Design Rainfall Depth Research Articles

Estimation of the Peak over Threshold-Based Design Rainfall and Its Spatial Variability in the Upper Vistula River Basin, Poland

The proper assessment of design rainfalls with long return periods is very important because they are inputs for many flood studies. In this paper, estimations are performed on daily design rainfall totals from 16 meteorological stations located in the area of the Upper Vistula River Basin (UVB), Poland. The study material consists of a historical series of daily rainfall totals from the period of 1960–2021. The peak over threshold (POT) method is used, and the rainfall depth over threshold is assumed to follow the generalized Pareto distribution (GPD) with parameters estimated from Hill statistics. Alternatively, the competitive method based on annual maxima (AM) is applied. The theoretical distribution of AM is assumed to follow a theoretical distribution function selected by using the Akaike information criterion (AIC) from a family of seven candidate distributions, the parameters of which are estimated by using the maximum likelihood method. The two methods are compared by using the root mean square error (RMSE) and the mean deviation error (MDE) criteria. It is found that the POT-based method with GPD and Hill estimators outperform the AM-based method when considering the highest rainfall events. The confidence intervals of the design rainfalls, derived by using the Monte Carlo simulation method, reflects their large spatial diversity across the UVB. It is shown that the station’s altitude strongly correlates with the threshold, variance, and design rainfall depth of the GPD. This proves the advantage of the GPD with Hill estimates, namely that it can accurately reflect the spatial properties of rainfall and its variability in the UVB. Results can be applied in water-management applications related to floods.

Required number of years of rainfall data to determine the design rainfall depth of source control in sponge city construction

Study Region: ChinaStudy Focus: In sponge city construction in China, rainfall data is the key to determining the rainwater source control scale. However, changes in rainfall characteristics can reduce the representativeness of the data. To obtain stable volume capture ratios (VCRs) of the annual rainfall through as little rainfall data as possible, this paper compares daily rainfall data from 159 cities in China in recent decades and finds the minimum number of years required to maintain stable VCRs under different design rainfalls. Finally, it gives the recommended observation periods (OPs) for different regions. New Hydrological Insights for the Region: For the last 35 years, the variation of daily rainfall in 75% of cities in China has been less than 0.66 mm, and the variation of skewness is less than 0.62. In general, the longer the observation period, the smaller the calculated VCR anomaly value and variation gradient will be. About 10% of cities cannot achieve stable VCRs by increasing the number of years of data. The denser urban distributed area needs larger OPs to determine the stable VCR; with the increase in design rainfall, the required OPs will also be lowered; in most cities, the VCR calculation does not require 30 years of rainfall data.

Improving flash flood risk assessment using a simple approach for extreme rainfall scaling and storms transposition

AbstractFlash flood risk management is among the key topics of the European Flood Directive. Design hydrographs of small river basins could underestimate the hydraulic risk in case of intense and short‐duration events because of the intensification of hourly rainfall and the design rainfall depths uncertainty in often ungauged river basins. The use of synthetic hyetographs obtained from past observed events can be useful for a better evaluation of the flash flood hazard at the river basin scale. For this reason, a simple approach based on rainfall scaling and storms transposition of occurred events is presented to identify areas where design discharges underestimate the flash flood risk. The methodology considers the spatial distribution of the observed storms over a specific zone and the areal reduction factors to scale the observed hyetographs for different river basins extensions. Hyetographs of past observed events are used as input of a hydrological model in a set of river basins located in Northern Tuscany (Italy). The results show how peak discharges of short‐duration events are usually greater than the design floods of the small river basins with an area generally less than 30 km2.

Effect of warming climate on extreme daily rainfall depth using non-stationary Gumbel model with temperature co-variate

Abstract In this study, non-stationary frequency analysis was carried out to apply non-stationarity of extreme rainfall driven by climate change using the scale parameter of two parameters of the Gumbel distribution (GUM) as a co-variate function. The surface air temperature (SAT) or dew-point temperature (DPT) is applied as the co-variate. The optimal model was selected by comparing AICs, and 17 of 60 sites were found to be suitable for the non-stationary GUM model. In addition, SAT was chosen as the more appropriate co-variate among 13 of the 17 sites. As a result of estimating changes in design rainfall depth with future SAT rises at 13 sites, it is likely to increase by 10% in 2040 and 18% in 2070.

