HS7.7 | Hydrometeorologic stochastics: from theoretical advancements in extremes, scales and probabilities to applications in industry
EDI
Hydrometeorologic stochastics: from theoretical advancements in extremes, scales and probabilities to applications in industry
Convener: Jose Luis Salinas Illarena | Co-conveners: Hannes Müller-Thomy, Carlotta Scudeler, Stergios Emmanouil, Gaby Gründemann
Orals
| Fri, 28 Apr, 14:00–15:45 (CEST)
 
Room 2.44
Posters on site
| Attendance Fri, 28 Apr, 08:30–10:15 (CEST)
 
Hall A
Posters virtual
| Attendance Fri, 28 Apr, 08:30–10:15 (CEST)
 
vHall HS
Orals |
Fri, 14:00
Fri, 08:30
Fri, 08:30
Over the last decades, a significant body of empirical and theoretical work has revealed the departure of statistical properties of hydrometeorological processes from the classical statistical prototype, as well as the scaling behaviour of their variables in general, and extremes in particular, in either state, space and/or time. Extremes and more generally the statistics of hydrometeorologic processes are the key input for hydrological applications, e.g. in natural catastrophe modelling. An example of this is the estimation of design rainfall. Beside the estimation of the absolute rainfall amount related to a certain return period, the intra-event rainfall distribution, its spatial extension and the rainfall intensities at neighbouring stations can be required depending on the intended application and thus the spatial and temporal scales of interest should be determined. Another good example are the large scale connections between hydrometeorologic extremes and climatic oscillations such as NAO or ENSO, and how these correlations can evolve in a changing climate. These are only two examples among numerous hydrologic applications.
On the one hand, the estimation of the hydrometeorological extremes and their probability distribution, the identification and incorporation of supporting information to improve these estimates, and their hydrologic application over a wide range of scales remain open challenges. On the other hand, hydrometeorologists had never access to so much computer power and data, including novel AI approaches, to face these open challenges.
This session welcomes, but is not limited to submissions on the following topics:
- Coupling stochastic approaches with deterministic hydrometeorological predictions, in order to better represent predictive uncertainty
- Development of robust statistics under non-stationary conditions for design purposes
- Development of parsimonious representations of probability distributions of hydrometeorological extremes over a wide range of spatial and temporal scales in risk analysis and hazard prediction
- Improvements for reliable estimation of extremes with high return periods under consideration of upper or lower limits due to physical constraints
- Linking underlying physics and hydroclimatic indices with stochastics of hydrometeorologic extremes
- Exploration of supporting data sets for additional stochastic information as well as the use of novel AI and machine learning approaches

Orals: Fri, 28 Apr | Room 2.44

Chairpersons: Carlotta Scudeler, Hannes Müller-Thomy, Jose Luis Salinas Illarena
14:00–14:05
Hydroclimatic Extremes in the Atmosphere
14:05–14:25
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EGU23-11933
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solicited
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On-site presentation
Francesco Comola, Siti Dawson, Michael Stahel, Hilary Paul, Bernhard Märtl, and Pascal Koller

North Atlantic hurricanes are one of the weather-related perils that most severely impact insured properties along the US East Coast, and thus represent a key exposure for most reinsurance and insurance-linked security (ILS) portfolios. The hurricane models traditionally used to quantify re/insurance risk account for the effect of fundamental climate circulation features, such as the El Niño Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO). However, the longer-term impact of global warming on hurricane-exposed reinsurance portfolios is still largely unknown. Here, we leverage recent scientific insights and historical records to explore the potential link between global warming and hurricane insured losses. Historical records suggest that the annual frequency of North Atlantic hurricanes does have a material impact on industry losses (rank correlation coefficient ~0.4). However, both models and historical trends seem to indicate no change, or even a slight decrease, in North Atlantic hurricane frequencies in a warmer climate. We also find that a potential increase in the proportion of hurricanes that reach major intensities, expected to be of the order of 10-20% according to the 2021 IPCC report, might lead to a 5-10% increase in industry losses. A similar increase in industry losses might also result from the higher hurricane precipitation rates, which are projected to increase by 11- 28% according to the 2021 IPCC report.  This suggests that the impact of global warming on hurricane insured losses may be significant, albeit not as critical as other fundamental loss drivers, such as urban development, demographic growth, as well as economic and social inflation.

How to cite: Comola, F., Dawson, S., Stahel, M., Paul, H., Märtl, B., and Koller, P.: North Atlantic hurricane activity in a warmer climate: implications for property catastrophe reinsurance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11933, https://doi.org/10.5194/egusphere-egu23-11933, 2023.

