Conditioning of Flow Projections under Climate Change on Hydrologic Signatures within the GLUE Framework

Climate change impact on water resources is generally quantified in terms of relative changes in characteristicflows (e.g. annual runoff, median annual flows, etc.) over a future period compared to the baseline one. Thesechanges are estimated under the assumed emission scenarios and with one or more modelling chains (combinationsof the Global and Regional Climate Models, and a hydrological model). Since different modelling chains yielddifferent projections, estimates of these relative changes are uncertain. High prediction uncertainty is reflected in awide 90 per cent prediction uncertainty band (90PPU) or in a distribution that resembles the uniform distribution.Therefore, research in robustness of the modelling chains has been conducted. The goal of the research is toappoint higher probabilities to the projections obtained by the more robust chains, and in that way reduce theuncertainty in flow projections under climate change.In this research, the hydrologic projections are conditioned on the hydrologic signatures within the GLUEframework. Namely, a relative change obtained with a modelling chain is assigned a likelihood depending on theperformance of the chain in terms of the hydrologic signatures over the baseline period. High flow projections (2ndpercentile of the daily flows) are conditioned on the high-segment of the flow duration curve (FDC), projectionsof the median flows are conditioned on the FDC mid-segment slope, and the projections of the low flows areconditioned on the FDC low-segment. The projections of total annual runoff are conditioned on the entire FDC.The likelihoods are quantified in terms of Nash-Sutcliffe efficiency coefficient (NSE) evaluated from the FDCs ofthe flows simulated by the modelling chains and the observed FDC.The methodology presented is applied to develop flow projections in the Kolubara River catchment in Ser-bia over the mid 21st century (2041-2070). Hydrologic projections are obtained by the HBV-light hydrologicmodel with input from five climate models (combinations of the Global and Regional Climate Models), all rununder A1B emission scenario. The outputs of the climate models are bias-corrected to reproduce distributions ofthe precipitation depths and temperatures observed in the baseline period (1961-1990). The best twenty parametersets out 25,000 sampled ones are kept in the analysis, resulting in 100 modelling chains.The GLUE conditioning did not significantly affect the median values of the projections, but only thewidth of the prediction bands. All modelling chains perform equally well in terms of the entire FDC and itsmid-segment. Therefore, the GLUE-conditioned projections of annual runoff volume and median flows are similarto the unconditioned ones (i.e. GLUE conditioning yields slightly narrower 90PPUs). Model efficiency in the highflow domain differs between the modelling chains: however, the GLUE conditioning leads to somewhat narrower90PPU. Only few modelling chains performed well in the low flow domain, therefore the width of the 90PPU wasconsiderably reduced by conditioning (from 61.5% to 36.8%)Geophysical Research Abstract

Historical rainfall for urban storm drainage design

Traditional design method for urban drainage systems is based on design storms and its major drawback is that frequencies of peak flows in the system are considered equal to frequencies of design storms. An alternative is to use historical storms with rainfall-runoff models to produce a series of possible flows in the system and their frequencies. The latter approach involves more computations and can be laborious for larger catchments. This paper considers ways to reduce the set of historical storms to be involved in design procedure and yet to lead to realistic flow frequencies. Frequencies obtained by rainfall-runoff simulation at an experimental catchment are compared with frequencies of observed peak flows in the system

Measurements, calibration of rainfall-runoff models and assessment of the return period of flooding events at urban catchment Kumodraž in Belgrade

For the purpose of re-design and improvement of the combined sewer system at the Kumodraz catchment in Belgrade, measurements of rainfall and runoff at the catchment were established in late 1997. Observed data are used for calibration and validation of two rainfall-runoff models: the detailed model BEMUS (Belgrade Model) and a conceptual hydrologic model Visual OTTHYMO. The major facilities of the recommended solution for re-design of the existing system are three retention ponds and outlet into a trunk. The paper briefly presents assessment of design flows for these four locations of the catchment based on results from the calibrated models. Data on intense storms that caused severe flooding within the catchment (and also all over Belgrade and other parts of Serbia) in June and July 1999 are used for comparison of design flows with a real event. During these storms the flow gauging equipment at the catchment was destroyed and only the rainfall data was available. In order to analyze the system under extreme conditions it is therefore necessary to perform hydrograph simulations. The basic idea was to check return periods of rainfall and runoff for these storms

Analiza uticaja nepoznavanja namene površina na rezultate simulacije modela kišnog oticaja na primeru Miljakovac

