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1 UC Irvine Faculty Publicatins Title Applicatin f multiscale water and energy balance mdels n a tallgrass prairie Permalink Jurnal Water Resurces Research, 30(11) ISSN Authrs Famiglietti, J. S Wd, E. F Publicatin Date DOI /94WR01499 License CC BY 4.0 Peer reviewed eschlarship.rg Pwered by the Califrnia Digital Library University f Califrnia

2 WATER RESOURCES RESEARCH, VOL. 30, NO. 11, PAGES , NOVEMBER 1994 Applicatin f multiscale water and energy balance mdels n a tallgrass prairie J. S. Famiglietti Department f Gelgical Sciences, University f Texas at Austin E. F. Wd Water Resurces Prgram, Department f Civil Engineering and Operatins Research Princetn University, Princetn, New Jersey Abstract. The mdels presented in the previus paper (Famiglietti and Wd, this issue) are applied at their apprpriate scales fr evaptranspiratin mdeling at the First Internatinal Satellite Land Surface Climatlgy Prject Field Experiment (FIFE) site. The lcal sil-vegetatin-atmspheric transfer scheme is applied at five flux measurement statins in the nrthwest quadrant f the FIFE site. Simulatins were perfrmed fr three f the fur FIFE "glden(clud-free) days" with gd results. The spatially distributed mdel was applied at the! 1.7-km 2 King's Creek catchment, als lcated in the nrthwest quadrant f the FIFE site, during FIFE Intensive Field Campaigns (!FCs) 1-4. Simulated catchment averagevaptranspiratin was cmpared t an average f bservatins made at the five afrementined measurement statins with gd results. The macrscale frmulatin was applied t bth the King's Creek catchment and the entire!5-km FIFE site fr evaptranspiratin simulatins. Macrscale mdel simulatins fr King's Creek were nearly identical t the spatially distributed results, implying that at this lcatin and at this scale, the assumptins invked in the develpment f the macrscale frmulatin are reasnable. The macrscale mdel was als emplyed t simulate evaptranspiratin frm the entire 15-km site fr the fur glden days. Simulated evaptranspiratin rates shw reasnably gd agreement with the 22-statin average f bservatins. Hwever, it is suggested that at 15-km and larger scales, simulatin errr may arise as a result f the macrscale assumptins f areally averaged atmspheric frcing, vegetatin parameters, sil parameters, and the methds by which these data and ther flux bservatins are aggregated. A methdlgy t cmbat these prblems at larger scales is reviewed. 1. Intrductin stream bttms t ridge tps, and is representative f the strip f native tallgrass prairie, km wide, that extends This paper presents the applicatin cmpnent f a bdy frm Kansas t Nebraska t Oklahma. In the summers f f research which addresses aggregatin and scaling issues 1987 and 1989, the First Internatinal Land Surface Climain multiscale hydrlgical mdeling. In the first paper [FamigIietti and Wd, this issue], a methdlgy was prpsed t aggregate lcal prcess physics acrss scales. A spatially distributed mdeling framewrk was prpsed fr tlgy Prject (ISLSCP) Field Experiment (FIFE) was cnducted n a 15 x 15 km regin f tallgrass prairie lcated near Manhattan, Kansas. FIFE was a large-scale field experiment whse purpse was t develp relatinships beuse at the catchment scale, and at the macrscale, a statis- tween satellite measurements and hydrlgic, climatic, and tical-dynamical framewrk was presented. The macrscale biphysical variables at the!and surface [Sellers et al., frmulatin is intended fr use as a land parameterizatin in 1992]. A secnd gal f the experiment was t cllect reginal and glbal atmspheric mdels. The purpse f this grund-based data t validate these relatinships, and t study is t apply the mdels f the previus paper [Famig!i- validate simulatin mdels f land surface prcesses frm etti and Wd, this issue] n a temperate grassland at their the pint scale t scales cmpatible with remtely sensed apprpriate scales. A secnd gal f this wrk is t investi- bservatins. During the summers f 1987 and!989, multigate sme f the simplifying assumptins utilized in the scale grund-based and remtely sensed water and energy develpment f the macrscale frmulatin using bserved balance data were cllected simultaneusly. Thus the FIFE field data. data set affrds unique pprtunities t bserve the scaling The site f these applicatins is the tallgrass prairie f behavir f hydrlgical prcesses and t test mdeling eastern Kansas (United States). The area includes rlling strategies ver a range f spatial scales. hills and shallw sils, with rughly 50 m f elevatin frm In this paper, the lcal sil-vegetatin-atmsphere transfer Cpyright 1994 by the American Gephysical Unin. Paper number 94WR ! 397/94/94 WR scheme (SVATS) is applied t mdel evaptranspiratin at five flux measurement statins (statins 2, 8, 10, 12, and!4) in the nrthwest quadrant f the FIFE site (see Figure 1). 3079

