POTENTIAL EFFECTS OF CLIMATE CHANGE ON GROUND WATER …

FEBRUARY 2003JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION

AMERICAN WATER RESOURCES ASSOCIATION

POTENTIAL EFFECTS OF CLIMATE CHANGE ONGROUND WATER IN LANSING, MICHIGANI

Thomas E. Croley II and Carol L. Luukkonen2

ABSTRACT: Computer simulations involving general circulationmodels, a hydrologic modeling system, and a ground water flowmodel indicate potential impacts of selected climate change projec-tions on ground water levels in the Lansing, Michigan, area.General circulation models developed by the Canadian ClimateCentre and the Hadley Centre generated meteorology estimates for1961 through 1990 (as a reference condition) and for the 20 yearscentered on 2030 (as a changed climate condition). Using thesemeteorology estimates, the Great Lakes Environmental ResearchLaboratory's hydrologic modeling system produced correspondingperiod streamflow simulations. Ground water recharge was esti-mated from the streamflow simulations and from variables derived

from the general circulation models. The U.S. Geological Surveydeveloped a numerical ground water flow model of the Saginaw andglacial aquifers in the Tri-County region surrounding Lansing,Michigan. Model simulations, using the ground water rechargeestimates, indicate changes in ground water levels. Within theLansing area, simulated ground water levels in the Saginawaquifer declined under the Canadian predictions and increasedunder the Hadley.(KEY TERMS: climate change; ground water hydrology; Lansing,Michigan; surface water hydrology; water policy; water resourcesplanning.)

CroleyII,ThomasE.andCarolL. Luukkonen,2003.PotentialEffectsof ClimateChangeon Ground Water in Lansing,Michigan.J. of the AmericanWaterResourcesAssociation(JAWRA)39(1):149-163.

INTRODUCTION

Great Lakes Climate Change Studies

Considerations of potential future climate situa-tions can help to identify possible effects of changingcarbon dioxide levels and can bound estimates offuture changed climate conditions. Preliminary

estimates of impacts in the Great Lakes consideredsimple constant changes in air temperature or precip-itation. Quinn and Croley (1983) estimated net basinsupply to Lakes Superior and Erie. Cohen (1986) esti-mated net basin supply to all Great Lakes. Quinn(1988) estimated lower water levels due to decreasesin net basin supplies on Lakes Michigan-Huron, St.Clair, and Erie.

Researchers have developed general circulationmodels (GCMs) of the Earth's atmosphere to simulateclimates for current conditions and for a doubling ofglobal carbon dioxide levels (2xC02). The U.S.Environmental Protection Agency (USEPA) used thehydrological components of general circulation modelsand assessed changes in water availability in severalregions throughout North America (USEPA, 1984),but the regions were very large. Regional hydrologicalmodels can link to GCM outputs to assess changesassociated with climate change scenarios. Allsopp andCohen (1986) used Goddard Institute of Space Sci-ences (GISS) 2xC02 climate scenarios with net basinsupply estimates. The EPA also coordinated severalregional studies of the potential effects of a 2xC02atmosphere (USEPA, 1989). They directed others toconsider alternative climate scenarios by simulatingGCM changes with historical meteorology. Changeswere made to historical meteorology similar to the dif-ferences observed between GCM simulations of 2xC02and 1xC02. Both the unchanged historical meteorolo-gy and the modified meteorology then were used withmodels to simulate the resultant hydrology. Thehydrological differences were interpreted as climatechange impacts. Cohen (1990, 1991) discusses otherstudies that use this type of linkage methodology and

lPaper No. 01051 of the Journal of the American Water Resources Association. Discussions are open until August 1,2003.2Respectively, Research Hydrologist, NOAA Great lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor,

Michigan 48105-2945; and Hydrologist, U.S. Geological Survey, Water Resources Division, 6520 Mercantile Way, Suite 5, Lansing, Michigan48911 (E-MaiVCroley: [email protected]).

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also presents his concerns for comparability betweenstudies using different types of linkages.

ABpart of the latter USEPA study, the Great LakesEnvironmental Research Laboratory (GLERL)assessed steady state and transient changes in GreatLakes hydrology consequent with simulated 2xC02atmospheric scenarios from three GCMs (USEPA,1989; Croley, 1990; Hartmann, 1990), representingboth "present" and 2xC02 steady state conditions.The USEPA studies, in part, and the high water lev-els of the mid-1980s prompted the International JointCommission (lJC) to reassess climate change impactson Great Lakes hydrology and lake thermal structure.GLERL adapted the USEPA study methodology forthe IJC studies (Croley, 1992) to consider 2xC02 GCMscenarios supplied by the Canadian Climate Centre(CCC). These previous studies assessed mean climatechanges but not changes in climate variability. Croleyet ai. (1998) then used transpositions of actual cli-mates from the southeastern and southwestern conti-nental United States (U.S.) because they incorporatenatural changes in variability within existing cli-mates, as well as mean changes. Similar studies weremade to transpose the climate occurring during the1993 Mississippi flood to assess climate changeimpacts on hydrology in the Great Lakes (Quinn etai., 1997). Most recently (Lofgren at ai., 2000),GLERL again applied its hydrologic models over theGreat Lakes to daily outputs from two GCMs: thenewer Canadian Centre for Climate Modeling andAnalysis global coupled model (CCCMA GCM) andthe United Kingdom Hadley Centre for Climate Pre-diction and Research second coupled ocean atmo-sphere GCM (Hadley GCM). Results of this recentstudy are used herein.

