Sao Paulo, the world's 12th largest city is suffering a severe water shortage.

This is starting to become a news and blog topic.

For example at Bloomberg , the BBC and Robertscribbler's blog .

A proposed mechanism is disruption of water transfer across Brazil due to deforestation and climate change.

Comments on Unthreaded on October 14th showed various attitudes. Since BH argues that such systemic changes in rainfall should not be happening I would be interested to hear more on the topic from those here.

Historical rainfall reconstructions here
http://www.nature.com/srep/2014/140613/srep05291/fig_tab/srep05291_F5.html
which looks to me like it was drier in NE South America in the past than currently, It also seems that there is precious little data to decide how unusual, if at all, this event is.

stewgreen
Perhaps compounded by rapid population growth and no matching infrastructure investment. The population of greater Sao Paulo doubled between 1970 and 2000, 8.1 M to 17.9 M and is currently estimated at 19.9M.

Rapid growth has led to pollution of traditional water sources

The Tietê River, and its tributary, the Pinheiros River, were once important sources of freshwater and leisure for São Paulo. However, industrial effluents and wastewater discharges in the last half of the 20th century caused the rivers to become heavily polluted. There are no large natural lakes in the region, so the Billings and Guarapiranga reservoirs on the southern outskirts of the city are used for power generation, water storage, and leisure activities. Most of the reservoirs serving the SPMA are completely polluted because of the development of slums around the streams and rivers that feed them. Thus far the lack of affordable housing in the urban areas of Sao Paulo means it has been impossible to reverse this informal land occupation, and it is anticipated that this encroachment pattern will continue.

For clean water, the SPMA depends on a neighboring watershed, the Piracicaba-Capivari-Jundiai, which provides water to the city via a diversion system (the Cantareira system). Today, the Cantareira supplies water to approximately 50% of the SPMA population. To meet rising water needs, a new water diversion project (expected to begin in the next two years) will withdraw water from the rio Ribeira de Iguape microbasin in the Vale do Ribeira (approximately 80 km south of the city). This project is expected to cost US$630 million, and will ensure a water supply for SPMA until only 2020—it is not a permanent solution to the problem of clean water scarcity.

source http://www.adaptiveinstitutions.org/Shifting_Course_SaoPaulo.pdf

Interesting that you got the name of that town past the profanity detector, Stewgreen. Or perhaps BH/Squarespace doesn't have one. I once got modded at the BBC for using the name Eyjafjallajökull, when it was fairly on-topic.

Sort of relevant here, and confirms something Steve Goddard has been posting about for as long as I can remember.

A new study using a reconstruction of North American drought history over the last 1,000 years found that the drought of 1934 was the driest and most widespread of the last millennium.

Using a tree-ring-based drought record from the years 1000 to 2005 and modern records, scientists from NASA and Lamont-Doherty Earth Observatory found the 1934 drought was 30 percent more severe than the runner-up drought (in 1580) and extended across 71.6 percent of western North America. For comparison, the average extent of the 2012 drought was 59.7 percent.

http://wattsupwiththat.com/2014/10/14/nasa-study-finds-1934-had-worst-drought-of-last-thousand-years/

Hopefully that's one worst ever dealt with but it's doubtful if it will make it on to the BBC TV News.

Posting on unthreaded too.

SandyS

I don't wish to sound picky, but Anthony Watts and Andrew Montford have spent years denying the hockey stick on the grounds that dendrochronology is unreliable. Is Watts changing his mind about tree rings?

EM
Are you saying that Tree Rings are wrong because they now show something other than impending disaster?

SandyS

I am not commenting on tree rings. I am commenting on the janus-like behaviour of Watts, who derides tree ring data when it disagrees with his beliefs and uses tree ring data when it suits his purpose.

If the work is of good quality I am quite willing to accept whatever the data shows, whether it supports my view or not. I still haven't had time to read the paper yet. What does it say, what does Watts say it says( not usually the same thing), and how is this relevant to current conditions in Sao Paulo?

Wake up, EM.
Anthony Watts posts some articles he agrees with and some articles he doesn't agree with. And he doesn't always say which, and doesn't always comment. Some people would call that being open minded. Reading the article in question, I cannot detect him expressing an opinion.

Perhaps you could go there, actually read the article, and then ask him yourself. But you said that he banned you from his blog.

Entropic man
It works like this for me
1 The Hockey Stick is in part, a large part, based on tree ring data
2 Sceptics say Tree rings don't make good climate gauges
3 CAGW say of course they do, and there's more
4 A study comes up which, using Tree Ring data, says something different from 1
5 Sceptics say this contradicts what you are saying using similar methods, data and proxy both can't be true.
6 If both can't be true, and we're sceptical of both, then we can't assume either is correct, it is more likely both are incorrect to a greater or lesser degree.

