Conifers capture the snow, but do they intercept it?

Cross-posted at Highly Allochthonous

split figure with snow covered conifer on left with bare ground underneath. On right, snow covered ground with snowy deciduous forest in background.

Conifers (left) capture much more snow than grass (right foreground) or deciduous forest (right background). But will they keep the ground dry all winter? (Photo by A. Jefferson, 2017)

If you’ve walked through the forest on a rainy day and noticed that it’s drier under the trees, you’ve experienced interception.

In hydrology, interception is when water gets hung up on vegetative leaves, needles, or branches and never makes it to the ground. The precipitation gets evaporated (if liquid) or sublimated (if solid) back into water vapor directly from the vegetative surface before it gets a chance to hit the ground and infiltrate or run off. (If the water hangs out in the vegetation for a while but eventually makes it to the ground, we call it stemflow or throughfall depending on whether it ran down the tree trunk or not.)

Interception can be a pretty significant component of the water budget. In forests, the vegetation can intercept 20-40+% of precipitation. In grasslands, the numbers are in the 10-20% range. Even litter, the dead plant material covering the soil, can cause interception. Interception rates depend on plant type and density, but also how much rain you get, how fast it falls, and how much evaporation can occur during and between storms.

In the winter, interception still happens during snowfall, but now vegetation type really matters. Since deciduous trees shed their leaves in the winter, they become pretty useless for interception. In the picture above, you can’t really see the difference between the deciduous forest and the lawn — they are both fully snow-covered. On the other hand, since conifers retain their needles, they can capture a lot of snow — and you can see that in the bare ground under the trees at left.

Whether the conifers truly intercept all that snow is more complicated. Conifers can initially hold large snow loads, but wind can blow that snow onto the ground, it can be dumped off in large clumps, and melting within the snowpack on the branches can allow the water to drip to the ground. In order to effectively intercept the water and return it to the atmosphere, we’d need sublimation to happen faster than those other processes. But does that happen?

In a study in Oregon’s Umpqua National Forest (Storck et al., 2002), mature conifers initially captured up to 60% of the snowfall (up to at least 40 mm). When conditions were warm and conducive to snowmelt after the snowstorm, 70% of the water left the canopy as meltwater drip and 30% left as masses of snow falling to the ground. Only if the weather remained below freezing after snowfall, could sublimation work to reduce the snow storage in the trees. But that goes slowly, at an average rate of ~1 mm/day. If the weather got above freezing, then melting and dumping took over. Overall, the study site got about 2000 mm of precipitation in the winter and the ground in the forested areas experienced about 100 mm less than the ground in the open areas, giving a winter interception rate of about 5%.

Of course, that’s only one study and other modeling and experimental work adds more nuance and complication. Climate and solar radiation affect sublimation rates. Canopy density affects sheltering by wind and interception. And more. High spatial resolution modeling of two sites in Colorado and New Mexico gives interception values of 19% and 25%, respectively (Broxton et al., 2015). When they consider all of the processes happening to redistribute snow around a patchy forest, they conclude that the driest areas are under tree canopies and the wettest areas are <15 m from the edge of the canopy. If you get farther out into an open area, it gets drier again, though not as dry as under the forest cover. And the differences are not small, snow water input can be 30-40% higher near the edge of the canopy than underneath it. So next time you walk through a forest in the rain or snow, be impressed by the hydrologic work the trees are doing to keep you dry, and know that interception adds up to a significant amount of water. But if it's a warm winter day, don't be surprised to feel a cold meltwater drip from the pine tree above you -- or get a load of snow dumped on your head -- because even conifers can't hang onto the snow long enough to keep the ground dry forever.
Read more:
Broxton, P. D., Harpold, A. A., Biederman, J. A., Troch, P. A., Molotch, N. P., and Brooks, P. D. (2015) Quantifying the effects of vegetation structure on snow accumulation and ablation in mixed-conifer forests. Ecohydrol., 8: 1073–1094. doi: 10.1002/eco.1565. (pdf available via ResearchGate)