Global climate models indicate that changes indaily air temperatures and precipitation are possiblewith changes in atmospheric carbon dioxide and sus-pended aerosols. Because ground water resources arenaturally replenished by infiltration of precipitationand subsequent percolation of water through geologicmaterials, a decline in precipitation or an increase inevapotranspiration would result in a decline inrecharge, possibly resulting in a decline in groundwater levels. In all of the climate studies mentionedhere, estimates of water availability were made forground water in the various riverine watershedsthroughout the Great Lakes. The estimates were ofvarious lumped areal ground water indices, however,and thus are considered too broad for specific sites.They have not been refined for individual sites withinthe Great Lakes basin. Loaiciga et ai. (2000) usedhydrologic models, historical data, and GCM resultsto investigate 2xC02 climate scenarios impacts onground water resources in Texas.

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Effects on Ground Water in Lansing, Michigan

Ground water from the Saginaw aquifer is the pri-mary source of water for residents and businesses inthe Tri-County region (the study area) shown as thebottom inset in Figure 1. Figure 1 depicts the studyarea and its relationship to both the encompassingGreat Lakes basin and the grids of the two GCMsused in this study. In 1992, more than 89 percent ofthe ground water withdrawn by public systems waswithdrawn from the Saginaw aquifer (Luukkonen,1995). Following a drought in 1988, which resulted inwater rationing in the Tri-County region, local com-munities began to assess the adequacy of waterresources for future needs. A regional water feasibili-ty study was done to evaluate the development of aregional water supply system, to assess the total sus-tainable yield of the aquifer system, and to identifyareas for future development (Tri-County RegionalPlanning Commission, 1992). To assist with the eval-uation of the regional water supply system, the U.S.Geological Survey (USGS) developed a steady stateground water flow model to simulate ground waterflow in the Tri-County region (Holtschlag et ai., 1996).Simulations with the Tri-County model usingincreased pumping rates, depicted lower groundwater levels both in the glacial deposits and in theSaginaw aquifer. These simulations assumed thatother parameters, such as hydraulic conductivity andrecharge, remained the same.

The USGS and the National Oceanic and Atmo-spheric Administration (NOAA) assessed the poten-tial impacts of climate change projections on amunicipality that relies on ground water supplies.Simulations were done to investigate the effects ofchanges in recharge and ground water withdrawalrates on ground water levels and flow to rivers aroundLansing, Michigan. Streamflow was calculated withGLERL's hydrologic modeling system by using theCCCMA and the Hadley GCM meteorology estimatesfor a 1961 through 1990 reference period and for 20years centered on 2030 under a changed climate.These changed climate scenarios extend presenttrends in accumulation of carbon dioxide andaerosols. Base flow (ground water contribution tostreamflow) was estimated for each of the streamflowsimulations and ground water recharge rates in theTri-County regional ground water flow model wereadjusted based on the predicted changes in base flow.The adjusted ground water recharge estimates wereused as input for the numerical ground water flowmodel (Holtschlag et ai., 1996) of the Saginaw andglacial aquifers in the Tri-County region surroundingLansing, Michigan, under 1995 and increased pump-ing scenarios.

150 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION

POTENTIALEFFECTSOFCLIMATECHANGEON GROUNDWATER IN LANSING,MICHIGAN

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Figure 1. Active Model Area in the Tri-County Region in the Lower Peninsula of Michigan,

DESCRIPTION OF STUDY AREA 432,700 people (U.S. Department of Commerce, 1991)who lived in this region relied on ground water with-drawals of about 1.86 m3/s [42.4 million gallonsper day (Mgal/d)]. The primary source of groundwater in the Tri-County region is the Saginaw aquifer,which is located within the Grand River and SaginawFormations of Pennsylvanian age. Aquifers in the

The Tri-County region, which consists of Clinton,Eaton, and Ingham Counties, covers about 4,395 km2(1,697 mi2) in the south central part of the LowerPeninsula of Michigan (Figure 1). In 1997, the


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glacial deposits and other bedrock units are alsoimportant ground water sources in some places.

