- 01 Oct 2004 10:29
#468111
The general concensus is that most of NSW has been in a drought for about 3-4 years. The further west you go, the longer the drought, where farmers in the far west complain of anything from a 5 year to a 10 year drought. There is a worsening water crisis in the major cities which is attributed to the "drought". The trouble with using the term "drought" is that it assumes that there will be a return to wetter conditions. Why is this assumed? The truth is, NSW rainfall averages have been falling steadily over 10 years or more.
Most people attribute the "drought" to a common phenomenom experienced here called the "El Nino" effect - which is a shifting ocean current in the pacific, which supposedly brings drought to eastern Australia, and the opposite to South America. Certainly El Nino has been linked to previous droughts, most notably in 1982-83. However, El Nino should result in a (relatively) short period of drougth, followed by a period of abnormally high rainfall (known as "La Nina"). Instead, we have been experiencing only drought - more or less for the last 10 years. The El Nino phenomenom is definitely a real event, which can be quantified using the Southern Oscilation Index (SOI) but scientists are unsure how exactly it effects rainfall patterns in Eastern Australia.
Instead, I have a different theory:
we are not in a drought, we are actually experiencing a long term decrease in rainfall patterns caused by global warming. This is only my own reasoning, but its logical that this is what would happen: the area that is affected by this "drought" (SE Australia) relies heavily on the frontal systems that pass the region courtesy of the belt of high pressure cells at this latitude - the so called "Ferrel Cell". These pass from west to east, and as they rotate in an anti-clockwise motion, they bring cold air from the arctic in a SW direction. As the winds reach further north, they meet the warmer air of the previous high pressure cell and where the warm and cold air meets, a "cold front" is created, thus:
this is in fact the main source of rainfall in the region. What happens in an El Nino event, is that the northerly air that feeds moisture into these fronts "dries up" because of what happends to the current in the Pacific ocean. Importantly, these frontal systems are still there during El Nino, they just don't produce much rain. However, what we have been experiencing recently is something different. Rather than having "dry" fronts passing through, we simply haven't been getting the fronts. Why? Invariably they end up passing too far south and miss most of NSW. Here's where global warming comes in: a warmer earth should result in a larger Hadley Cell - the belt of low pressure along the equator caused by the intense heat of the sun. Now the Ferrel Cell starts north (northern hemisphere) and south (southern hemisphere) of where the Hadley Cell finishes. Therefore, its logical to conclude that global warming would result in the Ferrel Cell existing further south in the Southern Hemisphere. In real terms, this would mean that the high pressure cells which pass Australia from west to east, would now pass further south. If this was indeed what is happening, then this would have huge ramifications on Australia's weather: the southern arm of the high pressure cells would extend further south, and they would be less likely to extend far enough north to produce the regular cold fronts we usually get roughly once a week. You can visualise this by looking at my diagram, and imagining the same map with the two high pressure cells further south.
I don't know why we don't consider this very real possibility instead of maintaining the myth of the drought. Water management policies are fundamentally flawed in that they are based on the assumption that we are in an abnormally low period of rainfall, and that "normal" high rainfall will inevitably return. Sooner or later I believe we will have to start planning for indefinitely low rainfall patterns.
Most people attribute the "drought" to a common phenomenom experienced here called the "El Nino" effect - which is a shifting ocean current in the pacific, which supposedly brings drought to eastern Australia, and the opposite to South America. Certainly El Nino has been linked to previous droughts, most notably in 1982-83. However, El Nino should result in a (relatively) short period of drougth, followed by a period of abnormally high rainfall (known as "La Nina"). Instead, we have been experiencing only drought - more or less for the last 10 years. The El Nino phenomenom is definitely a real event, which can be quantified using the Southern Oscilation Index (SOI) but scientists are unsure how exactly it effects rainfall patterns in Eastern Australia.
Instead, I have a different theory:
we are not in a drought, we are actually experiencing a long term decrease in rainfall patterns caused by global warming. This is only my own reasoning, but its logical that this is what would happen: the area that is affected by this "drought" (SE Australia) relies heavily on the frontal systems that pass the region courtesy of the belt of high pressure cells at this latitude - the so called "Ferrel Cell". These pass from west to east, and as they rotate in an anti-clockwise motion, they bring cold air from the arctic in a SW direction. As the winds reach further north, they meet the warmer air of the previous high pressure cell and where the warm and cold air meets, a "cold front" is created, thus:
this is in fact the main source of rainfall in the region. What happens in an El Nino event, is that the northerly air that feeds moisture into these fronts "dries up" because of what happends to the current in the Pacific ocean. Importantly, these frontal systems are still there during El Nino, they just don't produce much rain. However, what we have been experiencing recently is something different. Rather than having "dry" fronts passing through, we simply haven't been getting the fronts. Why? Invariably they end up passing too far south and miss most of NSW. Here's where global warming comes in: a warmer earth should result in a larger Hadley Cell - the belt of low pressure along the equator caused by the intense heat of the sun. Now the Ferrel Cell starts north (northern hemisphere) and south (southern hemisphere) of where the Hadley Cell finishes. Therefore, its logical to conclude that global warming would result in the Ferrel Cell existing further south in the Southern Hemisphere. In real terms, this would mean that the high pressure cells which pass Australia from west to east, would now pass further south. If this was indeed what is happening, then this would have huge ramifications on Australia's weather: the southern arm of the high pressure cells would extend further south, and they would be less likely to extend far enough north to produce the regular cold fronts we usually get roughly once a week. You can visualise this by looking at my diagram, and imagining the same map with the two high pressure cells further south.
I don't know why we don't consider this very real possibility instead of maintaining the myth of the drought. Water management policies are fundamentally flawed in that they are based on the assumption that we are in an abnormally low period of rainfall, and that "normal" high rainfall will inevitably return. Sooner or later I believe we will have to start planning for indefinitely low rainfall patterns.
- By Unthinking Majority
- By wat0n
- By Tainari88
- By RealPolitic