Storck, P., D. P. Lettenmaier, and S. M. Bolton, Measurement of snow interception and canopy effects on snow accumulation and melt in a mountainous maritime climate, Oregon, United States, Water Resour. Res., 38(11), 1223, doi:10.1029/2002WR001281. (open access)

GSA abstract: Abundance and Geomorphic Function of Wood in Urban Stream Systems

Later this month, Caytie, Garrett, and I will be representing the Watershed Hydrology Lab at the Geological Society of America Annual Meeting in Seattle, Washington. Garrett will be presenting the following talk on Monday at 2:55 in Conference Center Chelan 5.

Abundance and Geomorphic Function of Wood in Urban Stream Systems

Blauch, G. and Jefferson, A.

Large wood serves important geomorphic and ecologic functions in streams, as established by research set in relatively undisturbed watersheds. However, the dynamics and function of wood in urban streams has not received similar attention. Previous studies have not clearly distinguished between the effects of low recruitment potential due to developed riparian zones and hydrograph flashiness increasing wood mobility. In order to focus on the effects of hydrograph flashiness, our study focuses on wood abundance and function across urban northeastern Ohio streams where protected riparian buffers offer recruitment opportunities. Impervious surface cover is used as a proxy for urbanization’s effect on the stream hydrology. The frequency and geometry of large wood was surveyed within the bankfull channels in 11 stream reaches, with watersheds that span 0.39 – 88 km2 and 0.56 – 40.1% impervious cover. Geometry measurements cover length, diameter, and planform orientation for individual pieces and smaller jams, as well as 3D structure of significant wood jams in 7 of the 11 streams using Structure-from-Motion techniques. Measurements of the long profiles, stream banks, and streambed sediments provide indications of the geomorphic context of large wood with respect to pool formation, bank erosion, and sediment storage. Preliminary results show a decrease in the occurrence of large wood pieces from 36 per 100m of stream length in the least developed watershed to as little as 1 piece per 100m at higher impervious surface covers. Of those streams with wood stored as both individual pieces and as part of jams, 73% of the total wood (by count) is stored as jams on average. In the most developed, urban watersheds, early re-surveys show that even these larger jams can be mobilized. These results suggest that even though wood is available to the stream, flashy urban hydrographs still have an influence on the presence of wood within urban streams. With large wood often considered in management and restoration practices, protection of the riparian buffer is not enough to maintain the presence of wood – and the geomorphic and ecologic benefits provided by it – in these flashy urban systems.

wood jam spanning a stream, man on right side gravel bar looking at something in his hands.

Garrett get ready to take some data on this wood jam in West Creek, August 2017.

GSA abstract: Storage Dynamics Revealed by Water Isotopes Provide Insight into Water Quality Function of Stormwater Green Infrastructure

Later this month, Caytie, Garrett, and I will be representing the Watershed Hydrology Lab at the Geological Society of America Annual Meeting in Seattle, Washington. I will be presenting the following talk on Wednesday at 10:15 in WSCC Room 612.

Storage Dynamics Revealed by Water Isotopes Provide Insight into Water Quality Function of Stormwater Green Infrastructure

Jefferson, A., Sugano, L., Buzulencia, H., Avellaneda, P., and Kinsman-Costello, L.

Increasingly popular, stormwater green infrastructure is touted as improving water quality, through filtration and retention that allows plant uptake and biogeochemical processing to occur. Many data sets reveal large inter-storm variability of water quality in green infrastructure effluent, suggesting that internal dynamics that control water transit time may play an important role in the water quality functioning of green infrastructure. We hypothesized that collecting data on water stable isotopes, in addition to solute chemistry, would provide insight into transit times and would help explain variability in water quality flowing out of three forms of green infrastructure. Water isotopes, chemistry, and fluxes were measured from bulk precipitation, inflow, outflow, and surface water storage for a green roof, bioretention cell, and wetland at a site in northeastern Ohio.