14:25–14:35
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EGU23-731
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ECS
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On-site presentation
Nasrin Fathollahzadeh attar, Antonio Canale, and Francesco Marra

As recently shown by the storm Vaia that hit Northeastern Italy in the fall of 2018, extreme wind represents a critical weather-related hazard in this region. Over the course of this century, changes in the frequency of extreme windstorms are expected. Obtaining an accurate understanding of wind speed distribution in present and future conditions is thus vital. Robust estimates of the probability of occurrence of extreme winds must be developed and employed to save lives and reduce economic losses. The objective of this study is to develop a novel non-asymptotic statistical method to estimate extreme wind return levels at multiple temporal scales (wind gusts, hourly, daily). Our approach is based on the identification of independent wind storms and estimation of ordinary wind speed events, the latter defined over the Veneto region using multi-year observations from 146 stations. To model the cumulative distribution function of ordinary wind speed events, different parametric distributions are compared, including mixture models specifications. By separately considering storm occurrence and conditional wind speed intensity, the proposed method could improve our understanding of wind speed extremes in the area and provides a tool for projecting future extreme wind speed return levels based on available model simulations.

How to cite: Fathollahzadeh attar, N., Canale, A., and Marra, F.: Extreme windstorm hazard in northern Italy using non-asymptotic statistics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-731, https://doi.org/10.5194/egusphere-egu23-731, 2023.

14:35–14:45
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EGU23-8812
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Virtual presentation
Jürgen Grieser

On average, the largest registered hailstone per year in Europe has a diameter of about 11cm. Individual hail events can cause losses exceeding one billion Euros. Therefore, the insurance industry is interested in modelling local hail risk. In fact, questions can be as specific as ‘What is the probability that this specific solar panel or roof window gets destroyed by hail within the next year?’

Meteorological modelling on the other hand describes the probability of hail on synoptic scales. Moody’s RMS developed a hierarchy of statistical models downscaling the risk from the large synoptical scale down to individual objects at risk.

I will discuss how the models are designed and calibrated to characterize local risk as well as spatial correlation on various time scales. To make the final model applicable for the insurance industry a thorough validation analysis is performed and results of this validation are shown in this presentation.

How to cite: Grieser, J.: Modelling the Scales of Hail, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8812, https://doi.org/10.5194/egusphere-egu23-8812, 2023.

Advances in Extreme Precipitation Modelling
14:45–14:55
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EGU23-5074
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ECS
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On-site presentation
Nafsika Antoniadou, Hjalte Jomo Danielsen Sørup, Jonas Wied Pedersen, Ida Bülow Gregersen, Torben Schmith, and Karsten Arnbjerg-Nielsen

Extreme precipitation events can lead to severe negative consequences on society, the economy, and the environment. To mitigate related risks, it is crucial to understand their natural causes. There is a vast number of methods in the literature analyzing their connection to large-scale drivers. Recently there has been much interest in using machine learning (ML) methods instead of traditional statistical models like regression. ML methods are based on algorithms adapting and learning from data. By contrast, regression models are based on theory and assumptions and benefit from domain knowledge for model specification. Because of its adaptability, ML is claimed to offer superior predictive performance than traditional statistical modeling and better manage a greater number of potential predictors. A few studies in climate research have compared the performance between these two approaches, but their conclusions are inconsistent, and some have limitations. 

We used five predictor variables - Geopotential height at 500hPA, Convective available energy (CAPE), Total column water (TCW), Sea Surface Temperature (SST), and Surface Temperature (SAT) using ERA5, the latest reanalysis dataset from ECMWF, and data produced by the Danish Meteorological Institute. All the predictors were not used directly as inputs but were preprocessed before modeling. We trained models using logistic regression (LR) and three commonly used supervised machine learning algorithms - random forests (RF), neural networks (NNET), and support vector machines (SVM) to predict whether an extreme event occurred over Copenhagen. In the LR framework, the predictor variables were modeled using restricted cubic splines to address potential nonlinearity. The training data are highly unbalanced, so using a traditional performance metric such as accuracy (ACC) could be misleading. In light of this, we use performance metrics specialized for unbalanced datasets: the ROC (receiver operating characteristic) curve as the primary measure and the area under the precision-recall curve, the Brier score, and ACC together with the true positive rate and the false positive rate at the optimal threshold as secondary measures.

