Short-term capital flows make exchange rate more volatile, posing new challenges for decision-makers in China and US

From July 2005 until December last year, China's renminbi appreciated steadily. The exchange rate then unexpectedly fell, hitting the bottom of the daily trading band set by the People's Bank of China for 11 sessions in a row. Though the renminbi has since returned to its previous trajectory of slow appreciation, the episode may have signaled a permanent change in the pattern of the exchange rate's movement.

As long as China was running a trade surplus and receiving net inflows of foreign direct investment, the renminbi remained under upward pressure. Short-term capital flows had little impact on the direction of the renminbi's exchange rate.

There were two reasons for this. First, thanks to an effective, albeit porous, capital-control regime in China, short-term "hot money", capital coming into China aimed at arbitrage, rent-seeking, and speculation, could not enter and then leave freely and swiftly. Second, short-term capital flows usually would strengthen rather than weaken upward pressure on the renminbi's exchange rate, because speculators, persuaded by China's gradual approach to revaluation, bet on appreciation.

So why, if China was still running a decent current-account surplus and a long-term capital surplus, did the renminbi suddenly depreciate, forcing the central bank to intervene, although not very vigorously, to prevent it from falling further?

Many economists outside of China have argued that the December depreciation resulted from betting by investors that Chinese policymakers, facing the prospect of a hard landing for the economy, would slow or halt currency appreciation. But if that were true, we would now be seeing significant long-term capital outflows and heavy selling of the renminbi for US dollars in China's foreign-exchange market.

We see neither reaction. More importantly, the renminbi's slow appreciation resumed fairly promptly after December's dip, while investors' bearish sentiments about China's economy have remained consistent.

In fact, the renminbi's sudden fall in December reflects China's liberalization of cross-border capital flows. That process began in April 2009, when China launched the pilot Renminbi Trade Settlement Scheme, which enables enterprises, especially larger ones, to channel their funds between the Chinese mainland and the Hong Kong Special Administrative Region. As a result, an offshore renminbi market, known as the CNH market, was created in Hong Kong alongside the onshore market, now dubbed the CNY market.

In contrast to the CNY market, the CNH is a free market. Given expectations of renminbi appreciation and a positive interest-rate spread between the mainland and Hong Kong, the renminbi had a higher value in dollar terms on the CNH market than on the CNY market. That difference led to active exchange-rate arbitrage by mainland importers and multinational firms - one form of capital inflows from Hong Kong to the mainland. Correspondingly, renminbi liabilities owed by mainland Chinese and multinationals increased, as did renminbi assets held by Hong Kong residents.

Exchange-rate arbitrage by mainland importers and multinationals creates upward pressure on the CNY market and downward pressure on the CNH market. In an economy with flexible interest and exchange rates, arbitrage eliminates the exchange-rate spread quickly. But, because China's exchange rate and interest rates are inflexible, the CNH-CNY spread persists, and arbitragers are able to reap fat profits at the economy's expense.

Last September, however, the financial conditions in Hong Kong changed suddenly. The liquidity shortage caused by the European sovereign debt crisis led developed countries' banks - especially European banks with exposure in Hong Kong - to withdraw their funds, taking US dollars with them. As a result, the CNH fell against the dollar. At the same time, the shortage of dollars had not yet affected the CNY, which remained relatively stable.

The CNH therefore became cheaper than the CNY. Consequently, mainland importers and multinationals stopped buying US dollars from the CNH market and returned to the CNY market. At the same time, mainland exporters stopped selling dollars in the CNY market and turned to the CNH market.

The dollar shortage created depreciation pressures on the CNY, which China's central bank declined to offset. The CNY was thus bound to fall, which it did last September.

Reverse arbitrage meant capital outflows from the mainland. Correspondingly, renminbi liabilities owed by mainlanders and multinationals decreased, as did renminbi assets held in Hong Kong. In fact, increases in financing costs and uncertainty about renminbi appreciation prompted a partial sell-off of renminbi assets by Hong Kong residents.

In short, because the Renminbi Trade Settlement Scheme made cross-border capital movements much easier, short-term flows have become a major factor in determining the renminbi's exchange rate. External shocks affect the offshore exchange rate first, and then feed through to the onshore exchange rate.

The renminbi will continue to appreciate in the near future, owing to strong economic fundamentals, but the inherent instability of short-term capital flows will make its exchange rate more volatile. This change is bound to pose new challenges for decision-makers in the United States and China, particularly as they engage in a fresh round of debate about China's exchange-rate policy.

The author is president of the China Society of World Economics and a former member of the monetary policy committee of the People's Bank of China. Project Syndicate