Does global warming bring droughts or flooding?

Mike,

I understand what you’re saying and it can appear that a lot of contradictory statements are being made and the reason for this boils down to the fact that both weather and climate are phenomenally complicated.

Events such as floods and droughts are the consequence of relatively short-term atmospheric interactions (weather) and unless you happen to be in a part of the world that has very stable weather then it’s notoriously difficult to predict what will happen in the coming months or years.

If we take somewhere such as Australia as a whole, then we can confidently say that there will be both more droughts and more floods. Real world events are testament to the validity of such statements. What we can’t say with any degree of accuracy is that one particular place will be wetter or drier – at least not around the edges of Australia we can’t.

It’s also possible for the same place, even a comparatively specific place, to experience more droughts and more floods. Take the UK where I live for example, it’s a comparatively small island and one which has seen a 300% increase in the number of floods in recent decades, yet at the same time the country has seen a 300% increase in the number of heatwave events.

Despite the fact that it’s only March, tomorrow one third of the UK’s population will be subject to drought orders. Water levels in some places are the lowest they’ve ever been. This is becoming a regular occurrence, there were drought orders last year, the year before, the year before that etc.

The reason being that rainfall is far less predictable than it used to be. When it does come it falls onto dry ground and enters streams and rivers as run-off rather than penetrating the ground and replenishing the water table. You can have very intense rainfall and extensive flooding but if it just runs off into rivers then it’s not going to do much to alleviate the drought conditions.

The water companies are struggling to get this message across to people. Understandably the public see rains and floods and assume that the drought will be over, they’re not appreciating that the water is quickly lost again and that within days the drought is as bad as it was.

To answer your specific question: Some places will have more floods and less droughts (China for example), some will have more droughts and less floods (West Africa), some will have more of both (Western Europe) and some will have less of both (North Africa). It’s an inevitable consequence of weather disruption.

To answer your additional question. There are many examples of drought prone areas seeing increased rainfall. Similarly, some areas that used to receive too much rainfall now receive less. In a question I answered yesterday I listed these amongst the benefits of global warming. There’s quite a lot of benefits, some are listed in an earlier answer of mine: http://answers.yahoo.com/question/index?qid=201105...

You do realise Australia is the same size as the contiguous states of the US, right? The typical patterns we have had in most regions are long periods of reduced rainfall followed by flooding over 7-10 year periods. Our climate cycles are so different to the northern hemisphere patterns some have suggested we disregard the idea of four seasons in one year and focus more on the 7 year ENSO variation which explains more of the variation.

The climate predictions are for more severe droughts in the southeast (where I was living until last week) and more rain in the northwest. The drought broke in the southeast about two years ago, and we have had periodic floods since then. A trend opposing the predictions for the southeast will be if the droughts do not become more severe over the coming decades and the floods get worse or more frequent.

The reason we have floods after drought is because of the impacts on soils long periods without water has. Regular rainfall seeps into bedrock and moves slowly through aquifers but when soils are dry they become compacted and this reduces the amount of water they may absorb. This is worsened by things like deforestation and grazing. When you finally get significant rain, it runs across the top of the soil rather than being soaked into it like it does when rain is regular. This is why you get floods after drought. If the drought is worse, then the following floods are also likely to be worse.

So yes, we expect to have droughts and floods as usual. We also expect the severity of these to change. Come back to us in 30 years time when we will have had a few cycles which will indicate what the trend is. Until then, don't get excited.

Any answer to your question would have to be premised on you having at least a basic understanding of weather and the scale of the Earth, we already have a wide range of weather.

You seem intent at not understanding or pretending not to understand that weather varies wildly depending on where you are Florida, New York, Sydney, Tokyo, Nome, London or Ottawa.

Anything that messes with global weather is going to alter these systems and in some places cause droughts and in others floods. Deniers seem to spend a lot of time finding obscure reports or news stories on some of the sillier things that are possibly going to be affected, if we alter weather on a global scale there are going to be thousands of different local scale changes.

Then of course there is being deliberately misleading

"Averaged across Australia, 2011 was the second wettest year on record, with total rainfall of 705 mm, well behind 1974 with 760 mm but ahead of 2010 (third wettest) with 703 mm."