During the variable selection process, it was found that SST has the weakest relationship with extreme events, and its inclusion did not increase the model performance. Furthermore, the results showed that the LR performs similarly to more complex ML algorithms. SVM had the worst performance in all cases. While most of the top-ranked impacting predictors were nearly comparable amongst models, especially CAPE and TCW, we found discrepancies; SAT contributed to RF and NNET but not to LR.

How to cite: Antoniadou, N., Sørup, H. J. D., Pedersen, J. W., Bülow Gregersen, I., Schmith, T., and Arnbjerg-Nielsen, K.: Comparison of data-driven methods for linking extreme precipitation events to large-scale drivers: A case study from Copenhagen, Denmark, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5074, https://doi.org/10.5194/egusphere-egu23-5074, 2023.

14:55–15:05
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EGU23-7371
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On-site presentation
Katharina Lengfeld and Francesco Marra

Extreme precipitation is among the most devastating atmospheric phenomena, causing severe damage worldwide, and is likely to intensify in strength and occurrence in a warming climate. Quantifying the frequency of occurrence of short-duration extreme rainfall exceeding certain amounts is important for hydrologists and urban planners. In Germany, the official design storms are determined from long time series of stations measurements (KOSTRA DWD2010R). Stations, however, only represent a limited region and cannot provide information for ungauged areas. Weather radar networks represent an alternative to overcome these issues, but their time series currently span periods of up to a few decades. Therefore, estimating design precipitation from radar observations with traditional methods is prone to large uncertainties because only few extreme events are included in the statistical analyses. 
Recently, non-asymptotic approaches, such as the simplified metastatistical extreme value, proved promising in estimating design precipitation from short records of sub-daily data, such as the ones from weather radar archives. 
We will present the results obtained applying the simplified metastatistical extreme value approach to the 21-year time series of the German weather radar network, and compare them to traditional estimates from the KOSTRA DWD2010R and to estimates from station observations. Using the simplified metastatistical approach, we find a clear reduction in uncertainty of hourly to daily design precipitation with return periods of 5, 20 and 100 years. Last, we show that the simplified metastatistical approach is less sensitive to particularly extreme events (such as the July 2021 event in Western Germany) than traditional methods.

How to cite: Lengfeld, K. and Marra, F.: Improving estimations of design storms from weather radar observations using a simplified metastatistical extreme value approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7371, https://doi.org/10.5194/egusphere-egu23-7371, 2023.

15:05–15:15
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EGU23-5278
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On-site presentation
Francesco Marra, Eleonora Dallan, Efrat Morin, and Moshe Armon

The statistics of extreme precipitation over a location of interest are crucial for designing hydraulic structures and mitigating extreme events impact. These statistics emerge from (i) the presence of different storm types, (ii) the different intensity of storms of a given type, (iii) the spatial variability of storms during their life-cycle, combined with (iv) the advection of storms across the domain. Explicit separation of these components could help us establish links between atmospheric dynamics (i.e., the occurrence and frequency of different types of storms) and thermodynamics (i.e., the properties of different storm types) on one side, and the emerging statistics of extremes. Here, we make a first step in this direction by focusing on a semi-arid region in the southeastern Mediterranean in which precipitation is almost solely related to convective processes, minimizing the effect of point (i).

We use very-high-resolution (60 m x 60 m, 1 min) weather radar observations to track convective cells during 11 storms that occurred over 2 years (>1200 cells). We mimic rain gauge observation of the tracked cells by sampling the rainfall fields at random locations and we alter advection by applying synthetic velocities to the Lagrangian fields of the cells. This allows us to isolate the impacts of (ii) storm intensity, and (iv) advection. Then, we generate sets of synthetic cells with analogous properties (peak intensity, area, velocity) and different profiles to examine the impact of (iii) spatial variability.

We find that the spatial sampling of convective cells occurred during the 11 storms explains most of the variability of extreme precipitation in the region. The extremes emerging from this sampling are well described by Weibull tails. Return levels estimated from the 11 storms using a non-asymptotic extreme value method are comparable to the ones derived from 25 years of rain gauge observations (error in the 100-year return levels <15%). We discuss the sensitivity of extreme return levels to changes in properties and velocities of the convective cells.

How to cite: Marra, F., Dallan, E., Morin, E., and Armon, M.: Emergence of extreme precipitation statistics from the properties of convective cells, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5278, https://doi.org/10.5194/egusphere-egu23-5278, 2023.