Experimental catchments Miljakovac has been used in 1980-es for field studies of rainfall-runoff processes. The most accurate analysis of flow in storm sewer systems can be achieved when there is a land use map defined in details, with every single building, but that requires a lot of time for preparation of data. Standard designing procedure uses maps with zones of similar levels of urbanization. Usually, there are no data of measured rainfall and outflow events available, so the created model can be calibrated. Paper presents, that if data of measured flows are available with calibration of percentages of different surface types (roofs, other impervious and pervious areas) in each zone, difference between simulated and measured flow can be brought to minimum. There are two groups of data about urbanization growth, assumed and exact state. This paper analyses error that is made in assumed state, and influence of more and less detailed terrain model on flow from whole catchments, also on flow in single pipes.Eksperimentalni sliv Miljakovac je korišćen za ispitivanje procesa padavine oticaj tokom 1980-tih godina. Detaljna podela namene površina je najbolji način pripreme podataka, u analizi simulacionog modela tečenja u sistemima kišne kanalizacije, ali zahteva dosta vremena. U standardnoj projektantskoj praksi se najčešće pristupa izradi grubog" modela namene površina, gde se površina sliva deli u zone sa sličnim nivoom urbanizacije, ali obično ne postoje podaci o izmerenim oticajima, tako da nije moguće kalibrisati takav grubi model. U radu je pokazano da se kalibracijom procenata pripadajućih površina za svaku zonu, kada postoje podaci o izmerenim oticajima, dobija zadovoljavajuće slaganje maksimalnog simuliranog i izmerenog oticaja. Takođe se analizira greška koja se javlja u pretpostavljenom stanju novoizgrađenih objekata, njen uticaj, i uticaj detaljnosti konfiguracije terena, na oticaj na izlazu iz sliva i u izdvojenim cevima

Konsistentno određivanje računskih kiša

Design storms are the basic input for hydrologic assessment and design of the flood control structures. Small and medium sized catchments with shorter concentration times require design storms of shorter, sub-daily, duration, that are defined from the rainfall depth - duration - frequency (DDF) relationships. The DDF relationships are developed by statistical analysis of rainfall depths in intervals of various durations. The development of DDF curves is usually accompanied by many problems that can result in significant uncertainty in the resulting design rainfall depths and intensities. Most problems are related to the measurement errors and data processing; however, due to the customary shortage of this kind of data in Serbia, practicing engineers are forced to develop the DDF curves from a modest amount of the available data, without an insight in the uncertainties inherent in the process. This paper discusses these problems and proposes to Serbian practitioners to apply a robust method described in earlier work of Koutsoyanniset al. (1998) for consistent development of the DDF relationships. The method is illustrated using the short-duration rainfall data from Banja Luka.Računske kiše su osnovni ulazni podaci za hidrološke proračune i projektovanje objekata za zaštitu od velikih voda. Na malim i srednjim slivovima merodavna trajanja kiše su kraća od 24 sata i računske kiše se definišu zavisnostima visina kiše - trajanje kiše - povratni period (ili zavisnosti HTP), koje se dobijaju statističkom analizom visina kiše u intervalima vremena različitog trajanja. Konstrukciju zavisnosti HTP prate razni problemi koji mogu dovesti do velikih neizvesnosti u vezi sa rezultujućim računskim kišama. Većina ovih problema potiče od grešaka u merenju i obradi podataka merenja padavina, ali poslovični nedostatak ovih merenja dovodi inženjere u praksi do toga da zavisnosti HTP određuju na osnovu skromnih raspoloživih podataka, bez sagledavanja neizvesnosti koje postoje. U ovom radu se razmatraju navedeni problemi i ukazuje se na metode dostupne u literaturi za konsistentno određivanje zavisnosti HTP, a na primeru podataka sa meteorološke stanice Banja Luka

