2019 - Robert's botanical adventures in Northern California

[ian mcdonald]

Robert, does the rainfall in Sacramento penetrate the ground very far. What of the snow cover in higher altitudes, does that penetrate the ground or is it subject to quick run-off. In higher elevations in Scotland the snow can linger until summer. I wonder if the snow melt does not have time to penetrate the ground if a cold winter is followed by a sudden warm spell. A quick melt may cause the water held in snow to run-off too suddenly to penetrate the ground very much. This may be a cause of decreasing plant numbers and species in higher ground?

[Robert]

Ian,

These are great questions. You can see from the following that I am working on answering these questions and others. Give me some time to go over my data (this is a work in progress) and looking into other published material.

I was also giving thought to your other posting regarding the commodification of Nature (Reserves need to pay their way). Needless to say, this approach is too often a disaster for nature. This can be demonstrated to be true, however the ones setting these policies are not interested in data or facts. In addition, Nature is often altered beyond restoration to it's original condition before misguided policies can be stopped. The current state of the planet is a testament to this.

19 January 2019
0000 UTC

I just got back from the western slope of the Sierra Nevada in Eldorado National Forest. There is good news. The precipitation total, to date 18 January, on Peavine Ridge is now at 20.01 inches, 508.25 mm. This is an increase of 4.78 inches, 121.41 mm since the evening of 14 January. Unfortunately, the majority of the precipitation fell as rain. There was only 3.5 cm of snow on the ground with a liquid equivalent 0.36 inches, 9.14 mm.

Snow cover duration, is an important variable in forest vegetation type. Studies in the central Alps have demonstrated the relationship between hydric continentality [ratio of altitude (m) to annual precipitation (mm); the index can be expressed as tan^-1 (Z/P)], snow cover duration, and annual temperature range to forest vegetation type. I enjoy using simple modeling to express the climatic and vegetation changes taking place in El Dorado County and Eldordo National Forest.

[Robert]

Ian,

I got home late last night and now I have time to answer your questions.


To what extent does precipitation penetrate into the ground at our Sacramento home?

The soil around our Sacramento home is a deep alluvial clay-loam. 100 meters down the road it is very sandy loam. During heavy rainfall we get standing water that eventually infiltrates and percolates into the ground. There can be substantial run-off during heavy rain. I have never tested the soil percolation rate at our home (it is very easy-to-do), however from casual observation, despite the clay content of the soil, it appears to be fairly quick. Based on observations while digging in the garden, a goodly portion of the rainfall percolates deeply into the ground. Currently, methods to recharge the ground aquifers are being tested on agricultural land in California’s Central Valley. Fields are flooded and the water is allowed to infiltrate and percolate down to the aquifer. How successful this is I do not know.

The situation in the Sierra Nevada is much more complex. In El Dorado County (where I currently do most of my work) much of the higher terrain is part of the Sierra Nevada granite batholith. At elevations below the granite batholith, the under lying rock is either metamorphic of the Western Jurassaic terrane, Calaveras complex, or Shoo Fly terrane. In addition, there are the volcanic deposits of the Mehreten formation. About the only generalization I can make is that the quartz in the granites tend to break down into sand, the metamorphic rocks tend to break down into clay, and the volcanic rocks can create impenetrable caps that water does not easily penetrate. Depending on many variables peculations rates can vary form zero to extremely quick.

Another run-off variable in the Sierra Nevada is frozen soil. In general, the soil does not freeze deeply in our portion of the Sierra Nevada, however at high elevation when there is little or no snow cover and prolonged low temperatures, rainfall will run-off without percolating into the ground. These are isolated occurrences.

So, as you can see, from just the standpoint of soil types, there are many variables involved with soil infiltration rates, percolation rates, and the percentage of runoff/evaporation.

As I stated in my previous post, snow cover and the duration of the snow cover is an extremely important variable in the vegetation type at any given site. I do record many variables to incorporate into my eco-type/vegetation type modeling. The climatic shift toward higher snow levels, less snow cover, and declining duration of snow cover is having a profound affect on our Sierra Nevada ecosystems. Over time, as I record data, a much more precise picture of this will emerge.

Ian, I hope that I have at least partly answered your question. Each site is very distinct with their variables making a generalized answer difficult. Feel free to ask for clarity if necessary.

[ian mcdonald]

Thanks Robert, I did wonder if rainfall, when you get it, has time to penetrate the ground very far or if it evaporates off the ground surface.

[Robert]

Hi Ian,

I just touched a few of the variables involved concerning our native flora and precipitation, snow cover, runoff, evaporation, etc.

Yes, it is all very pertinent to the vegetation (and changes in vegetation) at any given site. I will be returning to this topic from time-to-time as it pertains to our native California flora.