Advances in IDF curves estimation
15:15–15:25
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EGU23-11147
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ECS
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On-site presentation
Bora Shehu and Uwe Haberlandt

Design extreme rainfall maps are essential for the construction of many water systems and works, and are typically achieved by regionalizing extreme rainfall statistics from ground-based observations. Different methods are used for such task, where the most popular are kriging and index-based regionalization. In a previous study conducted in Germany, Shehu et al. (2022) revealed that kriging with external drift performed better than index-based regionalization in terms of accuracy (smaller error obtained from cross-validation), however it is still unclear which of the method is superior in terms of precision (wideness of prediction intervals). As the risk may be underestimated due to different sources of uncertainty, a more certain method (in terms of narrower prediction intervals) is preferable (while maintaining a good accuracy). Therefore, the objective of this study is to investigate the propagation of different uncertainty sources for both kriging and index-based regionalization and compare these two in terms of precision and accuracy.

To conduct this study, around 1200 ground-based observations at fine temporal scales (5min) from the German Weather Service (DWD) for whole Germany are employed. For each ground-based observation the annual maximum volumes at different durations (from 5mins up to 7days) are extracted, and local IDF curves are estimated according to Koutsoyiannis et al. (1998). For spatial uncertainty evaluation in the kriging system sequential Gaussian simulation (sGs) together will local sample bootstrapping are employed as shown in Shehu and Haberlandt (2022). On the other hand, the uncertainty in index-based regionalization is evaluated based on a combination of regional sample bootstrapping and spatial simulations of the index. The precision of IDF curves from both methods in terms of 95% confidence interval width is compared on a cross-validation procedure at the locations with more than 40 years of observation.

 The results of this study reveal how the uncertainty of annual rainfall extremes propagates from local estimation to the regionalization of IDF curves based on kriging and index-based regionalization. The comparison of the uncertainty in terms of precision sheds light on which method can produce narrower prediction intervals and hence is more precise in regionalizing IDF curves. Additionally, the accuracy of both methods is advised in order to discuss the advantages and disadvantages of each method for generating spatial IDF curves.

References: 

Koutsoyiannis, D., Kozonis, D. and Manetas, A.: A mathematical framework for studying rainfall intensity-duration-frequency relationships, J. Hydrol., 206(1–2), 118–135, doi:10.1016/S0022-1694(98)00097-3, 1998.

Shehu, B., Willems, W., Stockel, H., Thiele, L., and Haberlandt, U.: Regionalisation of Rainfall Depth-Duration-Frequency curves in Germany, Hydrol. Earth Syst. Sci. Discuss. [preprint], https://doi.org/10.5194/hess-2022-118, in review, 2022.

Shehu, B. and Haberlandt, U.: Uncertainty estimation of regionalised depth–duration–frequency curves in Germany, Hydrol. Earth Syst. Sci. Discuss. [preprint], https://doi.org/10.5194/hess-2022-254, in review, 2022.

How to cite: Shehu, B. and Haberlandt, U.: Comparing uncertainty propagation of different methods for regionalized IDF curves in Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11147, https://doi.org/10.5194/egusphere-egu23-11147, 2023.

15:25–15:35
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EGU23-2313
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ECS
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On-site presentation
Abubakar Haruna, Juliette Blanchet, and Anne-Catherine Favre

Intensity-Duration-Frequency curves are useful in water resources engineering for the planning and design of hydrological structures such as sewer lines, culverts, drains, dams, dykes.  They provide the mathematical link between the rainfall intensity, I, over a given duration, D, that is expected to be exceeded on average, once every T years (frequency). As opposed to the common use of only extreme data to build IDF curves, here, we use all the non-zero rainfall intensities, thereby making efficient use of the available information. As a parametric model, we use the Extended Generalized Pareto Distribution (EGPD) of Naveau et al. (2016)  for the non-zero intensities. We consider three commonly used approaches for building IDF curves. The first approach is based on the scale-invariance property of rainfall, the second relies on the general IDF formulation of Koutsoyiannis et al. (1998) and the last approach is purely data-driven (Overeem et al., 2008), where the linkage of parameter and duration is empirically determined from data. Using these three approaches, and some extensions around them, we build a total of 10 models for the IDF curves. We then compare them based on their in-sample performance, parsimony in parameterization, as well as their robustness and reliability in a split-sampling cross-validation framework. We consider a total of 81 stations at 10 min resolution in Switzerland.  As a result of the marked seasonality of rainfall in the study area, we adopted a seasonal-based analysis.  The results reveal that the model based on the data-driven approach is the best model. It is able to correctly model the observed intensities across duration while being reliable and robust. It is also able to reproduce the space and time variability of extreme rainfall across Switzerland. While our study focused on Switzerland, the results can be generalized everywhere, especially for locations with high-resolution data availability. To our knowledge, our work is the first to consider using the EGPD in IDF curve modeling.

