Market procyclicality and systemic risk

We develop a model that captures, at the same time, the temporal dynamics of single-firm credit risk and the contagion across banks via a network of obligations and common assets. In particular, we enrich the continuous-time modelling approach of default by accounting explicitly for the procyclical loop between asset prices and leverage. Contagion can spread well before any default occurs, through the value of the obligations held by counterparties. Moreover, the extent of procyclicality effects depends explicitly on the structure of both the interbank network and the asset bank network. We analyse the model in a simplified scenario of a densely connected core of banks and we carry out a systematic investigation of how procyclicality emerges from the multiplicative interplay of market illiquidity and tightness of capital requirements.     

Contagion in the interbank market and its determinants

Carrying out interbank contagion simulations for the German banking sector for the period from the first quarter of 2008 to the second quarter of 2011, we obtain the following results: (i) The system becomes less vulnerable to direct interbank contagion over time. (ii) The loss distribution for each point in time can be condensed into one indicator, the expected number of failures, without much loss of information. (iii) Important determinants of this indicator are the banks’ capital, their interbank lending in the system, the loss given default and how equal banks spread their claims among other banks.     

Modelling the emergence of the interbank networks

Interbank contagion has become a buzzword in the aftermath of the financial crisis that led to a series of shocks to the interbank market and to periods of pronounced market disruptions. However, little is known about how interbank networks are formed and about their sensitivity to changes in key bank parameters (for example, induced by common exogenous shocks or by regulatory initiatives). This paper aims to shed light on these issues by modelling endogenously the formation of interbank networks, which in turn allows for checking the sensitivity of interbank network structures and hence, their underlying contagion risk to changes in market-driven parameters as well as to changes in regulatory measures such as large exposures limits. The sequential network formation mechanism presented in the paper is based on a portfolio optimization model, whereby banks allocate their interbank exposures while balancing the return and risk of counterparty default risk and the placements are accepted taking into account funding diversification benefits. The model offers some interesting insights into how key parameters may affect interbank network structures and can be a valuable tool for analysing the impact of various regulatory policy measures relating to banks’ incentives to operate in the interbank market.     

Modelling Deposit Insurance Scheme Losses in a Basel 2 Framework

This paper extends the existing literature on deposit insurance by proposing a new approach for the estimation of the loss distribution of a Deposit Insurance Scheme (DIS) that is based on the Basel 2 regulatory framework. In particular, we generate the distribution of banks’ losses following the Basel 2 theoretical approach and focus on the part of this distribution that is not covered by capital (tail risk). We also refine our approach by considering two major sources of systemic risks: the correlation between banks’ assets and interbank lending contagion. The application of our model to 2007 data for a sample of Italian banks shows that the target size of the Italian deposit insurance system covers up to 98.96% of its potential losses. Furthermore, it emerges that the introduction of bank contagion via the interbank lending market could lead to the collapse of the entire Italian banking system. Our analysis points out that the existing Italian deposit insurance system can be assessed as adequate only in normal times and not in bad market conditions with substantial contagion between banks. Overall, we argue that policy makers should explicitly consider the following when estimating DIS loss distributions: first, the regulatory framework within which banks operate such as (Basel 2) capital requirements; and, second, potential sources of systemic risk such as the correlation between banks’ assets and the risk of interbank contagion.     

