Sar Thet, the police chief of Battambang province, explained that although his officers try to take a hard line against rain bettors, the market is so diffuse and deep-rooted that there's little they can do. He denied, dubiously, that police accept or solicit bribes from bettors.
"Rain betting has existed for a long time and has now become the custom," he conceded. "Police do not support betting on rain, but it has also become a custom to them after so long."
It's unclear when rain betting first took root in Cambodia, but Ros Chantrabot, a prominent historian here, believes it was likely introduced by Chinese immigrants.
"In Cambodian history, we don't see any evidence of rain betting, just of praying for rain," Chantrabot said. "It must have originated from China, as only Chinese-Cambodians play it, and it's culturally very Chinese."
Vandara, 43, who has run a rain-gambling house out of his mobile telephone store in the city's Chamka Samrong commune since 1997, says the large concentration of ethnic Chinese in Battambang explains the game's immense popularity there. As he tells it, rain betting originated among tea farmers in China's Guangdong province, many of whom immigrated to the area after the Chinese Revolution.
A glass case of rhinestone-encrusted phones is on permanent display in front of Vandara's shop, but nobody pays much attention to them. The action all takes place in a dark corner inside, where Vandara's wife sits at a desk piled with stacks of Cambodian riel and Thai baht, six burbling walkie-talkies, and dozens of betting slips.
Vandara's office is a wooden platform five stories off the ground, where he perches with his 28-year-old assistant, Pheak. Here he spends most of his daylight hours sitting on the building's roof, watching the sky in order to set the house odds. They change approximately every three minutes, depending on the clouds. The men are surrounded by the tools of their trade. They use five walkie-talkies to communicate with men in the field and with Vandara's wife downstairs. Four cell phones keep them constantly in touch with sky-watchers on their payroll who are stationed in Pailin. Less frequently, they check the latest Internet weather reports. They smoke constantly.
Although all of the Battambang betting houses have their own techniques for measuring rainfall, there is only one official gauge of whether it has rained. By mutual agreement, this happens in an isolated and closely guarded mansion on the outskirts of town.
Although outsiders like me are forbidden from visiting the house, several bettors who had seen it described its elaborate procedure. A group of "watchers" monitor a stack of 13 layers of tissue paper on a table on the house's roof, which they must stay 3 meters away from at all times. If it rains enough to soak the tissues through so that water drips from them, it has officially rained and bets can be called in.
During my visit, rain broke just before 1 pm in a clear steady shower. Vandara's wife was glum. She had sold a lot of rain that morning, and lost a lot of money.
"Someone wins and someone loses every day," Vandara said with a shrug. "It's up to the odds, and up to the sky."
Additional reporting by Neou Vannarin