The impact of rainfall change on rainwater source control in Beijing

In sponge city construction in China, rainfall data is the basis for determining rainwater source control objectives. However, drastic change in rainfall caused by urbanization and climate change has dramatically reduced the rainfall data's representativeness. This study examines the impact of spatial-temporal rainfall changes over the past 50 years and evaluates the influence on the stability of rainwater source control effects in Beijing. The result shows that the rainfall variation trends differ in different regions in Beijing. In most areas, stable Volume Capture Ratio (VCR) cannot be achieved by a fixed size design rainfall depth, and highly urbanized areas are the most sensitive on source control effect. The design rainfall obtained from recent rainfall records may be on the low side, and the design rainfall should be increased to some extent to meet the 85% VCR goal in the future. Changping, Fangshan, Huairou, Mentougou, Yanqing have large spatial differences in design rainfall, and more attention should be paid to spatial differences in design rainfall.

Regional analysis of PROQ transforms for flood frequency estimation based on GRADEX principles

ABSTRACT The PROQ transform which converts rainfall P to runoff RO, then factored to produce peak discharge Q, can be used for regional design flood estimation. SPEED, a French method based on GRADEX principles is a PROQ transform. 1 in 100 annual exceedance probability discharges was estimated using SPEED for 40 Australian non-urban catchments. Inputs are catchment area and areal design rainfall depth. The SPEED transform involves three constant parameters: scaling factor a, non-linearity b and retention L. SPEED was found to be simple and effective (Nash-Sutcliffe E = 0.82). A local version of SPEED produced a similar performance (E = 0.74). A general form of PROQ was developed to explain similarities with other models such as the Probabilistic Rational Method and to develop the local SPEED transform. Gauge sites can be grouped based on a and L ‘bins’, using site-based mean values of these parameters. A PROQ model using two a bins and two L bins significantly enhanced predictive accuracy (E = 0.92).

The design flood under two approaches: synthetic storm hyetograph and observed storm hyetograph

This paper evaluates the design peak flow for several return periods using two approaches: 1) a flood frequency analysis; 2) rainfall-runoff model applied to a design storm. The design storm originates from the design rainfall depth, which is distributed throughout the rainfall duration via synthetic hyetographs. In the flood frequency analysis, the design peak flow was obtained from a 30-year series of flows estimated from rainfall observations at a five-minute time step. The design storm was routed with the same rainfall-runoff model and parameters to yield the design peak flow. The hyetographs tested were categorized as having advanced, delayed, alternating, uniform and empirical blocks that were built from rainfall observations. All design storms analysed undersized the hydraulic structures. The results, which were valid for the study region, indicated the need to rethink the concept of design storms, which associate the design storm depth with synthetic hyetographs, for a conservative standard.

A unified approach for hydrological modeling of arid catchments for flood hazards assessment: case study of wadi Itwad, southwest of Saudi Arabia

A unified and systematic approach for hydrological modeling is presented for assessing flood hazards in arid and semi-arid regions with wadi Itwad as a case study. The approach consists of the following steps: (1) estimation of the design storm duration, (2) estimation of the design rainfall depth, (3) development of the design storm hyetograph, (4) setup of the watershed hydrological system, (5) infiltration tests for estimate of soil characteristics, (6) land use and land cover analysis for curve number estimation, (7) how to incorporate dams (if any) and their reservoir characteristics for reservoir routing analysis, and (8) performing hydrological modeling under different scenarios, namely: lumped with and without the effect of dams and routed scenarios. An emphasis is made on the comparison between the SCS unit hydrograph and the unit hydrograph (UH) estimated for stream flow data. The UH method produces hydrographs that are typical of arid regions. It is characterized by a steep rising limb with a short time to peak, a rapid recession to zero base flow, and less flood volume due to transmission losses. The scenarios show that the lumped case overdesigns the protection schemes, while the lumped central basin with detention dams storing the flood water completely leads to underdesign in the downstream area. The routed scenario is more realistic, since it considers the detention dams with an overflow. The runoff volume (66.6 MCM) of the 10-year return period of the routed scenario is in the order of magnitude within the observed historical data (50 to 100 MCM) reported in the literature. The study concludes that the proposed approach is robust and takes into account the Saudi arid environment while performing flood risk assessment in KSA.

