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ADSL connections in Sydney, Australia seem to either not work, or work slower when it's been raining or after it's been raining.

I tried googling for ADSL and rain, and I got a lot of user-generated content, but not many reliable sources.

Does rain affect ADSL speed and reliability, or am I imagining it?

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    it could be that more people are using the internet and stepping on each others bandwith
    – ratchet freak
    May 27, 2012 at 11:11
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    I remember hearing from an engineer that water and moisture can affect phone lines if they aren't insulated correctly, might be a good direction to search for an answer from.
    – rjzii
    May 27, 2012 at 23:39
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    @RobZ: as an anecdotal evidence I can confirm that, have had problem after very intensive rains until badly insulated copper has been replaced by fiber-optics.
    – vartec
    May 29, 2012 at 11:44
  • @vartec - Progress on reference materials - Systems Studies Reference Library note the section on why cables are pressurized.
    – rjzii
    May 29, 2012 at 14:45
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    Is this more appropriate for Electronics.Stackexchange?
    – Sklivvz
    Jan 15, 2013 at 18:03

2 Answers 2

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From AT&T Southeast FAQ:

Can weather affect my DSL connection?

Answer: Yes, it can. The primary cause of poor connections due to weather are moisture related. Since ADSL technology is electrical in nature, all of the exposed equipment can be affected by moisture which is an excellent conductor of electrical current. This, combined with the fact that the properties of water allow for "seepage", gives greater exposure to equipment that would, otherwise, be impervious to other weather conditions.

While it isn't a research article, it is an answer provide by a company who provides DSL service on their FAQ page, so I would think that there is some credibility behind the answer.

Additionally, I have programmed ADSL modem device drivers in the past and I do know that ADSL does self adjust its transmission rate in order to maintain reliable communications. So if the weather is causing communication errors, then the ADSL modem will try slower data rates until it reaches a rate where reliable communications can be maintained.

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It's not really about ADSL, which is the technology responsible for connection from the switchbox to your home ("the last mile"), but more about the broadband relay links. These can be either wired (typically in densely populated areas) or wireless using microwave transmission relays (more typical in less populated areas).

Water particles, such as rain cause microwaves to scatter, thus causing path loss.

Rare events of temperature, humidity and pressure profile versus height, may produce large deviations and distortion of the propagation and affect transmission quality. High intensity rain and snow must also be considered as an impairment factor, especially at frequencies above 10 GHz.

This effect is so well known and documented, that it's actually used as a measure of rainfall's intensity. See "Rainfall estimation using microwave links" or "Identification of Dry and Rainy Periods Using Telecommunication Microwave Links".

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    I'm with you that a microwave link would be affected by rain, but it would surprise me if @Andrew, living in a city of 4.5m people, has a microwave link between him and any substantial part of the Internet. (Perhaps Andrew can confirm he isn't living in some secluded outpost?)
    – Oddthinking ♦
    May 29, 2012 at 13:20
  • @Oddthinking: valid point. As I've commented on the question, for effect on wired version, I've got only anecdotal evidence, and I haven't seen any studies on badly insulated copper wires ;-)
    – vartec
    May 29, 2012 at 14:15
  • @vartec - Proper documentation is out there somewhere, odds are it's going to be in an engineering text as opposed to a scientific journal though.
    – rjzii
    May 29, 2012 at 14:42
  • @Oddthinking I was living in Woollahra at the time, which is close-ish to Bondi Beach.
    – Andrew Grimm
    Jul 19, 2012 at 13:16
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    While the effect on microwave propagation is true, water also affects poorly installed copper wire connections and may well have a big effect on the sort of signal propagation properties relevant to the high frequencies of ADSL.
    – matt_black
    Jan 13, 2013 at 14:22

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