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<br />ABBS: INVESTIGATION OF PROBABLE MAXIMUM PRECIPITATION ASSUMPTIONS
<br />
<br />tion for these simulations also illustrates that changes in the
<br />moisture field feeds back to the dynamics by affecting both the
<br />intensity and movement of the storm.
<br />.. Despite these deficiencies in the assumptions used to esti-
<br />mate PMP we bliievc that there is no operational replacement
<br />available at present for the current PM P methodology, How-
<br />ever, improvements in Ihe estimation of PMP may soon be
<br />possible if increased effort is placed on (amongst other things)
<br />the numerical modeling of extreme rainfall t:vcnts. These im-
<br />provements are only possible if the results of these efforts are
<br />communicated to the hydrological community.
<br />
<br />4.3. Unanswered Questions and Problems
<br />
<br />The method used in this study to increase the moisture fields
<br />was adopted since it theoretically had the advantage of allow-
<br />ing us to increase the surface dewpoint temperature of the
<br />enhanced moisture simulations to values that were higher than
<br />the surface temperature of the original precipitation event. In
<br />addition, this method allowed us to retain a similar vertical
<br />moisture profile to that of the original event, ratber than grad-
<br />ually approaching an' atrnosphere that is saturated throughout
<br />its depth. Other method, of maximizing the moisture availabil-
<br />ity should be investigated to determine if the conclusions
<br />reached in nur study are met. For example, 21'"0 et al. [1997]
<br />increase the specific humidity thrQogh the depth of the atmo-
<br />sphere to cbange the precipitable water. Their method, com-
<br />bined with that used here, may allow a wider range of maxi.
<br />mization factors, and higher values, to be tested.
<br />As computing capabilities increase, it will become possible
<br />to model extreme storm~ at increasingly higher resolution. The
<br />advances in computing hardware make it possible to examine
<br />if further increasing the horizontal resolutimruf the simulated
<br />sturms changes the above conclusions.
<br />The natural extension of this project is to use the model-
<br />predicted precipitation fields to provide an obsetved precipi-
<br />tation field and then subject them to the analysis given to the
<br />extreme storms that constitute the GSAM database. After the
<br />application of identical maximization factors the results of the
<br />maximized storm should be compared with that of the equiv-
<br />alent simulated "increased moisture" storm.
<br />We believe that it is becoming feasible to perform simula-
<br />tions of a greater number of these events and to provide skillful
<br />quantitative precipitation forecasts of them. By utilizing a
<br />"team approach" in which hydrometeorologists and meteoro-
<br />logical modelers work together it is now possible to use me.
<br />soscale numerical models as tools for hydrological planning.
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<br />Acknowledgments. Thi~ project was initiated by the past Chief of
<br />the CSIRO Atmospheric Research, B. Tucker, and 13. Ryan. In addi-
<br />tion to the financial support fmm UWRAA research project WR-22,
<br />the project IUls been suppt)rted hy a numher uf intJivitJuals antJ orga-
<br />nizations. II Collon alltJ R. Piclke kintJJy provitJetJ the mudel ctltJe for
<br />RAMS, tJr.:velopetJ at ColoratJo Stalt.; Univr.:rsity under thr.: support of
<br />Ihr.: U.S. National Sdence FountJation and thr.: Army Research Oflke.
<br />The Sydney Water Curpori.llion pruvitJetJ the PMP estimates for the
<br />Warragamha Dam antJ H<iwkesbury-Nepean Ci.ltchments. The NSW
<br />Department of Public Works and Services providr.:tJ the PMP estimates
<br />for the catchments of the Oheron and Chiftey Dam. The terrain data
<br />were supplietJ by the AUstralian SUlVeying and LantJ Infllrnmtion
<br />Group. Meteorological data were supplied by the Bureau of Meteo-
<br />rulogy. S. Lee and A Stephens provitJed computing support for por-
<br />tions of the projecl. Discl.lssion with L. Minty frum the Hydrology
<br />Branch at the Bureau of Meteurology were very helpful in developing
<br />our understanding of the CUrrent PMP methodology. The project also
<br />
<br />795
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<br />benefited greatly from the suggestions and advice of the project ref-
<br />erence pand formed in October 1995.
<br />
<br />References
<br />
<br />Abbs, D. J., ami J. B. Jensen, Numerical modding of urngmphici.llly
<br />forceLl post-frontul rain, Mem. WCI/lher RCI'., 121, IX9-2U6, 1992.
<br />Abhs, D. J., <1111.1 S. II. Lee, The use of RAMS as a toul fur quantit;.ltive
<br />precipituti\Jl1 forecasting, paper prescllted ill ThirLl RAMS Us..:rs'
<br />Workshop, Echw.:a, Vil.:turia, Australia, July 1(1-12, 1997.
<br />Abhs, D. J., and B. F. Ryan, Num..:rical moddling of extn:mc prl'cip~
<br />itation, Rep. /3/,71 pr., Urhan Watcr Rcs. Assoc. of Ausl., T\kl-
<br />hourne, Victoria, Aust., 1997.
<br />Australian Nutional CummiUet.: un Lnrg~ Dams (ANCOLD), (;/lidt'.
