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How do droughts happen?
Answer 1:

Well this is a pretty complicated question. No one fully understands the causes because there are many factors that contribute to drought.

The first point to note is that the atmosphere is what we call a COMPLEX SYSTEM. Complex systems are all around us; the human body is one. An example: you go outside on a hot day; the sun falls on your body and you begin the heat up. Now the human body is a complex system. How does the “system’ respond to the influx of radiant energy?

Well you begin the SWEAT. Now as the sweat evaporates from your body (since the relative humidity is < 100%, it takes heat away from your body. That is , heat FROM YOUR BODY is used to vaporize the liquid water (sweat). Thus we see the body tries to regulate its own temperature by responding to a stimuli… the skin /body harts up due to external factor (sun light) and the body attempts to MODULATE this effect of body heating, by engaging in an activity (SWEATING) that OPPOSES the heating effect… By sweating, heat is REMOVED FROM your body and is taken away by evaporating water.

What does this have to do with DROUGHTS?

Well, the Earth’s atmosphere is another example of a vastly complicated COMPLEX SYSTEM. The climate and weather we live with are manifestations of the behavior of the Earth to spread the heat energy that comes into the EARTH, mainly at low latitudes around the globe.

This takes places by the movement of water currents in the oceans and by the currents of air we call winds. Atmosphere-ocean coupling affects northern hemisphere climate including California, mainly during the winter season, and the oceans play the most important role . Because plants put moisture BACK into the atmosphere (a process called evapotranspiration) if a dry spells occurs via random fluctuation in a complex system, then this can be AMPLIFIED by a positive feedback … Since without plants taking groundwater and putting it into the atmosphere, there is less moisture in the air and hence less precipitation. This is an example of a POSITIVE feedback the drier it gets, the even more dryer it becomes!!!!

So, it would be like the human body not sweating when its hot; the skin and body would get hotter and hotter !!!

Then the cause of drought can not be linked to any one simple factor, the details are in how the complex system we call climate, responds. What we do know is that increasing the concentration of carbon dioxide gas in the atmosphere means that MORE of the sun's incoming RADIANT energy remains WITHIN the atmosphere and oceans; and that, while causing more evaporation at low altitudes can actually dry out the atmosphere at higher temperate latitudes!!!

People that study the atmosphere and oceans have their work cut out for them because the system is very complicated. But it is also rewarding because with enough study we can figure out what is going on, and then take steps to enhance the feedbacks that help keep the Earth in a state that is good for us.


Answer 2:

Good question. There are a lot of people working on that and I'm pretty sure we don't have an answer yet.



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