3 3080 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS ii II ' 9 It ::':::':... I I ::::::::::::':::::.':. '"'-... "*"" ;5 ' l I ß : :/ e38 The scaling behavir f the varius hydrlgic fluxes ver larger spatial regins and in different climatic regimes is the subject f nging research. Finally, the macrscale frmulatin is used t mdel evaptranspiratin frm the entire 225-km 2 FIFE site. Mdeled evaptranspiratin is cmpared t the 22-statin average f bservatins made n the fur "glden(clud-free) days" during the summer f "9 it 3ø 2 5 II X22 ß ß ) II II II II 26 II ii P-PAM D-DCP SP-Super PAM ß ) SD-Super DCP 21 It 1 Km ß B-Bwen Rati Flux Measuremen X E-Eddy Crrelatin Flux Measurement... Site Bundary I t 1-70 === R-177 t matin system (FIS) which includes a 30-m gridded database f selected bservatins and!and surface characteristics. Figure 1. FIFE site shwing apprximate lcatins f King's Creek catchment (shaded area), flux measurement When catchment-scale and site-wide simulatins required statins, and meterlgical statins. Prtable autmated areally averaged inputs, mdel parameters and frcing data mesnet meterlgical statins are abbreviated PAM. U.S. were aggregated in ne f tw ways. Spatially distributed Army Crps f Engineers Data Cntrl Platfrm meter- infrmatin, such as sil parameters, tpgraphic variables, lgical statins are abbreviated DCP. and rainfall (described belw), were aggregated by averaging individual grid element values. Pint data, such as meterlgical and flux bservatins made at individual measure- When pssible, lcal meterlgical data, sil parameters, ment statins, were extracted frm the FIS [nd aggregated and vegetatin parameters are emplyed in the simulatins. by simple linear averaging. Alternative methds fr aggre- Next, the spatially distributed mdel is applied at the King's gating these data were nt investigated in this study. Creek catchment, an 11.7-km 2 watershed als lcated in the During FIFE 1987, mst land surface flux bservatins nrthwest quadrant f the FIFE site. Mdeled evaptrans- were made at even numbered statins (see Figure 1) during piratin is cmpared t the average f bservatins at fur 2- t 3-week-lng intensive field campaigns (IFCs 1-4). statins 2, 8, 10, 12, and 14. Spatially distributed fields f Therefre mdeled evaptranspiratin is cmpared t that mdel inputs and parameters are utilized in the simulatins bserveduring ifc 1 (May 26 t June 6, 1987), IFC 2 (June when available. Streamflw was a negligible cmpnent f 25 t July!5, 1987), IFC 3 (August 6-21, 1987), and IFC 4 the catchment scale water balance, and althugh mdeled, (Octber 5-16, 1987). Mst flux and meterlgical measure- [see Famiglietti, 1992] is nt reprted n here. Validatin f ments were made at half-hurly intervals. mdel simulated spatial sil misture patterns is best accm Meterlgical data. During summer 1987 a netplished by cmparisn t remtely sensed bservatins and wrk f 20 rain gages was used t measure rainfall ver the is the subject f past and current research [e.g., Famiglietti King's Creek catchment and vicinity. A kriging algrithm and Wd, 1991; Wd et al., 1993; Linet al., 1994]. The was applied t the rain gage data t prduce spatially simulatins at the King's Creek catchment are then repeated distributed rainfall images at 15-min intervals during strm with the macrscale frmulatin. Althugh the macrscale events. In this study, the 15-min rainfall data were cnverted frmulatin is intended fr use at larger scales (O(100- t 30-min data fr cnsistency with the FIFE data. These 10,000 km2)), cmparisn f the spatially distributed and images were cregistered with the 30-m FIFE database fr macrscale mdel simulatins shuld prvide insight int spatially distributed simulatin f the catchment. Precipitathe restrictiveness f the assumptins invked in the mac- tin images were averaged fr use in macrscale mdel rscale mdel develpment, albeit at a relatively small scale. simulatins King's Creek. Lcal mdel simulatins and These include assumptins f areally averaged atmspheric macrscale simulatins fr the entire FIFE site were cnfrcing, sil parameters, vegetatin parameters, and a sta- ducted nly n glden days, s that n rainfall data were tistical representatin f spatial variability in the tpgraphic-sil index, sil misture, and the water and energy fluxes. 2. Applicatin t a Tallgrass Prairie 2.1. Data The data required t run the mdels are described in the previus paper [Famiglietti and Wd, this issue]; mdel parameters are summarized in Table 1 f that paper. Lcal r areally averaged values f meterlgical data (precipitatin, shrtwave and lngwave radiatin, pressure, air temperature, humidity, and wind speed), sil parameters, and vegetatin parameters are required t drive the lcal and macrscale mdels, respectively. The spatially distributed mdel can accmmdate spatially variable fields f these data by cregistering available fields using a gegraphic infrmatin system (GiS). The spatially distributed and macrscale mdel frmulatins require sme descriptin f spatial variability in the tpgraphic-sil index, either in spatially distributed r histgram frm. Initial cnditins f varius mdel states must be estimated. In the present applicatins, all mdel frcing, parametric, and bserved flux data were retrieved frm the FIFE infr- required. Net radiatin and wind speed bserved at individual

4 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS 3081 Table 1. Sil Types and Prperties Parameter Value Ks Sil Type mm/ h 0 s 0 r ½c, m B Fractinal Cver Alluvial land Benfield-Flrence cmplex Clime-Sgn cmplex Dwight-Irwin cmplex Irwin silty clay lam Irwin silty clay lam (erded) Ivan and Kennebec silt lams Reading silt lam Stny steep land Tully silty clay lam statins were used in lcal mdel simulatins. Other lcal meterlgical data were nt readily btainable frm the FIS fr individual statins, s that areally averaged data fr the King's Creek catchment were used instead. Fr bth spatially distributed and macrscale mdel simulatins f King's Creek, areally averaged radiatin, humidity, pressure, and wind data were emplyed. Dwnward lngwave and dwnward shrtwave radiatin were nly cllected at FIFE meterlgical statins 5 and 21. An average f these data was used t drive simulatins. Wet and dry bulb temperatures, pressure, and wind speed were averaged frm at statins 2 and 10 is the Irwin si!ty clay lam, at statins 8 and 12 the Benfield-Flrence cmplex, and at statin 14, the Clime-Sgn cmplex. Simulatins using the lcal mdel at these lcatins used the crrespnding sil parameters. Actual patterns f the sil parameters were extracted frm the database fr spatially distributed simulatins f the King's Creek catchment. Macrscale mdel simulatins fr the King's Creek catchment and fr the entire FIFE site utilized areally averaged sil parameters frm the database. The remaining sil parameters were cnsidered spatially cnstant in this study. These include the bare-sil albed (a), bservatins at meterlgical statins 3, 5, and 7. Macr- the penetratin depth f the diurnal heating wave (D), the scale simulatins fr the entire FIFE site were driven with bare-sil rughness length (z0), and the rt zne depth the same shrtwave and lngwave radiatin data, but with (Zrz). These values were determined frm the FIS and are precipitatin, humidity, air temperature, pressure, and wind listed in Table 2. speed averaged ver all perating meterlgical statins Vegetatin data. Since mst f the regin is Sil data. A map f sil types fr the entire FIFE cvered by native tallgrass, vegetatin parameters were site is cregistered with the FIFE database. Fr each f the cnsidered spatially cnstant in all simulatins. Values f sil types in the regin, sil texture classificatins are leaf area index (LAI) and canpy height were extracted frm available frm the lcal U.S. Department f Agriculture Sil the FIS fr evaptranspiratin simulatins at individual Cnservatin Service sil survey [Jantz et al., 1975]. The statins. The fractins f bare and vegetated sil (fs, Brks and Crey [1964] sil parameters were determined were determined fr each IFC by the methd f Smith et al. fr each sil texture frm Rawls et al. [1982] and incrp- [1993] in terms f LAI and canpy height. Canpy rughness rated int the database. Table 1 lists the sil parameters fr length and zer plane displacement were assumed equal t each sil type in the King's Creek catchment. The sil type 15 and 67% f canpy height, respectively. Fr larger-scale simulatins, catchment and entire site average values f Table 2. Additinal Mdel Parameters canpy height and LAI were cmputed frm the FIS fr each IFC. Table 3 summarizes these vegetatin parameters. Parameter Value Nte that the LAI was treated as a tuning parameter in sme f the lcal SVATS simulatins and macrscale mdel Sil simulatins f the entire site. Therefre sme f the LAI a 0.!5 D, m 0.50 values shwn in Table 3 fr lcal and entire site simulatins Z, m are the tuned, nt FIS, values. The value f minimum zrz, m 0.5 stmatal resistance (rstmin) shwn in Table 2 is clse t that Vegetatin (wet canpy) 0.25 (dry canpy) 0.20 rstmi n, s/m ½crit, m !04 L, m/m 2.0 Ru, s/m 109 Tpgraphy (King's Creek) 3.73 (entire site) 5.03 f Smith et al. [1993], wh calibrated a bisphereatmsphere transfer mdel t bservatins at FIFE flux measurement statin 2. The critical leaf' water ptential (½crit), rt activity factr (F), rt density (L), and rt resistance (Ru) shwn in Table 2 were chsen s that the relatinship between transpiratin capacity and rt zne misture cntent was cnsistent with bservatins [Smith et al., 1992, Figure 9] Tpgraphic data. A 30-m U.S. Gelgical Survey digital elevatin mdel (DEM) is cregistered in the FIFE 30-m database. The tpgraphic-sil index was crn-