On the green roof, outflow isotopes were variable within storms, but flow-weighted averages were similar to bulk precipitation for each event, suggesting transit times of minutes to hours. First flush behavior for solutes was exhibited for some storms and some solutes, but much of the inter-event variability in solute export could be explained by precipitation amount and antecedent dry period of each storm. In the bioretention cell, inter-event storage and release of old water is sometimes observed in the outflow isotopes. Outflow nitrogen concentrations were generally lower when old water was discharged, suggesting that denitrification is occurring within the bioretention cell. However, antecedent dry period also appears to influence nitrogen concentrations, suggesting some discharge of new water even during moderately-sized storms. Isotopic hydrograph separation was possible for some storms in the wetland, and in these cases, solute concentrations in the outflow can be explained by mixing of new water with previously ponded water. Where solute concentrations can’t be explained by mixing, biogeochemical processing may be happening during the storm period.

This work builds on work I presented earlier this year at the HydroEco 2017 (June) and the GSA regional meeting (March).

GSA abstract: Soils and Geomorphology of Five Reclaimed Surface Mine Sites in the Cuyahoga Valley National Park, Ohio

Later this month, Caytie, Garrett, and I will be representing the Watershed Hydrology Lab at the Geological Society of America Annual Meeting in Seattle, Washington. Caytie will be presenting the following poster on Tuesday, October 24th in spot 257-4 in the Washington State Convention Center.

Soils and Geomorphology of Five Reclaimed Surface Mine Sites in the Cuyahoga Valley National Park, Ohio

Ruhm, C., Jefferson, A., Blackwood, C., Minerovic, A., and Davis, C.

Abandoned mine lands are common to human-altered landscapes. Despite the improvement of remediation techniques, the geomorphic and ecological function of historical abandoned mines persist as a concern to many regions. Cuyahoga Valley National Park (CVNP) is home to ~50 abandoned gravel, sand, and topsoil mines. After mining ceased, these sites were backfilled, compacted, and seeded. Following reclamation, rills and gullies appeared on some steep slopes within the sites. Additionally, reforestation efforts at these sites have not been successful. The causes of these failures are not well understood. Previous studies of coal mines have pointed toward altered chemical properties as a cause of reforestation failure. However, since the CVNP sites lack coal and associated tailings, further research is required to understand how the mining and reclamation affect erosion control and reforestation efforts.
Our research is investigating the geomorphology and soil quality of five of the abandoned mine sites within CVNP relative to four reference sites with similar slope and aspect, but mature forest. We aim to (1) determine the quality of the soils within the sites in comparison to the reference locations, (2) determine if the sites are currently undergoing erosion in exceedance of the reference locations, and (3) inform future reclamation projects to assist in the creation of successful practices.

We have collected ~250 soil samples from the five sites and four reference locations to analyze for grain size distribution, soil pH, concentrations of extractable Al, Ca, Fe, K, Mg, and P, and total C and N. Preliminary results indicate a marked difference in soil pH between the mined (pH 7-8) and forested reference (pH 3.6-6) sites. Measurements of infiltration capacity and bulk density are underway. Preliminary results of bulk density indicate that the density is very high (>2000 kg/m3) in the mined sites, which may be impeding plant growth and promoting overland water flow. Pressure transducers in three gullies on the mined sites indicate water flow during and following intense rainfall, and silt fences are allowing us to quantify sediment flux. Mapping of gully long profiles and cross-sections will enable us to calculate the volume of sediment removed by the gullies since reclamation occurred.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6
doi: 10.1130/abs/2017AM-303598

Grassy hill with trees in the background. Cloudy sky.

One of the sites that Caytie is studying, as it appeared in October 2016. The several acre site was host to invasive Phragmites reeds and a failed tree planting.