In the Tri-County region, sedimentary rocks ofDevonian, Mississippian, and Pennsylvanian ageoverlie Precambrian crystalline rocks. Rocks of Trias-sic, Lower and Middle Jurassic, and Cretaceous ageare missing (MandIe and West john, 1988). Glacialdeposits of Pleistocene age overlie Pennsylvanianrocks. The uppermost bedrock unit in the Tri-Countyregion consists of the Grand River Formation, whichcomprises uppermost massive coarse grained sand-stones, and the Saginaw Formation, which comprisesall remaining Pennsylvanian rocks including theParma Sandstone. As already noted, the Saginawaquifer is in the Grand River and Saginaw Forma-tions. These formations, which consist primarily ofsandstone, range in thickness from 0 to 90 m (0 to 300ft) and are thickest in the northern part of the Tri-County region. The glacial features in Michigan arethe result of ice advances during late Wisconsin time(35,000 to 10,000 years before the present). Theglacial deposits range in texture from lacustrine clayor glacial till to coarse alluvial and outwash deposits.These deposits also range in thickness from 0 to 90 m(0 to 300 ft) and are thickest in the northwestern partof the Tri-County region.

Ground water flow in the glacial deposits and inthe Saginaw aquifer is primarily from south to north.Flow from east or west of the Tri-County area, wherethe sandstone of the Saginaw Formation is very thinor absent, is minimal. The Saginaw aquifer isrecharged principally by leakage from the glacialdeposits. The bottom of the Saginaw aquifer isassumed to be impermeable.

Ground water withdrawals within the Tri-Countyregion equaled 1.82 m3/s (41.6 Mgal/d) in 1995.Ground water withdrawals increased from 1.75 m3/s(39.9 Mgalld) in 1992 to 1.86 m3/s (42.4 Mgalld) in1997, an increase of 6.3 percent or about 1.3 percentper year. Tri-County ground water withdrawals of2.79 m3/s (63.7 Mgalld) are projected for 2020 (JonColeman, Tri-County Regional Planning Commission,personal communication, 1994), an increase of 2.1percent per year. Following this same rate of increase,ground water withdrawals for 2030 are projected tobe 3.16 m3/s (72.2 Mgal/d). These projections arebased on anticipated changes in population and donot include potential changes in recharge due to wet-ter or drier conditions.

GENERAL CIRCULATION MODELS

Monthly mean data from GCM runs with trans-ient carbon dioxide content and sulfate aerosol

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concentrations were acquired from the Canadian Cen-tre for Climate Modeling and Analysis (Boer et ai.,2000a, 2000b) and from the United Kingdom HadleyCentre for Climate Prediction and Research (Johns etai., 1997). The resolution of these models in the neigh-borhood of the study area is illustrated in Figure 1(The bottom two squares on the figure denote theCCCMA GCM grid points used over the study areaand the bottom two circles denote the Hadley GCMgrid points used over the study area.) As can be seenfrom this figure, the resolution of both GCMs is crudeon the scale of the Great Lakes basin and particularlyon the scale of the study area, with only two pointsused from each GCM. Also, the Great Lakes are poor-ly represented in the GCMs; only three grid cells areparameterized as lake surface in the Hadley GCMand there are no cells parameterized as lake surfacein the CCCMA GCM. Although the effects of theGreat Lakes within the GCMs are limited, the GCMsshould capture large scale air mass movements.

These models (the CCCMA GCM and the HadleyGCM) extrapolated present trends in carbon dioxideincreases and differ from GCMs in the recent past,not only in the sophistication with which they handlecloud development and ocean currents, but alsobecause they are transient (as opposed to steady-state) and include the effects of sulfate aerosols (e.g.,see Reader and Boer, 1998). These aerosols mask thewarming effects of increasing carbon dioxide, an effectthat is likely to be temporary. The steady state natureof previous models allowed only an evaluation ofeffects from a doubling of carbon dioxide at some timeinto the future when conditions were consideredunchanging, rather than from a more realistic steadyincrease. The two models recreate the current condi-tions well (Sousounis and Albercook, 2000) but sug-gest slightly different climate scenarios for the GreatLakes region. As guided by the National Assessmentof Climate Change, the model period 1961 through1990 was considered as the reference period to becompared with the 20-year future model period cen-tered on 2030 at which time carbon dioxide doubles inthe GCMs. In general, the CCCMA GCM scenario isdrier and warmer than the Hadley GCM scenario.

HYDROLOGIC SIMULATION SYSTEM

The GLERL developed, calibrated, and verifiedconceptual model based techniques for simulatinghydrological processes in the Laurentian Great Lakesand integrated them into a hydrologic simulation sys-tem (Croley, 1990, 1993; Croley et ai., 1998). Theseinclude a model for rainfall/runoff, evapotranspira-tion, and moisture storage in the Grand River basin.