5 3082 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS Table 3. Vegetatin Parameters Canpy Height, Parameter m LAI fv IFC King's Creek Entire site IFC King's Creek 0.66! Entire site 0.47! IFC King's Creek Entire site IFC ! King's Creek Entire site Lcal-Scale Results In this sectin, the results f SVATS applicatins at individual statins are presented. The lcal SVATS is applied at statins 2, 8, 10, 12, and 14. Simulatins were perfrmed using half-hurly time steps and the data described abve. Mdeled evaptranspiratin was cmpared t that bserved n three f the fur FIFE glden (virtually clud-free) days (June 6, July 11, and August 15, 1987). Observed flux data fr statins 4 and 6, als lcated in the vicinity f the King's Creek catchment, were either unavailable r f questinable quality. Observed flux data were als0 unavailable fr statins 8, 10, 12, and 14 fr Octber 11, 1987, the final glden day f the 1987 FIFE campaign. When analyzing the lcal-scale results, it is imprtant t remember the fllwing pints. First, as was discussed abve, sme meterlgical data (e.g., air temperature and pressure) were nt readily available fr individual statins frm the FIS. Thus unavidable bias results frm driving lcal simulatins with nnlcal data. The situatin becmes mre cmplicated when measurement errrs in meterlgical data and bserved fluxes are cnsidered. Errrs induced by averaging air temperature, pressure, and humidity data further cmpund the prblem. Secnd, the structure f the lcal SVATS is greatly simplified relative t thers in current use s that it can be aggregated in space. Therefre ur lcal SVATS is designed t capture the essential dynamics f land-atmsphere interactin: there are likely mre detailed SVATS in peratin that can better reprduce evaptranspiratin bserved at individual statins. Mst errrs in the lcal simulatins are attributable t these tw surces and are nt discussed in depth belw. The results f lcal simulatins at statin 2 are shwn in Figure 2a. Statin 2 was lcated n fiat-lying, unburned, bttmland prairie, clse t the utlet f the King's Creek catchment. Simulated evaptranspiratin shws gd agreement with bservatins, with rt-mean-square errrs (rmse's) f 0.03 mm/h fr each f the glden day simulatins. puted fr each grid element in the regin by analysis f bth The rmse's fr all simulatin results presented in this rep the digital elevatin and sil survey infrmatin. Actual were cmputed between the daylight hurs f 1215 and 2345 patterns f the index were extracted frm the database fr UT. The mdel slightly underpredicts evaptranspiratin spatially distributed simulatins, while histgrams f the during midmrning hurs n June 6 and July 11. This is mst tpgraphic-sil index were created fr macrscale mdel likely a result f using nnlcal air temperature and humidity simulatins f the King's Creek catchment and the entire data t drive the lcal simulatin. FIFE site. Areally averaged values f the tpgraphic-sil Results f lcal simulatins at statin 8 are presented in index A fr the King's Creek catchment and the entire site Figure 2b. Statin 8 was lcated within the ne-dimensinal are shwn in Table 2. subwatershed n the Knza Prairie, n the sutheast side f Initializing mdel states. Initial rt and trans- the King's Creek catchment. It was a mderately slping, missin zne misture cntents were determined fr lcal, nrtheast-facing site, which was burned befre the 1987 catchment-scale, and macrscale simulatins during IFCs FIFE campaign as part f rutine prairie management. 1-3 by assuming gravitatinal equilibrium in the lcal sil Evaptranspiratin is verpredicted n the afternn f prfiles (by substituting ½ = z in (6a) f Famiglietti and June 6 and slightly underpredicted at the peak f the diurnal Wd [this issue]). This prcedure resulted in initial cndi- cycle n all three glden days. Daytime rmse's fr the three tins that were t wet fr IFC4. In thse simulatins, a simulatins are 0.06, 0.06, and 0.03 mm/h. gamma distributin f rt zne misture cntent was as- Lcal simulatins at statin 10 are shwn in Figure 2c. sumed, with lw misture cntent values crrespnding t Simulatins at statin 10 were nt as successful as thse at steep, well-drained slpes (lw values f the tpgraphic- statins 2 and 8. Daytime rmse's fr the three glden day sil index), and wet sil misture values crrespnding t simulatins are all rughly 0.06 mm/h. The cmputed diurnal fiat, prly drained areas such thse adjacent t stream cycle f evaptranspiratin lags behind the bserved cycle channels (high values f the index). Average water table by nearly 1 hur in each simulatin. The reasns fr this are depth was initialized at 2.1, 2.4, 3.0, and 3.0 m fr simula- again related t the meterlgical frcing data used. The air tins at all scales during IFCs 1-4, respectively. Canpy temperature and humidity data were averaged ver three water strages were assumed dry t initialize simulatins. unburned tpland r slping sites, tw f which face nrth,

