Deliberate Changes to weather: Cloud seeding, Dam construction, Greenhouses

Greenhouses

• These are used to grow plants that are susceptible to frost during frosty conditions.
• They create a micro-climate.
• They are made up of glass or a thin layer of polythene usually colored green hence their name.
• Short UV waves from the sun can pass through the glass/plastic.
• When these heat the ground they are converted into longer infra-red waves (heat) which cannot pass through the plastic.
• The result is that greenhouses are warmer than the surrounding areas.

How a greenhouse works. Image via Hydroponics.

Other methods used to protect crops from frost

• Heating the lower layers of the soil using either primitive oil fired “smudge pots” or modern gas or electrically powered frost prevention heaters.
• Covering the crops using a thin layer of polythene for example growing tunnels also known as polythene tunnels.
• Spraying the crops with water which acts as an insulator although the efficacy of this method is doubtful at best and it is useless against extreme frost/cold.
• Blowing air around the fields in order to mix the cold layers of air below with the warmer lays above.

Cloud seeding

A cloud seeding plane. Image via DavidStockMan

• Not all condensation leads to precipitation sometimes due to the lack of condensation nuclei in the atmosphere.
• Cloud seeding less well known as rain making involves the injection of silver iodide or dry ice into clouds.
• In a natural process the clouds would have been provided with materials like soot, dust, sea salt, volcanic ash and ice to use as nuclei.
• Silver iodide or dried is sprayed into likely looking clouds in a bid to spur precipitation.
• The clouds’ droplets grow bigger around the introduced nuclei and eventually fall as rain.
• The success of cloud seeding depends on the clouds being seeded.
• Arguments have been made that in most cases rain would have eventually fallen from the seeded clouds.
• There have also been allegations of “rain stealing” where people contend that a seeded cloud would have taken its rain elsewhere (usually neighboring areas) where rain would have fallen were it not for the interference of cloud seeding.

How cloud seeding works. Image via NSW

Dam construction

Mini “Tornado” over Lake Victoria. Image by National Geographic.

• Dams can change weather conditions in the vicinity  by creating a humidity and precipitation.
• The areas surrounding Lake Kariba receive more precipitation when compared to the more further areas ever since the dam was constructed.
• Lake shore breezes not unlike Sea and Land breezes also occur around the Lake.
• Areas around the Lake are generally cooler and the diurnal temperature range smaller than that of areas further from the Lake.
• Research has also shown that Lakes can cause freak rain storms for exam water spouts/mini tornadoes sometimes occur on and around the Lake.

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