POTENTIALEFFECTSOFCLIMATECHANGEON GROUNDWATER IN LANSING, MICHIGAN

Croley et al. (1998) summarizes details of this andother models in the system. The runoff model subdi-vides precipitation into watershed intraflows based ona cascade among five reservoirs: the snow pack, uppersoil zone, lower soil zone, ground water zone, and sur-face storage. These moisture storages are arranged asa serial and parallel cascade of tanks to coincide withthe perceived basin storage structure. Precipitation isconsidered rainfall if the air temperature is aboveO°C. Otherwise, it is considered snowfall and stored inthe snow pack until it melts. Water enters the snowpack, which supplies the basin surface (degree daysnowmelt). Infiltration is proportional to this supplyand to non saturation of the upper soil zone (partialarea infiltration). Excess supply is surface runoff.Flows from all tanks are proportional to theiramounts (linear reservoir flows). Evapotranspirationis proportional to available water and to sensible heat(a complementary concept in that energy used forevapotranspiration is unavailable as sensible heatand vice versa). Mass conservation is applied to calcu-late snow pack and tank storages; energy conserva-tion is applied to calculate evapotranspiration.Complete analytical solutions exist for the resultingsystem of conservation equations. The partitioning ofrainfall or snowmelt between surface runoff and infil-tration and the partitioning of infiltration into perco-lation, interflow, deep percolation, ground water flow,and evapotranspiration are calculated by using dailymaximum and minimum air temperature and nineempirically calibrated parameters.

The hydrologic simulation system used variablesderived from the GCM runs: daily maximum, mini-mum, and average air temperature, precipitation, rel-ative humidity, cloud fraction, and wind speed. Theaverage monthly changes in these variables from thereference period (1961 through 1990) to those fromthe period centered on 2030 are expressed as differ-ences or ratios of monthly means. Temperaturechanges were expressed as differences and otherchanges were expressed as ratios.

These differences and ratios were calculated ateach GCM grid point for each variable and for eachmonth ofthe year, based on the reference period (1961through 1990) and on the average GCM mean values.The CCCMA model was run three times and theHadley model four times for the entire length of themodel run, using different initial conditions. The dif-ferences and ratios were then interpolated to theGrand River basin. Daily observations of the inputvariables over the period 1954 to 1995 (42 years) werealso spatially interpolated to the Grand River basin.The differences and ratios associated with each GCMwere then applied to these 42 years of daily GrandRiver meteorology to generate two 42-year scenarios

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION

of daily meteorology, one for each GCM. The scenariosare referred to by the GCM used to make the adjust-ments. Figure 2 depicts the average monthly varia-tion in precipitation and air temperature, used in theGrand River Basin runoff model, which result fromscaling of historical data by GCM generated adjust-ments. The hydrologic simulation system was runusing the 42 years of observed meteorology as a refer-ence or base case; it was also run for each scenario of42 years of adjusted daily meteorology for each set ofGCM generated adjustments.

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DEVELOPMENT OF RECHARGE ESTIMATES

Base case values of streamflow at the mouth of theGrand River were compared to actual flows measuredat the USGS gaging station for the Grand River atGrand Rapids, Michigan (Station No. 04119000).Flows at Grand Rapids are assumed to be similar tothose at the mouth of the Grand River. Figure 3 illus-trates the approximate agreement in the cumulativedistribution functions of the base case flow rates (sim-ulated) and of the measured (actual). Actual flow

153 JAWRA

CROLEYAND LUUKKONEN

rates should be less than simulated, as shown in Fig-ure 3 for flows greater than 50 m3/s (1,800 ft3/s), sincethe simulated flow site is slightly downstream fromthe measured flow site. For flow rates less than 50m3/s (1,800 fiNs), Figure 3 shows the two flow ratesare close, but the simulated value is slightly less thanthe actual value. This could result because the simu-lated flows represent more natural streamflow condi-tions while the measured flows overestimate naturalstreamflow by including wastewater or other dis-charges. However, the agreement in Figure 3 isjudged acceptable with possible underestimation oflow flows.

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Figure 3. Comparison of Actual and SimulatedGrand River Discharge (1 m3/s =35.31 ft3/s).

A streamflow hydrograph, which is a graph of dis-charge over time, can be divided into a direct runoffcomponent and a ground water component. The directrunoff component is associated with precipitation thatenters the stream as overland runoff, and the groundwater component, also called the base flow com-ponent, is associated with ground water flow into thestream. Rutledge (1998) developed programs that usestreamflow partitioning to estimate a daily record ofbase flow under the streamflow record. The methoddesignates base flow to be equal to streamflow ondays that fit a requirement of antecedent recession,linearly interpolates base flow for other days, and isapplied to a long period of record to obtain an esti-mate of the mean rate of ground water flow into thestream. Streamflow estimates generated usingGLERL's hydrologic simulation system are averagedover the annual cycle for comparison purposes in Fig-ure 4. All simulated streamflows are used with the

method of Rutledge (1998) to compute simulated base

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flows for the base case meteorology and for theCCCMA and Hadley adjusted meteorologies.

Changes in base flow (not shown) reflect changes inthe amount of water available for recharge to, or dis-charge from, the ground water system. The changedclimate scenario estimates of base flow for the years1954 to 1995 were compared to the reference condi-tion to determine whether base flow increased or

decreased due to the GCM meteorology estimates.The mean and standard deviation of the percent dif-ference between the CCCMA GCM changed climateand reference estimates of base flow is -19.7 plus orminus 4.7 percent. The mean and standard deviationof the percent difference between the Hadley GCMchanged climate and reference estimates of base flowis 4.1 plus or minus 3.3 percent. Thus the changed cli-mate scenarios indicate a possible decrease or slightincrease in ground water recharge.

