have the greatest impact on their capital position and to explain why those variables are the most relevant for the institution’s risk profile.

Step 6: Validate the Scenarios Through Independent Review

The HKMA requires that stress testing scenarios be subject to independent validation, separate from the business lines that generate the exposures. The validation function must assess whether the scenarios are sufficiently severe, internally consistent, and relevant to the institution’s risk profile. The 2024 circular introduced a specific requirement that the validation report must include a comparison of the institution’s scenarios against the HKMA’s own published scenarios and against scenarios used by peer institutions.

The validation process should also test the stability of the model outputs. If small changes in variable assumptions produce disproportionately large changes in capital ratios, the institution must explain the non-linearity or adjust the model. The HKMA’s 2024 Annual Report noted that “several institutions have been required to enhance their scenario design after validation revealed excessive sensitivity to a single variable.”

Step 7: Prepare for Supervisory Challenge

The HKMA conducts an annual supervisory stress test for the largest institutions and reviews the internal stress tests of all authorised institutions on a risk-based schedule. During these reviews, the HKMA’s examiners will challenge the scenario assumptions by asking three standard questions: why the severity level was chosen, what historical precedent supports the assumed variable paths, and how the scenario accounts for the institution’s specific risk concentrations.

Institutions should prepare a written response to each of these questions in advance. The response should cite specific data points, reference HKMA publications, and explain any deviations from the HKMA’s own assumptions. A bank that assumes a slower property price decline than the HKMA’s 25% assumption, for example, must demonstrate that its mortgage portfolio has lower loan-to-value ratios or is concentrated in less vulnerable districts.

Actionable Takeaways for Compliance Officers and Risk Managers

• Review your institution’s current stress test scenarios against the HKMA’s October 2024 circular and ensure that a Hong Kong-specific stress scenario has been added to the mandatory scenario set.
• Calibrate the severely adverse scenario to be at least as severe as the HKMA’s published assumptions of 2.5% Mainland China GDP growth, a 4.5% Hong Kong GDP contraction, a 6.5% unemployment rate, and a 25% property price decline.
• Document the rationale for each macroeconomic variable assumption with a clear reference to historical stress periods, published forecasts, or internal modelling results.
• Conduct a sensitivity analysis to identify which variables have the greatest impact on your institution’s capital ratios and prepare a written explanation for any non-linear model behaviour.
• Schedule an independent validation of your stress test scenarios before the HKMA’s next supervisory review and ensure the validation report includes a comparison against the HKMA’s own industry-wide stress test results.

This does not constitute legal advice. Consult a solicitor or regulatory compliance professional for your specific institution’s obligations under the Banking Ordinance (Cap. 155) and the HKMA’s Supervisory Policy Manual.