Monitoring the hydrologic cycle in the Sierra Nevada mountains

Photo © Roger J. Wyan Photography

What is the hydrological cycle?

Why do scientists measure the hydrological cycle?

Who we are and where are we located?

How do we calculate the water balance for a tree?We measure

Collecting and retrieving data.

Effect of increased density of the forest and forest treatments on water cycle.

What is the hydrologic cycle?The hydrologic or water cycle is the movement of water on, above, below, and through the earth’s surface.

Biological Property

TranspirationPhotosynthes

is

Chemical PropertyPrecipitationDissolution

EnergyEnergy transfers through the water cycle

Processor Properties of Water (Adapted from Ripl and Hilmann, 2000)

“Water: the Bloodstream of the Biosphere”

Why do scientists measure the hydrologic cycle?

Weather forecasting Water use forecasting Understand climate trends Flood preparation Hydrologic modeling

Why is it important for scientists to measure the hydrologic cycle?

Who We Are: The Southern Sierra Critical Zone Observatory

Professors, students and staff from over 9 different universities and institutions

Main site is located 10 mi E of Shaver Lake

Second site in Sequoia National Park

3 additional flux tower sites at different elevations

Image courtesy SSCZO

The Southern Sierra Critical Zone Observatory

The Critical Zone lies between rock and sky... where water, atmosphere, ecosystems, and soils interact. It is essential to life on Earth, including food production and water quality. (NSF 2005)

The SSCZO is one of 10 observatories throughout the US

We focus on how the CZ interacts with water Key goal: to predict how water budgets and

vegetation will respond to climate change, land management and disturbance.

4 measurement stations located west to east transect at approx. 800 m elevation intervals beginning at 405 m.

All the sites were on soil developed from granitic parent material, and had vegetation that had not been disturbed recently.

Four Critical Zone measurement stations in and around the Upper Kings River basin

.

.. .Illustrated map courtesy Lynn Sullivan

From Goulden et al., 2012

Water BudgetPrecipitation (P) = Evapotranspiration (ET) +Runoff (Q) +Recharge (R) +Change in Storage (ΔS) (can be soil moisture or groundwater)

P = ET + Q + R + SP ET + Q + S

Note: in granitic mountains, such as the Sierra Nevada, R & ΔSgroundwater are often very small

Precipitation (P)Tree transpiration (T)

Evaporation from soil (E)

Runoff (Q)

Deep percolation (R)

Which are the stores & which are the fluxes?

Rainfall Partitioning

Tree image courtesy SSCZO

Groundwater

Atmosphere

Soil Moisture

Infiltration/Recharge (R)

Precipitation

Domestic

Evapotranspiration

Sublimation

Irrigation

Infiltration

ReservoirsRunoff

Environmental Flows

Can one scale up from a single tree to estimate the water balance of a forest?

Measuring Streamflow

Flumes make the stream fit into a known shape.

Runoff is the movement of water over the land surface.

Stream flow is the flow of surface water runoff contained in a stream channel.

Water depth sensors measure the height of water.

Photos courtesy SSCZO and USFS

Tipping Bucket rain gauge measures liquid and solid precipitation

Precipitation measurementsPrecipitation is the general name given for any form of condensed water that falls to Earth’s surface.

Snow depth sensors use sound to record snow depth

Snow pillow records weight of snow

Photos courtesy SSCZO and USFS

Measuring evapotranspiration

The movement of water from the liquid phase to the gas phase occurs by evaporation and/or transpiration.

Evaporation is the change of water from a liquid to a gas by heating.

Transpiration is water released from plants.

Combined, this process is called evapotranspiration.

Sap flow

Flux tower instruments

Photo © Roger J. Wyan Photography

Photo courtesy SSCZO

Measuring evapotranspiration

The eddy-covariance flux tower measures water vapor from the surrounding forest. The tower measures: - wind speed and direction- CO2 and H2O gas concentrations- air temperature - relative humidity- solar radiation

The flux tower extends high above the surrounding forest.

Photo © Roger J. Wyan Photography

Visualizing tree's heartbeat: A sap-flux meter monitors a Critical Zone Tree.

Photo courtesy SSCZO

Measuring soil moisture

Water that does not flow to the stream channel moves through the soil and/or rock through a process called infiltration. This water is known as groundwater.

Soil moisture sensors buried at different depths underground.

A series of soil moisture sensors buried underground to understand water uptake by tree roots.

c

Photo courtesy SSCZO

Image courtesy SSCZO

Weather stations

This weather station is used to

measure:

- air temperature- wind speed- relative humidity- solar radiation - precipitation- snow depth

Peak snow depth many years ago

Photo courtesy SSCZO

Collecting and retrieving data An immense amount of data are collected

each year. Instruments are located in remote areas,

making it hard to collect data on foot during the winter

Data stored on a datalogger and can be

downloaded with a laptop

From Kerkez et al., 2012 Photo © Roger J. Wyan Photography

Collecting and retrieving data

The wireless embedded sensor network (WSN) was developed to make it easier to collect data remotely.

Cell phone on the flux tower can be called to retrieve data.

Small radios send data from one node to the next, and end at the base station at the flux tower.

Photo © Roger J. Wyan Photography

From Kerkez et al., 2012

Powering instruments

A series of solar panels and

batteries power all the

instruments within the basin.

Photo courtesy SSCZO

Photo courtesy SSCZO

Photo © Roger J. Wyan Photography

Explore a tree root model by P. Hartsough: https://youtu.be/L9F-QgQb2YY

Fun with Trees:One large healthy tree can lift up

to 4,000 liters of water from the ground and release it into the air.

A tree can absorb up to 48 pounds of carbon dioxide per year and sequester 1 ton of carbon dioxide by the time it is 40 years old.

One large tree can provide a day's supply of oxygen for up to four people.

By late summer, trees transpire more water than we can measure in the soil. Perhaps there is a deeper rooting depth.Excavate the tree to discover the root system.

Image courtesy SSCZO

TRANSPIRATION

Image courtesy OpenStax

TRANSPIRATION

Stoma open, transpiration draws water outside the leaf

RoothairsWater uptake in roots

Cohesion (H-bonds) and adhesion (to cell walls) in the xylem draw the water to the leaves

Wat

er P

oten

tial G

radi

ent

Outside air Ψ= -10 to -100 MPa

Root xylem ψ=-0.6MPa

Soil ψ = -0.3MPa

Trunk xylem ψ=-0.8MPa

Leaf (cell wall) Ψ= -1Mpa

Leaf (air spaces) Ψ= -7MPa

Negative ψ (high)

More negative ψ (low)

Ψ = water potential (units = Pressure)Image courtesy SSCZO

Sierra National forests have had a tradition of fire suppression for the last 100 years.What might be some of the consequences of fire suppression?

FOREST HISTORY

Photo by Eric Knapp, USFS

THINNED UNIT WITH CONTROL IN BACKGROUNDSTANISLAUS-TUOLUMNE EXPERIMENTAL FOREST

How much water is being lost due to excess tree canopies?

How much moisture is getting caught in the canopy and evaporating into the air?

Photos by Matthew Meadows

Summary Water balance is accounting for the

partitioning of precipitation into various fluxes and stores.

Water accounting can be done on any time step; we often do it on an annual time step.

Soil moisture is a store important for tree growth.

We can do a water balance on a tree (sapflux) or a forest (flux tower).

Scaling up from a point measurement involves making assumptions about spatial patterns.

Sierra Nevada forests are overgrown.

Complex-forested terrain surrounding P301, with patchy snow.

Photo by Matthew Meadows