 

 

References

Koutsoyiannis, D., Kozonis, D., & Manetas, A. (1998, April). A mathematic cal framework for studying rainfall intensity-duration-frequency relationships. Journal of Hydrology, 206 (1-2), 118–135. Retrieved 2021-09-06, from https://linkinghub.elsevier.com/retrieve/pii/S0022169498000973 doi: 10.1016/S0022-1694(98)00097-3

Naveau, P., Huser, R., Ribereau, P., and Hannart, A.: Modeling jointly low, moderate, and heavy rainfall intensities without a threshold selection, Water Resour. Res., 52, 2753–2769, https://doi.org/10.1002/2015WR018552, 2016.

Overeem, A., Buishand, A., & Holleman, I. (2008, January). Rainfall depth duration-frequency curves and their uncertainties. Journal of Hydrology, 348 (1-2), 124–134. Retrieved 2021-11-30, from https://linkinghubelsevier.com/retrieve/pii/S0022169407005513 doi:10.1016/j.jhydrol.2007.09.044

How to cite: Haruna, A., Blanchet, J., and Favre, A.-C.: Modeling Intensity-Duration-Frequency curves for the whole range of precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2313, https://doi.org/10.5194/egusphere-egu23-2313, 2023.

15:35–15:45
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EGU23-13498
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Virtual presentation
Ludovico Nicotina, Edom Moges, Mohammad Sharifian, Sonja Jankowfsky, Shuangcai Li, and Arno Hilberts

As Catastrophe models tend to focus more on Fluvial Flood Risk, Pluvial Flood Risk can be sometimes underestimated or neglected. However, when high intensity and short duration events such as hurricanes Ida and Ian occur in urban and semi urban areas, failure to account for Pluvial Flood Risk is consequential. To this end, the importance of accurately estimating Pluvial Flood Risk has strengthened.

In this study, we investigate the sensitivity of Pluvial Flood Risk to design rainfall characteristics. In particular, we explored the trade-off between flood extent and flood depths for different design rainfall durations, as well as the resulting economic losses at different spatial scales covering local, catchment and county levels. The study focuses on urban and semi-urban areas, where besides rainfall duration and intensity, drainage characteristics are expected to play a significant role in Pluvial Flood Risk.

How to cite: Nicotina, L., Moges, E., Sharifian, M., Jankowfsky, S., Li, S., and Hilberts, A.: Design Rainfall controls on Pluvial Flood Risk at different spatial and temporal scales – a U.S. case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13498, https://doi.org/10.5194/egusphere-egu23-13498, 2023.

Posters on site: Fri, 28 Apr, 08:30–10:15 | Hall A

Chairpersons: Hannes Müller-Thomy, Carlotta Scudeler, Jose Luis Salinas Illarena
Scaling in hydrometeorogical extremes
A.102
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EGU23-3257
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ECS
Felix S. Fauer and Henning W. Rust

Extreme precipitation is one of the biggest climate-change-related threats in middle Europe with flooding events leading to high death tolls and huge existential and financial losses. Evaluating how the probability of such events changes with respect to climate change can help preventing casualties and reducing impact consequences. Our analysis aims for the creation of Intensity-Duration-Frequency (IDF) curves which describe the major statistical characteristics of extreme precipitation events (return level, return period, time scale). They provide information on the probability of exceedance of certain precipitation intensities for a range of durations and can help to visualize how extreme the event for different durations is. We modeled the underlying distribution of block maxima with the Generalized Extreme Value (GEV) distribution. The scarce availability of data, a core problem when modeling extremes, can be addressed by using the available data more efficiently. Therefore, including maxima from different measurement durations is useful for (1) gathering more information from the data and (2) estimating return periods for different time scales with a consistent modeling approach. Duration-dependence is implemented directly into the parameter estimation (Koutsoyiannis et al., 1998) and enables a consistent model, i.e. without quantile-crossing.

To include large-scale information, each of the GEV parameters was modeled with a linear dependence on the large-scale variables temperature, blocking situation, humidity, year and North Atlantic oscillation (NAO), all spatially and monthly averaged. We show that the probability of extreme events increases with time, temperature and humidity over all seasons (summer, winter, whole year). The effects of blocking situation and NAO depend on the season with positive NAO leading to stronger events only in winter and blocking leading to stronger events only in summer and vice versa. A cross-validated model verification shows improvement over a reference model without large-scale information. This study is conducted on precipitation data from ~200 stations across Germany with temporal measurement resolutions from minutes to days.

