Look, I do have an earth sciences background (although admittedly not in hydrology, beyond a couple of undergrad classes a long time ago) so it’s not like I’m just being argumentative in some sort of folksy anti-intellectual way. What I think might be going on here is the all too common situation where you come up with a very reasonable-sounding model that seems to work very well for explaining the empirical observations in a very specific set of circumstances, but doesn’t really hold up if you try to broaden the scope. The model they’ve come up with here seems to work if you only look at recorded time, but I find it hard to imagine that it works for all the prehistoric time when there were no water diversions and yet the variation in lake level looks exactly the same.
And you keep saying “actual scientific data” as if it’s some unimpeachable gospel. What they have are some limited measurements and assumptions they’re using to try to interpolate to the actual data they want re: inflow, diversions, evaporation, etc. I say “I don’t dispute” the measurements and assumptions they’ve made in that I think they’re perfectly reasonable ones, but having a perfectly reasonable-seeming model is no guarantee against being wrong.
Onto the nitty-gritty, you say “historic lows” but they’re really not. Firstly, saying the north half of the lake is at historic lows is pretty misleading given that it’s only been a separate entity for a few decades. With overall lake levels, they were still much lower back in the early 1960’s, and of course have been about as low or lower dozens times in the past 800 years.
You mention the high lake levels in the 1980’s: of course those were due to climate and higher inflows. My “alternate theory” is that they’ve overestimated the effects of diversions relative to natural inflow and evaporation. The high water interval in the 1980’s is maybe the best illustration of that. Looking at the prehistoric data (and the one previous high-water interval in the 1860’s) there’s been about 1-2 high water intervals per century for the past 800 years. The 1980’s high interval looks completely normal compared to those. If diversions were really having a major effect, I would expect it to be at least near the low end. Sure, an alternate explanation is that maybe the extra inflow during the 1980’s was unusually high compared to the prehistoric high-water intervals so lake levels would have been even higher were it not for the diversions, but we don’t have good inflow data for the earlier ones so who knows. FWIW, knowing a little about the recent climate history of the region, I don’t think there’s any reason to think the 1980’s were an unprecedentedly wet time.
Uhh, guys – in “Prehistoric time” the lake was MUCH bigger. Lake Bonneville (prior to 14,000 BP) was huge, with the structures still visible and called “The Benches” being the beaches of the Lake, Posters put out in the mid-1980s during the floods predicted the Return of Lake Bonneville, and showed the water rising to the level of the Angel Moroni on the Salt Lake Temple.
Clearly the lake levels change with time. I’m surprised to see that 12,000 years BP the lake was actually smaller than the present Great Salt Lake (so my naive understanding that the GSL is the still-shrinking remnant of Bonneville is incorrect).
The question is whether the current fall is mainly due to human activity, and it seems to me the answer to that has to be “yes” – where else would the water be going? Human activity draining runoff its different watersheds and diverting it to places where it can evaporate, rather than run into the GSL would seem much more probable that any naturall,-developing alternate routes for the water, which should otherwise all drain into the Salt Lake Basin.
It’s not a question of “Was the Salt Lake Level Changing Before Man?” We know that it did, and likely would have continued to change in response to random natural events. The question is “Are the actions of people hastening the decline?” and I suspect the answer is “Yes”.
Lake Bonneville dried up (and drained via spectacular floods) very quickly at the end of the Pleistocene. It reached the size of the modern GSL well over 10,000 years ago. Since then, the evaporation and inflow rates have been more or less in equilibrium so, while there’s been huge short term variations, averaged over time the lake hasn’t been growing or shrinking.
The major line of evidence that the lake has continually undergone the high/low cycles since the last Lake Bonneville period is through lake bed coring stratigraphy and paleoshorelines. The maximum and minimum Holocene levels of the lake have long been known, as well as that it’s gone through many expansions and contractions. The tree ring study I keep harping on studied the tree rings and ages from several areas around the lake that are occasionally inundated, which is interesting because it gives a much more precise idea of the timing and magnitude of the most recent high/low cycles.
No, it looks like you are argumentative without rigorous logic.
