Is vote-buying behind India's $9 billion cash spike?

India's money supply has surged by as much as $9 billion in recent weeks, and the country's central bank is perplexed.

"We are trying to understand it," Reserve Bank of India chief Raghuram Rajan said last week.

Why do Indians have more cash on hand, and not in the bank? Theories abound. But the most likely explanation is also the most unsavory: Indians are flush with cash because of corruption ahead of elections in five states between now and the end of June.

"We see some possibility of around election time, cash with the public does increase. You can guess as to reasons why. We also guess," Rajan said. "You see some not just in the state which is going for elections, but also in neighboring states."

Indian media have widely interpreted the comments to be a reference to vote buying.

The scourge of vote buying in India is well documented. Journalists routinely uncover evidence that cash, alcohol, drugs and other incentives are traded for votes in state and national elections. The problem is so severe that the Indian Election Commission reportedly monitors regional airports in the hope of catching cash and other goods meant to be used as bribes.

"That money is paid to voters for their vote is known to those who are familiar with grass root polities of India," the nonprofit Centre for Media Studies wrote in a 2014 report. "The trend has become of threatening proportion to the very fundamentals of democracy."

The amount of extra cash in the system, which Rajan estimated at $7.5 billion to $9 billion, could reflect the massive number of Indians set to go to the polls. The five states holding elections -- Assam, Puducherry, Kerala, Tamil Nadu and West Bengal -- have a combined population of 225 million, which would rank them as the world's fifth most populous country.

Rajan left open the possibility that some other factor may explain the excess cash. But other theories, which include rumors that larger bank notes will be removed from circulation in a crackdown on corruption, are less convincing.

"There's something there," Rajan said. "We need to understand it better."

(CNN)