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Figure 4. Average Daily Grand River Basin RunoffEstimated With the Runoff Model.

GROUND WATER FLOW MODEL

The ground water flow code, MODFLOW (McDon-ald and Harbaugh, 1988), was used to simulate theregional, steady state response of the Saginaw aquiferto major ground water withdrawals in the Tri-Countyregion surrounding Lansing, Michigan. Details onmodel development, parameters, and calibration aredescribed by Holtschlag et al. (1996). This model waslater refined to better represent flow within the nine-township area (see Figure 1) surrounding Lansing,Michigan (Luukkonen et al., 1997). Some details onmodel development and calibration are brieflydescribed below.

The Tri-County regional model simulates groundwater flow by dividing the Tri-County region into a

154 JOURNALOFTHEAMERICANWATERRESOURCESASSOCIATION


variably spaced grid of cells in two layers. Within thenine-township area, cells are 200 m (660 ft) per side.Outside of this area, cells increase in height andwidth from 200 to 270 to 340 m (660 to 880 to 1,100ft) and then to a constant 402 m (1,320 ft). The upperlayer of the model represents the glacial deposits, andthe lower layer represents the Saginaw aquifer. Waterenters the glacial deposits as recharge from precipita-tion and moves to streams or to the Saginaw aquiferin response to hydraulic gradients. Ground waterexits the model at streams or wells. No-flow bound-aries are located at drainage and ground waterdivides; constant-head cells are located along theGrand River on the south and Maple River on thenorth (Figure 5). Simulated well pumpages areassumed to come from the centers of the grid cells.

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Small pumpages from domestic wells were not includ-ed. Of the ground water withdrawals in 1995, 10 per-cent was withdrawn from aquifers in the glacialdeposits and 90 percent was withdrawn from theSaginaw aquifer. Of the withdrawals from the Sagi-naw aquifer, 91 percent were from wells in the nine-township area (Figure 1).

Within the Tri-County model, the spatial variationof average ground water recharge rates for 1951through 1980 was determined from an analysis relat-ing base flow characteristics of streams to land useand basin characteristics in the Lower Peninsula ofMichigan (Holtschlag, 1994). Recharge to the glacialdeposits shown in Figure 5 averaged 17 cmly (6.7 in/y)and ranged spatially from 11 to 42 cmly (4.4 to16.5in/y).

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Department of Environmental Quality, Land and Water Management Division.)


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The horizontal flow of water in the glacial depositsis controlled by the hydraulic conductivity of theunconsolidated materials. The vertical flow of waterbetween the glacial deposits and the Saginaw aquiferwas assumed to be controlled by the verticalhydraulic conductivity in the glacial deposits.Because of the local variability and nonhomogeneityof the glacial deposits, estimates of the spatial varia-tion in the horizontal and vertical hydraulic conduc-tivities in the glacial deposits were determined on thebasis of a geostatistical analysis of available lithologiclogs. The horizontal hydraulic conductivity of theglacial aquifer ranged from 6.8 to 26.7 mid (22.3 to87.5 ftJd), while the vertical hydraulic conductivitiesranged from 1.6x10-4 to 1.2x10-2 mId (4.7xlO-4 to4.0xlO-2 ftld). The horizontal hydraulic conductivitiesare highest in the west central part of the model areaand lowest in the north and south parts of the modelarea. Vertical hydraulic conductivities of the glacialdeposits are highest in the southern part of the modelarea and lowest in the northern part of the modelarea. The horizontal flow of water in the Saginawaquifer was assumed to be proportional to the com-posite sandstone thickness in the Pennsylvanianrocks; therefore, the spatial variation of transmissivi-ty in the Saginaw aquifer was associated with thecomposite sandstone thickness and a constanthydraulic conductivity. Model transmissivities rangedfrom 7.0 to 363.8 m2/d (75.7 to 3,430 ft2/d) in the Sagi-naw aquifer. Transmissivities are highest in the cen-tral part of the model area and lowest along the west,south, and east boundaries of the model area.

The glacial deposits and the Saginaw aquifer wereeach modeled as a single layer. The permeable unitsin each layer are separated by less permeable unitsthat likely affect local flow and head characteristics.Any vertical variations in head and flow within eachlayer are not represented in the model. Model cellsare assumed to reflect homogeneous hydraulic proper-ties. Additionally, hydraulic properties in the aquiferswere assumed to be transversely isotropic. Initial esti-mates of hydraulic properties were interpolated byanalysis of available data. However, the interpolationprocess produces estimates of hydraulic propertiesthat are less variable than the corresponding proper-ties in nature.