6 FAMIGLIETTi AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS 3083 a statin 2 b Statin 8 June 6, 1987 June 6, 1987 [] bscrve, d cmputed bserved cmputed m 0 12 July 11,1987 July 11, August 15, 1987 I 12 August 15, Figure 2. Lcal SVATS simulated evaptranspiratin rates versus bservatins fr FIFE Glden Days June 6, July 11, and August 15,!987, at (a) flux measurement statin 2, (b) statin 8, (c) statin 10, (d) statin!2, and (e) statin 14. Statin 10 was lcated n burned, west-facing, bttmland an unburned, mderately slping, east-facing site. Cmprairie. Thus the actual air temperature and vapr pressure puted evaptranspiratin rates were slightly lwer than deficit at statin 10 may have differed significantly frm thse bserved at midday n June 6 (rmse 0.02 tampa). thse given by the averaged frcing data. Observed flux data were unavailable fr July 11 at statin 14. Figure 2d shws the results f glden day simulatins Cmputed evaptranspiratin rates fr August 15 agreed statin 12. Statin 12 was an unburned, steeply slping, well with bservatins (rmse 0.03 mm/h). nrth-facing site. The simulatediurnal cycle f evaptrans~ 2.3. Catchment-Scale Results piratin fr June 6, as abve, was biased lw in the mrning and high in the afternn, resulting a daytime rmse f 0.07 In this sectin, the spatially distributed mdel is applied at ram/h. Simulated evaptranspiratin fr July! 1 agreed well the King's Creek catchment (see Figure 1). Simulatins were with bservatins (rmse, 0.02 mm/h). Evaptranspiratin perfrmed using half-hurly time steps and the data previwas verpredicted during midday hurs fr August 15 (rinse, usly described. Example spatially distributed input data are 0.07 mm/h). shwn in Plate 1. Mdeled catchment-scalevaptranspira- Simulated evaptranspiratin at statin!4 agreed well tin (see equatin (29) f Farniglietti and Wd [this issue]) with bservatins (see Figure 2e). Statin!4 was lcated n is cmpared t the average f bservatins made at statins

7 _ 3084 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS C Statin 10 June 6, 1987 d Statin 12 June 6, 1987 bserved cmputed [] bscrvcd 0 cmputed n 5 ra ' 1 - p July 11, 1987 July 11, 1987 cpc O I l August 15, 1987 August 15, 1987 r cl m ½ c m 0 time (h) I time Oh) Figure 2. (cntinued) 2, 8, 10, 12, and 14 fr ifcs 1-4. As in the case f the lcal SVATS applicatins, the unavidable prblem arises f driving lcal (i.e., grid element) simulatins with nnlcal data. Even in a field experiment such as FIFE, it is unreasnable t expect that high-reslutin, spatially distributed fields f meterlgical data (e.g., air temperature, pressure, wind speed) culd be prvided fr cntinuus simulatin during the IFCs. Thus available meterlgical and flux data were linearly averaged as described abve. With the exceptin f the King's Creek rainfall data, which was measured with a dense rain gage netwrk, alternative methds f averaging r prducing spatially distributed fields f input data were nt cnsidered. Prbable errrs induced by ur apprach were discussed under lcal-scale results. It is wrth nting, hwever, that such high-reslutin meterlgical data can be prvided by atmspheric mdels (e.g., large eddy simulatin). This fact, cmbined with the widespread availability f GIS fr representing spatially variable land surface characteristics, makes spatia!ly distributed hydrlgical mdeling a viable apprach fr detailed studies f land-atmsphere interactin. Results f the catchment-scale simulatins fr IFCs 1-4 are shwn in Figure 3. In each f Figures 3a t 3d, time step zer crrespnds t 0515 UT (0015 lcally), n June 1, June 25, August 6, and Octber 5,!987, respectively. In genes, cmputed evaptranspiratin fr all IFCs agrees well wi the five-statin average. Daytime rmse's were cmputed f 0.06 mm/h fr IFC 1, 0.07 mm/h fr IFC 2, 0.06 mm/h fr IFC 3, and 0.05 mm/h fr IFC 4. Observatins made at e FIFE site indicated that during mst f the field experimeat (IFCs 1-3), evaptranspiratin ccurred at ptential rates. An analysis f the simulated result shwed that the mdel

