Laboratory Exercise: Interacting Earth Spheres
We have been studying the Earth’s spheres; hydrosphere, lithosphere (or pedosphere if we are
just examining shallow soil systems), and atmosphere. Although we often learn about each
system separately, they do not exist as isolated sphere. A water molecule may be found in the
pedosphere one day, and the next day it may be taken up by a plant (biosphere) and then
transferred to the atmosphere through evapotranspiration. Gases given off from a volcano travel
from the lithosphere to the atmosphere, and then can dissolve into atmospheric moisture and fall
back to land in a raindrop. In this activity, we will study how these systems interact through 2
drought case studies.
Pre-lab Exercises
In this lab activity, we are thinking about the interactions of Earth spheres, and in particular, the
exchange of water from one sphere to another (does this remind you of our water cycle lecture?).
Which type of transfer does each describe? Check your answers at the bottom of this page.
1. Water evaporates from the surface of a lake.
2. Rainwater infiltrates and recharges the soil.
3. Animals drink water from a stream.
4. Water evaporates from soil.
5. Plants take up water from the soil.
Options include:
A. atmosphere-hydrosphere interconnection
B. hydrosphere-pedosphere interconnection
C. biosphere-pedosphere interconnection
D. hydrosphere-biosphere interconnection
E. atmosphere-biosphere interconnection
F. pedosphere-atmosphere interconnection
Drought in California
Since 2012, California has been in the midst of a severe drought.
Lakes are drying up, soils are dry and cracked, and people are being
asked to conserve water in any way they can. If you live in
California, the evidence is everywhere. As scientists in training, you
are being asked to examine the evidence below. What factors
determine whether there is, or will be, a drought? Can you look at
just one month’s worth of climate data?
,Palmer’s Drought Indices
From NOAA’s National Climatic Data Center Website (see citations at the end)
“The Palmer drought indices measure the balance between moisture demand
(evapotranspiration driven by temperature) and moisture supply (precipitation).
The Palmer Z Index depicts moisture conditions for the current month, while the Palmer
Hydrological Drought Index (PHDI) and Palmer Drought Severity Index(PDSI) depict the
current month's cumulative moisture conditions integrated over the last several months.
While both the PDSI and PHDI indices show long-term moisture conditions, the PDSI
depicts meteorological drought while the PHDI depicts hydrological drought.
The PDSI map shows less severe and extensive drought in the West and parts of the
Plains than the PHDI map because the meteorological conditions that produce drought
are not as long-lasting as the hydrological impacts.”
For questions 1 & 2 below, look at the U.S. national chart showing the Palmer Z-Index for and
the U.S. national charts showing the Palmer Hydrologial Drought Index for the same months.
1. Palmer Z-Index:
a. If you ONLY look at the Palmer Z-Index for September, 2014 would you say
that California is in the midst of a drought? Why or why not?
b. How does the Palmer Z-Index map for March, 2015 compare to the map for
September, 2014?
, 2. Palmer Hydrological Drought Index (PHDI) maps:
a. If you look at the PHDI maps September, 2014 as compared to March, 2015
would you say that the drought in California has gotten better or worse?
b. What other state(s) are impacted by extreme drought in March 2015?
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