Water Levels – Lake Tahoe

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Pro: Climate Change is Causing Lake Tahoe Water Levels to Fall

Climate Change will lead to longer and more severe droughts.  California is especially vulnerable with a water system that depends on ever decreasing Sierra snowpack.

CBS News science contributor Michio Kaku says drought conditions may be the new standard for the state.

“If you look at tree rings and lake sediments, you realize you’d have to go back centuries to find a drought of this kind of magnitude,” Kaku said. “And we begin to realize droughts have lasted decades, even centuries, in the history of California. So yeah, some people are saying this could be a mega-drought, this could be the new normal.”


And from the Proceedings of the National Academy of Sciences.

California’s nickname is the Golden State, a name that owes as much to the golden hue of its landscapes during the dry summer season as to the 19th century Gold Rush or the fields of golden poppies. The grasses green up again in late fall when the midlatitude storms and rainfall return. What happens if those rains come late, come little, or in some cases don’t come at all?  Such has been the case in recent years.

California is experiencing extreme drought. Measured both by precipitation and by runoff in the Sacramento and San Joaquin river basins, 10 of the past 14 y have been below normal, and the past 3 y have been the driest and hottest in the full instrumental record. A plot of temperature and precipitation anomalies over the full instrumental record from 1895 through November 2014 shows that the 3-y period ending in 2014 was by far the hottest and driest on record (Fig. 1). As of the publication of this commentary, the state appears headed into a fourth consecutive year of water shortfall, leading to massive groundwater overdraft, cutbacks to farmers, reductions in hydroelectricity generation, and a range of voluntary and mandatory urban water restrictions.

California temperature (°F) and precipitation (inches) anomalies from January 1895 to November 2014, plotted as 3-y anomalies relative to 1901–2000 mean. Data from the National Climatic Data Center nClimDiv dataset.


Con: Lake Tahoe Levels Are Fluctuating Normally


Mother nature put a stake in the heart of this short-lived issue. Lake Tahoe has reached the maximum allowable water level during each of the past three years (2017-19), requiring special water releases into the Truckee River. The 2015-16 northern California drought was very brief and followed by three consecutive years of abundant precipitation and maximum allowable Lake Tahoe water levels. Alarmists claiming the 2015-16 drought signaled a “new normal” of drought and low water levels caused by climate change have been embarrassed and proven wrong.

Alarmists and their media allies frequently asserted (see here and here, for example) that the 2015-16 California drought and low Lake Tahoe water levels signaled a “new normal.” Since then, however, Lake Tahoe water level has reached its maximum allowable limit of nine feet above gage height (6,229 feet elevation) during each of the past three years, requiring special water releases into the Truckee River. This is shown in Figure 1, below. As often happens, alarmists claimed a normal, variable event like a brief drought signaled a permanent climate emergency, only to be proven wrong yet again.

Figure 1: Lake Tahoe has reached its maximum allowable limit during each of the past three years, as measured by the U.S. Geological Survey. Source: U.S. Geological Survey: https://nwis.waterdata.usgs.gov/nwisweb/graph?agency_cd=USGS&site_no=10337000&parm_cd=00065&period=4478.

Finally, it would require several hundred years of detailed lake level data both before and after 1850 to accurately determine whether the natural trends and fluctuations of Lake Tahoe water levels have been altered by the 1.3 parts per ten thousand increase in atmospheric carbon dioxide since 1850.  This is the period during which human activity contributed a portion of the increase of CO2 in the atmosphere, most of which occurred since 1940.  Without such sufficient data, no scientific comparisons and conclusions concerning the impact of the tiny increase in carbon dioxide in the atmosphere would be statistically meaningful.

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