Analysis of Design Rainfall Depth in Sponge City Construction — a Case Study of Hefei, China

The design rainfall depth is an important parameter in the construction of sponge cities. Based on the analysis of 39 year daily precipitation data in Hefei city, this paper concludes that the inter-annual and intra-annual distribution of precipitation in Hefei is uneven. Based on the comparison and analysis of volume capture ratio of annual rainfall calculation method and rainfall percentage control calculation method for design rainfall depth, it is proposed that the designed rainfall in Hefei should not be too high, and it provides suggestions for the construction of the sponge city in Hefei.

The characterization of Extraordinary Extreme Events (EEEs) for the assessment of design rainfall depths with high return periods

The characterization of Extraordinary Extreme Events (EEEs) for the assessment of design rainfall depths with high return periods

Bias correction of d4PDF using a moving window method and their uncertainty analysis in estimation and projection of design rainfall depth

Bias correction of d4PDF using a moving window method and their uncertainty analysis in estimation and projection of design rainfall depth

Uncertainty Quantification of Future Design Rainfall Depths in Korea

One of the most common ways to investigate changes in future rainfall extremes is to use future rainfall data simulated by climate models with climate change scenarios. However, the projected future design rainfall intensity varies greatly depending on which climate model is applied. In this study, future rainfall Intensity–Duration–Frequency (IDF) curves are projected using various combinations of climate models. Future Ensemble Average (FEA) is calculated using a total of 16 design rainfall intensity ensembles, and uncertainty of FEA is quantified using the coefficient of variation of ensembles. The FEA and its uncertainty vary widely depending on how the climate model combination is constructed, and the uncertainty of the FEA depends heavily on the inclusion of specific climate model combinations at each site. In other words, we found that unconditionally using many ensemble members did not help to reduce the uncertainty of future IDF curves. Finally, a method for constructing ensemble members that reduces the uncertainty of future IDF curves is proposed, which will contribute to minimizing confusion among policy makers in developing climate change adaptation policies.

Application of the non-stationary peak-over-threshold methods for deriving rainfall extremes from temperature projections

Concerns about climate change are amplifying interest in future rainfall extremes. However, there are big differences between the statistics of rainfall extremes obtained using future rainfall time series produced from various climate models. Such large uncertainties create a lot of confusion in establishing climate change adaptation measures. Looking at future rainfall extremes at a particular site yields increasing trends in some climate models and decreasing trends in others. The spatial patterns of rate of change in rainfall extremes also vary widely, depending on the climate model. As a result, they often do not gain the public’s trust. We believe that this difficulty in obtaining credibility does not come from a lack of theory or technique, but from an approach that persuades the public of uncertain future rainfall extremes. In this study, we employed a novel approach to integrate a co-variate of the not-stationary Peak-Over-Threshold (POT) – Generalized Pareto distribution (GPD) model identified at each site with its future projection information for obtaining future rainfall extreme ensembles. Rainfall extremes are obtained from the observed rainfall time series using the POT method, and the scale parameter among GPD parameters are applied as a function of surface air temperature (SAT) or dew-point temperature (DPT). At this time, the threshold of the POT series is set to match the results of frequency analysis of the annual maximum series and the POT series for each site as much as possible. The behavior of future rainfall extremes is analyzed by inputting the future SAT or DAT produced from various climate models into the non-stationary frequency model using the co-variate. As a result of comparing the rainfall extremes obtained using the future rainfall time series directly with the future rainfall extremes obtained indirectly using the proposed method, it was found that the proposed approach projected future design rainfall depths with much less variation between climate models. The spatial pattern of rate of change was also consistent regardless of climate model. The proposed method is expected to contribute to the public’s confidence in future rainfall extremes under climate change scenarios and to be of practical help in formulating reasonable climate change adaptation policies.

