Sensitivity of Australian roof drainage structures to design rainfall variability and climatic change
Introduction
A key function of the built environment is to protect people and property from adverse meteorological conditions. In many design processes, a minimum level of protection from specific weather-related hazards is mandated by design guidelines, building codes and standards. While operational performance can be determined to a relatively high degree of confidence, by empirical tests [1,2] or known physical relationships [3], achieving a similar degree of confidence in design rainfall values for low-probability meteorological extremes is more difficult [[4], [5], [6], [7]]. This is acknowledged in scientific literature [[8], [9], [10]], although the degree to which it would influence design varies between structural elements of the built environment [11,12].
In the design of hydraulic structures, risk is assessed on three factors; the probability of extreme rainfall events occurring, the likelihood of performance failure from such events, and the cost of failure should it occur [13,14]. The probability of extreme rainfall events is characterised using a relationship between Intensity-Frequency-Duration (IFD), Intensity-Duration-Frequency (IDF) or Depth-Duration-Frequency (DDF) [[18], [19], [20]]. Designs for large structures, or networks, are likely to give a greater consideration to parameter uncertainty than small plot-level structures because of the higher associated costs of failure. However, the aggregated costs of multiple plot-level structures simultaneously failing can be substantial, such as when extreme events occur in urban areas [[15], [16], [17]].
Site-specific IFD rainfall values used in the design process are model estimates and are subject to large uncertainty [21]. IFD estimates may not accurately represent actual rainfall values at a site due to gaps in available rainfall data [22,23], the statistical methods used [6,8,10,24] and the climate baseline over which the data has been collected [4,5]. As superior statistical methods are developed, and the quantity and quality of the observations in datasets increase, improved IFD estimates can be produced. For example, the 2016 revision of Australian IFD relationships resulted in changes in intensity values of between +19.7% and −32.6% compared to 1987 IFD values, at point locations in capital cities [25]. IFD estimates can also change with the timespan of available rainfall data because of short to medium term periodic metrological drivers [26,27], and longer term anthropogenic forcing of the climate system [[28], [29], [30], [31]]. These elements combine to create an environment of non-stationary IFD design rainfalls, under which hydraulic designers attempt to maintain a specified performance level over a hydraulic structure's lifetime [[18], [19], [20]].
While methods exist to estimate [5,6,32,33], or account for [[34], [35], [36]], uncertainties in IFD values, the data and technical knowledge required to apply them limits their use in the design of plot-level hydraulic structures. Pappenberger and Beven [11] noted in a review that the technical challenges associated with assessing uncertainty in IFD estimates is a common justification for ignoring the uncertainty in the hydraulic design process. An additional challenge is modelling the influence of climate change on IFD estimates over the structure's operational life. Although the influence of climate change on IFD estimates is difficult to quantify with confidence, the literature indicates that the intensity of rainfall in short-duration events is increasing as more moisture is stored in a warmer atmosphere [37]. The more moisture the atmosphere can hold, the greater is the extreme rainfall event, which forms a basis for updating pre-existing IFD relationships for future temperature increases.
Roof drainage systems are common small catchment hydraulic structures designed using an IFD design rainfall value for a single point location. The objective of this study is to determine the ability of current Australian design standards for roof drainage systems with box gutters to accommodate deviations in design rainfall values. Possible deviations from IFD estimates are assessed based on two sources of variability: spatial variation in proximate IFD values, and changes in climate conditions from anthropogenic forcing. Box gutters located within a buildings perimeter, were chosen as the model structure because exceedance of hydraulic capacity will result in water ingress into the building envelope and performance can be determined satisfactorily using existing hydraulic theory. Although, Australian design guidelines have been used in this study, there are many similarities to design guidelines employed in the USA and Europe.