How to cite: Fauer, F. S. and Rust, H. W.: Large scale influence on extreme precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3257, https://doi.org/10.5194/egusphere-egu23-3257, 2023.

A.103
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EGU23-4837
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ECS
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Kanneganti Bhargav Kumar and Pradeep P Mujumdar

Extreme flood events are rare but catastrophic and have tremendous adverse impacts on human lives and the economy. The frequency and magnitude of such events have increased globally and are likely to worsen in the future. Traditional flood risk methods estimate the extreme quantiles based on the assumption that historical data recorded at gauge stations contain a spectrum of extreme flood magnitudes. However, the available gauge station record lengths are small for several gauge stations, and these records are less likely to capture the full range of likely flood magnitudes. Hence, it is necessary to develop methods to extrapolate better the dynamics of large and rare events from historical data containing only small but frequent fluctuations. This study aims to use the scaling relation of return intervals, which is invariant for various thresholds in long-term correlated historical records and accurately estimate the risk associated with rare events. The analysis is carried out on 212 daily streamflow series across the major river basins in peninsular India. Persistence in the streamflow series is examined by estimating the Hurst coefficient with a Detrended Fluctuation Analysis. Return level distribution parameters are then estimated using the analytic equations between parameters and the Hurst coefficient. The threshold-invariant scaling of the probability of return intervals and the ratio of return levels to mean return levels allows the formulation of hazard functions, which are, in turn, used to estimate the risk of rare events. This work provides an approach for obtaining flood event sets that may contain  a wider range of magnitudes than present in the historical data. The present study contributes towards improving the at-site frequency analysis of floods using the temporal scaling law of return levels. Simultaneous occurrence of different extremes may alter the return levels of rare events such as, for example, flooding in coastal areas caused by the compound effect of storm surge and streamflow. This work can be extended to understand the effect of long-term memory and the cross-correlation of causal factors on risk estimation of compound extremes.

How to cite: Bhargav Kumar, K. and P Mujumdar, P.: Towards Temporal Scaling Laws for the Risk Analysis of Rare Flood Events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4837, https://doi.org/10.5194/egusphere-egu23-4837, 2023.

A.104
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EGU23-8939
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ECS
Jannick Alpers, Hannes Müller-Thomy, Patrick Nistahl, and Kai Schröter

Design rainfall is required for numerous applications in hydrology. If based on rain gauge time series, an adoption in space without further processing leads to an overestimation of spatial rainfall extreme values. Areal reduction factors (ARF) reduce point extreme values in space to achieve more realistic areal rainfall extreme values. The necessity of reduction increases with higher temporal resolution. However, the low density of most rain gauge networks hinders the estimation of representative ARF. In this study ARF are derived from 5 min rainfall time series of the high-density WegenerNet in Austria with 143 rain gauges distributed over 300 km² (~ 0.5 gauges per km²).

ARF dependency on area (up to 81 km²), rainfall duration (5 min to 6 hours), return period (1 year to 10 years), seasonality (four seasons) and altitude (260 m to 400 m) are studied. The results provide new insights into the research field, especially for the short durations. In addition to providing explicit ARF values, the main conclusions are:

  • ARF decrease with increasing areal extent considered for all durations.
  • ARF decrease with increasing temporal resolution for all return periods.
  • While ARF for hourly values (and coarser) decrease with increasing return period, the opposite is found for shorter durations.
  • ARF vary strongly between seasons, with lowest values found for spring.
  • Altitude-dependency of ARF increases with areal extent considered, whereby ARF values increase with altitude.

The resulting ARF data set is unique with its applicability for high-resolution extreme values as needed for urban hydrology. The results are assumed to be transferable to other regions with similar hydro-climatologic characteristics.

How to cite: Alpers, J., Müller-Thomy, H., Nistahl, P., and Schröter, K.: Scale-dependent differences of areal reduction factors: from minutes to hours, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8939, https://doi.org/10.5194/egusphere-egu23-8939, 2023.