8 FAMIGL!ETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS 3085 predicted evaptranspiratin at atmspherically cntrlled rates fr mst f IFCs 1-3. Figures 3a t 3c shw that mdel cmputed actual evaptranspiratin agrees well with the five-statin average fr this time perid. In additin t mdel errr surces previusly discussed, bias between simulated and bserved results can als be attributed t verpredictin r underpredictin f ptential evaptranspiratin rates during this perid. During IFC 4, drier rt zne sil misture cnditins resulted in sil-cntrlled evapratin frm bare sil and stmatal cntrl f transpiratin. The lack f sil water fr evaptranspiratin was evident at the field site, as the dry cnditins resulted in senescence f the native tallgrass. Analysis f the simulated results and the agreement between cmputed and bserved evaptranspiratin in Figure 3d suggest that the mechanisms f sil and vegetatin cntrl are fairly well represented within the mdel. Hwever, the mdel tends t verpredict evaptranspiratin during and immediately after strm events. This suggests that ptential evaptranspiratin rates r sil- r vegetatincntrlled evaptranspiratin rates are verpredicted during these brief perids. Mdeled rt zne misture cntent is shwn in the tp panels f Plate 2 in spatially distributed frmat. The tp left panel f Plate 2 shws the spatial distributin f initial rt zne misture cntent emplyed in the!fc 4 simulatin. The tp right panel shws the simulated distributin at midday n Octber 9, The decrease in dark blue and green grid elements and the increase in red and yellw grid elements frm Octber 5 t Octber 9 indicates that the mdeled rt znes are smewhat drier after 4 days, althugh nt much wing t lw evapratin rates at that time f year. The bttm panels f Plate 2 shw mdeled midday evaptranspiratin rates fr the crrespnding times in the tp panels. Evaptranspiratin rates vary frm near 0 t 0.4 mm/h. These images give sme indicatin f the degree f spatial variability in evaptranspiratin rates within the e Statin 14 June 6, 1987 bserved cmputed! August 15, 1987 I Figure 2. (cntinued) dependent n misture cntent, the crrespndence between the tp and bttm f Plate 2 is understandable. The larger number f dark blue and green grid elements in the bttm f Plate 2 fr Octber 5 indicates that evaptranspicatchment. Such high-frequency variability was nt sampled ratin rates were higher than n Octber 9. The decrease in by the flux measurement statins, since nly ne statin was evaptranspiratin rates during that perid is due t the lcated within the catchment, and a ttal f 22 statins were catchment-wide decrease in rt zne misture cntent, lcated within the entire!5-km site. Furthermre, lgistical cnsideratins required that mst statins be lcated n prairie tplands and mderate slpes, s that steep slpes and valley bttms were undersampled. Thus spatial patterns such as thse shwn in the bttm panels f Plate 2 are difficult t ve_rify. Hwever, FIFE investigatrs HlwiIl and which resulted in decreased exfiltratin and transpiratin capacities lcally. T demnstrate the surface runff capabilities f the mdel, the runff-prducing strm event f IFC 3 (August 13, 1987) was simulated independently f the wrk presented previusly. In this simulatin the mdel was tuned s that Stewart [1992] and Jedlvec and Atkinsn [1992] shwed the vlume f cmputed strm runff matched that bthat such high-frequency variatin existed using highreslutin remtely sensed imagery. The patterns shwn in served. All mdel parameters are given in Tables 1-3. As in the evaptranspiratin simulatin f IFC 4, a gamma distrithe bttm panels f Plate 2 are cnsistent with the micr- butin f initial rt zne misture cntent was assumed. tpgraphic variatin shwn in the imagery prduced in bth Cmputed streamflw was tuned t that bserved by inf these studies. creasing the rt zne depth frm 0.5 t 0.75 m and by Cmparisn f the tp and bttm panels f Plate 2 shws increasing the saturated hydraulic cnductivities f Table 1 a strng relatinship between spatial patterns f rt zne by a factr f 5. Such independentuning was required misture cntent and evaptranspiratin. Evaptranspira~ wing t a lack f runff-prducing strm events during the tin rates decrease with decreasing rt zne misture summer f!987. T prperly calibrate and verify runffcntent. Wetter grid elements lcated alng the stream related mdel parameters, rainfall and streamflw data frm netwrk evaprate at higherates than drier lcatins, such a number f events wuld be required. Since these data were as thse lcated near ridge tps. As was described abve, nt available, n attempt was made t identify ne ptimal IFC 4 was drier than the previus IFCs, resulting active parameter set fr cntinuusimulatin. sil and vegetatin cntrl f evaptranspiratin, particu- Spatially distributed rainfall images fr 0145 and 0215 UT, larly at midday [see FarnigIietti and Wd, this issue, Figure August!3, 1987, are shwn in the tp panels f Plate 3. The 4]. Sinc exfiltratin and transpiratin capacities are strngly catchment-average precipitatin intensities are 51 mm/h and

9 3086 FAMIGLIETTI AND WOOD' APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS 00 (ram/h) ,.. "'.3. ' ".,-,5.;' Plate 1. Example input data fr the spatially-distributed mdel. Catchment area is 11.7 km 2, and grid element reslutin is 30 m; nrth is at tp f page. Clckwise frm upper left: precipitatin, slar radiatin, sil type, and tpgraphic-sil index. 40 mm/h, respectively. The middle panels f Plate 3 shw mdeled rt zne misture cntent befre the start f the simulatin, at 0015 UT, August 13, 1987 (left), and after the peak precipitatin intensity, at 0215 UT (right). The scale frm blue t yellw represents vlumetric misture cntents ranging frm 0.48 t 0. Nte the increase in mdeled rt zne misture cntent after the strm. The bttm panels f Plate 3 shw the lcatins and rates f runff generatin fr the tw time steps f peak precipitatin intensity shwn in the tp panels. Since there were n saturated regins f land surface at this time, all surface runff was prduced by the infiltratin excess mechanism. The scale red t blue/white represents runff generatin rates frm 30 mm/h t near 0 mm/h. The dark blue backgrund represents the remaining catchment grid elements where n surface runff was generated. As the precipitatin intensity reaches its peak at 0145 UT, runff is generated where the intensity is highest and the sil wettest. The increase in the number f surface runff- prducing lcatins between 0145 and 0215 UT in the bttm panels f Plate 3 crrespnds t the catchment-wide increase in surface misture cntent, which results in decreased infiltratin capacities, s that runff generatin is mre widespread. Cmparisn f the middle and bttm panels shws that in general, as in the case f evaptranspiratin, higher magnitude fluxes are generated by the wetter catchment grid elements. These lcatins are fund adjacent t the stream netwrk and have relatively lw infiltratin capacities. Within bth bttm images in Plate 3, the magnitude f surface runff rates increases with increasing rt zne misture cntent, increasing precipitatin intensity, and decreasing infiltratin capacity Macrscale Results King's Creek. In this sectin, the macrscale frmulatin is applied at the King's Creek catchment. Mdel parameters are listed in Tables 1-3, and atmspheric frcing data have been previusly described. Cmputed, areally averaged evaptranspiratin rates [see Famiglietti and Wd, this issue, equatin (35)] are cmpared with the

