Who’ll Stop The Rain?

Guest Post by Willis Eschenbach

I haven’t posted here at WUWT in a bit. I’ve been preoccupied writing for my own blog, Skating Under The Ice.  It’s a work in progress. However, my climate work continues. There’s a paper out about a year old, unfortunately paywalled, regarding precipitation with some interesting conclusions. [UPDATE: available here, h/t to commenter Taphonomic]. The paper is called Changes in annual precipitation over the Earth’s land mass excluding Antarctica from the 18th century to 2013, by W.A. van Wijngaarden and A. Syed. Here is what ScienceDirect lists as the key points of the paper:

Highlights

• Over 1½ million monthly precipitation totals observed at 1000 stations in 114 countries analysed.

• Data record much longer than 3 recent conflicting studies that analysed a few decades of data.

• No substantial difference found for stations located at northern, tropical and southern latitudes.

• No substantial difference found for stations experiencing dry, moderate and wet climates.

• No significant global precipitation change from 1850 to present.

The Abstract of the paper reads:

Precipitation measurements made at nearly 1000 stations located in 114 countries were studied. Each station had at least 100 years of observations resulting in a dataset comprising over 1½ million monthly precipitation amounts. Data for some stations extend back to the 1700s although most of the data exist for the period after 1850. The total annual precipitation was found if all monthly data in a given year were present. 

The percentage annual precipitation change relative to 1961-90 was plotted for 6 continents; as well as for stations at different latitudes and those experiencing low, moderate and high annual precipitation totals. The trends for precipitation change together with their 95% confidence intervals were found for various periods of time. Most trends exhibited no clear precipitation change. 

The global changes in precipitation over the Earth’s land mass excluding Antarctica relative to 1961-90 were estimated to be: -1.2 ± 1.7, 2.6 ± 2.5 and -5.4 ± 8.1% per century for the periods 1850-2000, 1900-2000 and 1950-2000, respectively. A change of 1% per century corresponds to a precipitation change of 0.09 mm/year.

Being a visual kind of guy, I converted the one sigma errors to 95% confidence intervals, and graphed up the trends:

rainfall-change-since-start-date

As you can see, there is no statistically significant change in global rainfall, whether we look back fifty, a hundred, or a hundred and fifty years.

How are we to understand this? Well, to start with it is another example of the amazing stability of the global climate system.

However, I have to ask myself, given that in general a warmer world is a wetter world .. why so little change? This is often a valuable exercise, trying to understand a negative result.

One thing that comes to mind is that the effect may be there, but not be big enough to see. After all, the land has warmed up something like one degree Celsius or so since 1850, from something like 14°C to 15°C.

So … IF we assume that atmospheric water goes up linearly with increasing absolute temperature T, the temperature has gone up from about 287 Kelvin to 288 Kelvin, which is about a third of a percent … so we wouldn’t expect to see that.

On the other hand, IF water vapor goes up by T^4, then the increase is a bit larger. But it’s still only a percent and a half, which still would not be visible.

Finally, IF atmosphere water goes up from approximately zero at 0°C to 100% at 100°C … well, even then it’s only one degree, so that would still only be 1%.

So one possibility is that warmer is wetter, but the temperature change over the last century and a half is not large enough to cause an observable change in rainfall.

Another possibility is more subtle. As I write this, the wind outside is pushing the rain sideways at something like 20° from the vertical. This means that my rain gauge shown below, complete with a chambered nautilus shell in the window that we picked up on some beach “long ago and in another country”, that gauge is not recording the actual rainfall amount.

my-rain-gauge

So … how much is the error? Well, at the simplest level it’s equal to the cosine of the angle of the vertical. If the rain is falling at 45° the gauge will read about 30% less than the true value. At 20° from the vertical like today, it only reads about 6% low. However, in reality of course it’s much more complicated. For example, for a given wind, smaller droplets are more likely to be blown away from the gauge. So light rains will have a greater error than heavy rains.

The total analysis is quite complex, depending on the exact shape of the rain gauge and how it is affected by the winds. There’s a fascinating analysis here.

Setting the details aside, it is clear that a slow secular change in either global average wind speed or global average raindrop size could easily make a 1% change in the long-term rainfall records …

In any case, it seems that the rumored droughts and floods due to rising global temperature are not visible in either the global or regional analyses, nor in the short, medium, or long-term analyses, nor in the tropic, subtropic, or polar analyses, nor in the dry, medium or wet locations. Here is their final conclusion:

Stations experiencing low, moderate and heavy annual precipitation did not show very different precipitation trends. This indicates deserts/jungles are neither expanding nor shrinking due to changes in precipitation patterns. It is therefore reasonable to conclude that some caution is warranted about claiming that large changes to global precipitation have occurred during the last 150 years.

Another alarmist myth run aground on an inconvenient reef of facts …

Best to all,

w.

PLEASE: In your comments, be so kind as to QUOTE THE EXACT WORDS YOU ARE REFERRING TO. This prevents misunderstandings regarding your subject.

REGARDING THE POST TITLE:

WHO’LL STOP THE RAIN—Creedence Clearwater Revival Band

Long as I remember the rain been comin’ down
Clouds of mystery pourin’ confusion on the ground.
Good men through the ages tryin’ to find the sun.
And I wonder, still I wonder, who’ll stop the rain.

I went down Virginia seekin’ shelter from the storm
Caught up in the fable I watched the tower grow
Five year plans and new deals wrapped in golden chains.
And I wonder, still I wonder, who’ll stop the rain.