Extreme precipitation statistics
A.105
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EGU23-7626
Harald Schellander, Marc-André Falkensteiner, Gregor Ehrensperger, and Tobias Hell

For the estimation of daily precipitation extremes, the metastatistical extreme value distribution (MEVD) is known to perform superior to classical approaches like the generalized extreme value distribution, especially for small sample lengths. This is due to the fact that the MEVD incorporates all ordinary rainfall events within a block rather than only the extremes, which then emerge from repeated sampling of ordinary events. For daily rainfall extremes, the MEVD combines the Weibull distribution of ordinary daily rainfall events and the number of wet days per year as additional random variable. The MEVD provides yearly distributional parameters, which makes it already capable of analyzing temporal trends in daily precipitation extremes.

But still, the MEVD in its current formulation does not take into account the seasonal, i.e. sub-yearly character of ordinary precipitation events. This problem becomes apparent when events originating from fundamentally different precipitation regimes show very similar MEVD parameters.

In this contribution we therefore propose to explicitly model both the temporal trend and interannual seasonality of daily rainfall extremes and present an explicitly non-stationary MEVD formulation which is called temporal MEVD or TMEV. The TMEV is then used to derive historical trends of rainfall extremes in Austria. It is shown that the 50-year return level of daily rainfall in Austria has significantly increased over the last 30 years at the majority of Austrian observation sites. Furthermore the temporal change of the extreme value distribution is analyzed with respect to seasonality. 

How to cite: Schellander, H., Falkensteiner, M.-A., Ehrensperger, G., and Hell, T.: Accounting for seasonality in trends of extreme precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7626, https://doi.org/10.5194/egusphere-egu23-7626, 2023.

A.106
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EGU23-12635
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ECS
Nur Banu Ozcelik, Stefan Strohmeier, Cristina Vásquez, Christine Stumpp, Andreas Klik, Peter Strauß, Georg Pistotnik, Shuiqing Yin, Tomas Dostal, and Gregor Laaha

In our ACRP funded project EROS-A we aim at a comprehensive analysis of the erosive energy of rainfall, estimated soil loss, and reported damage using statistical and process-based methods. In this particular study, we evaluate the return periods of erosive rainfall events at 26 meteorological stations in Austria. The main focus is on daily cumulative rainfall and the maximum 30-min rainfall intensity (I30) as these were identified as key parameters for rainfall erosivity assessment. The extreme value series were obtained using both the Annual Maxima Series (AMS) and Peak Over Threshold (POT) approach, in order to assess which of the methods will be most accurate. The assumptions of stationarity and independence of the extreme value series were carefully checked using statistical trend and independence tests and no significant deviations were found.

Generalized extreme value (GEV) and generalized Pareto (GPD) probability distributions were fitted using L-moment and maximum likelihood procedures. The GEV distribution is suited for AMS or block maxima data, whereas the GPD is suited for the POT series. For the obtained GEV and GPD models we examined extreme events with return periods of 2, 5, 10, 25, 50, and 100 years. We found that threshold selection is crucial for the POT, with diagnostic tools (such as mean residual life plots) not being fully decisive. Finally sensitivity analysis was performed where convergence of the fitted GPD to the GEV (AMS approach) helped determining robust thresholds for the GPD. The results show that the POT approach for daily cumulative precipitation is the most accurate in 69% of the cases and the AMS approach in 8% of the cases (different return periods and stations), while they have similar performance in 23% of the cases. Similar results are obtained for I30, were the success rates are 80% for the POT, 8% for the AMS and 12% for similar performance. In the next step, we will extend frequency analysis to a regional context, in order to map extreme rainfall erosivity across main agricultural production zones in Austria.

How to cite: Ozcelik, N. B., Strohmeier, S., Vásquez, C., Stumpp, C., Klik, A., Strauß, P., Pistotnik, G., Yin, S., Dostal, T., and Laaha, G.: Extreme value statistics of erosive rainfall events – a comparative assessment for agricultural production zones in Austria, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12635, https://doi.org/10.5194/egusphere-egu23-12635, 2023.

Applications In Industry
A.107
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EGU23-16031
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Ravikumar Ganti, Manjusha Nadgouda, and Hani Ali