基于共同冲击和异质风险叠加传导的风险传染研究——来自中国上市银行网络的传染模拟

本文将银行系统遭遇外部共同冲击作为研究起点,建立了一个共同冲击和异质风险交互传导与放大的简化模型,冲击的传导包括“原始冲击”、“增量冲击”和“违约冲击”三个风险传染阶段。基于2018年我国15家上市银行的股票收益率和年报数据、2006年至2018年的银行评级数据,本文构建了贝叶斯分层图模型和银行间拆借矩阵,并利用蒙特卡洛模拟测度不同触发银行所引发的系统性风险损失、单个银行的系统性风险杠杆能力(文中定义为“传染乘数”指标)以及政府监管介入的效果。模拟结果显示:共同冲击损失远大于异质风险损失;规模和网络关联性是决定传染乘数的重要因素,且当规模因素不突出时,网络关联性对传染乘数的决定作用相对更强,极容易出现小规模、高关联性银行具有较高的传染乘数;当银行风险资产损失率在10%至25%之间时,造成系统性风险损失的杠杆能力普遍增强;政府监管介入能较好地降低系统性风险。本研究的相关结论为系统性风险的监管设计提供经验证据和参考。     

Assessing financial contagion in the interbank market: Maximum entropy versus observed interbank lending patterns

Interbank markets allow banks to cope with specific liquidity shocks. At the same time, they may represent a channel for contagion as a bank default may spread to other banks through interbank linkages. This paper analyses how contagion propagates within the Italian interbank market using a unique data set including actual bilateral exposures. Based on the availability of information on actual bilateral exposures for all Italian banks, the results obtained by assuming the maximum entropy are compared with those reflecting the observed structure of interbank claims. The comparison indicates that, under certain circumstances, depending on the structure of the interbank linkages, the recovery rates of interbank exposures and banks’ capitalisation, the maximum entropy approach overrates the scope for contagion.     

A network model of systemic risk: stress testing the banking system1

Although there are many definitions of systemic risk, most agree that it manifests itself by an initial shock that results in the failure of one or more banks and then spreads out to the entire system by a contagion mechanism which can result in the failure of more banks in the system. Assuming that bank failures in the initial shock are randomly dependent on the failure probabilities of the individual banks and that the ensuing contagion process is deterministic, depending on interbank exposures, in this paper we propose a network model to analyse systemic risk in the banking system that, in contrast to other proposed models, seeks to obtain the probability distribution of losses for the financial system resulting from the shock/contagion process. Thus, calculating the probabilities of joint failures by simulation and assuming that the matrix of bilateral interbank exposures is known, we represent systemic risk in the financial system by means of a graph and use discrete modelling techniques to characterize the dynamics of contagion and corresponding losses within the network. The probability distribution of losses, risk profile for the Mexican banking system, is obtained through an efficient, complete enumeration procedure of all possible bank default events in the system. This, in turn, allows the use of the wide variety of well-established risk measures to describe the fragility of the financial system. Additionally, the model allows us to perform stress tests along both the bank default probabilities and the interbank exposures and is used to assess the risk of the Mexican banking system. Copyright © 2009 John Wiley & Sons, Ltd.     

Borrowers under water! Rare disasters,regional banks,and recovery lending

We show that local banks provide corporate recovery lending to firms affected by adverse regional macro shocks. Banks that reside in counties unaffected by the natural disaster that we specify as macro shock increase lending to firms inside affected counties by 3%. Firms domiciled in flooded counties, in turn, increase corporate borrowing by 16% if they are connected to banks in unaffected counties. We find no indication that recovery lending entails excessive risk-taking or rent-seeking. However, within the group of shock-exposed banks, those without access to geographically more diversified interbank markets exhibit more credit risk and less equity capital.     

TARP announcement,bank health,and borrowers’ credit risk

Theory suggests that unhealthy banks exhibit more pronounced flight-to-quality behavior during financial crises and, hence, the infusion of capital through unhealthy banks is less effective in relieving the liquidity shocks of vulnerable borrowers. We test these predictions by investigating how the financial health of leading US banks influenced their borrowers’ credit risk surrounding the announcement of the Troubled Asset Relief Program (TARP). Changes in borrower credit risk, measured by credit default swap (CDS) spreads, should reflect the expected relief from liquidity shocks and other benefits of rescuing banks, such as maintaining the existing lending relationships. Consistent with the theory, prior to the TARP capital infusions, unhealthy banks’ borrowers with high leverage experienced a greater increase in their credit risk relative to similar healthy banks’ borrowers. Following the event, the CDS market anticipated less liquidity relief to these vulnerable unhealthy banks’ borrowers, but more liquidity relief to the vulnerable healthy banks’ borrowers.     