Section snippets
Box gutter design
The rational (or equilibrium) method [38,39] is a commonly used approach to estimate the peak flow rate in small to medium catchments. Peak flow rate is often the only hydrologic metric considered in the design process of many hydraulic structures, particularly in small urban catchments [[40], [41], [42]]. Its applicability to flood analysis has been questioned for landscape-level catchments with heterogenous surface conditions and greater variation in spatial and temporal patterns of rainfall [
Location of study sites
Nine areas around Australia were included in this study. The study areas were centred on the central business districts (CBD) of Brisbane, Sydney, Canberra, Melbourne, Hobart, Adelaide, Perth, Darwin and Cairns (Fig. 1). The locations include all the state capitals as well as Cairns (which receives some of the most extreme rainfall intensity values in Australia). These locations were chosen as they have a high density of small catchment hydraulic structures and comparatively long-term and
Box gutter sensitivity
The sensitivity of box gutter designs to an increase in flow rate, ΔQMAX, varied substantially, from 1.125 to 4.063, between the overflow types (Table 3). Each overflow design had a unique range of sensitivity with no overlap of ΔQMAX values. The least sensitive design option was the rainhead, which could accommodate increases in flow rates of more than threefold, for a 300 mm wide gutter, to fourfold, for a 600 mm wide gutter. Values of ΔQF for the rainhead are also dependent on width and
Conclusion
Evaluation of potential existing and future deviations in design rainfall intensity in relation to the hydraulic sensitivities of designs can aid the designer in determining if adaption measures are necessary. In this study, deviations in design rainfall values were found to be primarily driven by existing spatial variability rather than future uncertainties at most locations. Therefore, adaptation measures are pertinent not only to possible future climates but are valuable to improve the
Acknowledgements
The authors would like to acknowledge and thank the Australian Government Bureau of Meteorology for the rainfall and temperature datasets used in this research. The data set can be obtained from http://www.bom.gov.au/climate/data/stations/. L. Verstraten is grateful for funding support from the Association of Hydraulic Services Consultants Australia. C. Wasko is grateful for funding support provided by the University of Melbourne Mckenzie Postdoctoral Fellowship.
References (110)
- et al.
Comparing empirical water depth observations of a box gutter roof drainage system to three different international design guidelines
J. Build. Eng.
(2017) - et al.
Uncertainty quantification in rainfall intensity duration frequency curves based on historical extreme precipitation quantiles
Proc. Eng.
(2016) - et al.
Uncertainty of Intensity–Duration–Frequency (IDF) curves due to varied climate baseline periods
J. Hydrol.
(2017) - et al.
Uncertainty estimation of Intensity–Duration–Frequency relationships: a regional analysis
J. Hydrol.
(2018) - et al.
Stationarity is undead: uncertainty dominates the distribution of extremes
Adv. Water Resour.
(2015) - et al.
Barriers to climate change adaptation in the Australian construction industry – impetus for regulatory reform
Build. Environ.
(2018) - et al.
A review of severe thunderstorms in Australia
Atmos. Res.
(2016) - et al.
Rainfall depth-duration-frequency curves and their uncertainties
J. Hydrol.
(2008) - et al.
Global sensitivity analysis in hydrological modeling: review of concepts, methods, theoretical framework, and applications
J. Hydrol.
(2015) Strategies to adapt to an uncertain climate change
Glob. Environ. Chang.
(2009)
Constraining continuous rainfall simulations for derived design flood estimation
J. Hydrol.
Hydrological modelling of urbanized catchments: a review and future directions
J. Hydrol.
Influence of rainfall spatial variability on rainfall–runoff modelling: benefit of a simulation approach?
J. Hydrol.
Impact of spatial and temporal resolution of rainfall inputs on urban hydrodynamic modelling outputs: a multi-catchment investigation
J. Hydrol.
Uncertainty in the model parameters due to spatial variability of rainfall
J. Hydrol.
Correcting bias in radar Z – R relationships due to uncertainty in point rain gauge networks
J. Hydrol.
Quantification of the spatial variability of rainfall based on a dense network of rain gauges
Atmos. Res.
An overview of methods to evaluate uncertainty of deterministic models in decision support
Environ. Model. Softw
Preparation of future weather data to study the impact of climate change on buildings
Build. Environ.
What are the best covariates for developing non-stationary rainfall Intensity-Duration-Frequency relationship?
Adv. Water Resour.