Development of an integrated flood hazard assessment model for a complex river system: a case study of the Mun River Basin, Thailand

Flooding is the most frequent natural disasters in Thailand, resulting in the loss of life and damage. In this research, we develop an integrated hydrologic and hydraulic model of the Mun River Basin, Thailand, and employ it to predict flood hazard maps at 10-, 25-, 50-, and 100-year return periods. The ‘goodness-of-fit’ statistics for probability distributions of rainfall data are investigated to select the best-fit distribution, which is used to derive the design rainfall depths for the scenarios (10-, 25-, 50-, and 100-year return periods). The results highlight the diversity of probability distributions even in the basin scale. The model demonstrates satisfactory results, and the flood hazard maps reveal that the extent of flooding is greater on the left bank than the right, and that the flood depths vary mostly between 0 and 4 m. The results also demonstrate that approximately 60% of floodplain inundation is < 1 m, which is mostly observed at the upstream and central areas of the river. The extent of flooding downstream is not as large as the upstream, but generally deeper. Due to the flat topography, the duration of flooding is long, which could damage crop growth and yield, including cities in the flooded areas. This information is essential for the government and authorities to develop flood-control measures and flood management strategies. In this case, planning and regulation of the use of land, and levees to protect the exposed cities are recommended. The integrated model can be further developed for the design of flood mitigation measures and flood forecasting and warning systems. The approach and parameters (both initial and calibrated ranges) can be used to guide future model development and in other basins with similar catchment characteristics, particularly where gauge data are not available.

Disaggregation of fixed time interval rainfall to continuous measured rainfall for the purpose of design rainfall estimation

Design rainfall estimates are primarily used in single-event deterministic design flood estimation methods where estimates of the peak discharge are based on the critical storm duration or time of concentration (TC) of a catchment. Therefore, daily design rainfall depths used in flood estimations must either be decreased or increased from durations less than or longer than 24 hours to the design rainfall depths for a rainfall duration of TC. This paper presents the comparison of two South African methods used to convert or scale 1-day fixed time interval observed rainfall (08:00 to 08:00) to continuous measures of n-hour rainfall for selected TC durations at a quaternary catchment level, in the C5 secondary drainage region in South Africa as pilot case study. In each quaternary catchment, the annual maximum series (AMS) of the 1-day fixed time interval point rainfall were extracted, infilled, converted and scaled to appropriate continuous measures of TC-hour point rainfall using conversion factors (Adamson, 1981) and scaling factors (Smithers and Schulze, 2003), respectively. Thereafter, all the TC-hour observed point rainfall values were averaged to observed catchment rainfall at a quaternary catchment level using the Thiessen polygon method. In using the two methods to estimate continuous short-duration n-hour (TC ≤ 24 hours) and long-duration n-hour (TC &gt; 24 hours) catchment rainfall from 1-day fixed time interval point rainfall, an acceptable (0.71 &lt; r2 ≤ 0.86) and high (r2 ≥ 0.93) degree of association were achieved, respectively, despite the different approaches used in each method. Overall, the results confirmed that fixed time interval rainfall should be scaled to continuous measures of rainfall using the Smithers-Schulze scale invariance approach for various TC durations in the case study area. In comparison to the Adamson conversion methodology, the Smithers-Schulze scaling methodology is also based on a more extensive and recent rainfall database as incorporated in software for design rainfall estimation in modern flood hydrology practice in South Africa.

A probabilistic framework to evaluate the uncertainty of design hydrograph: case study of Swannanoa River watershed

ABSTRACTThis study presents a probabilistic framework to evaluate the impact of uncertainty of design rainfall depth and temporal pattern as well as antecedent moisture condition (AMC) on design hydrograph attributes – peak, time to peak, duration and volume, as well as falling and rising limb slopes – using an event-based hydrological model in the Swannanoa River watershed in North Carolina, USA. Of the six hydrograph attributes, falling limb slope is the most sensitive to the aforementioned uncertainties, while duration is the least sensitive. In general, the uncertainty of hydrograph attributes decreases in higher recurrence intervals. Our multivariate analysis revealed that in most of the return periods, AMC is the most important driver for peak, duration and volume, while time to peak and falling limb slope are most influenced by rainfall pattern. In higher return periods, the importance of rainfall depth and pattern increases, while the importance of AMC decreases.