Heard the singers playin’, how we cheered for more.
The crowd had rushed together tryin’ to keep warm.
Still the rain kept pourin’, fallin’ on my ears
And I wonder, still I wonder, who’ll stop the rain.

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128 thoughts on “Who’ll Stop The Rain?

  1. Willis:

    Very nice post.

    Here is the bit I question:

    “So … how much is the error? Well, at the simplest level it’s equal to the cosine of the angle of the vertical. If the rain is falling at 45° the gauge will read about 30% less than the true value. At 20° from the vertical like today, it only reads about 6% low.”

    If you make an adjustment for wind – are you not comparing apples (adjusted rain gauges) to oranges (older rain gauges but not adjusted for wind).

    You either have to adjust all the precipitation data or none – but not just going forward (in my opinion).

    If you adjust it all – it makes no difference, so why bother?

    • Well according to Wentz et al “How much More Rain will Global Warming bring ?” SCIENCE July 13 2007, the answer is a one degree hike in surface Temperature will bring a 7% increase in total global precipitation.

      But if it was me, I would look for the discrepancy in that claim of a one degree C increase in global Temperature in 150 years.

      I for one don’t believe any surface Temperature data prior to about 1980.

      G

    • Wind makes no difference. The amount of rain falling through that several square inch funnel atop the gauge is the same amount falling on the same square inches on the ground.

      • Mike McMillan January 3, 2017 at 4:40 pm

        Wind makes no difference.

        Mike, I linked a paper titled “Estimation of Wind-Induced Error of Rainfall Gauge Measurements Using a Numerical Simulation”. You see that part about “wind-induced error”? Read the paper, it’s very interesting. Skip any math you don’t understand, look at the graphs and the graphics. Wind does indeed make a difference.

        Best regards,

        w.

      • Wind makes a difference, but not for the reason Willis explained. If the ground was covered by millions of densely packed rain gauges, they would intercept the same amount of rain as the bare ground. It’s the wind flow around an isolated gauge that reduces catchment.

      • So if warmer air can HOLD more.water vapor, how would this translate into more rain rather than simply more ambient atmospheric moisture? Presumably the ability to hold more moisture would equate to the likelihood of retaining more moisture during rain events. I would think that it would be a wash

      • I read the linked paper by Nespor and Sevruk. What is described is not a cosine effect (as in “So … how much is the error? Well, at the simplest level it’s equal to the cosine of the angle of the vertical”), but an effect of raindrops having their paths disturbed while approaching or entering a rain gauge due to winds around the top of the rain gauge having different velocities (in magnitude and/or direction, mostly both) from the wind velocity far from the rain gauge. In some cases, some smaller raindrops that enter the rain gauge get blown back out by a wind eddy in the rain gauge.

        Raindrops facing a rain gauge area (or swimming pool area, or farm area, or any other area) reduced according to the cosine of their falling angle from vertical have their velocities with respect to what they will soon land on increased accordingly. Raindrops falling at 20 MPH in a 20 MPH horizontal wind are moving at 28.3 MPH towards the points that they are approaching.

      • When the rain follows the prevailing wind, my house has a fairly large rain shadow on the Eastern and Southeaster sides.
        Dry enough that many plants require frequent watering.

        When the wind changes quarter and the storm arrives with wind from the East, the rain shadow switches temporarily to my Western side.
        My front door faces East, during these East wind storms, water easily runs in the front door when it is open.

        Wind direction matters very much regarding how much rain falls where.

      • Roy Spencer is correct. The wind around an isolated rain gauge does have an affect. The larger the top opening of the funnel the more accurate it will be. That is just one of the problems with the modern electronic gauges- the opening is usually smaller than the old manual gauges. I bought an Oregon gauge with a tipping mechanism sending by radio the count of the tips every ninety seconds. I calibrated with weighed water a different rates in comparison to a manual type. The markings on the manual one was 100% bias accurate with a reading error of +/- 0.1mm. With the electronic one for a start it was 30% low in the bucket size and it had problems reading low at low rates and very high rates. Any way I ran them side ob side for nearly nine months to see if I could get a correction curve but the error was unacceptable. I have continued with the manual reading every day. If I am away for a week or two I have the cumulative total and portion it for known relations with a number of official gauges in a 15km radius (a Dept of Ag station, two airports, a race course, a bowls club and two others) plus a couple of private ones who put figures on the internet. I now have rain data since 1892 which shows patterns of higher and lower rainfall (eg the Australian Federation drought from 1901 to 1919) Overall there is no significant trend in yearly or seasonal rainfall. The range is 3997mm 1898 to 519 mm in 1905. The January rain (summer) averages 264mm but I have recorded over 250mm in one day a number of twice in Jan, Feb and Mar. with the record one day in Fe 1893 close to one metre

      • The angle must make a difference, regardless of the gauge being isolated or not.

        At any angle other than vertical the rain ‘sees’ less opening to fall through.
        Consider the extreme: at 90° to the vertical (ie horizontal) no rain will enter the gauge.

      • Markx, No! The size of the projected horizontal opening is accounted for on the reading scale of the repository.

      • Does the size of the opening and the projected reading magically know the wind velocity and angle?

      • David A, The wind and the resultingturbulence and distortion of the air flow around the opening is another factor which is being discussed at length by others. Markx’s comment was purely a geometrical one.