A conditional disaggregation algorithm for generating fine time-scale rainfall data in a warmer climate
J. Hydrol.
Continuous rainfall generation for a warmer climate using observed temperature sensitivities
J. Hydrol.
Flow in roof gutters
Bur. Stand. J. Res.
The design of conventional and siphonic roof-drainage systems
J. Water Environ.
Regime shifts in annual maximum rainfall across Australia – implications for intensity–frequency–duration (IFD) relationships
Hydrol. Earth Syst. Sci.
Tall tales about tails of hydrological distributions. II
J. Hydrol. Eng.
Tall tales about tails of hydrological distributions. I
J. Hydrol. Eng.
Ignorance is bliss: or seven reasons not to use uncertainty analysis
Water Resour. Res.
Natural Hazards in Australia: Identifying Risk Analysis Requirements
Risk analysis for flood-control structure under consideration of uncertainties in design flood
Nat. Hazards
A statistical analysis of insurance damage claims related to rainfall extremes
Hydrol. Earth Syst. Sci.
On the occurrence of rainstorm damage based on home insurance and weather data
Nat. Hazards Earth Syst. Sci. Discuss.
BS EN 12056-3:2000 Gravity Drainage Systems inside Buildings - Part 3: Roof Drainage. Layout and Calculation
International Plumbing Code
Standards Australia/Standards New Zealand. AS/NZS 3500.3:2015 Plumbing and Drainage - Stormwater Drainage
New design rainfalls for Australia – lessons learned…
Updates to NOAA precipitation frequency atlases
Design rainfall estimation: comparison between GEV and LP3 distributions and at-site and regional estimates
Nat. Hazards
Rainfall IFD data system
Monitoring and understanding trends in extreme storms: state of knowledge
Bull. Am. Meteorol. Soc.
An analysis of late twentieth century trends in Australian rainfall
Int. J. Climatol.
Reduced spatial extent of extreme storms at higher temperatures
Geophys. Res. Lett.
Increase in hourly precipitation extremes beyond expectations from temperature changes
Nat. Geosci.
Changes in precipitation with climate change
Clim. Res.
IPCC, 2013: Climate Change 2013: the Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
Spatial modelling framework for the characterisation of rainfall extremes at different durations and under climate change
Environmetrics
Decision strategies for handling the uncertainty of future extreme rainfall under the influence of climate change
Water Sci. Technol.
A quasi-global assessment of changes in remotely sensed rainfall extremes with temperature
Geophys. Res. Lett.
On the use of self-registering rain and flood gauges in making observations of the relations of rainfall and flood discharges in a given catchment
Proc. Inst. Civ. Eng.
The relation between the rainfall and the discharge of sewers in populous districts
Trans. Am. Soc. Civ. Eng.
Cited by (8)
Automating rainfall recording: Ensuring homogeneity when instruments change
2022, Journal of HydrologyCitation Excerpt :The temporal pattern of rainfall effects infiltration, erosivity, vegetation interception (Van Dijk et al., 2005; Vernimmen et al., 2007), as well as risk-based infrastructure design (O’Shea et al., 2021), particularly in urban settings, small catchments, hillslopes, and second order drainage networks (Ball, 1994; Grimaldi et al., 2021; Heneker et al., 2001; Verstraten et al., 2019).
A case study on the effects of data temporal resolution on the simulation of water flux extremes using a process-based model at the grassland field scale
2021, Agricultural Water ManagementCitation Excerpt :Such changes would alter the characteristics of the water fluxes generated, as the soil properties of the field will change, meaning the determination of an appropriate resolution to simulate water fluxes may also change from the hourly resolution suggested here. This is analogous to other hydrological studies where, for example, different overflow designs in roof drainage structures have markedly variable responses to rainfall intensity increases (Verstraten et al., 2019). Key model input variables such as precipitation can determine the impacts of simulation time-steps on the performance of hydrological models; for example, the duration and temporal variability of a precipitation event in relation to the rainfall–runoff lag time (Ficchì et al., 2016).
Review: Can temperature be used to inform changes to flood extremes with global warming?
2021, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering SciencesEstimating design hydrologic extremes in a warming climate: Alternatives, uncertainties and the way forward
2021, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences