Implementing hydrology (groundwater and rivers) into...

Gonzalo Miguez MachoNon-linear Physics Group

Universidade de Santiago de Compostela

Implementing hydrology (groundwater and rivers)

into RAMS

Gonzalo Miguez Macho,Group of non-linear Physics

Universidade de Santiago de Compostela, Galicia, Spain

Ying Fan (1), Chris P. Weaver (2), Robert L. Walko (3), Alan Robock (2)

Departments of (1) Geology and (2) Environmental SciencesRutgers University, New Brunswick, New Jersey, USA(3) Department of Civil and Environmental Engineering

Duke University, Durham, NC , USA



What does groundwater do for climate?



What does groundwater do?

- redistributes soil water in space

- sustains stream flow in humid and sub-humid climate, receives loosing streams in arid climate

- temporarily holds wet-period infiltration, and later supplies dry-period evapotranspiration

1. Atmosphere

2. Soil-Vegetation 3. River Network

4. Groundwater

OceanNear Surface

Subsurface



10

9

8

7

6

5

4

3

2

1

0

0.50.40.30.20.10.0

Soil Water Content

Silt Loamcapillary rise 0.45meffective porosity 0.35pore-size distrib. index 1.20

10

9

8

7

6

5

4

3

2

1

0

0.50.40.30.20.10.0

Soil Water Content

Sand Loamcapillary rise 0.25meffective porosity 0.25pore-size distrib. index 3.30

10

9

8

7

6

5

4

3

2

1

0

De

pth

Belo

w L

and

Surf

ace (

m)

0.50.40.30.20.10.0

Soil Water Content

Clay Loamcapillary rise 0.90meffective porosity 0.45pore-size distrib. index 0.44

Equilibrium soil water profile above a water table at four depths (1, 2, 5, and 10m) for the three soil types in Salvucci and Entekhabi (1995).

The water table acts as a lower boundary condition for the unsaturated soil



Water table depth (m) measurements over the U.S.

Shallow water

tables cover large

areas of North

America.



Temporal Variability30

20

10

0R

ain

fall (

mm

)

3603303002702402101801501209060300

2.0

1.5

1.0

0.5

0.0

(m)

3603303002702402101801501209060300Day in 2003

1.6

1.4

1.2

1.0

0.8

0.6

(m)

270265260255250245240235230225220215210205200195190185180Day in 2003

6.0

5.0

4.0

3.0

W

ate

r T

ab

le D

ep

th

3603303002702402101801501209060300Day in 2003

6.0

5.6

5.2

4.8

4.4

W

ate

r T

ab

le D

ep

th

270265260255250245240235230225220215210205200195190185180Day in 2003

(a)

(b)

(c)

(d)

(e)

(f)

Bound Brook Hourly Precipitation Station

Morrell 1 Well (depth = 3.35m)

Readington School 11 Well (depth = 15.24m)

Readington School 11 Well (depth = 15.24m)

Morrell 1 Well (depth = 3.35m)

Bound Brook

Rainfall

Station

Readington

School 11

Well

Morrell 1

Well



15

10

5

0

10 100 1000

6

4

2

0

109876543210

20151050

10 100 1000

43210

109876543210

200150100500

10 100 1000

54321

109876543210

20151050

10 100 1000654321

109876543210150100

500

10 100 1000

9

8

7

109876543210

12

8

4

0

10 100 1000

432

109876543210

403020100

10 100 1000

432

109876543210

100

50

0

10 100 1000

5432

109876543210

120

80

40

0

10 100 1000876543

109876543210

100

50

0

10 100 1000

432

109876543210

1 Oregon

California

3 Idaho

4 Montana

5 Utah

6 New Mexico

2

7 Texas

8 Nebraska

9 Kansas

10 Louisiana

Year since 01-01-1990 Period (days)



A strong annual

cycle is present at most sites,

along with even longer-term

variability.

The memory of both event-scale

and seasonal-to-interannual

variations are contained in the

groundwater record.