August climate impacts stories: Hurricane Harvey, other climate change fueled-floods, and more

August 30th: Harvey reminds us that we should treat climate change as we treat other public health threats. That’s the argument in this New York Times op-ed: Harvey, the storm that humans helped cause.

Holthaus-harveyAugust 29th: The most sobering hot-take on Harvey is by Eric Holthaus: Harvey is what climate change looks like.

August 27: Michael Mann offered a clear explanation of the climate change-Hurricane Harvey connection.

Climate change boosts hurricanes through higher and hotter seas say @KHayhoe @AndrewDessler: The relationship between hurricanes and climate change.

August 26: Rapid hurricane intensification, like we’ve seen with Harvey, is consistent with climate change, writes Chris Mooney.

August 25: First tanker crosses Arctic from Europe to Asia-without icebreaker help. Fleet of 15 coming soon.

August 24:Alaska’s permafrost is thawing, and that has huge implications, locally, regionally, and globally. (My colleagues Beth Herndon and Lauren Kinsman-Costello are studying how permafrost melt, wetlands, carbon, and phosphorus interact in the Alaskan tundra.

2017WarmNights_cleveland_en_title_lgAugust 23: As the number of warm nights is increasing, it makes it harder to recover from heat waves.

August 22: Britain’s seabird colonies face catastrophe as warming waters disrupt their food supply. But we don’t know exactly how big problem is because the UK government won’t fund a new seabird census. The last one was done in 2000.

August 20: High Ground Is Hot Property as Sea Level Rises: Climate Gentrification in Miami.

August 19: Climate gloom and doom? Bring it on. But we need stories about taking action, too. (via @ClimateCuddles)

August 16:Humid heat waves that can kill healthy people in hours will affect millions in South Asia in decades.

August 15:

August 14th: 91 volcanoes discovered under the West Antarctic Ice Sheet!!!! This is so exciting on multiple levels, from the pure geo-nerdery to the potential climate change impacts. Geeking out. (Read Andrew Freedman’s article for all of the details, but its possible that (1) geothermal heating associated with the volcanoes will contribute to melting and destablization; (2) melting the ice sheet could enhance volcanic activity as the pressure is released; and (3) the volcanoes will help anchor the ice sheet in place and reduce the possibility of catastrophic collapse. These are not mutually exclusive possibilities.)

 

August 13th: Flooding in Miami now happens every spring tide. Rainfall & storm surges don’t help out either. I liked the headline in the Washington Post: “Flooding in Miami is no longer news – but it is certainly newsworthy.”

August 12th: Sometimes you just have to laugh, so you don’t cry. Talking about climate politics, with humor. Thanks, Stephen Colbert.

 

August 11th: Climate change fueled a mega-rainstorm that flooded Louisiana 1 year ago, and the vulnerable people caught in the flood are still picking up the pieces. Special and important reporting by Climate Central.

August 10th: A new paper in Science shows that European floods have shifted in timing, up to 2 weeks earlier per year, since 1950. What’s particularly intriguing about the study is that the timing shifts haven’t just occurred in snowy regions, but also in places where rainfall is causing water tables to rise and soils to become more saturated earlier in the spring.

August 9th: Erratic weather affects subsistence rice farmers in Madagascar, further proof that some of the worst climate change impacts will be felt by those least responsible for causing it.

August 7th: Peru’s glaciers have made it a laboratory for adapting to climate change. It’s not going well. This is a really nice feature story from the Washington Post.

August 5th: A new report says that extreme heat & weather could kill 50x more people per yr in Europe by 2100 than today. That may be overestimate, but a more reasonable number in the report is that 2 out of every 3 Europeans will be affected by weather disasters (per year?) compared to 1 in 20 today. Heat waves will account for 99% of all the excess deaths predicted, and it’s awfully hard to relocate away from a heat wave.