Beogradski kanalizacioni sistem u uslovima ekstremnih padavina

The Belgrade waste water system started being built more than 100 years ago. It is getting larger in accordance to urban development aimed at collecting most of waste water including rainfall runoff and communal and industrial water. Separate systems for rainfall runoff and for waste water are constructed at recently developed areas, but in general, combined systems dominate to a far extent. Existing systems are reconstructed and even completed since urbanization of already dense urbanized areas are developed more what furthermore contribute to a much higher rainfall runoff during extreme rainfalls. Major existing trunks, pipes and outlets into the Sava and Danube rivers and brooks is given in General master plan of 60ies, including a series of retention ponds for detention of natural streams floods. Within the General master plan from the year 2002 major issue was development but not with consequences upon drainage of rainfall runoff events accounting for retention as well as separation of different waters haven't been solved properly. Those aspects arise when measurements in the waste water system are performed and when waste water treatment plant is constructed. This paper consists of certain comments of the recently occurred extreme rainfalls and flooding at particular streets of Belgrade during summertime of the year 2009 in connection to rapid urban development and reconstruction of Belgrade waste water system in relation to standards EN 754. .Beogradski kanalizacioni sistem, stariji od 100 godina, prati širenje urbanizacije kako bi se prihvatile i odvele gotovo sve gradske otpadne vode, i to: kišni oticaji, upotrebljene vode iz domaćinstva i otpadne vode iz industrije. U novijim delovima grada postoje separatni sistemi za kišne vode i posebni za fekalne vode, ali se može reći da dominiraju opšti kanalizacioni sistemi. Postojeći sistemi se stalno dograđuju za povećane oticaje u najgušćem gradskom jezgru jer velika izgradnja u starijim delovima doprinosi povećanju kišnog oticaja, pogotovu pri pojavi ekstremnih kiša što se u poslednjoj deceniji češće javlja. Sadašnja osnovna kanalizaciona mreža, uključujući glavne kolektore i ispuste u reke Savu, Dunav i druge potoke koncipirana je studijama i Generalnim planom iz 60-ih godina, uključujući najvažnije - zadržavanje ekstremnih oticaja sa prigradskih potoka u brojnim retenzijama po obodu grada. Planom iz 2002. g. koji se nekritički bavi samo izgradnjom, ali ne i njenim posledicama, pitanje retenziranja, kanalisanja i ispuštanja upotrebljenih voda nije rešeno. Takođe nije obrađeno razdvajanja kišnih voda od ostalih, što se uočava kroz sistematska merenja u kanalizaciji a najviše po izgradnji postrojenja za prečišćavanje kišnih voda. Uzevši u obzir ubrzanu i neplansku izgradnju objekata i sistema, razvoj i dogradnju kanalizacije, kao i povećanje merodavnih perioda za gradske kanalizacije u okviru EN 754, ovde se komentarišu poslednje ekstremne velike kiša i poplave u Beogradu tokom leta 2009. godine radi preliminarne ocene mogućih uzroka tih sve češćih pojava.

Conditioning of Flow Projections under Climate Change on Hydrologic Signatures within the GLUE Framework

Climate change impact on water resources is generally quantified in terms of relative changes in characteristicflows (e.g. annual runoff, median annual flows, etc.) over a future period compared to the baseline one. Thesechanges are estimated under the assumed emission scenarios and with one or more modelling chains (combinationsof the Global and Regional Climate Models, and a hydrological model). Since different modelling chains yielddifferent projections, estimates of these relative changes are uncertain. High prediction uncertainty is reflected in awide 90 per cent prediction uncertainty band (90PPU) or in a distribution that resembles the uniform distribution.Therefore, research in robustness of the modelling chains has been conducted. The goal of the research is toappoint higher probabilities to the projections obtained by the more robust chains, and in that way reduce theuncertainty in flow projections under climate change.In this research, the hydrologic projections are conditioned on the hydrologic signatures within the GLUEframework. Namely, a relative change obtained with a modelling chain is assigned a likelihood depending on theperformance of the chain in terms of the hydrologic signatures over the baseline period. High flow projections (2ndpercentile of the daily flows) are conditioned on the high-segment of the flow duration curve (FDC), projectionsof the median flows are conditioned on the FDC mid-segment slope, and the projections of the low flows areconditioned on the FDC low-segment. The projections of total annual runoff are conditioned on the entire FDC.The likelihoods are quantified in terms of Nash-Sutcliffe efficiency coefficient (NSE) evaluated from the FDCs ofthe flows simulated by the modelling chains and the observed FDC.The methodology presented is applied to develop flow projections in the Kolubara River catchment in Ser-bia over the mid 21st century (2041-2070). Hydrologic projections are obtained by the HBV-light hydrologicmodel with input from five climate models (combinations of the Global and Regional Climate Models), all rununder A1B emission scenario. The outputs of the climate models are bias-corrected to reproduce distributions ofthe precipitation depths and temperatures observed in the baseline period (1961-1990). The best twenty parametersets out 25,000 sampled ones are kept in the analysis, resulting in 100 modelling chains.The GLUE conditioning did not significantly affect the median values of the projections, but only thewidth of the prediction bands. All modelling chains perform equally well in terms of the entire FDC and itsmid-segment. Therefore, the GLUE-conditioned projections of annual runoff volume and median flows are similarto the unconditioned ones (i.e. GLUE conditioning yields slightly narrower 90PPUs). Model efficiency in the highflow domain differs between the modelling chains: however, the GLUE conditioning leads to somewhat narrower90PPU. Only few modelling chains performed well in the low flow domain, therefore the width of the 90PPU wasconsiderably reduced by conditioning (from 61.5% to 36.8%)Geophysical Research Abstract