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A Discussion of Groundwater Modeling and Climate Change By Leslie Llado

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Title: A Discussion of Groundwater Modeling and Climate Change By Leslie Llado


1
A Discussion of Groundwater Modeling and
Climate Change By Leslie Llado
2
Introduction
  • Discuss importance of incorporating groundwater
    into climate models
  • Existing groundwater and climate modeling methods
  • Review of three coupled groundwater-climate
    models
  • Problems and suggested modifications

3
Why include groundwater in climate change models?
  • Although groundwater accounts for small
    percentage of Earths total water, groundwater
    comprises approximately thirty percent of the
    Earths freshwater
  • Groundwater is the primary source of water for
    over 1.5 billion people worldwide and over
    fifty-percent of the U.S. population
  • Depletion of groundwater may be the most
    substantial threat to irrigated agriculture,
    exceeding even the buildup of salts in soils
  • (Alley, etal, 2002)

4
Groundwater Modeling Methods
  • Most commonly use MODFLOW software
  • - 3-D finite difference groundwater flow modeling
  • Factors emphasized vary due to
  • Politics
  • Sustainability requirements
  • Location and aquifer characteristics
  • Natural and Urban groundwater recharge mechanisms
  • (Pierrehumbert 2002)

5
Natural Groundwater Recharge
Natural groundwater recharge accounts
for Components of the hydrologic cycle
precipitation, evaporation, transpiration,
sublimation, runoff, infiltration, recharge, and
baseflow Heterogeneity of geological structures,
local vegetation, and weather conditions (Alley
etal, 2002)
6
Urban Groundwater Recharge
  • Urban Recharge
  • Natural Factors Human Influences
  • Anthropogenic activities affect groundwater
    availability
  • Increased Pumping
  • Increased Impervious Cover
  • Diversion of groundwater
  • (Sharp 2006)

7
LSM and GCM Models
  • Land Surface Model (LSM)
  • Consider a surface heat balance equation, a
    surface moisture equation, and a variable to
    represent snow cover
  • Accounts for land topography, but does not
    consider groundwater conditions
  • In locations where groundwater is close to the
    land surface, soil moisture is higher, resulting
    in a cooler land surface
  • Global Climate Model (GCM)
  • When coupled with LSM, can simulate soil
    moisture conditions, humidity, and precipitation
    changes
  • Cannot assess the relationship between changing
    soil, vegetation, and topography
  • By incorporating an aquifer system into the
    model, the interaction between global climate
    systems can be interpreted based on specific
    watershed parameters
  • (Hartmann 264)

8
Integration of Groundwater Modeling into existing
LSMs
  • CLASP II Simulation
  • - York, etal
  • 2. Three-layer Variable Infiltration Capacity
    Model (VIC-3L)
  • - Liang and Xie
  • 3. Soil Hydrological Model
  • - Chen and Hu

9
CLASP II Simulation
  • ATMOS
  • Atmospheric model
  • Single data column using historical atmospheric
    data
  • VOS
  • Vegetation-overland flow-soil model
  • Represents soil vegetation zones with MODFLOW
  • Allows for specification of types of soil and
    vegetation
  • MODFLOW
  • Groundwater modeling program issued by USGS
  • Aquifer properties are simulated by
    incorporating numerical aquifer characteristics
    and the equations for heterogeneous, anisotropic
    media

Coupled aquifer-land surface-atmosphere model to
show decadal impact of climate change on aquifer
using 9 years of historical data
10
CLASP II (continued)
  • Results
  • Reproduced monthly and yearly trends for
    precipitation, evapotranspiration, and stream
    discharge
  • Low calculated soil moisture
  • 5 - 20 of evapotranspiration drawn from aquifer
  • Forty-year drought produced 15 m water table
    decline
  • Aquifer response time of 200 years

11
Three-layer Variable Infiltration Capacity Model
(VIC-3L)
  • Modifications on existing VIC-3L LSM
  • Include infiltration excess runoff mechanism by
    considering effects of subgrid spatial soil
    heterogeneity
  • Account for effects of surface-groundwater
    interactions on soil moisture, recharge rate, and
    evapotranspiration
  • Accounts for
  • One vegetation layer with bare soil
    evapotranspiration
  • Upper soil layer where soil moisture is derived
    from rainfall
  • Lower soil layer that accounts for seasonal soil
    moisture

12
Three-layer Variable Infiltration Capacity Model
(VIC-3L) (continued)
  • Results
  • Successfully simulated the groundwater table
    position and total runoff
  • Correctly represented water budgeting among the
    soil layers, evapotranspiration, and recharge
    rate
  • Showed that when surface-groundwater
    interactions are considered, evapotranspiration
    will be higher

13
Soil Hydrological Model using NCAR MM5
Considers the water exchange between the
unsaturated zone and groundwater using a
soil-surface model where soil water is the result
of groundwater and precipitation Four soil
layers at 0.1, 0.15, 0.25, and 0.5 meters from
the surface with diffusive fluxes between
layers Saturation hydraulic conductivity varies
in a vertical distribution, accounting for the
decrease in soil permeability with increasing
depth
14
Soil Hydrological Model (continued)
  • Average evaporation almost double the
    evaporation for a model of the same area without
    groundwater
  • In the first meter from the surface, soil
    moisture content in the model that included
    groundwater was twenty-one percent higher than
    soil moisture content in the model without
    groundwater
  • With a lower groundwater table, the influence
    of groundwater on soil moisture decreases

15
Conclusions
  • Effects of groundwater can significantly change
    LSM results, especially when aquifer is close to
    land surface
  • Groundwater is an important resource and must be
    considered in climate change studies
  • Large data sets (200 years) needed to
    accurately show groundwater response to climate
    change
  • Extreme climate conditions are useful in
    groundwater modeling
  • LSMs that include groundwater more accurately
    simulate actual land surface conditions
  • With advances in technology, it may be possible
    to incorporate aquifer systems into GCMs

16
References
  • Agenda 21. lthttp//www.un.org/esa/sustdev/docum
    ents/agenda21/index.htmgt, October 31,
    2006.
  • Alley, W.M., Healy, R.W., LaBaugh, J.W., Reilly,
    T.E., 2002, Flow and Storage in Groundwater
    Systems. Science, p. 1985-1991.
  • Hartmann, Dennis L., 1994, Global Physical
    Climatology. Academic Press San Diego, CA, 411
    p.
  • Liang, X., and Xie, Z., 2003, Important factors
    in land-atmosphere interactions surface runoff
    generations and interactions between surface and
    groundwater. Global and Planetary Change, p.
    101-114.
  • Pierrehumbert, R.T., 2002, The hydrologic cycle
    in deep-time climate problems. Nature, p.
    191-198.
  • Sharp, J. M., Jr., 2006, Hydrogeology Notes
    Department of Geological Sciences, The University
    of Texas at Austin, Austin, Texas, 352 p.
  • York, J.P., Person, M., Gutowski, W.J., Winter,
    T.C., 2002, Putting Aquifers into atmospheric
    simulation models an example from the Mill Creek
    Watershed, northeastern Kansas. Advances in
    Water Resources, p. 221-238.
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