dr. nicolas zegre understanding the hydrologic cycle
TRANSCRIPT
Dr. Nicolas Zegre
Understanding the Hydrologic Cycle
Global Water Resources• Oceans = 96.5% of all water on Earth• 0.001% in the atmosphere
• Freshwater = 2.5% of total global storage• 69.56% is in icecaps, glaciers, & frozen water• 30.1% is groundwater & 0.05% is soil moisture• Leaving 0.29% surface water (0.008% of all water on Earth!)
Dingman Table 3-1
Oceans96.5%
Fresh water2.5%
Ice & snow69.56% Liquid
water30.44%
Groundwater98.8%
Soil moisture0.2%
Streams, lakes1%
All water Fresh water Liquid fresh water
Water as a scarce resource
• Human constraints• Population growth• Urbanization• Industry and agriculture• Wasteful practices
• Conflicts• Between human uses• Between different groups of humans• Between humans and ecosystems
“There is no shortage of water in the desert but exactly the right amount…There is no lack of water here, unless you try to establish a city where no city should be.” Edward Abbey, Desert Solitaire
Laituri, CSU
Where we are headed…
•qualitative and quantitative understanding of concepts and physical principles that govern occurrence, distribution, and circulation of water
•emphasis on physical understanding and parameterization of hydrologic processes
- how does rainfall become streamflow? - how long does water stay in a watershed?
Overview Hydrologic Cycle
To understand hydrological processes, we need to focus on a manageable control volume: the catchment or watershed
Why the watershed?
• Known inputs• Known boundaries• Integrates multiple systems
• e.g. biochemical, ecological, hydrological
Eagleson, 1991
Space-time scales
Localscale
Hillslope/fieldscale
Headwater/catchmentscale
Riverbasinscale
Continentalscale
Brutsaert, 2005
Stream Order
•Streams within watersheds are often classified hierarchically
•Segments categorized by their order in the system
Horton – Strahler method
About 85% of all stream miles in the U.S. are first to third order streams … close to 3 million miles
Hydrologic Cycle
Hendriks 2010
The Hydrologic Cycle
From Ross Woods
AtmosphereContinent
Hydrologic Continuity Equation
• General terms: Rate of accumulation of mass or volume in system = Input rate - output rate
• Hydrologists (density ~ constant w/ T, thus use V):
• Assumptions:• We can measure or estimate all of the components• Storage
)()( tOtIdt
dV
Water Balance Components
Et
ETGWQGWQPdt
Vdoutoutinin 0
Residence time
Atmospheric water
Surface water
Ocean water
Groundwater
OorI
VorMTr
Residence time, Tr: measure of the average time a molecule of water spends in a reservoir
Average residence times
4 y
20,000 y
2,650 y
0.02 y
Controls on the Hydrologic Cycle
Climate, Morphology, & Landcover
Controls on hydrology
Jones et al, 2012
WAT
ER-L
IMIT
ED
ENER
GY-L
IMIT
ED
Controls on hydrology Climate, Morphology, & Landcover Including topography, organization, soils & geology
McGuire et al., 2005 WRR
5 6 7 8
1
2
3
4
5M
ean
tra
nsi
t ti
me,
m [
y]
ln(a/tan)
100 150 200 250 300
1
2
3
4
5
r2=0.85 r2=0.72
Median flowpath length, L [m]
WS02 WS03 WS08 WS10 MACK LOOK
0.2 0.3 0.4 0.5 0.6
1
2
3
4
5
r2=0.64
Median flowpath gradient, G [-]
0 500 1000 1500
1
2
3
4
5
r2=0.91
L/G [m]
5 6 7 8
1
2
3
4
5
Mea
n t
ran
sit
tim
e, m
[y]
ln(a/tan)
100 150 200 250 300
1
2
3
4
5
r2=0.85 r
2=0.72
Median flowpath length, L [m]
WS02 WS03 WS08 WS10 MACK LOOK
0.2 0.3 0.4 0.5 0.6
1
2
3
4
5
r2=0.64
Median flowpath gradient, G [-]
0 500 1000 1500
1
2
3
4
5
r2=0.91
L/G [m]
Controls on hydrology
Climate, Morphology, & Landcover Including topography, organization, soils & geology
Climate, Morphology, & Landcover
Controls on hydrology
Flow Paths to the Stream
saturation excessinfiltration excess
Surface flow – rapid delivery of water to stream
Subsurface flow – slower delivery of water to stream
Flow Paths to the Stream
Importance of existing moisture in watershed (pre-event water)
Flow Paths to the Stream
Basin Stores & Processes
Hendriks 2010
Input or output processes
Storage
Lowercase = hydrologic processes