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Discussion > Sao Paulo drought. Climate change?

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.

Oct 14, 2014 at 12:52 PM | Unregistered CommenterEntropic man

Entropic man -
Just a brief note of caution against extrapolation. You wrote at the original discussion on Unthreaded: "7000 years ago ... at the Holocene climatic optimum. Current temperatures and CO2 are both higher now than then." On pCO2 I think there is agreement. The comparison of temperatures seems unjustified. I make the assumption (knowing its risks!) that you rely here on Marcott et al. 2013 -- but such was a global estimate, and the context demands a local estimate. Marcott et al. has a dearth of South American Atlantic proxies, and nothing near São Paulo. The closest seems to be from near Recife, quite a bit away -- and looking at the source data there is little to no change in that proxy between 7 Kyr ago and now.

If anything, the fundamentals suggest that SH temperatures would naturally be on the increase since the Holocene optimum, based on the astronomical facts. The Holocene optimum aligns with a peak in high-latitude NH insolation.

Oct 14, 2014 at 2:02 PM | Registered CommenterHaroldW

Historical rainfall reconstructions here
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.

Oct 14, 2014 at 3:03 PM | Unregistered CommenterSandyS

Find a weather service which is NOT predicting rain for Sao Paulo with the next week

- I think this is probably more about reservoirs being low, rather than actual "no rain" and that's one of those climate stories that is being given legs by green media orgs looking for a "confirmation bias" story.

Oct 14, 2014 at 3:24 PM | Registered Commenterstewgreen

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.


Oct 14, 2014 at 4:01 PM | Unregistered CommenterSandyS

Yes one of those WET droughts where it rains upto 2cm in one day ..In September in rained on 8 days ..not much but it did rain see Accuweathers observtions

Same in other places in the state like Campinhas or Riberao Preto
..I think the further north you are, the later the big rains are when they come at the end of October every year

(ha in September it rained less here in Scunthorpe than in Sao Paulo ..but then we did have more than 15cm of rain in August)

Oct 14, 2014 at 7:29 PM | Registered Commenterstewgreen

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.

Oct 14, 2014 at 8:15 PM | Unregistered Commentermichael hart

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.

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.

Oct 15, 2014 at 7:34 AM | Unregistered CommenterSandyS


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?

Oct 15, 2014 at 5:07 PM | Unregistered CommenterEntropic man

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

Oct 15, 2014 at 10:24 PM | Unregistered CommenterSandyS


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?

Oct 16, 2014 at 5:42 PM | Unregistered CommenterEntropic man

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.

Oct 17, 2014 at 4:18 AM | Unregistered Commentermichael hart

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.

Oct 17, 2014 at 8:12 AM | Unregistered CommenterSandyS

Still mixed messages.

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

Oct 17, 2014 at 10:29 AM | Unregistered CommenterEntropic man

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.

Oct 17, 2014 at 11:34 AM | Unregistered CommenterEntropic man

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.

Oct 17, 2014 at 11:51 AM | Unregistered CommenterEntropic man

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?

Oct 17, 2014 at 1:25 PM | Unregistered CommenterSandyS

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.

Oct 17, 2014 at 4:24 PM | Unregistered Commentermichael hart

sandyS, Michael hart

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

Oct 17, 2014 at 10:10 PM | Unregistered CommenterEntropic man

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.

Oct 18, 2014 at 9:37 AM | Unregistered CommenterSandyS

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.

Oct 18, 2014 at 12:18 PM | Unregistered CommenterEntropic man

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?

Oct 18, 2014 at 5:42 PM | Unregistered CommenterJames Evans

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.

Oct 18, 2014 at 8:16 PM | Unregistered CommenterEntropic man

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..

Oct 19, 2014 at 8:07 AM | Unregistered CommenterSandyS


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?

Oct 19, 2014 at 12:13 PM | Unregistered CommenterEntropic man