Interbank Credit Lines as a Channel of Contagion

This paper assesses the potential for contagion in the Swiss interbank market using new data on bilateral bank exposures as well as on credit lines. A simulation approach is applied to assess the banking system's inherent instability. Moreover, the spill-over effects of a simulated default situation in the interbank market on the liquidity and solvency of banks are measured. The main findings are, first, that there is a substantial potential for contagion. Second, the exposure as well as the credit line contagion channel are relevant for Switzerland. Third, a lender of last resort intervention could reduce spill-over effects remarkably. Finally, the structure of the interbank market has considerable impact on its resilience against spill-over effects: Centralized markets are more prone to contagion than homogenous ones. JEL classification: C81, G21. The opinions expressed herein are my own and not those of the Swiss National Bank.     

Interbank connections,contagion and bank distress in the Great Depression✰

Liquidity shocks transmitted through interbank connections contributed to bank distress during the Great Depression. New data on interbank connections reveal that banks were vulnerable to closures of their correspondents and their respondents. Further, banks were less responsive to network liquidity risk in their management of cash and capital buffers after the Federal Reserve was established, suggesting that banks expected the Fed to reduce that risk. The Fed's presence weakened incentives for the most systemically important banks to maintain capital and cash buffers against liquidity risk, and thereby likely contributed to the banking system's vulnerability to contagion during the Depression.     

The International Transmission of Bank Liquidity Shocks: Evidence from an Emerging Market

I exploit the 1998 Russian default as a negative liquidity shock to international banks and analyze its transmission to Peru. I find that after the shock international banks reduce bank‐to‐bank lending to Peruvian banks and Peruvian banks reduce lending to Peruvian firms. The effect is strongest for domestically owned banks that borrow internationally, intermediate for foreign‐owned banks, and weakest for locally funded banks. I control for credit demand by examining firms that borrow from several banks. These results suggest that international banks transmit liquidity shocks across countries and that negative liquidity shocks reduce bank lending in affected countries.     

The formation of financial networks

Modern banking systems are highly interconnected. Despite various benefits, linkages between banks carry the risk of contagion. In this article, I investigate whether banks can commit ex ante to mutually insure each other, when there is contagion risk in the financial system. I model banks' decisions to share this risk through bilateral agreements. A financial network that allows losses to be shared among various counterparties arises endogenously. I characterize the probability of systemic risk, defined as the event that contagion occurs conditional on one bank failing, in equilibrium interbank networks. I show that there exist equilibria in which contagion does not occur.     

The relationship between liquidity risk and credit risk in banks

This paper investigates the relationship between the two major sources of bank default risk: liquidity risk and credit risk. We use a sample of virtually all US commercial banks during the period 1998–2010 to analyze the relationship between these two risk sources on the bank institutional-level and how this relationship influences banks’ probabilities of default (PD). Our results show that both risk categories do not have an economically meaningful reciprocal contemporaneous or time-lagged relationship. However, they do influence banks’ probability of default. This effect is twofold: whereas both risks separately increase the PD, the influence of their interaction depends on the overall level of bank risk and can either aggravate or mitigate default risk. These results provide new insights into the understanding of bank risk and serve as an underpinning for recent regulatory efforts aimed at strengthening banks (joint) risk management of liquidity and credit risks.     

