What's the biggest problem for illicit marijuana cultivators? In the Netherlands, it might be snow. According to local police, dwellers whose houses are oddly snow-free despite precipitation are being closely monitored and suspected of illegally cultivating marijuana.

On Thursday, Dutch police released a photo of one cannabis plantation in the city of Haarlem that was revealed due to a strange lack of white cover.

The cultivation of marijuana requires temperatures that are far above those common in residential buildings. Dutch news reports indicate that the police strategy of looking for snow-free areas is routinely used and that Dutch authorities have uncovered illegal pot plantations in residential homes throughout the country.

On Monday, for instance, officials had raided a pot farm in the city of Zutphen where they found a bedroom filled with 88 marijuana plants. Two days later, one person was arrested in Arnhem after police discovered a similar plantation.

The news might seem strange given the country's global reputation: the Netherlands is usually known for its liberal policies regarding the possession and growth of cannabis. However, the Dutch government only tolerates the cultivation of up to five cannabis plants, and the carriage of up to five grams of weed (0.17 ounces) per citizen.

Contrary to some other countries and states in the U.S., the Netherlands has recently made efforts to limit the consumption of marijuana. Only residents are allowed to consume the drug in coffee shops, but most municipalities do not enforce this rule.

In other countries, investigators have adopted more sophisticated approaches that do not depend on snowfall. British police officers use heat-sensing helicopters to uncover illegal cannabis plantations, for instance.

In 2013, the West Midlands Police department released a video on YouTube that showed a plantation through such a camera. Back then, authorities raided an apartment in which they found 143 cannabis plants.


West Midlands Police Deputy Air Operations Manager Martin Knowles said in 2013: "Our thermal cameras can detect unusually high temperatures coming from properties several thousand feet away – anyone growing cannabis on a commercial scale, using rows of heat lamps, runs the very real risk their criminality will be rumbled from the skies."

The Netherlands prove that normal eye vision might be equally sufficient to achieve this goal. On Thursday, Harleem's police emphasized this by advising citizens via Twitter to report suspicious rooftops.

As of Friday, however, reactions to this recommendation were primarily negative. Some users pointed to the fact that such advice could lead to wrong suspicions against sauna owners. One commentator was saddened by the loss of those "poor plants", whereas another Twitter user advised the police to investigate real criminals, such as bankers and police officers.

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