You seem to have neglected to mention what the BOM attribute this to and it isn't AGW but the current La Nina which always brings heavy rain and flooding to the regions that have been affected.

They have a hundred years of correlation between La Nina and strong flooding

http://www.bom.gov.au/lam/climate/levelthree/c20th...

Your BOM quote seems to come from this although yours has been altered and they certainly mention La Nina, it's at the start of the introduction at the top of page 2.

http://www.bom.gov.au/climate/current/statements/s...

You have asked questions like this before, but then you ignore everyone that gives a real answer.

We can expect droughts and flooding both from global warming. We may have a decrease in rainfall one place and an increase somewhere else. You could even have worse floods and worse droughts IN THE SAME PLACE, because it is not all that unusual for places to have periods of drought followed by flooding--California is well known for that.

And are you really provincial enough to call Australia "...one geographic location..."? And they make fun of Americans for being self-centered and poor at geography. Anyway, let's look at the climate of Sydney as an example, and if you think about the answer honestly maybe you'll see why asking these yes or no questions is misguided.

Let's call a year a drought year if it's in the lowest 5% of rainfall years, and we'll call it a flooding year if it's in the highest 5% of rainfall years at a location. For Observatory Hill in Sydney the mean rainfall for ALL years (1859-2011) in the record is 1215 mm, with the lowest 5% being less than 779.8 mm and the highest 5% being greater than 1817.4 mm. Now if we just look at the time period 1961-1990, we find that the mean is somewhat higher, 1302.2 mm, and the lowest 5% is now 769.7 mm and the highest 5% is 1925.0 mm.

What does this mean? For one thing, it's interesting that what we now call "drought" years ARE EVEN DRIER than they were for all years, even though the mean rainfall is greater. Perhaps less surprisingly the "flood" years have even greater rainfall than they had before. Overall, both the droughts and floods are worse in this time period than in the complete record. That's because the spread in the statistics is greater. This is a clue to where you might be confused by statements from various climate scientists. Even if the mean value of precipitation is unchanged, if the variability in a location is increased from the present, that place may very well have both worse droughts AND worse flooding in the future.

I think much of the denier confusion is because what appears in the popular media is quite imprecise and vague. You really need to ask questions like "What will happen to the mean rainfall/temperature/cloudiness/whatever at the location XYZ under global warming?" And "What will happen to the variability of the rainfall/temperature/cloudiness at the location XYZ under global warming?" At least then you may be asking a question that is well formed.

Global warming definitely does cause droughts or floods. They can also cause many other natural disasters. However, we can put a stop to this by not cutting down trees. Not cutting down trees helps because when trees are standing normally, they take in carbon dioxide (CO2), and when they are burnt or cut down, they give out carbon dioxide (CO2) which is released into the earth's atmosphere and trapped there which causes global warming. So if we don't cut down tress, the carbon dioxide will not be released into the atmosphere.

" let's look at a real example of basically one geographic location which is a relatively small portion of the Earth's surface, Australia."

When you have to call a continent that stretches across two Hadley cells "one location" to make your argument, you're setting a new standard of redefinition - even by your Y question history. Even the quote you offered had to localize to south-eastern Australia to make a meaningful climate statement.

Same with NSW - in 2007 our dams were so empty that it seemed desalination plant would be the only way to secure water. Now , due to strong La Nina the dams are overflowing So extrapolating this increase over the next 100 years does this mean that the solar system will be full of water?

They tend to focus on any bad climate they can find and suggest that is the new norm. I remember when winter snows were a thing of the past a few years ago. There were weeping alarmists whining that their children would never experience a white Christmas. In California here, we were warned that warming would destroy the snow pack and then we had a near record year. When it becomes dry again, I am sure the alarmists will go back to warming about drought.

I think the question should be, "Are our emissions of CO2 causing more droughts and or floods?" That question would obviously be answered with a "We don't know".

Will warming bring more droughts and flooding? That certainly seems likely to me. It also will bring better weather overall for most of the North America and Europe based on the past warming trends.

Both, if you understood grade school level science you would know that

First of all define Global Warming.

Quote by Steven Guilbeault, Canadian environemental journalist and Greenpeace member: "Global warming can mean colder, it can mean drier, it can mean wetter."

Do you expect to get a coherent answer when GW is that ambiguous? It is as ambiguous as Climate Change.