‘Slow-burn’ spillover and ‘fast and furious’ contagion: a study of international stock markets

‘Fast and furious’ contagion across capital markets is an important phenomenon in an increasingly integrated financial world. Different from ‘slow-burn’ spillover or interdependence among these markets, ‘fast and furious’ contagion can occur instantly. To investigate this kind of contagion from the US, Japan and Hong Kong to other Asian economies, we design a research strategy to capture fundamental interdependence, or ‘slow-burn’ spillover, among these stock markets as well as short-term departures from this interdependence. Based on these departures, we propose a new contagion measure which reveals how one market responds over time to a shock in another market. We also propose international portfolio analysis for contagion via variance decomposition from the portfolio manager’s perspective. Using this research strategy, we find that the US stock market was cointegrated with the Asian stock markets during four specific periods from 3 July 1997 to 30 April 2014. Beyond this fundamental interdependence, the shocks from both Japan and Hong Kong have significant ‘fast and furious’ contagion effects on other Asian stock markets during the US subprime crisis, but the shocks from the US have no such effects.     

Financial stability and Basel II

The Basel II Advanced Internal Ratings (AIRB) approach is compared to capital requirements set using an equilibrium structural credit risk model. Analysis shows the AIRB approach undercapitalizes credit risk relative to regulatory targets and allows wide variation in capital requirements for a given exposure owing to ambiguity in the definitions of loss given default and exposure at default. In contrast, the Foundation Internal Ratings Based (FIRB) approach may over-capitalize credit risk relative to supervisory objectives. It is unclear how Basel II will buttress financial sector stability as it specifies the weakest regulatory capital standard for large complex AIRB banks.      

An Assessment of Basel II Procyclicality in Mortgage Portfolios

In this paper we develop a probability of default (PD) model for mortgage loans, taking advantage of the Spanish Credit Register, a comprehensive database on loan characteristics and credit quality. From that model, we calculate different types of PDs: point in time, PIT, through the cycle, TTC, average across the cycle and acyclical. Then, we compare capital requirements coming from the different Basel II approaches. We show that minimum regulatory capital under Basel II can be very sensitive to the risk measurement methodology employed. Thus, the procyclicality of regulatory capital requirements under Basel II is an open question, depending on the way internal rating systems are implemented and their output is utilised. We focus on the mortgage portfolio since it is one of the most under researched areas regarding the impact of Basel II and because it is one of the most important of banks’ portfolios.     

Interbank contagion and resolution procedures: inspecting the mechanism

This paper develops a network model of a stylized banking system in which banks are connected to one another through interbank claims, which allows us to study the diffusion of default avalanches triggered by an exogenous shock under a number of different assumptions on the degree of interconnectedness, level of capitalization, liquidity buffers, the size of the interbank market and fire-sales. We expand upon the existing literature by comparing two alternative resolution mechanisms: (i) liquidations triggered by either illiquidity or insolvency-related distress implying asset sales and compensation of creditors; and (ii) a bail-in mechanism avoiding bank closure by forcing a recapitalization provided by bank creditors. Our model speaks to how contagion dynamics unravel via illiquidity-driven defaults in the first case and higher-order losses in the latter one. Within this framework, we show how the liquidity risk externality can be resolved, and we put forward a macro-criterion to assess the adequacy of the liquidity ratio introduced with Basel III.     

债券违约对流动性影响的传染效应研究

2014年以来我国信用债市场违约事件频发,信用风险的积聚可能引发债券市场流动性恶化。本文以2014―2019年交易所和银行间市场信用债为研究对象,实证考察违约事件对债券流动性影响的传染效应。研究发现:违约事件在同一发行主体的债券之间具有流动性传染效应,当公司的某期债券出现违约时,公司其他未到期债券的流动性水平显著下降;违约事件对同行业其他公司债券的流动性具有传染效应,当行业中出现债券违约事件时,行业内其他公司的债券流动性显著降低;违约事件爆发越密集或者违约事件越严重,对债券流动性的负面影响越大,而且民营企业债受到的影响要大于国有企业债,低信用等级债受到的影响要大于高信用等级债;在市场密集爆发违约事件或出现较为严重的违约事件时期,宏观流动性增加能够改善债券流动性。