      • So … how much is the error? Well, at the simplest level it’s equal to the cosine of the angle of the vertical. If the rain is falling at 45° the gauge will read about 30% less than the true value.

        That does not make sense to me. A large rain gauge opening (swimming pool or lake size) ought to collect all the water that falls on it no matter what angle it falls at. A cosine fraction for the angle of rain captured must be offset an equivalent cosine effect of more rain entering from a longer pathway. The angled path contains more rain.

        The lower reading must be due to edges and eddies.

      • Markx:

        Consider the extreme: at 90° to the vertical (ie horizontal) no rain will enter the gauge.

        The horizontal path would be of infinite length and contain an infinite amount of water.

    • So … how much is the error? Well, at the simplest level it’s equal to the cosine of the angle of the vertical. If the rain is falling at 45° the gauge will read about 30% less than the true value.

      Fuzzy thinking Willis. What falls into your couple of square inches of horizontal opening is what matters, irrespective of the angle at which it was travelling at when it landed: it is still just as wet.

      The flux of rain per unit area, measured perpendicular to its direction of travel, would be 30% greater than the vertical flux for similar geometrical reasons. The two cancel and the rain gauge get it right

  2. In my glorious days as a soil research scientist in Indonesia, I had access to daily rainfall data going back over 100 years for about 120 weather stations on the island of Java. I performed Markov Chain analysis on these data and found consistent rainfall patterns over the time period.
    I am intrigued by the statement that wind would cause a lower amount of rainfall measured. Need to think about this. Walking through the rain does not make you less wet when there is wind and the amount falling per meter square should not change.

    • Yes, this makes intuitive sense to me. Some rain that would have fallen vertically into the cup is blown laterally, so it misses and is not measured.

      But, some of the rain outside the cup that would fall to the ground on the up wind side, will also be blown laterally and into the collection cup.

      So, these would about balance out.

      • Consider a rain gauge with the rain moving approximately horizontally, perhaps from wind sweeping up the side of a mountain. In that case you would not get any rain in your gauge. This is different than walking in the rain, where horizontal rain gets you just as wet.

        But for the real details, read the paper I linked.

        w.

      • The question of walking in the rain is interesting; do you get less wet if you run?

        This carries similar discussion of exposed areas and angles but also how long you are exposed ( assuming that you are running to shelter ) and the relation of the direction of travel to the direction of the wind. It’s rather more complicated than the static rain gauge which stays there for the full time it is raining.

      • Some of you using the using this analogy seem to be forgetting that motion of the gauge (on the roof of the car or whatever) is increasing the effective surface area exposed to the rain over the same time in compensation. Willis’s link puts it rather more technically for those not convinced

    • I think Willis’ assertion that the angle of the rain will introduce an error in rain gauge collection rate is a red herring. A simple thought experiment: Picture the rain in an imaginary vertical cylinder on a still day falling straight down into the rain gauge vs. a windy day where the vertical cylinder is distorted laterally by the wind. It still contains the exact same amount of water even though the amount of water per unit volume is less.

      The article he links to is more on point: the turbulence and distortion of the air flow around the opening of the rain gauge leads to errors in the measured collection rate. Water that “should” have gone into the gauge gets swirled away and dumped just outside the gauge – essentially the area just around the gauge experiences locally increased precipitation rates vs. the gauge itself!

      I would guess that the simple solution is use a rain gauge with a bigger mouth since these are edge effects – use the swimming pool!

      • Another way to conduct the “thought experiment” is to have two rain gauges on a rainy day with no wind. One gauge is at a fixed location, the 2nd is mounted on the roof of a car that drives at 15 MPH in a straight line. Both gauges will collect the same amount of water. If you disagree, please explain why.

      • Hi Rob,

        Is the “you” in your question me? If so, I don’t disagree at all – that was the point of my first paragraph!

        Perhaps I introduced some confusion. When I re-read the paragraph I realize it is not clear that the “It” I refer to in the last sentence is the imaginary, distorted column of air, not the rain gauge! The rain gauge will show the same amount of water (neglecting the effects discussed in the paper W refers to). Apologies if my wording was clumsy – wish there was an edit function!

      • BlueEvent: No, the “you” was not YOU, it was rhetorical, in the sense that if one thinks my two rain gauges would have different measures, I’m asking them to please elaborate. I concur with your example, and was trying to simplify it to make it a bit easier to understand.

      • Rob Bradley – read the linked paper. The geometry effect isn’t the most significant. The rain gauge attached to the car will collect less, mainly due to massive turbulence in the mouth of the gauge preventing rain from entering.

      • Yes, the impersonal pronoun “one” has sadly all but disappeared from current dialects of English, though it is much clearer than saying “you” when you are NOT meaning the person you are talking to.

        I like to use ‘one’ for clarity but hesitate sometimes because it tends to sound pretentious nowadays.

        All part of the general degradation of the language, like using verbs where a noun is required: eg. saying “a fail” instead of a failure; doing “a shop” instead of doing the shopping.

    • This harkens back to the old question … If the cafeteria is 100 yards from your office and it is raining but there is no wind, will you get wetter if you walk to lunch or run to lunch?

  3. I am too lazy to look for the source but I recall that one of the assumptions about CAGW is constant relative humidity. ie. as the temperature increases more water is evaporated into the atmosphere. If that didn’t happen, the relative humidity would decrease.