You haven’t pointed to anything which accounts for what the lake would look like without the diversion and you are seriously underestimating its effects.
I’ll repeat the quote again from the study.
Thirty nine percent is not a trivial amount and by all accounts should easily overwhelm any possible effect of some change in the rate of evaporation of any possible temperature differences in the same time period.
All you are saying is that prehistorically, there were swings in the water level, so we can’t possible know anything. That’s simply wrong. They are measuring the inflow of water and the water levels and have been doing this for years, enough so that they can get a reasonable estimate.
If you have a cite where the estimates of the prehistoric inflows and lake levels are seriously out of sync then it would help your argument.
In you opinion, how much of a difference should one expect if the inflow is reduced by 39%? Less than 5%? Less than 10%? Less than 15%? Less than 20%? Less than 25%?
I never knew that almost 60 years is a “few” decades. Learn new things all the time, I guess.
I also wasn’t aware that a foot is “much,” and since water no longer flowing through the breach in the causeway, that the overall level would be a third less than that, so we’re within 8" of the historic low overall.
And again, what has happened over the past 800 years means nothing because we didn’t have the data we have now. You keep harping on the fact that there were droughts before, but we didn’t know with the precision of what we know now.
And this is why I can’t take you very seriously. I lived in Salt Lake for most of my life until I moved to Japan in 1990, and the relationship between the snow pack and the lake level is not contested by any serious scientist.
I’ve helpfully bolded the part which demonstrates the relationship between water coming into the Great Salt Lake and the water level.
As you see, since the lake lacks an outlet, when there are massive amounts of water coming in, the lake can only rise more. Likewise, when not as much water comes in, the water level goes down.
As only a certain amount of water is diverted, when there is flooding, as happened in the early 80s, the excess is going to go straight into the lake.
From your quote, “FWIW, knowing a little about the recent climate history of the region, I don’t think there’s any reason to think the 1980’s were an unprecedentedly wet time.” I would rewrite it as "knowing [del]a[/del] little about the recent climate history of the region. . .
They estimate that 39% of the current inflow is being diverted, but keep in mind that the diversion volume is more or less fixed, but the total inflow volume isn’t. I find the 39% figure completely plausible for where we are now, at the nadir of a dry cycle, but during wetter years with higher inflow the diversion percentage is going to be much, much lower.
If we’re just talking about the past 800 years, we don’t have precise data for the regional micro-climate but we’ve got a very good idea of what the global climate has been doing. We see the lake levels responding to the Little Ice Age, for example. Since then, we’ve seen both high and low lake levels in excess of both the historical minimums and maximums that don’t seem to correspond to anything major, climatically speaking.
Probably much less than you’d think. The evaporation rate declines drastically as the surface area shrinks and salinity increases.
If we’re talking about 17 decades of recorded history and 80 decades of prehistoric history, yeah, 6 decades is a few decades.
And, yeah, when you’re talking about a lake level that’s only varying by about 10 feet in either direction, a foot or two is significant. (Although admittedly I just looked at the current level and it is about two feet lower than I thought it was.)
They’re claiming that the current conditions are a departure from the previous normal conditions, so the lines of evidence we have about what those previous conditions were are absolutely relevant, even if our data for those conditions are less complete.
I am not even remotely contesting that either. My whole point is that the feedback interaction between inflow and evaporation is the driver of lake level. The major driver of inflow is snowpack and the major drivers of evaporation are climate and lake size/salinity. The water diversions are certainly a factor, but I’m simply not entirely sold on the idea that it’s the decisive factor it’s being made out to be here.
Sorry, by “recent climate” I mean recent geologically speaking. That period in the 1980’s were of course wet compared to the preceding and succeeding decades, but we’ve seen wet periods a few times a century going back to the Pleistocene, so a wet period by itself is not unusual. What I’m arguing is that if the record-high lake levels would have been even higher were it not for the diversions, then the 1980’s wet period must have been an unprecedentedly wet one. Which is certainly a possibility, but I think it’s more likely that it was just a normal one and the diversions weren’t very significant compared to the drastically elevated inflow volume.