Rivers and lakes are modeled using head depen-dent conditions and are represented in the numericalmodel using the MODFLOW river package. This rep-resentation permits water to flow from the streaminto the aquifer or into the stream from the aquifer;however, it does not account for the amount of waterin the river, thus a losing reach of a stream may pro-duce more water than is physically possible.

Estimates of recharge in the Tri-County regionalground water flow model were adjusted on the basis

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of the -19.7 percent (CCCMA GeM adjustments) and4.1 percent (Hadley GCM adjustments) differences inbase flow and the model was then used with wellspumping at 1995 and 2030 rates, as estimated in thesection, Description of Study Area. This is an ideal-ized approach that does not capture transient changesin ground water conditions at seasonal, monthly, ordaily time scales, which may be more pronouncedthan changes averaged annually using a steady statemodel. Water use and withdrawal tend to be reason-ably uniform and therefore a steady state approxima-tion is appropriate in determining the impacts ofwithdrawals on ground water conditions. For groundwater recharge, however, changes at seasonal andmonthly scales are expected with altered climates dueto shifting patterns of snow accumulations and melt-ing. Thus, this approach to modifying steady staterecharge in the Tri-County model preserves presenttiming of variations in recharge while altering theabsolute magnitudes, and serves only as a prelimi-nary estimate of climate change effects on groundwater.

RESULTS

Changes in ground water levels, as well as changesin flow to river cells within Lansing Township, werecompared for both the CCCMA and Hadley GCM pre-dictions under each pumping scenario. Model simula-tions using the 19.7 percent decrease in base flow tostreams predicted by the CCCMA GCM resulted indeclines in ground water levels from the referencecondition in both the glacial deposits and in the Sagi-naw aquifer in the Tri-County region (see Table 1 andFigures 6 and 7). These changes in ground water lev-els were greater when pumping rates were increasedto those projected for future demands (Figures 8 and9). Within Lansing Township, where most groundwater is withdrawn from the Saginaw aquifer, waterlevels in the Saginaw aquifer declined 0.3 to 1.2 m(1 to 4 ft) from the reference condition under 1995pumping rates and 0.3 to 2.3 m (1 to 7.6 ft) from thereference condition under projected future (2030)pumping rates. Because simulated pumping remainedthe same between the base case and the alteredclimate ground water simulations in each comparison,these changes can be attributed to changes in re-charge.

The 4.1 percent increase predicted by the HadleyGCM resulted in a rise in ground water levels fromthe reference condition in both the glacial depositsand the Saginaw aquifer. Under 1995 pumping condi-tions, water levels were higher under the HadleyGCM conditions than under the reference condition as

156 JOURNALOF THEAMERICANWATERRESOURCESASSOCIATION

POTENTIAL EFFECTSOF CLIMATE CHANGE ON GROUND WATER IN LANSING, MICHIGAN

TABLE 1. Changes* in Ground Water Levels in the Glacial and Saginaw Aquifers.

*Positive changes indicate decreases in ground water levels, negative changes indicate increases in ground water levels; average values areenclosed in parentheses.

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Figure 6. Drop in Head in Layer One From Reference Conditions to CCCMAGeM Predictions Under 1995 Pumping Conditions.


Changes in Ground Water LevelsClimate Scenarios 1995 Pumping Rates Future Pumping Rates

CCCMA Predictions - Layer 1 0.0 to 2.7 m (64 em) 0.0 to 3.5 m (64 em)0.0 to 8.9 ft (2.1 ft) 0.0 to 11.5 ft (2.1 ft)

CCCMA Predictions - Layer 2 0.0 to 2.6 m (61 em) 0.0 to 2.6 m (64 em)0.0 to 8.5 ft (2.0 ft) 0.0 to 8.5 ft (2.1 ft)

Hadley Predictions - Layer 1 -55 to 0.0 em (-12 em) -82 to 0.0 em (-12 em)-1.8 to 0.0 ft (-0.4 ft) -2.7 to 0.0 ft (-0.4 ft)

Hadley Predictions - Layer 2 -52 to 0.0 em (-12 em) -52 to 0.0 em (-12 em)-1.7 to 0.0 ft (-0.4 ft) -1.7 to 0.0 ft (-0.4 ft)

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Figure 7. Drop in Head in Layer 'l\vo From Reference Conditions to CCCMA GCM Predictions Under 1995 Pumping Conditions.

expected due to higher recharge. The changes inwater levels between the reference condition and theHadley GCM predictions were greater under project-ed future (2030) pumping rates than under 1995 con-ditions. This means that the greater pumping underprojected future rates had less of an effect on waterlevels due to increased recharge than did the 1995pumping rates. Water levels were lower overall underthe projected future rates; with increased recharge,however, water levels were generally higher comparedto the reference condition under the 2030 rates thanunder 1995 pumping conditions. Within LansingTownship, water levels in the Saginaw aquiferincreased 0.1 to 0.2 m (0.2 to 0.5 ft) from the referencecondition under 1995 pumping rates and 0.1 to 0.3 m

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(0.3 to 1.0 ft) from the reference condition under pro-jected future rates.