    The foundation of CAGW is that CO2 will cause warming which will, in turn, cause more water in the atmosphere which will, in turn, trap more heat. (ie. positive feedback)

    If we don’t have more precipitation, that means we don’t have more evaporation because, over time they have to equal. True, the atmosphere would hold more water but that is a small amount compared with the amount of precipitation and evaporation.

    I think we have here another proof that CAGW isn’t happening.

    • And the flaw in that CAGW positive feedback mechanism is ignorance of convection. This is most often from confusion of water vapor, clouds and liquid water. Three phases, convection only happens with the gas and it is quite powerful.

      Air has a dry average molecular weight of ~29. Water has a molecular weight of ~18. Bouyant force depends on molecular weight only.

      Precipitation = evaporation. But heat flux only varies with altitude. Rising surface temps only changes the lower condensation level.

  4. Thank you sir. Interesting. I was thinking of that same CCR song this morning on my way to work, as I often try to imagine new illustrations for folks who might be persuaded to question the climate “consensus” based on models. Consider this: no one is measuring and capturing a record of the rain that evaporates before it hits the ground. Who’ll stop THAT?

    • @David Dibbell, the CCR song also brings back great memories, but as of today I wonder if some one shouldn’t write a new song?
      Who’ll stop the snow?

  5. I’m confused by one thing though. The visual satellite data show a noticeable greening of some desert areas (Antarctica is a notable exception). Maybe there is no data gathered there (too remote?), or maybe the greening requires no excess water, simply the increase in CO2. Or perhaps there’s some other reason? I just would have thought that the greening would’ve required more than a simple increase in CO2.

    • with increase CO2, plant stomata reduce in size effectively requiring less H20 and nitrogen for success

  6. “If the rain is falling at 45° the gauge will read about 30% less than the true value.” Consider a “gauge” of a square mile. Why would wind have such an effect? Why would a square inch gauge behave differently?

    • Consider rain being blown at 90 degrees. None will enter the cup. The cup will collect as per the area of the cup exposed to the direction of the rain.

      • Adding to Dave’s comment
        From my drafting days I would believe the opening has less available area to receive the drops moving sideways to the receptacle.
        A simplified version.
        Take a pill bottle(most seem to have these laying around these days) or cup and start turning the opening until it is 90 degrees from you staring across the opening.
        The shape of the opening changes, becomes an ellipse, as the angle changes allowing for less of the opening available to accept the droplets.

      • It is impossible for rain to fall at 90 degrees unless there is significant upward wind velocity (side of a mountain). Gravity force is always present and rain falling in a steady 100 mph wind still has some downward component. The question above is valid. What screws up a rain gauge in wind is the induced edge effects from the lip and body of the container.

      • Consider a rain gauge with the rain moving approximately horizontally, perhaps from wind sweeping up the side of a mountain. In that case you would not get any rain in your gauge. This is different than walking in the rain, where horizontal rain gets you just as wet.

        But for the real details, read the paper I linked.

        w.

      • Consider 2 cups each 1 inch x 100 inches arranged at 90 degrees to each other – 1 across the wind the other downwind. Do they collect the same amount? Not in my book – yet each has the same area exposed to the direction of the rain.

      • “Consider rain being blown at 90 degrees. None will enter the cup. “
        None will land on the ground either. The horizontal collecting surface fairly reflects the rain that actually falls on the surface.

      • Thanks for the link Willis. So it is interpolated based on the wind speed and angle. That probably only works if the wind speed and angle is constant. What if the wind stops for a period and then gusts to a high speed? I link to Mt Washington in NH where the wind can gust over 100 mph at times. I wonder (don’t know) what kind of rain gauge they use. And the snow depth there must be equally difficult to gauge. Just thought that a wider area of collection might be more accurate…
        JPP

      • Nick Stokes January 3, 2017 at 4:39 pm

        “Consider rain being blown at 90 degrees. None will enter the cup. “

        None will land on the ground either. The horizontal collecting surface fairly reflects the rain that actually falls on the surface.

        Read the paper I linked on wind-induced error. The idea that the cup gets the same rain as “the surface” is totally disproven by the paper. The paper clearly shows that the error is a function of the droplet size and the wind speed, and also depends in a complex manner in the exact aerodynamics of the cup itself..

        w.

      • “…The horizontal collecting surface fairly reflects the rain that actually falls on the surface…”

        Geez Nick. Denying science? Your famous relative must be rolling over in his grave at your inability to understand a paper that should align perfectly with your alleged CFD expertise.

      • Not possible, because the rain falls at the same speed no matter what the horizontal wind speed is.

      • Thanks for the diagrams. The problem is that the velocity of fall and thus the flux ( kg/m^2/s ) is greater along the line of travel than it is in the vertical direction, and by the same cosine factor. So if you have a rain gauge inclined to face into the wind, it will measure a greater rain fall than is experienced by the horizontal ground below.

        There may be some more subtle arguments about the body of the rain gauge perturbing the lamina air flow but the cosine argument is a mistake.

      • If the rain is blowing at 90 degrees it will not hit the ground, so the rain gauge is accurate.

      • Willis:

        Read the paper I linked on wind-induced error. The idea that the cup gets the same rain as “the surface” is totally disproven by the paper. The paper clearly shows that the error is a function of the droplet size and the wind speed, and also depends in a complex manner in the exact aerodynamics of the cup itself..

        That paper is about aerodynamic effects. Pure geometry (with no aerodynamic fluid flow effects) should give the cup the same rain as the surface it covers.