10 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS i' ua ; ' i I! I "1 ' I...!... i...! ''1 '"'I... I...! I I I I I 'l' I I I! I... I i I! 24 4a a as l i lq tim(h) Figure 3. Mdeled and bserved evaptranspiratin fr the King's Creek catchment using the spatially distributed frmulatin. Observatins crrespnd t the five-statin average described in the text: (a) FIFE IFC1; time 0 represents June 1, 1987, 0445 (UT);(b) IFC2; time 0 represents June 25, 1987, 0445 (UT); (c) IFC3; time 0 represents August 6, 1987, 0445 (UT); and (d) IFC4; time 0 represents Octber 5, 1987, 0445 (UT). five-statin average f bservatins made in and near the in the tpgraphic-sil index and the crrespnding water watershed. and energy fluxes is represented statistically [see Famiglietti Results f macrscale mdel simulatins are shwn in and Wd, this issue]. Meterlgical frcing, vegetatin, Figure 4 fr IFCs 1-4. Mdeled evaptranspiratin agrees and sil parameters are represented as spatial averages. well with the five-statin average fr all IFCs. In additin t Therefre ptential errr surces include the lss f explicit the surces f errr already mentined, ther surces arise pattern representatin and the manner in which mdel when the macrscale frmulatin is emplyed. Explicit parameters, mdel inputs, and field bservatins are aggrepatterns f land surface-atmsphere interactin are n gated t the scale f applicatin. Cmparisn f Figure 4 and lnger represented by the mdel structure. Spatial variability 3 shws that the macrscale and spatial!y distributed f.rmu-

11 ß.., 3088 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS I l I. [ I ' 1 ß ',.?:..'... t,'7 '. '7 ;5,.---: :.., gg {.'... 1,,.,; -.,,....: õ O.OOOO0 -n.ldrr;'.4sa. :-ca' '(OO O.'2aa 2a 0.4-OOlOO0'!'I.'IOOODD O.OCla(X ''l O. OO! 'øø 'c J aa. a OO Plate 2. (tp left) Spatial distributin f initial rt zne misture cntent used in simulatin f IFC 4. Units are vlume percent; scale is given in Plate 1. (tp right) Simulated spatial distributin at midday n Octber 9, (bttm left) Spatial distributin f simulated evaptranspiratin at midday n Octber 5. Units are millimeters per hur. (bttm right) Simulated spatial distributin at midday n Octber 9. latins yield nearly identical results fr the King's Creek catchment and, in fact, the rmse's are the same as thse previusly reprted fr the spatially distributed simulatins. The implicatin f these results is reserved fr the discussin sectin. Althugh the spatial scale studied is relatively small, the discussin shuld still prvide initial insight int the impact f the assumptins utilized in develping the simpler, macrscale frmulatin. Nte that Famiglietti and Wd [1994] (hereafter referred t as paper 3) als applied the lcal SVATS at the King's Creek catchment scale, with implicatins fr the degree f spatial variability required t adequately mdel catchment-scale evaptranspiratin. The reader is referred t that reprt fr a detailed discussin f the scaling behavir f areally averaged evaptranspiratin frm the pint t the catchment scale Entire site. Results f macrscale mdel evaptranspiratin simulatins fr the entire 15 x 15-km FIFE site are shwn in Figure 5 fr the fur glden days. All mdel parameters are given in Tables 1-3, and meterlgical frcing data have been described previusly. Figure 5 shws that mdeled evaptranspiratin agrees reasnably well with the 22-statin average, with simulatins f glden days 3 and 4 reprducing bservatins better than glden days I and 2. Rmse's fr glden days 1-4 are 0.08, 0.06, 0.04, and 0.01 mm/h, respectively. Surces f errr have been described in earlier sectins. Althugh the simulatin results shwn in Figure 5 are reasnable given the simple mdel structure, simulatins fr the entire IFCs were nt as gd as thse fr the smaller King's Creek catchment. The reasns behind this are the subject f nging research. Initial analysis indicates that at the 15-km scale, the mdel results are rather sensitive t the manner in which meterlgical and flux data are aggregated. N attempt was made t run the spatially distributed frmulatin at this large scale. Hwever, in the

12 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS 3089! "' J t G2.0000, ( ( t. B00<1,., O <> O.OOOO0 g.soo0<), 2. a. BO*..t.S OOCO B I m I! Plate 3. Spatially distributed rainfall images fr (tp left) 0145 and (tp right) 0215 UT August 13, 15)87, fr the King's Creek catchment. Units are millimeters per hur. Scale is given in Plate I. Initial rt zne misture cntent befre the start f the simulatin at (middle left) 0015 UT, August 13, 1987, and (middle right) simulated misture cntent shrtly after the peak precipitatin intensity at 0215 UT. Units are vlume percent. Lcatins and rates f runff generatin fr the tw time steps f peak precipitatin intensity shwn in Plate 3a. Units are millimeters per hur.

13 3090 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS I I [ [, time(h) [ [ I > ' ! time(h) Figure 4. Mdeled and bserved evaptranspiratin fr the King's Creek catchment using the macrscale frmulatin. Observatins crrespnd t the five-statin average described in the text: (a) IFC 1, (b) IFC 2, (c) IFC 3, and (d) IFC 4. Times crrespnd t thse in Figure 3. next sectin, we speculate n pssible differences between spatially distributed and macrscale simulatins as spatial scale increases. 3. Discussin This discussin fcuses n the implicatins f the simulatin results f the previus sectin. Specifically, we are interested in the implicatins f the agreement between macrscale mdel and spatially distributed simulatins f evaptranspiratin fr the King's Creek catchment, and hw these might change as spatial scale is increased. As a first step tward understanding the aggregatin and scaling prperties f land surface prcesses, we cnducted a detailed investigatin f the scaling behavir f evaptranspiratin frm lcal t catchment scales (paper 3). Simulatin studies such as the present wrk and paper 3 are imprtant because they prvide insight int the rle f naturally hetergeneus land surface prperties and prcesses and hw imprtant spatial variability can be included in macrscale hydrlgical

14 FAMIGLIETTI AND WOOD' APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS 3091 frmulatins. These types f studies prvide a framewrk within which land hydrlgy parameterizatins can be cntinually mdified and ur understanding f large-scale hydrlgical prcesses imprved. The assumptins invked in the develpment f the macrscale frmulatin include an areally averaged representatin f meterlgical inputs, sil parameters, and vegetatin parameters. Spatial variability in the tpgraphic-sil index, sil misture, surface runff, and the energy fluxes is represented statistically, rather than explicitly, as in the spatially distributed frmulatin. Cmparisn f Figures 4 and 3 shws that fr the 11.7-km 2 grassland King's Creek catchmenthese are reasnable assumptins, since macrscale mdel and spatially distributed results are nearly identical. Sme discussin regarding why these results are similar and when they might differ shuld prvide insight int the restrictiveness f the macrscale assumptins at larger spatial scales and in different gegraphic lcatins. By cmparing macrscale and spatially distributed evaptranspiratin equatins, Famiglietti and Wd [this issue] shwed that the difference between evaptranspiratin cmputed with the tw frmulatins wuld depend upn tw factrs. The first is related t the degree f spatial variability in mdel parameters and inputs. The secnd factr is that the macrscale frmulatin represents spatial variability statistically rather than with explicit spatial patterns. At the King's Creek catchment, with the exceptin f tpgraphy and sil misture, the degree f spatial variability in sil prperties, vegetatin prperties, and meterlgical inputs was nt significant enugh t yield differences in simulatins with the tw mdels. Table 1 shws that nearly 90% f the catchment has similar sil parameters. Mst f the catchment is cvered by native tallgrass, which shwed minimal spatial variability in LAI n unburned prairie [Schimel et al., 1991]. Analysis f the precipitatin data shwed that many f the spatially distributed images exhibited minimal spatial variability. Cmparisn f Figures 4 and 3 further suggests that a statistical representatin f spatially variable tpgraphy, sil misture, and surface fluxes is adequate at the scale f the King's Creek catchment. This issue is discussed in mre detail in paper 3. In regins f similar scale but higher degrees f spatial variability, r in larger-scale applicatins where increased spatial variability is encuntered, mdel results may well diverge. Fr example, althugh the spatially distributed mdel was nt run at the scale f the entire 15-km FIFE site, spatially distributed and macrscale mdel results mst likely wuld nt shw the same agreement displayed at the catchment scale. Differences in land use (agricultural versus nnagricultural), prairie management (burned versus unburned, grazed versus ungrazed), atmspheric frcing (rain versus n rain), and vegetatin and sil type cmplicate the prcess f aggregating macrscale mdel input data. The prblem is cmpunded by the fact that there are numerus methds fr aggregating bserved flux data, and that such areally averagedata d nt necessarily represent a "true" areal average. June 6, 1987 July 11, August 15, 1987 i i Octlxx 11, time(h) Famig!ietti and Wd [this issue] prpse a methdlgy fr dealing with increased spatial variability in macrscale Figure 5. Macrscale mdel glden day evaptranspiratin simulatins fr the entire 15-km FIFE site. Observamdel applicatins. When sil and vegetatin prperties are tins represent a 22-statin average: June 6, July 11, August crrelated with tpgraphy (e.g., sil texture parameters, 15, and Octber 11, LAI) the apprpriate parameters can vary jintly with each interval f the tpgraphic-sil index. In larger-scale climate i