As stated previously most ground water is with-drawn from the Saginaw aquifer by wells in the nine-township area; however, inspection of Figures 6through 9 indicates that some of the larger groundwater level declines occur outside the nine-townshiparea and thus away from large pumping centers.Total ground water withdrawals were small relativeto the reference condition rate of recharge (6.5 percentfor 1995 pumping rates and 11.2 percent for 2030pumping rates). Ground water withdrawals by apumping well would typically affect local groundwater levels; however, ground water pumping alsocauses a diversion to the well of water that was



-i_.

!I0____

;:oLO

--CX)

...fiL ;::.;

oJ

iI+-

oIo

5 10 kilometersI

I I5 10 miles

~:\.~

~ "

Figure 8. Drop in Head in Layer One From Reference Conditions to CCCMA GCM PredictionsUnder Projected 2030 Pumping Conditions (black areas depict dry cells).

moving to its natural, and possibly distant, area ofdischarge. Ground water levels are a function not onlyof the discharge rate of the well, but also the trans-mitting properties of the aquifers and confining units,distance to ground water system boundaries, and thespatial distribution of recharge (Alley et ai., 1999).Thus pumping of many wells can have regionally sig-nificant effects on ground water levels. Stresses onthe aquifer by changes in recharge rates and increas-es in pumping can have unexpectedly nonuniformeffects. For example, reduced recharge from precipita-tion has caused more water to be induced fromstreams, thus creating the bull's eye patterns frompumping in Figures 6 through9. These effects will bemost pronounced where areal recharge rates are low


and the hydraulic properties of the aquifers and con-fining units are low.

Changes in recharge rates combined with increasedpumping rates projected for future demands led todewatering of some areas within the glacial deposits.For the reference condition, areas of about 1 km2 (0.4mi2) south and west of Lansing were dewatered dur-ing model simulations. An area of about 0.5 km2 (0.2mi2) was dewatered in the same general location inthe simulation of the Hadley predictions despite anincrease in recharge. For the simulation of theCCCMA predictions, areas of about 4.4 km2 (1.7 mi2)to the south, west, and southeast of Lansing weredewatered during model simulations.

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CROLEYAND LUUKKONEN

...:J

3:oLO

o 5 10 kilometersI I II Io 5 10miles

(]

Figure 9. Drop in Head in Layer 'l\vo From Reference Conditions to CCCMA GeMPredictions Under Projected 2030 Pumping Conditions.

Flow through river cells was investigated to deter-mine the possible impacts of changes in pumpingunder the same recharge conditions and changes inrecharge under the same pumping conditions (Table2). Changes in flow to river cells due to an increase inpumping from 1995 to 2030 rates were determined forthe reference, CCCMA, and Hadley scenarios.Changes in flow to river cells due to changed rechargewere determined from the reference to the CCCMAscenario and from the reference to the Hadley sce-nario. Percent differences for river flow in the modelarea were determined by using model budget sum-maries and in Lansing Township by using flowthrough the faces of 117 cells comprising portions of

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the Grand River, Red Cedar River, and SycamoreCreek (see Figure 5). With increased pumping, flow toriver cells in the model area and in Lansing Townshipdecreased under each climate scenario. With adecrease in recharge, flow to river cells in the modelarea and in Lansing Township decreased under both1995 and projected future rates. With an increase inrecharge, flow to river cells in the model area and inLansing Township increased under 1995 and project-ed future rates. Because net flows through cells wereused, decreases greater than 100 percent indicate asituation in which a river cell changed from gaining tolosing.However,becauseactual streamflowswere notconsidered further, work is needed to determine


POTENTIAL EFFECTSOF CLIMATE CHANGE ON GROUND WATER IN LANSING, MICHIGAN

TABLE 2. Percent Changes* in Flow to River Cells.

Increase in Pumping From1995 to Future Pumping Rates

Decrease in RechargeFrom Reference

Conditions to CCCMAGCM Conditions

1995 FuturePumping Pumping

Rates Rates

Increase in RechargeFrom Reference

Conditions to HadleyGCM Conditions

1995 Future

Pumping PumpingRates Rates

-22.1 -23.4 4.6 4.9

-32.2 -110.8 6.3 22.5

*Positive changes indicate increased flow to river cells, negative changes indicate decreased flow to river cells.

whether this change in flows is realistic because a los-ing reach could lose more water than is being carriedin the stream.

The accuracy of the model is limited by the dataavailable to estimate the transmissivity of the Sagi-naw aquifer, the horizontal hydraulic conductivity ofthe glacial deposits, and the vertical hydraulic con-ductivity between the Saginaw aquifer and the glacialdeposits. The Tri-County model simulates the region-al response of the Saginaw aquifer to changes in with-drawals and recharge. Ground water flow in theglacial deposits was modeled to support analysis offlow in the Saginaw aquifer. Local flows over dis-tances smaller than the dimensions of the grid cellcannot be represented accurately. Additional geologicand hydrologic data, as well as finer discretization ofthe model, would be needed to simulate local flow sys-tems.