August 4th: If you are not yet listening to smart & human commentary on climate change, what’s stopping you?

 

August 2nd: A visualization that condenses space and time to tell a powerful story about the local and global impacts of climate change through the 20th century and beyond.

 

Congratulations Garrett and Caytie!

Congratulations to the Watershed Hydrology Lab’s two first year MS students for each achieving two big accomplishments. They have both successfully defended their MS thesis proposals, putting them in a great position to be productive on their research this summer.  Also, both Caytie and Garrett were awarded Geological Society of America student research grants to help support their research.

Caytie's work focuses on the soils and geomorphology of abandoned surface mines in Cuyahoga Valley National Park.

Caytie’s work focuses on the soils and geomorphology of abandoned surface mines in Cuyahoga Valley National Park.

Garrett's work focuses on the abundance and mobility of wood in urban streams. 

Garrett’s work focuses on the abundance and mobility of wood in urban streams.

 

#365climateimpacts: Snow, ice, flooding, and football (February 1-15)

In January, I launched the #365climateimpacts project, in which I’ll spend a year tweeting stories of the many ways climate change is impacting people, ecosystems, and the earth; ideas for how to communicate about climate change more effectively; and analyses of technologies and policy proposals that show promise for combatting climate change. Here’s what I’ve shared in the last two weeks.

February 1:
The Climate Feedback project looks like an awesome way to see how scientists read climate change news.

The most recent analysis on the site is of an article called "The big melt: global sea ice at a record low", published by USA Today.

The most recent analysis on the site is of an article called “The big melt: global sea ice at a record low”, published by USA Today.

February 2 (Groundhog Day):
Climate Change versus Groundhogs: Even Common Species Will Suffer. (Not pictured: the groundhog who is digging up by back garden.)

February 3:
Melting glaciers affect water supply in Andes of Peru & scientists are on it. Video by @LaurenDSomers.

February 4:
Screen Shot 2017-02-12 at 4.01.04 PM

I see a trend – and my eyes don’t deceive. Great Lakes annual average ice cover declined 71% from 1973-2010.

February 5 (Superbowl Sunday):
Is Climate Change Making Temperatures Too Hot for High School Football? Will it get too hot for football in the South? State rules aim to prevent heat deaths.

February 6:
Screen Shot 2017-02-12 at 2.55.54 PM
What does a graph like this mean? It means ocean is taking up heat that CO2 emissions would otherwise add to atmosphere.

February 7:
I got a bit gif happy with today’s #365climateimpacts tweetstream, so you should really head over to twitter to enjoy the thread. I like snow. I like to sled, build snowmen, snowshoe, and how pretty snow is. Loss of snow is one reason I care about climate change. Today it is 57 F and raining steadily here in NE Ohio. I keep thinking about how we’d have a foot of snow if it were cold enough. Instead, I spent an hour in my class talking about the fun ways hydrologists have of measuring snow. With bare ground outside.

The average US snow season shortened by 2 weeks since 1972. Snow covered area is decreasing. The figure below is from the US EPA’s great Climate Change Indicators site, under the heading “Snow Cover.

This figure shows the timing of each year’s snow cover season in the contiguous 48 states and Alaska, based on an average of all parts of the country that receive snow every year. The shaded band spans from the first date of snow cover until the last date of snow cover.

This figure shows the timing of each year’s snow cover season in the contiguous 48 states and Alaska, based on an average of all parts of the country that receive snow every year. The shaded band spans from the first date of snow cover until the last date of snow cover.

Climate normals say that my area averages 45″ of snow per winter, but I haven’t seen anywhere near that most of the 5 years I’ve lived here. Of course, 5 years isn’t long enough to identify any trend (I’m not arguing it is), but my experience fits in the pattern of less snowy winters that are being observed across the United States. Here’s some data stretching 60 years. The figure below is from the US EPA’s great Climate Change Indicators site, under the heading “Snowfall.” Red is less snow, more rain.

