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