The response of the ground water system depictedin these simulations depends on the particular stresspattern described (different ground water withdrawalamounts or locations would result in a different distri-bution of ground water levels) and represents steady-state conditions. Under steady state conditions,stresses such as ground water pumping and rechargeare constant; in reality, however, ground water with-drawals and recharge can vary temporally, both sea-sonally and annually, and spatially. Local variationsin recharge rates, for example those associated withimpermeable surfaces, are not accounted for in themodel. One potential climate change effect, thechanges in ground water recharge, was investigatedin this study in order to illustrate potential effects onground water levels and flow, to demonstrate thatdevelopment of ground water resources affects surfacewater resources, and to show that the potential effectsof future climate changes differ. Other effects of cli-mate change that were not modeled in this studyinclude more severe or longer lasting droughts,changes in vegetation resulting in changes in evapo-transpiration, and possible increased demands for


ground water or surface water as a backup source ofwater supply (Alley et at., 1999).

Based on available climate change estimates, thispreliminary analysis suggests that ground watershould be managed from the perspective of ananticipated broad range of climate possibilities thatmay result from global warming. It would be insuffi-cient to merely plan for drier conditions. Withchanges in ground water levels, ground water man-agers may need to consider well reconstruction, alter-native sources of supply, or changes in water qualityresulting from different ground water source areas.With changes in base flow to streams, other factorsmay need to be considered. These include the effectsof reduced or increased flows on aquatic habitat, theeffects of reduced or increased water quality on aquat-ic habitat, and the effects of flows on lakes (such aslake level and shoreline changes). Earlier studies ofthis type in the Great Lakes (with other GCM simula-tions of global warming) all indicate decreases instreamflow. The estimates of future climates differ intheir forecasts of the direction, magnitude, and timingof changes. Coupled with the assumptions used in theapproach taken here (which preserve current timingof changes while allowing variations in magnitude),the evaluation of impacts associated with globalwarming, estimated from available GCMs, should beviewed as preliminary only.

SUMMARY

The potential impacts of selected climate changeprojections on streamflow and ground water levels inthe Lansing, Michigan, area were assessed by theUSGS and NOAA by using a sequence of computersimulations. Monthly mean data from GCM runs(with increasing carbon dioxide content and sulfateaerosol concentrations) were acquired from the Cana-dian Centre for Climate Modeling and Analysis

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Reference CCCMA HadleyRiver Cells Condition GCM GeM

Tri-County ModelArea -5.5 -7.1 -5.3

Lansing 'lbwnship -71.0 -104.6 -66.6

CROLEYAND LUUKKONEN

(CCCMA) and from the Hadley Centre for ClimatePrediction and Research. Variables derived from theGCM runs were used in GLERL's hydrologic modelingsystem to generate streamflow estimates for theGrand River. The base flow portion of total stream-flow was determined from simulations with historicaldata from 1954 through 1995 modified with GCMgenerated adjustments for the 1961 through 1990 ref-erence period and for the 20 years centered on 2030for the changed climate condition. Ground waterrecharge estimates used in the Tri-County model,developed to simulate the regional steady stateresponse of the Saginaw aquifer, were adjusted by thepercent difference in base flows between the referencecondition and each of the GCM changed climate pre-dictions. This resulted in a 19.7 percent decrease inrecharge using the CCCMA GCM predictions and a4.1 percent increase using the Hadley GCM predic-tions. Changes in ground water levels and flowsthrough river cells were compared for each GCM pre-diction using 1995 and projected 2030 pumping ratesin the ground water model of aquifers near Lansing,Michigan.

Ground water levels in both the glacial and Sagi-naw aquifers declined from reference conditions levelsunder both pumping conditions when recharge rateswere decreased by the 19.7 percent predicted by theCCCMA GCM. Some areas within the glacial depositswere dewatered under the increased pumping condi-tions. Water levels in both the glacial and Saginawaquifers increased slightly over reference conditionlevels under both pumping conditions when rechargerates were increased by the 4.1 percent predicted bythe Hadley GCM. Some areas within the glacialdeposits were dewatered under the increased pump-ing conditions. Flow through river cells decreased asrecharge was decreased for the CCCMA GCM predic-tions and increased slightly as recharge wasincreased for the Hadley GCM predictions.

ACKNOWLEDGMENTS

This is GLERL Contribution No. 1198. The Tri-County regional

ground water flow model was developed in cooperation with the Tri-County Regional Planning Commission and a coalition of 22 com-munities in the Tri-County region. The GCM results and theirtransference to hydrological impacts for change climates withGLERL's hydrology models were part of the work undertaken bythe Great Lakes Regional Assessment Team regarding the potentialimpacts of future climate change and variability in the Great Lakesregion. It complements work being prepared by the NationalAssessment Synthesis Team as part of the National Assessment ofClimate Change conducted by the U.S. Global Change ResearchProgram.

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