Why this August was a particularly bad month for emerging-market investors

Argentina imploded. Beijing let the yuan slip to the lowest in at least a decade. Global central banks signaled they’re spooked about slowing growth by rushing to cut rates. By almost any measure, August was a month to forget for emerging-market investors.

Consider the following: Developing-nation currencies had their worst August in at least 22 years, puncturing a carry trade bet that had just begun to turn positive. Investors yanked so much cash from exchange-traded funds that flows are poised to turn negative for the year. On top of that, dollar-bond sales fell to a 42-month low.

Malcolm Dorson, who helps manage