[Robert]

21 January 2019
2130 UTC



The following chart summarizes the snow pack water equivalents for the 2018-2019 season, to date in Eldorado National Forest (where I am most active these days). The recent storms have brought totals up to near average levels, to date. Unfortunately, the trend toward higher snow levels continues. Much of the precipitation from the last set of storms fell as rain below 6,000 feet elevation. The snow totals for Robb’s Power House (5,150 feet) are very indicative of the shift toward higher snow levels. From 27 December 2018 through 4 January there was no snow on the ground. Current snow totals on the ground are much below average to date. This is becoming a more frequent occurrence during the winter snowfall season. In a future posting, I will discuss the impacts this is having on our local ecosystems.

I made a very quick WX forecast for the coming week in our region. Not only do I see no precipitation during this time frame, but in addition, temperatures will rise dramatically. I would not be surprised if we see record or to near record high temperatures in the coming week.

As a last comment, in future postings I will further the discussion of the relationship between hygric continentality, duration of snow cover, temperatures and vegetation types. I have comparative data from both Scotland and Austria, which may help put our situation in perspective based on known sites in Europe.

[Robert]

I finally had a chance to make a more detailed analysis of the WX for the coming week. The next 3 days appear to be cool with strong gusty north winds on Friday, with a chance of snow showers in the Sierra Nevada Mountains as wave passes southward on the east side of the Sierra.

Saturday will be the start of a warming trend. Record high temperatures are in the low 70’s (21-22 C) at the Placerville farm during this time period. I do not think that any records will be set at this time, however temperatures will be well above average for this time period.

At this point I do not see any meaningful precipitation in our region. With the warm temperatures later in this time period, it will be interesting to see how well the snow pack holds up. As of today, the snow pack in the Sierra Nevada looks near average to date, especially at the higher elevations. The WX is very changeable this time of year, so stay tuned.

[Robert]

27 January 2019
2300 UTC



On Thursday, my wife accompanied me on my weekly snow survey in the Sierra Nevada Mountains. The storm total results we quite encouraging. Although for the most part snow levels were quite high, temperatures eventually fell before the precipitation ended. Snow levels dropped to 2,800 feet. On Peavine Ridge, 5,146 feet (2,841 meters), I recorded 17 cm of snow on the ground with a water content of 1.73 inches (43.94 mm). In addition, the storm dropped 2.96 inches (75.18 mm) of total precipitation, which brings us very close to average for this date.



Less encouraging is the trend toward fewer snow cover days in the Sierra Nevada Mountains. The above graph is of snow cover days at the Placerville farm from 1988 through 2017. The number of snow cover days has declined by over 40% over the last 30 years. The same trend is playing out in the higher elevations of the Sierra Nevada Mountains. Fewer snow cover days contributes directly to snow/ice-albedo positive feedback in the higher elevations of the Sierra Nevada. Fewer snow cover days exposes bare ground, with a much lower albedo. The bare ground in turn absorbs solar radiation, raising temperatures (both soil and air). This in turn leads to further losses of snow cover. This in turn creates a cascade of many other events that alters the ecosystem.



Well we had a busy day and much to do, but not without some fun and a few snowballs.

28 January 2019
1600 UTC

We will see what today brings, temperature wise. Yesterday’s GOES satellite sounding over Sacramento indicated a strong inversion. It was 4 C near the surface and 5 C at 700 mb (≈ 10,000 feet, 3,048 meters)! Yesterday’s high temperature at the farm was 70 F, 21.1 C. This morning there are somewhat overcast skies, which may reduce the maximum temperature, reached today. The high temperatures are still below record levels, but they are close.

[Robert]

I was out earlier this week doing my weekly snow survey. Right now I am extremely busy, however I hope to follow up as soon as I can. 

[Robert]

The government shut-down has affected many of us here in the U.S.A. - even non-governmental employees. There has been much catch-up to do. I will have some stories to tell when the dust settles. 

In the mean time enjoy a few recent photographs.



Snow at the farm.



Snow on Peavine Ridge.



The first good snow at this elevation in years.



This is how it was in the past! 78 cm of snow at 5,000 feet. It is all great news for us here in Northern California.

After some meetings, I hope to get up on the Ridge and take some more photographs before the next (SNOW) storm arrives.             

[ian mcdonald]

Good snowy scenes, Robert. None here yet but there is still time.

[Robert]

Hi Ian,

The snow in the Sierra Nevada is great!    I have not seen snow like this in a while. I have a good story to tell about the recent shift in the weather and its impacts. I should be able to get back to reading the forum and writing soon.    Until then...   

[Robert]

13 February 2019
0600 UTC



What wild and extreme weather we are having here in Northern California!