<br />litles UII Desigll f1uoeb- It),. Dams, llarlun, A. C T., Au~t.. ltJt\tJ.
<br />BureaU of Meteurology, The estimation of prohahle maximum pi\:l'ip-
<br />italion in Australia for short L1uration ilnd small areas, Bull. 5/. .15
<br />pr., Canberra, A. CT., AusL, 198-1.
<br />Bure.lU of Meteorology, A rcport on the hcavy rainfall and 111 Iud C\''':llt
<br />in thl.l Sydney metropolitan antJ nearby areas over the pcrintJ ~-7
<br />August 1986, special rl.lport, 50 pp., N. S. W. Regional om..:..:, Syd.
<br />ney, N. S. W., Aust., 1987.
<br />Chen, C, and W. R. Couon, A one-dimensional simulalion of the
<br />stratocumulus-cappcd mixed layer, Boundary-Layer Me/coro/., 25.
<br />289-32t. 1983a.
<br />Chen, c., anLl W. R. Couon, Numerical experiments with a onc-
<br />L1imcnsional higher order turbulence model: Simulation of thc Wan-
<br />gara Day 33 Case, BVlllldary-Luyer !tIe(eo,.o/., 25, 375-404, 1983b.
<br />Chen, S. S., i.lnd W. M. Frank, A numcriC<11 study of the genesis of
<br />extratropical convective mesovortices, I, Evolution and dynamics, 1.
<br />A/mos. Sci., 50, 2401-2426, 1993.
<br />Churchill, D. D., anLl R. A. Houze Jr., Developmcnt and structure of
<br />winter monsoon cloud clusters on 10 December, 1978,J. Almos. Sd.,
<br />41.933-960, t984,
<br />Colton, W. R., M. A. Stephens, T. Nehrkorn, and G. J. Tripoli, The
<br />Colorado State U nivcrsity three-diml.losional cloud/mesoscale moJ-
<br />cl-1982, 2, An ice: parameterization,J. Reclr. Almos., /6, 295-320,
<br />1982,
<br />Cotton, W. R., G. J. Tripoli, R. M. Rauber, and E. A Mulvihill,
<br />Numerical simulation of Ihc effects of varying ice crystal nuclciltion
<br />rates anLl aggn:gation pruccsscs on ()rogmphic snowf.lil, J. Clim.
<br />App/. Ml.'leorol., 15, 1658-1680, 1986.
<br />Dutton, J. A, and G. H. Fichtl, Approximate equations of motion for
<br />gases and liquids, J. Almos. Sd., 26, 241-249, 1969.
<br />Ferrier, B. S., J. Simpson, and W.-K. 1'ao, Factors responsible for
<br />precipitation efficiencies in midlatitude and tropical squall simula-
<br />tions, MOil. Wealher Rev., 124,2100-2125, 1996.
<br />Flatau, P. J., G. J. Tripoli. 1. Verlinde, and W. R. Cotton, The CSU-
<br />RAMS cloud microphysics module: General theory and code doc-
<br />umentation, Almos. Sc:i. Pap. 451, Dep. of Atmos. Sci., Colo. Statc
<br />Univ., Fort Collins, 1989.
<br />Frank, W. L., and C. Coh!:n, Properties of tropical cloud ensemblcs
<br />estimated using a cloud model and an observed updraft population,
<br />J. A/mos. Sci., 42, 1911-1928, 1985.
<br />Frank, W. L., and C. Cohen, Simulation (If tropical convective systems,
<br />1, A cumulus paramcterization, J. Amros. Sd., +J, 3787-3799, 1981.
<br />Gal-Chcn, T., and R. C. J. Somcrville, On thc use of a coordinntc
<br />transformation for the solutiun of the N,wier-Stokes equatiolls,
<br />J. Compo Pllys., 17, 209-228, 1975a.
<br />Gal-Chen, T., anLl R. C. J. SomcIVille, Numerical solution of the
<br />Nilvier-Stukcs L:quations with topogruphy,1. Compo Pllys., 17, 276-
<br />3111, t9751>,
<br />GuILling, B. W., and L. M. Leslie, The impact of resolution .lOd for.
<br />mulatioll nil moLld simulations of an ~ast euast luw, Am'l. /IktL'()/~}/.
<br />MII.~., -12, 1lI5-llb, IlJlJ3.
<br />I hlllscn, E. M., Probahle maximum precipitation fm L1esig.n Hoods in
<br />the UnitetJ Stales, J. Hydro/., 96, 267-278, IlJ87.
<br />llart, T. L., Survey of probable maximum precipitation using the syn-
<br />optic method uf storm transposition.alltJ maximisation, in Workshop
<br />Oil Spillway De:iigll,A WRC Conf. Ser., Vol. 6, Aust. Gov. Print. SCIV.,
<br />Cunbcrra, Aust., 1982.
<br />Hess, G. D., Numl.lrical simulation of the August 1986 heavy rainfall
<br />event in the Sydney area, J. Geophys. Re.~., 95, 2073-20S2, 1990.
<br />Holland, G. J., A H. Lynch, and L. M. Leslie, Australian ensH:oast
<br />cyclunes, I, Synoptic o....cIView and case stuLly, MOil. Wt'dther Rei'.,
<br />JJ5. 3112~-31136, 1987,
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