Equations:

Mass balance in groundwater storage:

Darcy’s Law for lateral groundwater flow:

Darcy’s Law for groundwater – river exchange:

Mass balance in surface water storage:

River flow routing from cell to cell to the ocean:(linear reservoir model)

rQQyRx

dt

dSn

g−+∆∆= ∑

8

1

( ) ( )∑

−= rr

rb

rbrbr Lw

b

KzhQ

snrhs QIQQ

dt

dS−++= ∑

7

1

Qs = Ss / ks

Incorporating water table dynamics into the Regional Atmospheric Modeling System (RAMS)

−

⋅=

∫ ⋅+∫ ⋅∞∞

s

hhwQ

nwtdwtd n dzKdzKn

n

2



Atmospheric model grid cell

Soil-Hydro modelgrid cell

rQQR

dt

dn −+= ∑

8

1

wtd

Recharge

Water table depth

Lateral flowDischarge to rivers

Mass balance

Land surface

Recharge4m

Water table 1

15 Soil Layers

Water table 2

Ql lateral flow

Qr river discharge

variable thickness



−

⋅=

∫ ⋅+∫ ⋅∞∞

s

hhwQ

nwtdwtd n dzKdzKn

n

2Lateral flow

wi,j

i, j

Q1

Q2 Q3

Q4

Q5Q6

Q7

Q8

Plan view

h i,j

Mean sea level

Sg

Q8

Q4

R Qr

Cell ij

Cross section view

width of flowcross section

TransmisivityHead difference

divided by distance

conductivity



Surface water (rivers and lakes)

snrhs QIQQ

dt

dS−++= ∑

7

1

s

ss

k

SQ =

( )rbedwtdrcondQr −⋅=

Surface runoff

Groundwater

discharge River inflow from

neighboring cells

River outflow

Mass balance

Residence time

River

conductanceRiver bed





Simulation domain (hydro 12.5 km res., atmosphere 50 km res.)and elevation (m) for the hydro cells.



Initial conditions for water table depth, river flow and soil moisture

-First calculate “equilibrium water table depth” at high resolution (~1.25 km):

Start at the surface and find the depth at which the mean annual recharge compensates lateral flow (recharge estimated from VIC model 50 year simulation at 1/8º resolution).

Dry climate

Humid climate



1.25 km res.







Topography exerts greatest influence

1.25 km res.



Simulation Period 1: Hydrology spin-upGroundwater + River flow: 10 yr (1987-1997), using observed Prep. and VIC estimated ET and surface runoff

1. Atmosphere

2. Soil -Vegetation 3. River Network

4. Groundwater

Ocean

P

Q

Inf

1 layer

ET

Water table

Qr to rivers

forcing

water table

response

baseflow

Example for a location in Kansas





Simulation Period 2: Unsaturated soil layers and vegetation addedGroundwater + River flow + Unsaturated Soil + Vegetation: 12 months (01-01-1997 to 12-31-1997), 60-sec step, using observed atmospheric and radiation forcing

1. Atmosphere

2. Soil -Vegetation 3. River Network

4. Groundwater

Ocean



Infiltration (mm)

Soil moisture (volumetric)

Water table depth (m)

Quick in learning

Slow in forgetting



Simulation Period 3: Evaluating the impact of the newly implemented processes. Compare to gravitational drainage or no drainage at the bottom. Atmospheric and radiative conditions from observations or reanalysis.6 months (05-01-1997 to 09-30-1997)

Groundwater

Control Run: RAMS-Hydro

3 Experiments:

Free-Drain (FD) No-Drain (ND)



Monthly precipitation from observations



Water table depth

The pattern doesn’t vary much. Water table depths oscillate (order 1m) around the equilibrium value



Soil moisture in the root zone (top 2m)

Soil moisture horizontal distribution resembles the water table map, even after a dry summer. Groundwater increases persistence of soil moisture conditions



Recharge : flux of water to or from the water table

Blue areas are regions where groundwater is supplying water to the unsaturated soil layers on top



Difference in root zone soil moisture: water table run – free drainage run

Run with free drain scheme is much drier in shallow water table areas



Difference in root zone soil moisture: water table run – no drain run

Run with no drain scheme is much wetter over extensive areas



Conclusions:

-Groundwater has a strong influence on near surface soil moisture distribution at continental scale.

-There is a large spatial variability in water table depth across a continent. Any uniform treatment of soil water drainage (free drain, no drain) will likely bias certain regions.

-Groundwater is quick in learning and slow in forgetting the climate forcing. This has important implications for atmospheric processes and land-surface feedbacks. Past climatic events are preserved in the subsurface and can be recalled at a later time to affect soil water fluxes and river flow.



Groundwater

Control Free-Drain No-Drain

?

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