This figure shows the average rate of change in total snowfall from 1930 to 2007 at 419 weather stations in the contiguous 48 states. Blue circles represent increased snowfall; red circles represent a decrease.

This figure shows the average rate of change in total snowfall from 1930 to 2007 at 419 weather stations in the contiguous 48 states. Blue circles represent increased snowfall; red circles represent a decrease.


(PDF versions of the Snow Cover and Snowfall pages)

February 8 (National Kite Flying Day):
Good morning, Twitter. It’s National Kite Flying Day! Do you think I can tie that to climate change?
President Obama has been appreciating kite flying, recently.
Back in the day, it wasn’t just surfboards powered by wind. It was big ships. Admittedly, with sails, not kites, but I’m doing the best I can to tie to #nationalkiteflyingday.
Modern shipping produces huge amounts of greenhouse gas emissions and wind is a renewable, carbon-free energy source.
One idea is to attach big kites to ships to provide free & CO2-free energy.

February 9:
It’s the middle of winter & something is seriously wrong with Arctic sea ice. Sea ice hit record low extents in November, December, and January. Nice reporting at Mashable by Andrew Freedman.
seaice

February 10 (National Umbrella Day):I
Climate change intensifies the water cycle, increasing heavy rainfall events. The figure below is from the US EPA’s great Climate Change Indicators site, under the heading “Heavy Precipitation”.

This figure shows the percentage of the land area of the contiguous 48 states where a much greater than normal portion of total annual precipitation has come from extreme single-day precipitation events. The bars represent individual years, while the line is a nine-year weighted average.

This figure shows the percentage of the land area of the contiguous 48 states where a much greater than normal portion of total annual precipitation has come from extreme single-day precipitation events. The bars represent individual years, while the line is a nine-year weighted average.


(pdf version of the Heavy Precipitation Climate Change Indicators page)

February 11:
The first year’s results from NASA Project OMG (Oceans Melting Greenland) reveal that Greenland’s thick glaciers in deep water are most affected by warmer ocean waters. Follow the project lead scientist Josh Willis @omgnasa on Twitter.

February 12:
Suburbs are increasingly threatened by wildfires due to climate change. The wildland-urban ecotone is where warmer winters longer droughts & climate change consequences flare up.

February 13:
With lots of attention focused on the massive rainfall, flooding, and dam and levee safety issues in California, it seemed like a good time to find out how climate change is expected to alter rainfall patterns in the state. Sure enough, “pineapple express” storms (that bring lots of rain to high elevation areas where it normally snows) are expected to increase as the climate warms.

Satellite image showing narrow band of clouds stretching from Hawaii to California

A “pineapple express” atmospheric river takes aim at California in December 2014. (NOAA/NASA GOES image)

February 14:
Minnesota Public Radio ran a fantastic feature on how climate change is affecting ice cover on Lake Superior between Bayfield and Madeling Island, Wisconsin. For 250 year-round residents of the island, winter offers an ice road and the freedom to move back and forth without being tied to the ferry schedule. Except that, for two years running, the ice hasn’t been thick enough to drive on and the ferry has run all winter. This story is personal for me, because my family has owned land on Madeline Island for 4 generations, and I remember the thrill and terror of driving the ice road on winter visits.

The view from our family's land on Madeline Island, February 3rd, 2017. Photo courtesy of J. Jarvis.

The view from our family’s land on Madeline Island, February 3rd, 2017. Photo courtesy of J. Jarvis.

February 15:
The New York Times highlights a rare Republican call to climate action, in which the “elder statesmen” of the Climate Leadership Council calls for a carbon tax. A report out earlier this month from the Yale Program on Climate Change Communication, shows that 62% of Trump voters support either taxation or regulation of greenhouse gases. The question is: Will Republican politicians listen to the elders or the voters, or will they continue to deny climate change and obstruct meaningful actions to slow its course.