Multivariate frequency analysis of urban rainfall characteristics using three-dimensional copulas

Urban runoff is a major cause of urban flooding and is difficult to monitor in the long term. In contrast, long term continuous rainfall data are generally available for any given region. As a result, it has become customary to use design rainfall depth as a proxy for runoff in urban hydrological analyses, with an assumption of the same frequency for runoff and rainfall. However, this approach has lack of overall coordination and cannot fully reflect the variability of rainfall characteristics. To address this issue, this study presents a three-dimensional copula-based multivariate frequency analysis of rainfall characteristics based on a long term (1961-2012) rainfall data from Guangzhou, China. Firstly, continuous rainfall data were divided into individual rainfall events using the rainfall intensity method. Then the characteristic variables of rainfall (design rainfall depth, DRD; total rainfall depth, TRD; peak rainfall depth, PRD) were sampled using the annual maximum method. Finally, a copula method was used to develop the multivariate joint probability distribution and the conditional probability distribution of rainfall characteristics. The results showed that the copula-based method is easy to implement and can better reflect urban rainstorm characteristics. It can serve a scientific reference for urban flood control and drainage planning.

HYDROLOGICAL MODELLING OF UNGAUGED ARID VOLCANIC ENVIRONMENTS AT UPPER BATHAN CATCHMENT, MADINAH, SAUDI ARABIA

Hydrological modelling of ungauged catchments is still a challenging task especially in arid regions with a unique land cover features such as highly fracture volcanic basalt rocks. In this study, upper Bathan catchment (103 km2) in Madinah, western of Saudi Arabia is selected. The aim of this paper is to simulate the hydrological responses of volcanic catchment to daily design storm events. The weighted areal average of two daily design rainfall depth scenarios are computed, which are 50 years and 100 years return period and correspondent predicted rainfall are 80.6 mm and 94.1 mm, respectively. SCS Type II temporal synthetic distribution of daily rainfall is selected to disaggregate the daily rainfall into smaller time interval. Excess rainfall is computed using Soil Conservation Services Curve Number (SCS-CN) method based on Land Cover and Land Use (LCLU) and hydrological soil groups (HSG) maps, while direct runoff hydrograph is developed using Soil Conservation Services dimensionless unit hydrograph (SCS-UH) method using lag time equation. HEC-HMS software is used, and it showed that the runoff volumes of the two rainfall scenarios are 50% and 54% of the total rainfall depth, and the peak discharges are 123 m3/sec and 158 m3/sec. This study provided an indication of the hydrograph characteristics of basaltic catchments and the result of this paper can be used for further flood studies in arid ungauged volcanic catchments.

Discussion about initial runoff and volume capture ratio of annual rainfall.

In recent years, runoff pollution from urban areas has become a major concern all over the world. But there exists a worldwide confusion about how much stormwater should be captured for the purpose of runoff pollution control. Furthermore, the construction cost and pollution control efficiency are closely linked with the size of stormwater facilities, which is then related to the first flush (FF) phenomenon and volume capture ratio of annual rainfall (VCRa). Based on this background, analysis of the random and changeable characteristics of the occurrence of FF was carried out first, which was proved to vary with catchment characteristics and pollutant types. Secondly, the distribution of design rainfall depth toward 85% VCRa in China and its causes have been analyzed. Thirdly, the relationship between initial runoff and VCRa has been studied at both conceptual and numerical levels, and the change rule of VCRa along with design rainfall depth in different regions has been studied. The limitation of initial runoff has been illustrated from the perspective of runoff characteristics of single rainfall events in the first part, and from the perspective of regional differences in the two subsequent parts.

Parameter Uncertainty and Nonstationarity in Regional Rainfall Frequency in Qu River Basin, East China

AbstractTraditionally, regional frequency analysis was developed for stable environmental conditions. Nevertheless, recent studies have identified significant changes in hydrological records under changing environments. Besides, uncertainty in hydrological frequency analysis is persistent. This study aims to investigate the impact of one of the most important uncertainty sources, parameter uncertainty, together with nonstationarity, on design rainfall depth in Qu River Basin, East China. A spatial bootstrap is first proposed to analyze the uncertainty of design rainfall depth estimated by at-site frequency analysis and by regional frequency analysis based on L-moments and the index variable method. Meanwhile, a method combining the generalized additive model with a 30-year moving window is employed to analyze nonstationarity existing in an extreme rainfall regime. The results show that the uncertainty of 100-year design rainfall depth due to parameter uncertainty reaches 15.42 and 12.45% with generalized ...