      • Greg January 4, 2017 at 3:56 am
        Canman January 4, 2017 at 12:15 pm

        Danged if you ain’t both absolutely correct. I stand corrected.

        But there IS this little thought experiment! :-)

        Consider a finite rain-cloud of a finite base area which will release a certain set amount of rain over a set period of time:

        1. Re Greg’s comment. (That the 45° drop/stream is moving proportionately faster) :
        In the above scenario, it does not matter what the actual velocity of the raindrop (stream) is. Ith the rain falling at a 45 degree angle, at the end of the rain-shower, less rain will have entered that rain gauge than it would have had the rain fallen vertically.

        2. Re Canman’s comment: (that the gauge gives a true measure per unit surface area)
        Yes, per ‘unit area of rain-gauge’ the measure will be true.

        But, consider, if you will, the case where that finite rain-cloud of a finite base area is releasing its set amount of rain over a set period of time….. in a finite, impervious valley of larger size than the rain-cloud area, such that all rainfall in either case falls within the valley and is channeled into a dam.
        The 45 degree rainfall event will record about 30% less rainfall in the gauge, but the dam catchment will still be exactly the same as had the rain fallen vertically, with the increased gauge reading.

        I guess my mind had subconsciously put in all those provisos….. :-)

    • What is the rainfall? For me it is how deep a water would collect at a 1 km2 flat field if we prevent evaporation and outflow. Subdividing that square filed into a million 1 m2 gauges does not change the amount of water collected. Subdividing a 1 m2 gauge into 10,000 1 cm2 gauges does not change the amount of water collected. Should it rain strictly horizontally, no water would reach the ground in any of these cases.

  7. Hi Willis!
    A 1 Celsius degree rise in temperature increases saturated water vapor pressure by about 7%, because vapor pressure is roughly an exponential function of temperature. See the section “Meteorology and climatology” at https://en.wikipedia.org/wiki/Clausius-Clapeyron_relation . Assuming relative humidity of 50%, a 1 degree rise in global temperatures would also increase water vapor by 7%. This is one reason for the importance of positive water vapor feedback in estimating climate sensitivity. OTOH, doubling CO2 from 300 to 600 ppmv produces about 0.6 degree warming (not counting feedbacks) because the accepted radiative forcing of 3.7 W/m^2 comes from computer calculations of increased absorption for a cloud-free troposphere. Clouds decrease the path length and the number of vibrationally excited CO2 molecules which are responsible for the increased absorption centered at 618 and 721 cm^-1 (see the Section “Spectral transitions”, Diagram 3, at http://www.barrettbellamyclimate.com/ and note the increased absorption between the green and blue curves in the MODTRAN computed spectra at https://en.wikipedia.org/wiki/Radiative_forcing ), so the accepted value of 1 degree warming (not counting feedbacks) is too high. A 0.6 degree rise in temperature increases water vapor by only 4%, not 7% (see tables of water vapor pressure in the Handbook of Chemistry and Physics). The reduced water vapor feedback corresponding to a reduced climate sensitivity (before feedbacks) means that positive feedback is no more than 50% (100% if one uses the formula for an infinite geometric series), and not the 200% that triples the accepted value of 1 degree to 3 degrees after feedbacks. When negative cloud feedbacks are included, the net feedback is going to be small, so the overall climate sensitivity (including water vapor and cloud feedbacks) is around 0.6-0.7 degrees, not 3 degrees. This explains why all the computer projections of CO2-driven warming are too high when compared to actual temperature data. I enjoy reading your articles, Willis.

    • Thanks, Roger. I’m aware that the CC relationship implies a much larger effect, something like 7%. However, that’s not what we’re seeing in the results. We’re seeing 0% … so I was looking for alternative explanations.

      All the best,

      w.

    • Oceans warm from radiation and cool from convection. Greater evap means cooler oceans AND more precip. The whole “forcing” hypothesis is without any merit. Water vapor is highly bouyant and this drives convection. Latent heat transport via this convection cools the surface irrespective of thermometer measurements, unless you are in that rising mass of condensing vapor.

  8. This reminds me of “weather not climate”.
    If the effect on rainfall of a change in temperature is too small for us to discern day-by-day then… look at the effect over decades.

    So, we can’t see a change in measured rainfall on daily measurements. That doesn’t mean the change isn’t there. Absence of evidence isn’t evidence of absence.
    Every observation looks like a nail through a hammer-o-scope.

    Are deserts growing or shrinking?
    Are we getting less return on fertiliser or not?
    These are climate questions.

    The link between measured weather and the effect of the average climate is not simple.
    I’m still a sceptic. But this does not convince.

    • Are deserts growing or shrinking?
      From the paper:
      “Stations experiencing low, moderate and heavy annual precipitation did not show very different precipitation trends. This indicates deserts/jungles are neither expanding nor shrinking due to changes in precipitation patterns. It is therefore reasonable to conclude that some caution is warranted about claiming that large changes to global precipitation have occurred during the last 150 years”

    • M Courtney January 3, 2017 at 2:52 pm

      This reminds me of “weather not climate”.
      If the effect on rainfall of a change in temperature is too small for us to discern day-by-day then… look at the effect over decades.

      Huh? The paper looked at the effect from five decades to a century and a half. There was nothing.

      w.

  9. Willis, why do the error bars get larger as you move forward in time? Do we really know less about rainfall in 1950 than 1850? What am I missing?

      • The true problem here is trying to define experimental measurement uncertainty from statistical properties of the data, especially when measuring mythical quantities like global averages of rainfall or temperature etc. over incompatible climate regions with grossly variable coverage throughout the record.

        does it even make any sense physically to ‘average’ tropical rainfall histories with those of temperate zones, or those of ocean dominated SH with more land biased NH?

        Yet again, the average of apples and oranges is a fruit salad.

  10. Willis,
    I think if you were to surround the top of the gauge with a tube say ~ 5x dia of collecting dish & same ht above rim of dish, that would remove turbulence from top of collecting dish & allow gravity to take charge of direction of water droplets.
    You already have one side shielded by the house so rain coming from that direction will tend to fall verticaly-ish.

    • Willis, I can’t tell from the picture, but it appears your rain gage is quite close to the building, and that may have a large affect (see comment from 1saveenergy at 3:43 pm). The AMO should have rain gage citing standards. This info is also available if you buy a True Check rain gage. Also, please see here: http://www.nws.noaa.gov/om/coop/standard.htm
      Thanks,

  11. Besides the turbulence effect, the authors in the link provided pointed out that the streamlines move up and over the top of the rain gauge, carrying smaller raindrops with them. They therefore stated that the error increases with the amount of blockage. However, the total error for windspeeds of 2-3 mps for the Hellman gauge ranged only from 3-5%, and for windspeeds of 3-4 mps from 3-10%, with the high-end errors associated with the lowest rate of rainfall. I conclude first that rain gauge errors are relatively small and second that they would not affect trends unless windspeeds and/or rainfall rates are themselves trending.

    • Lance, the errors are small … but the problem is, so are the trends. So while they are small they are big enough to make the results uncertain.

      w.

  12. Nice post Willis. I guess too, it’s you we have to thank for this latest news about Dr Judith Curry’s resignation. I remember you asking her many times to look at what the real world had to say about IPCC nonsense, and many ensuing debates.
    It shows what integrity looks like in the scientific community. Let’s hope the dam breaks quickly in the era of President Trump!
    https://pindanpost.com/2017/01/04/what-honesty-and-integrity-look-like-in-science/

    • Tom, I had nothing to do with Dr. Judith’s resignation. After hundreds of papers and years of teaching and assisting her students, she’s moving on in her life. My only contribution was to wish her the very best in whatever she does next, and thank her for her contribution to the climate discussion.

      w.

      • Tom, I would suggest reading the interactions in the comments before placing a judgement. That was a very good sharing/exchange that JC and Willis had and it was very beneficial to the climate community at large. I believe it opened some doors that were previously nailed shut and opened many eyes. I have the utmost respect for Dr. Curry and think she can handle some critical constructive discussion as she has for many years since 2010, post climategate. That was, after all, her tipping point I believe. Just sayin, it ain’t Willis that made her retire from comments/blog posts from 7 years ago. C’mon man

      • I didn’t say Willis made her retire, just that he planted some of the first seeds of doubt. Before this post just 3 months after Climategate in 2010, Curry was an avowed believer in AGW.

  13. The new cry will be, “Sure, it’s not changing on an annual average…but it’s being concentrated so that we get more extreme rainfall events and longer dry periods as opposed to the natural/perfectly flat trend,” lol.

  14. So… we need to add a weather vane to rain collection cups – then the ambient wind will push the cup so the rain enters a ‘normal-to-wind’ surface area that remains constant no matter how much wind there is… :D

  15. Rain gauges meant to provide the most accurate measurements have a wind screen around them. Again, it’s because an *isolated* gauge has wind flow around it that tends to diverge and reduces the catch by the gauge….but has nothing to do with the angle at which the rain is coming down, which has no effect because the fall speed of the drops is still the same (avg. of 10 m/s, depending on drop size). This is Meteorology 101 stuff, folks.

  16. How does the rain gage data compare to flood events? To stream flow data? Droughts? Some other rain dependent measurable thing not corrupted by other man made changes?

  17. Another source of info, from 2016:

    “Trends in Extreme Weather Events since 1900 – An Enduring Conundrum for Wise Policy Advice”

    Abstract
    It is widely promulgated and believed that human-caused global warming comes with increases in both the intensity and frequency of extreme weather events. A survey of official weather sites and the scientific literature provides strong evidence that the first half of the 20th century had more extreme weather than the second half, when anthropogenic global warming is claimed to have been mainly responsible for observed climate change. The disconnect between real-world historical data on the 100 years’ time scale and the current predictions provides a real conundrum when any engineer tries to make a professional assessment of the real future value of any infrastructure project which aims to mitigate or adapt to climate change. What is the appropriate basis on which to make judgements when theory and data are in such disagreement?

    https://www.omicsgroup.org/journals/trends-in-extreme-weather-events-since-1900–an-enduring-conundrum-for-wise-policy-advice-2167-0587-1000155.pdf

    • Actually, more CO2 should cause weather to moderate. Milder nights, milder winters, etc. Venus, with a very slow rotation rate, gets roughly the same temperature noon, midnight, poles to equator. Of course, Venus has massively more CO2 than Earth, but Earth has temperatures ranging from -90 C to 55 C.

      What I don’t understand is the high surface temperature of Venus. Latest estimates of Bond albedo (the correct albedo for calculating planetary temperatures) are .90, so, if it has this albedo along with an Earth-like atmosphere, if would be significantly colder than Earth. Plugging these numbers into Venus’ distance and atmospheric pressure, I get a low CO2 temperature of around 490 C, and actual CO2 with actual pressure of 530-550 C, depending on feedbacks.

      • thomasl3125,

        “[Venus] gets roughly the same temperature noon, midnight, poles to equator.”

        Yes, and so does the solid surface of the Earth beneath the deep ocean whose temperature is about 0C. Both are the consequences of the PVT profile of the ocean above, where the Venusian ocean is CO2 which has about the same mass as the H2O in Earth’s oceans, moreover; the lower km or so of the Venusian atmosphere is a supercritical fluid form of CO2, sharing properties with liquid water.

        “What I don’t understand is the high surface temperature of Venus.”

        This is because the surface of Venus is not heated in in the same way as the surface of Earth, which is not the solid surface as you are considering for Venus, but a virtual surface comprising of the top of the oceans and the bits of solid surface that rises above it.

        On Earth, this virtual surface is in direct equilibrium with the Sun, while the Venusian virtual surface that’s in direct equilibrium with Sun is high up in its cloud tops, where the PVT profile of the ocean below sets the solid surface temperature via a reverse lapse rate.

        Venus is a case of runaway clouds and not the result of any kind of runaway GHG effect. This concept is a red herring designed to reinforce the faulty concept that runaway positive feedback from GHG’s is a plausible hypothesis.

      • Venus has no free water. Instead sulfuric acid is the primary liquid forming cloud aerosol albedo.

        The boiling point of sulfuric acid is why Venus has a high temperature. The high atmospheric pressure only makes it hotter.

  18. Not gonna post details here. Rather a general reminiscence. My father was posted as commander of the 409th typhoon chasers off Guam starting 1948. He was a commnd pilot on those 24-36 hour flights in modified B-29s. Worst intercept resulted in a tail 18degrees off true. Bent by turbulence. He landed the plane anyway. It never flew again. Some of us been there, done that, at least by proxy of true heros.

    • ristvan, hats of to your dad, ( And you btw I follow your posts with great interest). How in the heck did your dad and his team keep those 29’s up there for that long? Double crews and extra fuel tanks? It would be nice to have links to see how they managed that in those days? It must have been terrifying. They did great work. Thanks.

  19. The global changes in precipitation over the Earth’s land mass excluding Antarctica relative to 1961-90 were estimated to be: -1.2 ± 1.7, 2.6 ± 2.5 and -5.4 ± 8.1% per century for the periods 1850-2000, 1900-2000 and 1950-2000, respectively.

    Their error ranges are as large or larger than the results. Seems pretty meaningless to this layman. I don’t think this paper gives us any useful conclusion.

  20. Willis,
    Have you given any thought as to why the 1950 error bars are so much larger than for the other two time periods?

  21. So … how much is the error? Well, at the simplest level it’s equal to the cosine of the angle of the vertical.

    I suggest you actually read the paper you linked to Willlis.

    It is nothing like that at all…

    • DP,

      A constant wind vector is like no wind at all, relative to the collected rain. While some rain will blow pass the collector cup, an equal amount of rain will fall in the cup that would have fallen outside of the cup in the absence of wind.

  22. Thanks for bringing this artcle to light.

    The issue of wind effects on rain guage error is complex as Willis said. The guage body is a cylinder in the air stream and therefore cause pressure and velocity changes as the wind passes around and over the guage. The air passing around the guage body would most likely be in the laminar range (Nre <2300), however I would expect some turbulence as the wind passes over the top of guage. I believe that turbulent flow would reduce the penetration of raindrops into guage. The higher the wind velocity, greater the error, assuming my previous sentence is correct.

    Brooks

  23. Willis,

    “I converted the one sigma errors to 95% confidence intervals”

    Odd that the confidence interval is so much wider for newer data while I would expect older data to have more uncertainty. Are you sure that +/- 8.1% doesn’t mean +/- 8.1% of -5.4 which is about +/- 0.44 which would seem more reasonable.

  24. With regard to wind driven rain and rain gauges. Ignoring turbulence, Reynold Numbers and the like…

    When the rain is falling vertically it is collected by the full area of the rain gauge. As the wind increases the apparent collection area steadily reduces by the sin of the rain angle.

    Horizontal rain – Sin 0 = 0 therefore no apparent collection area and no rain collected.

    Rain at 30 degrees to the horizontal – the landing area seen by the falling rain drops is 0.5 x full area of the collector

    Rain falling at 60 degrees to the horizontal – the landing area seen by the falling rain drops is 0.88 x full area of the collector

    cheers edi (with fond memories from 1956 – trudging 1 km each way to collect/record the data from a Stevenson “box” at Paardevlei, western cape)

  25. Roy Spencer January 3, 2017 at 5:32 pm
    “It’s the wind flow around an isolated gauge that reduces catchment.”

    WR: How would the conclusions in the paper (and the post change), when a correction for ‘wind speed measurement effect’ is made?

  26. Hi Willis,

    Good to see an analysis of another measurement in the weather records.

    Any chance of looking at barometric pressure?

  27. Your question:
    ” I have to ask myself, given that in general a warmer world is a wetter world .. why so little change?”

    Answer:
    No warmer world.

    Case closed.

  28. Willis and others: In case you are not aware, the increase in precipitation with warming is intimately intertwined with climate sensitivity. For simplicity, let’s assume an ECS of 3.7 K/doubling or 1 K/(W/m2) or 1 W/m2/K. If ECS is 3.7 and if reflection of SWR doesn’t change (more later), then TOA OLR must increase 1 W/m2/K as surface temperature rises.

