Thomas Einfalt

A radar rainfall forecasting method designed for hydrological purposes

Abstract Advanced techniques in sewer management need a reliable rainfall forecasting methodology to satisfy the urban hydrologist. In close cooperation with the users, a community remotely controlling a suburban county of Paris, specific requirements were precisely defined. The proposed forecasting method is based on recent advances of pattern recognition and image processing. Its user-defined hydrological features focus on heavy rainfall and on accuracy at a small time-area scale. The reliability of the actual forecast is calculated and issued in real-time. By comparison with earlier forecasting methods, the proposed method proved to be slightly superior in hydrological terms. However, the appropriate quality criteria always depend on the application. Further research is being undertaken in this direction. The method has been in operational use since May 1988.

Nowcasting of rainfall and of combined sewage flow in urban drainage systems

Nowcasting of rainfall may be used additionally to online rain measurements to optimize the operation of urban drainage systems. Uncertainties quoted for the rain volume are in the range of 5% to 10% mean square error (MSE), where for rain intensities 45% to 75% MSE are noted. For larger forecast periods up to 3 hours, the uncertainties will increase up to some hundred percents. Combined with the growing number of real time control concepts in sewer systems, rainfall forecast is used more and more in urban drainage systems. Therefore it is of interest how the uncertainties influence the final evaluation of a defined objective function. Uncertainty levels associated with the forecast itself are not necessarily transferable to resulting uncertainties in the catchments flow dynamics. The aim of this paper is to analyse forecasts of rainfall and specific sewer output variables. For this study the combined sewer system of the city of Linz in the northern part of Austria located on the Danube has been selected. The city itself represents a total area of 96 km2 with 39 municipalities connected. It was found that the available weather radar data leads to large deviations in the forecast for precipitation at forecast horizons larger than 90 minutes. The same is true for sewer variables such a CSO overflow for small sub-catchments. Although the results improve for larger spatial scales, acceptable levels at forecast horizons larger than 90 minutes are not reached.

Radar data quality control methods in VOLTAIRE

In the scope of the EU-project VOLTAIRE (Validation of multisensors precipitation fields and numerical modelling in Mediterranean test sites) a software library for automatic and rapid radar data quality check and modification has been developed and tests have been performed with data from different countries. Automatic procedures will never replace an experienced observer, but they help him to do his work and they can be used at places, where observation is not possible.This paper gives an overview over the algorithms that have been adopted or developed during the VOLTAIRE project for radar data quality control. Two examples of these algorithms illustrate the possibilities for data correction but also their limitations. These examples are a clutter correction combined with speckle removal for Plan Position Indicator (PPI) data in particular of non-Doppler radars and a beam blockage correction for PPI data, where no Digital Elevation Model (DEM) is available.

Determination in real time of the reliability of radar rainfall forecasts

Abstract Quantitative rainfall forecasts obtained from interpretation of radar data can be of great interest in urban hydrology, provided their reliability is known in real time. The aim of this study was to examine the feasibility of an a priori estimation of forecast reliability from characteristics of rainfall areas and atmospheric vertical structure. The first step has been to design a method to check the relevance of a criterion of forecasting quality to a particular application of the forecasts. This method was applied to the case of real-time control of a drainage network in a suburban area of Paris, and led to the definition of a new quality criterion, consistent with the users utility function. Potential predictors of forecasting quality were then defined, to be calculated in real time from radar and rawinsonde data. In the final step, statistical and heuristic techniques, applied to a learning set of examples taken from 46 rainfall events, provided decision rules which can be used in real time to estimate the quality of radar forecasts. Although these rules are valid only in a specific operational context, the methodology is general, and can be transferred to other forecasting problems in hydrology, as well as in other domains.

Decision Support for Adaptation Planning of Urban Drainage Systems

AbstractUrban drainage networks are under constant pressure caused by a permanently changing environment. For proactive planning, management, and adaptation of urban water infrastructure, a robust ...

Limited Flow Acceleration - A Measure for Reduction of Hydraulic Stress from Storm Flows into Rivers and Creeks

Urban rivers are characterized by an altered runoff regime. Flash-flows are closely linked to rainfall. The flow regime of natural catchments is a lot smoother than that of urbanised areas. A slow rise in flow acceleration of the water body permits the biocenosis to retreat to their shelters, e.g. in the gap system of the hyporheic interstitial zone. A limitation of flow acceleration for urban storm water runoff, even for basin overflows helps to stabilise the population in a creek because the macro invertebrates are not drifted away by the force of the flow. A comparison of the flow regimes of several natural catchments has yielded a first approach for a standardised limited flow acceleration function which is proposed to be applied to storm flows from drainage systems into rivers and creeks up to a catchment area of 200 km 2 . Such a standardised function seems a suitable criteria for assessing the hydraulic stress for the organism in urban running waters.

Quality control of rainfall measurements in Cyprus

The basic condition for using precipitation data from raingauges and radars is data quality control. This aspect is important for comparing and using rainfall data, for example in models. In the scope of the EU-project VOLTAIRE (Validation of multisensors precipitation fields and numerical modelling in Mediterranean test sites) rain data from Cyprus have been analysed. Different quality control methods have been applied to the rainfall data of 158 raingauges and the data of 11 events (in 2002 and 2003) of the C-Band radar in Kykkos. The first results of the use of ground clutter algorithms for radar data in Cyprus are presented in the paper. Copyright

Summer 1990 in Seine-Saint-Denis: forecast versus measured areal rainfall values

Abstract The use of the Trappes radar images has been routine since 1981 in the real-time control project of the Seine-Saint-Denis sewer system. In May 1988, a forecast of areal rainfall for a one-hour lead time was added. This paper discusses different ways of comparison between forecast and “reality” and describes the results of the SCOUT rainfall forecast on the main events of 1990.

Coordinated Precipitation Evaluation of Damage-Producing Events: First Steps

Damage after rainfall events requires detailed analysis of causes and rainfall extremity for the determination of liability: the question who has to pay for what. Recent years have shown that damage has increased, but also the insight that extreme events call for the whole municipal community and not only the single citizen or sewer agency. The determination which rainfall category occurred requires thorough inspection of all available data. This includes weather radar, station data, flow data and damage data. It is important to be able to rely on quality controlled high resolution data for detailed analyses in mainly urban areas. This contribution presents important corner stones on the road towards a more harmonized way of evaluating damage producing precipitation events.

Ensembles of radar nowcasts and COSMO-DE-EPS for urban flood management

Sophisticated strategies are required for flood warning in urban areas regarding convective heavy rainfall events. An approach is presented to improve short-term precipitation forecasts by combining ensembles of radar nowcasts with the high-resolution numerical weather predictions COSMO-DE-EPS of the German Weather Service. The combined ensemble forecasts are evaluated and compared to deterministic precipitation forecasts of COSMO-DE. The results show a significantly improved quality of the short-term precipitation forecasts and great potential to improve flood warnings for urban catchments. The combined ensemble forecasts are produced operationally every 5 min. Applications involve the Flood Warning Service Hamburg (WaBiHa) and real-time hydrological simulations with the model KalypsoHydrology.