The French Riviera in the Alpes Cote d’Azur province of France has been experiencing severe flash floods in the last decade. These recurring flash floods are usually a combination of meteorological factors such as cloudbursts and orographic shifts resulting from the proximity to the sea. In addition, studies also indicate that climate change plays an important role in the recurrence of such flash floods.  The current study focuses on the reconstruction of the October 2015 event footprint and on the reprojection of the event in the 2050 future climate scenario. The event has been driven by heavy rainfall which mostly affected the cities of Cannes, Antibes, and Nice. In most of the regions more than 100 mm of rain fell in less than 2 days, with Cannes reaching 200 mm in 24 hours.  According to Merad et al. 2021 the precipitation and discharge return period relative to this event exceeds 100 years.  The SCS Curve method was used to reproduce the hydrological response of the system during the event, with observed GPM precipitation data, CORINE 2018 Land use/Land cover, and observed discharge hydrograph implemented as input forcings, parameters and boundary conditions of the model.  The final inundation for the 2015 scenario was obtained by means of hydraulic modelling in HEC-RAS 2D and the resulting footprint has been successfully validated both in terms of extent and flood depth against JBA footprint and available satellite imageries.  For the reprojection of the event in the 2050 future climate scenario, we referred to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) and implemented an upliftment of 10% to both the precipitation and discharge.  HEC-RAS 2D unsteady state flow was run under the new forcings to generate the reprojected event footprint, which revealed a significant increase in both flood depth and extent.   Given the detailed inundation map relative to the future climate scenario, this study is particularly useful for designing flood mitigation measures in the French Riviera to protect life and property from the risk arising from similar catastrophic flash flood events. In addition, climate change associated risks represent a big concern for many industries including the insurance and re-insurance and this study can be used to estimate the risk and future losses associated to this and similar events. 

 

How to cite: Ganti, R., Nadgouda, M., and Ali, H.: Real disaster scenario of Cannes 2015 flash flood event with climate change projection for 2050, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16031, https://doi.org/10.5194/egusphere-egu23-16031, 2023.

A.108
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EGU23-15212
Sonja Jankowfsky, Shuangcai Li, Jose Salinas, Ludovico Nicotina, and Arno Hilberts

High lake water level-induced flooding could cause catastrophic property damage and loss of life. The frequency and severity of lake flooding has been increasing in recent years, likely due to climate change . To quantify the lake flooding risk, accurate modeling of lake water level is critical. However, simulation of lake water level is a challenging problem in the field of hydrology, due to the various hydrological and morphological characteristics of river-lake systems. To solve this challenge, Moody's RMS has developed a coupled physical based – Machine Learning model, using a Long-Short-Term-Memory (LSTM) neural network which incorporates both dynamical variables and static variables . This model is tested and validated with representative lakes in the Southeastern US, and compared with other models including linear, dense, decision tree regression, random forest, and convolution neural network, which demonstrates the reliability and superiority of LSTM in lake water level modeling

How to cite: Jankowfsky, S., Li, S., Salinas, J., Nicotina, L., and Hilberts, A.: Lake water level modeling using a Long-Short-Term-Memory (LSTM) neural network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15212, https://doi.org/10.5194/egusphere-egu23-15212, 2023.

Posters virtual: Fri, 28 Apr, 08:30–10:15 | vHall HS

Chairpersons: Jose Luis Salinas Illarena, Carlotta Scudeler, Hannes Müller-Thomy
vHS.11
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EGU23-15084
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ECS
Rajat Lall and Sagar Chavan

Design flood estimation is necessary for the effective planning and management of various hydrologic
structures such as dams. Mostly these structures are located in remote locations where observed
streamflow data is seldom available. There is a need to develop effective strategies to predict reliable
estimates of design flood at ungauged locations. The concept of Synthetic Unit Hydrograph (e.g.,
Snyder’s method, Soil Conservation Service method, Taylor and Schwarz method, Mitchell’s method,
etc.) that considers the use of catchment descriptors related to stream network and topography in
predicting the design flood estimates at ungauged locations is being widely used. The Central Water
Commission (CWC) method was specifically developed for predicting reliable estimates of design
floods at the ungauged locations in India. In the present study, we have estimated the design flood
estimate for Swan river which is a tributary of Satluj River in India located in upper Indo-Ganga
plains. Design flood estimates are obtained corresponding to a rainfall input having return periods of
100 years. In addition, physical upper bound of precipitation i.e. probable maximum precipitation is
also considered for estimating the probable maximum flood (PMF) for the catchment. The design
flood corresponding to 100-year return period rainfall is found to be 2537 cumecs while the PMF is
observed to be about 7863 cumecs. Further, a comparative study between the CWC method-based
design flood estimate and design flood estimates based on Snyder’s method, Soil Conservation
Service method, Taylor and Schwarz method, and Mitchell’s method are performed. These estimates of
design flood can be used to plan river training works on Swan river.

How to cite: Lall, R. and Chavan, S.: Design Flood Estimation based on Synthetic Unit Hydrograph Method for an Indian catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15084, https://doi.org/10.5194/egusphere-egu23-15084, 2023.