We can make it rain in the deserts!
Meteorological Observations in Torbay on the U.K. South West Coast
During the main Holiday seasons it frequently rains here in Torbay. It can be hot and dry for weeks prior to the main holidays but as soon as the massive influx of motorists arrive the rain with uncanny synchronisation also arrives.
This could be just another coincidence but it does happen most years. Jokingly people have long argued that the holidaymakers bring the rains with them. And there may be some truth behind this.
What changes have occurred that might be responsible for causing it to rain during the main holidays and could we put this to good practice elsewhere?
Vehicle Exhaust emissions are increased when the seasonal influx of holidaying people arrive , especially during the last week in July and first week of August when most companies close for 2 weeks.
Can we make it rain in the deserts?
Seeding clouds with fine particles is a practice that involves releasing dust from aircraft’s and put to good effect where crops at risk from prolonged drought. Salt crystals for example have been used and the idea behind this is that droplets form around dust particles inducing rain to fall.
All vehicles release particles in their exhaust fumes and the hot exhaust gasses rise into the atmosphere along with a considerable amount of water and carbon dioxide or C02.
The combined weight of CO2 and H2O is emitted by burning one US gallon of gasoline is 27 pounds. One gallon of petroleum weighs 6.3 pounds, the amount of Oxygen converted to H2O and CO2 by burning the gasoline is 21.7 pounds and 7 pounds of water is produced.
The US Military for example are recovering 1 gallon of potable water from burning 2 gallons of fuel in a Hummer.
21 pounds of Oxygen is removed from the atmosphere by combustion with petroleum through the engine, and emitted from the exhaust as H2O and CO2.
When you multiply that 21 pounds by the consumption of gasoline by the local and holiday traffic patrolling the coastal roads it is not difficult to understand how vehicles could be responsible for priming the local climate and inducing rain.
The hot exhaust gasses rapidly cool lowering the air pressure next to the coast and the moisture laden clouds are drawn in from the sea as the air cools and is pulled down towards the ground.
A similar natural process over forested areas, where transpiration provides a drop in temperature of 2-4 degrees compared to arid land devoid of vegetation has been shown to induce more rainfall.
More to the point a heated tarmac road surface provides the opposite effect where hot dry air or thermals rise high into the atmosphere and effectively prevents the influx of moisture from the ocean to the land by causing an effective thermal barrier, much the same as the heated sands and stones on a desert coastline prevents moisture from fog, mist and rain clouds from crossing on to the parched arid landscapes.
On occasions the moisture from the ocean is sufficiently cooled to cause fog and provides us with a visible means of observing it's behaviour over various land surfaces.
In our particular part of the coast we are privileged to be visited by some unusual low level clouds, we call mist or fog, rolling along the coastline. This provides us with a visual understanding of how a seemingly innocent looking road surface and sandy beach can prevent moisture from crossing onto the land and condensing on the leaves of trees to fall to the soil.
In this video, during a rare occasion where moisture is visible, we can see a bank of fog hugging the coastline and moving along the coast rather than crossing on to the land, except for a narrow corridor of woodland no wider than the width of a dual carriageway in Preston, located in Torbay, Devon, UK.
The moisture is prevented from crossing on to the land and cannot cross over the hot dry coastline beyond the solar heated road surface.
On the ocean side of the road, we can clearly see that it is shrouded in fog, while the land side of the coastal road is bathed in bright sunshine and devoid of moisture during a very warm summers day. This event has been witnessed many times and can last for many hours as the mist rolls around like washing in a tumble dryer and is channelled along the coast.
Where the narrow corridor of trees meet the sea in Hollicombe the mist is observed to roll inland and hugs the wooded areas but goes no further than above the tree line. Walking in the trees on these particular days the temperature is several degrees below that outside of the trees and the air is saturated with water, the trees are dripping and the ground is moistened.
When the mist finally vanishes it remains shrouding the trees and the trees milk the remaining water from the air over several hours more
Thermals rising from the hot tarmac road can be seen as you drive along it. You can see the wavy thermal pattern as the heat rises. These thermals rise high into the atmosphere and form an invisible barrier against ocean born humidity. These same thermals cause the same barrier along desert coastlines and are undoubtedly responsible for the inherent lack of rainfall in these areas.
Trees transpire vast amounts of water into the atmosphere and in doing so remove the thermal barrier that prevents cloud and mist from crossing onto the land. They lower the temperature and as warm moist air rises it is cooled causing a downdraught which causes warm air to rise in a density flow and indeed this can be seen happening at times when dew point has been reached.
The UK holiday traffic in Torbay involves a massive increase in vehicles cruising along the hot roads.
The exhaust emissions contain collectively a vast amount of water vapour released into the atmosphere along with particles which rise due to the heat from combustion. These gasses quickly cool transferring the heat into the atmosphere and fall back towards the ground while the hot dry air rises again generating the same flow and return system that the trees perform.
This additional water from exhausts also blocks out some of the suns energy and like the trees removes the thermal barrier so that moisture from the ocean can again cross onto the land and fall as rain.