Now to my mind you're having your cake and eating it not the Bishop and the Sceptics here.

This was my initial point which you seem to have misunderstood, possibly deliberately, that being sceptical of one study doesn't stop you using another, which is equally shaky, to further disprove the first.

I'm not sure that The Bishop has actually said he believes this recent work, as I haven't read a comment about it from him. I posted the link in response to your initial comment on Sao Paulo (Which seems as much down to resource management and a rapidly expanding population as an unusual drought.) and was vaguely relevant here.

Still mixed messages.

From the state, discussing a severe drought and the water company saying " no problem ".

Michael hart

I have just read the Science abstract, NASA's press report and Watt's article. As I read them, the combined message is that the American Southwest is prone to drought when La Nina conditions allow a blocking high pressure ridge to form off the California coast. This happened in the 1930s and poor agricultural practice helped make it the most extensive in 1000 years. The same pattern recurred in the 1970s and is in place at present.

The poor agricultural practice may well have a parallel in deforestation reducing water transport across the Amazon basin.

I am indeed banned from WUWT, perhaps you could ask him on my behalf.

This won't help , a heat wave in southern Brazil . If the storms come in next week, it would at least bring the temperatures doown, though not much help with the drought in the short term if that 50% drop in annual rainfall continues.

Entropic man
When were you banned? I don't recall seeing your name, whereas I can remember it from the BBC Richard Black blogs.

What exactly was your question?

Sandy, EM isn't big on asking questions. He prefers giving answers. I don't believe he has a genuine question about Anthony Watts opinion of the article under discussion, it was just a bit of rhetorical politicking.

sandyS, Michael hart

About two years ago, I think. My question to Watts would be, "Which dendrochronoly studies does he regard as valid?"

EM
can I ask the same question of you?

My answer in this instance would be I would regard any study using a proxy as suspect.

Next time I notice an appropriate thread early enough I may post said question.

That would be at a time I looked at WUWT most days, which I don't do now, I don't remember the exchange.

I regard most proxies as valid, within their limits. Any proxy has uncertainties, which any competent scientist will discuss as part of the paper. I would regard conclusions as invalid if they push beyond the limits of the data.

Remember that all temperature measurements are proxies, physical processes which change with temperature. This applies whether you are using oxygen isotope ratios in an ice core, tree ring widths, electron flow in a thermocouple or a glass tube of mercury. What varies is the amount of effort involved in the calibration, and the amount of interaction with other, non-temperaure related processes.

This calibration and the effort that went into desgning an accurate and reliable measuring device are often invisible to the user, and taken for granted. In science papers they are overtly discussed and you may be inclined to overestimate the problems.

Tree ring growth, for example, is also affected by drought and air pollution. This has to be taken into account.

A modeller of my acquaintance is retired from the Dupont works outside Londonderry and we once chatted about this. When he started work his temperature measuring devices included mercury and alcohol thermometers, bimetallic strips and Wheatstone bridges. These were read manually, in inconvenient and uncomfortable locations, and recorded on clipboards. Gradually they started installing analogue thermocouples and the readouts were rolling paper charts in the control room. By his retirement the plant ran mostly using digital thermocouples feeding computer control systems.

Each upgrade required calibration and had its own uncertainties and quirks. Ultimately they all measured temperature. The engineers calculating fatigue lives for the pressure vessels were confident enough to use all the temperature records, regardless of technique or instrument.

Climate proxies are the same. They need varying degrees of work and their own quirks have to be taken into account. They also give useful information about past climate. Like other independent checks they are also best used in combination. That is why I rely on Marcott et al for pre-industrial Holocene temperatures, rather than individual proxies.

Isn't it the case that one of the problems with using tree rings as temperature proxies is that tree growth tends to be much more sensitive to changes in rainfall?

A relatively wide tree ring indicates a good growing year for the tree. A sequence of rings gives a record of growing season quality. Variables which influence growing conditions include the amount of sunlight, rainfall, length of growing season, damage from pollution and temperature.

Under natural conditions average growing season temperature is the most significant, which is why tree rings give (rather noisy) information about temperature.

Under natural conditions average growing season temperature is the most significant, which is why tree rings give (rather noisy) information about temperature.

In plain English: tree rings are no good at giving unambiguous data on climate. Therefore one should be sceptical of any study using tree ring data in regard to historical climatic conditions, and what is average for an area in the past..

SandyS

There is no unambiguous information on climate, or much else in the world! :-)

That is why you can find human beings supporting any opinion you can name. Who was it said that the only certainties are death and taxes?