15 3092 FAMIGLIETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS mdeling applicatins, the mdel culd be implemented in msaic mde [Avissar and Pielke, 1989; Kster and Suarez, 1992; Seth et al., 1994] s that subgrid-scale variability in atmspheric frcing and majr vegetatin types culd be represented between subgrid patches. Within each patch, spatial variability in tpgraphy, sils, vegetatin, sil misture, and the runff and energy fluxes wuld be represented. Althugh such an apprach is idealized, and there are certainly mre detailed methds fr mdeling large-scale land-atmsphere interactin, it is imprtant t remember the philsphy behind the macrscale frmulatin. The mdel simplifies the representatin f vertical sil-vegetatinatmsphere transfer s that lateral hetergeneity can be incrprated in the mdel structure withut significantly increasing cmputatinal cmplexity relative t currently peratinal SVATS. 4. Summary In this paper the mdels f Farniglietti and Wd [this issue] were applied at their apprpriate scales fr evaptranspiratin mdeling at the FIFE site. FIFE was a largescale field experiment held in the summers f 1987 and 1989, n a 15 x 15 km regin f tallgrass prairie lcated near Manhattan, Kansas. During the experiment, multiscale grund-based and remtely sensed water and energy balance data were cllected simultaneusly, s that the data set prvides unique pprtunities t develp and test mdeling strategies ver a range f spatial scales. All mdel frcing, parametric, and bserved flux data were retrieved frm the FIFE infrmatin system. The lcal SVATS was applied t mdel evaptranspiratin at five flux measurement statins in the nrthwest quadrant f the FIFE site. When available, lcal atmspheric frcing, vegetatin, and sil data were utilized. Simulatins were perfrmed fr three f the fur FIFE "glden(clud-free) days" with gd results. The simplified SVATS structure, the use f nnlcal frcing data, and bservatin errrs were identified as surces f errr in the simulatins. Fr catchment-scale and site-wide evaptranspiratin simulatins, mdel parameter and frcing data were aggregated in tw ways. Spatially distributed infrmatin, such as sil parameters, tpgraphic variables, and rainfall were aggregated by averaging individual grid element values. Pint data such as flux data bserved at individual measurement statins were aggregated by simple linear averaging. Alternative methds fr aggregating these data were nt investigated in this study. The spatially distributed mdel was applied at the km 2 King's Creek catchment fr evaptranspiratin mdeling during FIFE intensive field campaigns (IFCs) 1-4. The IFCs were rughly 2-week-lng perids during which mst flux bservatins were made. Catchment-average evaptranspiratin was cmpared t an average f bservatins made at five measurement statins in and near the watershed. Simulatin results were gd and additinal surces f errr, beynd thse listed abve, were identified as peridic verpredictin f ptential evaptranspiratin rates and sil r vegetatin-cntrlled evaptranspiratin rates. Mdel results were shwn in spatially distributed frmat fr selected times during the simulatins and shwed general agreement with patterns derived by ther researchers using remtely sensed infrmatin. The macrscale frmulatin was applied t bth the King's Creek catchment and the entire 15-km FIFE site fr evaptranspiratin simulatins. Macrscale mdel simulatins fr King's Creek were nearly identical t the spatially distributed results, implying that at this lcatin and at this scale, the assumptins invked in the develpment f the macrscale frmulatin are reasnable. The macrscale mdel was then emplyed t simulate evaptranspiratin frm the entire 15-kin site fr the fur glden days. Simu- lated evaptranspiratin rates shwed reasnably gd agreement with the 22-statin average f bservatins. Resuits fr the third and furth glden days shwed better agreement with bservatins than the first and secnd. It was suggested that at this and larger scales, additinal errr may arise as a result f the macrscale assumptins f areally averaged atmspheric frcing, vegetatin parameters, sil parameters, and the methds by which these data and ther flux bservatins are aggregated. A methdlgy t cmbat these prblems at the grid scale f atmspheric mdels was reviewed. Acknwledgments. This wrk was supprted by NASA grants NAG 5-899, NAGW 1392, NGT 60153, and NAS ; this research supprt is gratefully acknwledged. This paper was written and revised while the first authr was a U CAR Climate System Mdeling Prgram pstdctral fellw visiting Princetn University and the Natinal Center fr Atmspheric Research. We thank these hst institutins fr the use f their facilities. We thank William Crssn fr his advice regarding vegetatin parameters at the FIFE site. The cmments f tw annymus reviewers helped t cnsid- erably imprve the riginal manuscripts. Page charges fr this paper were paid by the Gelgy Fundatin f the Department f Gelgical Sciences at the University f Texas at Austin. References Avissar, R., and R. A. Pielke, A parameterizatin f hetergeneus land-surface fr atmspheric numerical mdels and its impact n reginal meterlgy, Mn. Weather Rev., 117, , Brks, R. H., and A. T. Crey, Hydraulic prperties f prus media, Hydrl. Pap. 3, Cl. State Univ., Frt Cllins, Famiglietti, J. S., Aggregatin and scaling f spatially-variable hydrlgical prcesses: Lcal, catchment-scale and macrscale mdels f water and energy balance, Ph.D. dissertatin, Princetn Univ., Princetn, N.J., Famiglietti, J. S., and E. F. Wd, Cmparisn f passive micrwave and mdel derived estimates fr sil misture field, paper presented at the 5th Internatinal Cllquim--Physical Measurements and Signatures in Remte Sensing, Eur. Space Agency, Curcheval, France, Jan , Famiglietti, J. S., and E. F. Wd, Multiscale mdeling f spatially variable water and energy balance prcesses, Water Resur. Res., this issue. Famiglietti, J. S., and E. F. Wd, Effects f spatial variability and scale n areally averaged evaptranspiratin, Water Resur. Res., in press, Hlwill, C. J., and J. B. Stewart, Spatial variability f evapratin derived frm aircraft and grund-basedata, J. Gephys. Res., 97(D!7), 18,623-!8,628, Jantz, D. R., R. F. Hamer, H. T. Rwland, and D. A. Gier, Sil Survey f Riley Cunty and Part f Geary Cunty, Kansas, 71 pp., Sil Cnserv. Sent., U.S. Dep. f Agric., Washingtn, D.C., Jedlvec, G. J., and R. J. Atkinsn, Variability f gephysical parameters frm aircraft radiance measurements fr FIFE, J. Gephys. Res., 97(D17), 18,913-18,924, Kster, R. D., and M. J. Suarez, Mdeling the land surface bundary in climate mdels as a cmpsite f independent vegetatin stands, J. Gephys. Res., 97(D3), , Lin, D. S., E. F. Wd, J. Famiglietti, and M. Mancini, Impact f micrwave derived estimates fr sil misture fields, paper pre-

16 FAMIGLiETTI AND WOOD: APPLICATION OF MULTISCALE WATER AND ENERGY BALANCE MODELS 3093 sented at the 6th Internatinal Sympsium n Physical Measure- Smith, E. A., H. J. Cper, W. L. Crssn, and Weng Heng-yi, ments and Signatures in Remte Sensing, Eur. Space Agency, Val d'isere, France, Estimatin f surface heat and misture fluxes ver a prairie grassland, 3, Design f a hybrid physical/remte sensing bi- RawIs, W. J., D. L. Brakensiek, and K. E. Saxtn, Estimatin f sphere mdel, J. Gephys. Res., 98(D3), , sil water prperties, Trans. ASAE, 25, , 1328, Wd, E. F., D-S. Lin, M. Mancini, D. Thngs, P. A. Trch, T. J. Schime!, D. S., T. G. F. Kittel, A. K. Knapp, T. R. Seastedt, W. J. Jacksn, J. S. Famiglietti, and E. T. Engman, Intercmparisns Partn, and V. B. Brwn, Physilgical interactins alng re- between passive and active micrwave remte sensing and hysurce gradients in a tallgrass prairie, Eclgy, 72(2), , drlgical mdeling fr sil misture, Adv. Space. Res., 13(5), , Sellers, P. J., F. G. Hall, G. Asrar, D. E. Strebel, and R. E. Murphy, An verview f the First Internatinal Satellite Land J. S. Famiglietti, Department f Gelgical Sciences, University Surface Climatlgy Prject (ISLSCP) Field Experiment (FIFE), f Texas at Austin, Austin, TX ( jfamiglt@maestr. J. Gephys. Res., 97(D17), 18,345-18,371, ge.utexas.edu) Seth, A., F. Girgi, and R. E. Dickinsn, Simulating fluxes frm E. F. Wd, Water Resurces Prgram, Department f Civil hetergeneus land surfaces: An explicit subgrid methd emply- Engineering and Operatins Research, Princetn University, ing the Bisphere-Atmsphere Transfer Scheme (VBATS), J. Princetn, NJ Gephys. Res., 99, 18,651-18,667, Smith, E. A., et al., Area-average surface fluxes and their timespace variability ver the FIFE dmain, J. Gephys. Res., (Received September 17, 1993; revised May 26,!994; 97(D17),!8,599-18,622,!992. accepted June 8, 1994.)