The temperatures in January were much above the 30-year mean. In addition, precipitation was above average, bringing us very close to the seasonal average to date. This was very welcome as we were experiencing well below average precipitation before the January storms arrived.

On 30 January, I conducted a snow survey in the northern portion of El Dorado County near Gerle Creek at ≈ 5,500 feet (1,676 meters). The storms in early January were reasonably wet and cold with snow levels running at about 5,000 feet (1,524 meters). The last storm of January, during 20 – 21 January, started with very warm temperatures and snow levels at ≈ 6,500 feet (1,981 meters). Much of the existing snow pack below this elevation was severely eroded by the rain. The remaining snow was saturated with moisture and became frozen, brick hard, as nighttime temperatures dropped to well below freezing behind the exiting weather front.

During the following week daytime temperatures were extremely mild, near record levels. Strong temperature inversions developed. As an example, on 26 January the 1200 UTC Sacramento GOES Skew-T revealed an extremely strong temperature inversion. Surface temperatures were 0 C. At 850 mb (≈ 1,500 meters) the temperature was 10 C! At 700 mb (≈ 3,000 meters) the temperature was 2 C.



Despite freezing temperatures each night, clear skies and high daytime temperatures were melting the snow pack. As I hiked into the survey site, the sensation was that of spring runoff. Every ditch and gully was running swiftly with snowmelt, and this was early in the morning.



I measured snow depths, averaging 3 samplings at each location, at several locations at the site. In flat open sites the snow averaged 42 cm in depth. On the north facing slopes, 68 cm was the average depth. Snow cover on south facing slopes was variable; however often there was little or no snow.



I have been studying the impact of rising snow levels in this region of the Sierra Nevada Mountains. The snow/ice albedo positive feedback can accelerate the melting of the existing snow cover (it can work in the opposite direction too). Heat conduction in the soil becomes an issue as well as the build up of latent heat as snow/ice turn to liquid (more on this a bit later). These changes can impact the vegetation and other components of an existing ecosystem. These same processes can play out in our gardens and impact the performance of the alpine species we grow.



I enjoy the peace and quiet of the Sierra Nevada during the snowy winter months. There is also much to keep me busy these days, so the time to hike back to the Outback arrived far too soon.

[Robert]

A few days after I arrived back in Sacramento the weather reversed completely. The warm mild days with much above average temperatures gave way to snow and record, to near record, low daytime temperatures. On Peavine Ridge, over 78 cm of snow fell during the period of 2 to 5 February. The snow level dropped to below 1,460 feet (445 meters), where only 6 mm fell. The weather remained cold and an additional storm dropped more snow. As of this writing, the snowline is at ≈ 2,500 feet (762 meters).



Shortly after the storm I visited Peavine Ridge. This scene (pictured) is reminiscent of this part of Peavine Ridge 35 to 40 years ago when deep snow consistently lined the road during the winter. This is an interesting statement! Currently I have proxy data to validate this statement and I am currently analyzing data that will hopefully support this statement. The idea is to identify and quantify the changes and impacts that are taking place in this part of the Sierra Nevada.



The snow on the conifer branches was so very beautiful. Frequently during sunny weather much of this snow vaporizes via sublimation. When I visited the ridge the weather was consistently overcast with daytime temperatures only slightly above freezing. Many of the branches were tipped with long icicles. My camera refused to work in the cold. This was a shame as the icicles were a striking sight.



Much of the January snow had melted from this portion of Peavine Ridge during late January. There was considerable moisture in and on the soil before the early February snow arrived. Despite over 78 cm of snowfall, the latent heat of the liquid water (and heat conduction of the soil to a lesser degree) prevented the accumulation of snow at this site. This is one of the indicators of snow/ice albedo temperature feedback that I am watching closely.

For clarity and accuracy the heat capacity of water is 4.1855 kJ (kg K)^-1, about 4 times that of soil. This too is a major consideration. I apologize for omitting this important detail.



Now as I write, yet another major weather shift is taking place in our area. Ferocious winds are now blowing as the next storm arrives. The moisture from this storm is subtropical in origin. Temperatures are rising quickly and snow levels are forecast to rise to above 7,000 feet (2,134 meters). Heavy rainfall is forecast. Considerable flooding is possible as the rain erodes the deep snowpack in the Sierra Nevada. It is possible that there will be some cold air advection as the subtropical moisture exits the region. Snow levels could drop once again to the 2,500 - 2,000 foot level (762 to 610 meters).

Stay tuned…

[fermi de Sousa]

Hi Robert,
Your weather sounds as bizarre as ours!
At least you are getting more precipitation though there is then the threat of flooding.
Enjoy your time in the hills and getting back to your garden 🙂
And keep us informed!
cheers
fermi