    If a rise in surface temperature sends an additional 1 W/m2/K out the TOA, it must also send an additional 1 W/m2/K from the surface to the atmosphere – to maintain a steady state flux through the atmosphere the atmosphere. Warming increases surface emission by 5.4 W/m2/K. If we assume 333 W/m2 of DLR arises from a blackbody model at 277 K (1.7 km above the surface), then DLR rises 4.8 W/m2/K. (Or we can use MODTRAN with constant relative humidity and get the same answer for a US Standard atmosphere.) If evaporation rises 7%/K (like saturation vapor pressure) and evaporation currently carries 80 W/m2 of latent heat from the surface, then latent heat will rise at 5.6 W/m2/K. The total change in the surface energy balance is 6.2 W/m2/K – far above the 1 W/m2/K of additional heat escaping from the TOA.

    One solution to this dilemma is for reflected SWR to increase by 5.2 W/m2/K. Our current 30% albedo reflects 100 W/m2 of SWR back to space and would need to increase 5.2%/K, which is an increase from 30% to 31.6% for 1 K of warming. For 3.7 K of warming, albedo would need to be a whopping 35.8%. Such a major shift in albedo with temperature probably would already have been detected during seasonal warming.

    If reflection of incoming SWR doesn’t compensate, then precipitation and evaporation must be suppressed from 7%/K to about 1%/K. Climate models accomplish this by slowing “convective turnover” of the atmosphere, which raises humidity over the oceans and thereby slows evaporation. The change is global precipitation is being measure by satellites from space.

    So, if climate sensitivity is high, then the increase in evaporations/precipitation must be about 1%/K instead of 7%/K or albedo must increase to 36% or some combination of these two.

  29. given that in general a warmer world is a wetter world .. why so little change?
    it may have to do with where the thunderstorms happen and the thousands of rain gauges in the bermuda triangle on the planet of Sea

  30. Are we now going to see post hoc revisions of rain gauge readings? Change of instrument discontinuities? Recalculation for Time of Observation bias to eliminate evaporative errors? Homogenization by reference to more obedient gauge locations?

  31. Willis writes

    given that in general a warmer world is a wetter world

    Is that really a given? If the amount of rainfall increases, then the amount of energy as latent heat that is removed from the surface, increases (and is deposited high in the atmosphere to be radiated away as clouds form) and consequently the surface must cool. More rain = negative feedback.

    We often think of the tropics as warm and wet but then again, the tropics receive much more energy than the higher latitudes.

    I’d start with this basic assumption. Maybe its not actually justified.

  32. Another problem is that precipitation is not proportional to humidity (ie, to temperature and evaporation). Precipitation is more effected by the confluence and interaction of warm and cold airmasses – whether that is continental sized airmasses, or simply a tarmac car park and cooler farmland causing convection.

    So a rise on 1 degree is not necessarily going to increase rainfall.

    R

  33. Thanks Willis, as always food for thought but you haven’t solved my lifelong dilema. Will I get less wet in the rain if I dash across the parking lot to the Pub, or park upwind and walk at the windspeed.?
    Any suggestions?
    Oh! and Happy New Year to all on WUWT.

  34. Regarding: “On the other hand, IF water vapor goes up by T^4, then the increase is a bit larger. But it’s still only a percent and a half, which still would not be visible.” The relationship between water pressure of water and temperature is well known, and in the temperature range at which water is liquid the mathematical formula is an Arrhenius one. As temperature changes zero to 30 degrees C, 273-303 K, the equilibrium vapor pressure of water changes from 4.6 to 31.8 mm Hg, and the variation in this temperature range is close to exponential at a rate of doubling every 11 degrees C. In this temperature range, it is also close to absolute temperature raised to the 18.5 power. Either way, a 1 degree C increase, such as from 14 to 15 degrees C, causes water vapor to increase about 6.6 percent.

    However, I expect a 1 degree C temperature increase to increase rainfall a lot less than 6.6 percent, at least where this temperature increase does not cause lack of convection to be replaced by convection. (Increase of greenhouse gases generally cools the tropopause.) More water vapor being moved around means more heat being moved around. I think that this means the wind will slow down, at least mostly, so that heat transport from the tropics to the poles keeps up with the difference between the tropics gaining heat and the poles losing heat.

  35. All right, everybody. I solved the geometric rain angle problem! See my comments above:

    https://wattsupwiththat.com/2017/01/03/wholl-stop-the-rain/comment-page-1/#comment-2388417

    https://wattsupwiththat.com/2017/01/03/wholl-stop-the-rain/comment-page-1/#comment-2388427

    The cosine opening reduction effect is offset by a cosine, more rain containing, longer pathway increase

    The reduced rain gauge measurements have to be due to edges or eddies or something else.

      • I looked at the problem. I don’t see how the rain gauge being in a valley (on tilted land) would collect less rain than if it were on flat land as long as the gauge was always pointing straight up (not necessarily perpendicular to the ground).

      • Sorry, the tilt of the valley was not the point. Simply consider it as a catchment area.
        A certain amount of rain falls there, filling a reservoir to a certain level.
        If there is a stiff breeze blowing, the gauge will record less than had the rain fallen vertically (and even less if we take the turbulence paper into account!)
        Yet the same amount of rain will have fallen within the area.

        But… I think I belabour the point, pointlessly. :-(

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