Radar hydrology: rainfall estimation.

It is well acknowledged that there are large uncertainties associated with radar-based estimates of rainfall. Numerous sources of these errors are due to parameter estimation, the observational system and measurement principles, and not fully understood physical processes. Propagation of these uncertainties through all models for which radar-rainfall are used as input (e.g., hydrologic models) or as initial conditions (e.g., weather forecasting models) is necessary to enhance the understanding and interpretation of the obtained results. The aim of this paper is to provide an extensive literature review of the principal sources of error affecting single polarization radar-based rainfall estimates. These include radar miscalibration, attenuation, ground clutter and anomalous propagation, beam blockage, variability of the Z–R relation, range degradation, vertical variability of the precipitation system, vertical air motion and precipitation drift, and temporal sampling errors. Finally, the authors report some recent results from empirically-based modeling of the total radar-rainfall uncertainties. The bibliography comprises over 200 peer reviewed journal articles.

Review of the Different Sources of Uncertainty in Single Polarization Radar-Based Estimates of Rainfall

Radar for hydrology: unfulfilled promise or unrecognized potential?

Accuracy of radar rainfall estimates for streamflow simulation

Comparison of neural network methods for infilling missing daily weather records

Use of a weather radar for the hydrology of a mountainous area. Part I: radar measurement interpretation

Geostatistical radar–raingauge merging: A novel method for the quantification of rain estimation accuracy

The Bollene-2002 Experiment was aimed at developing the use of a radar volume-scanning strategy for conducting radar rainfall estimations in the mountainous regions of France. A developmental radar processing system, called Traitements Regionalises et Adaptatifs de Donnees Radar pour l’Hydrologie (Regionalized and Adaptive Radar Data Processing for Hydrological Applications), has been built and several algorithms were specifically produced as part of this project. These algorithms include 1) a clutter identification technique based on the pulse-to-pulse variability of reflectivity Z for noncoherent radar, 2) a coupled procedure for determining a rain partition between convective and widespread rainfall R and the associated normalized vertical profiles of reflectivity, and 3) a method for calculating reflectivity at ground level from reflectivities measured aloft. Several radar processing strategies, including nonadaptive, time-adaptive, and space–time-adaptive variants, have been implemented to a...

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Bollène-2002 Experiment: Radar Quantitative Precipitation Estimation in the Cévennes–Vivarais Region, France.

In the French Alps the quality of the radar Quantitative Precipitation Estimation (QPE) is limited by the topography and the vertical structure of precipitation. A previous study realized in all the French Alps, has shown a general bias between values of the national radar QPE composite and the rain gauge measurements: a radar QPE over-estimation at low altitude (+20% at 200 m a.s.l.), and an increasing underestimation at high altitudes (until −40% at 2100 m a.s.l.). This trend has been linked to altitudinal gradients of precipitation observed at ground level. This paper analyzes relative altitudinal gradients of precipitation estimated with rain gauges measurements in 2016 for three massifs around Grenoble, and for different temporal accumulations (yearly, seasonal, monthly, daily). Comparisons of radar and rain gauge accumulations confirm the bias previously observed. The parts of the current radar data processing affecting the bias value are pointed out. The analysis shows a coherency between the relative gradient values estimated at the different temporal accumulations. Vertical profiles of precipitation detected by a research radar installed at the bottom of the valley also show how the wide horizontal variability of precipitation inside the valley can affect the gradient estimation.

https://www.mdpi.com/2073-4433/10/6/306/pdf

Impact of the Altitudinal Gradients of Precipitation on the Radar QPE Bias in the French Alps

EnglishThis article describes a methodology to estimate rainfall based on raingauge and radar data available from operational networks in the Cevennes-Vivarais region, France. Applied over the year 2008, this approach intends to produce long-term rainfall reanalyses for hydrological applications. The radar mosaic and the raingauge network are "in competition" with the application of three estimation methods based on each observation system separately, and their fusion. We show that the radar contributes effectively only for the rainy periods when the 0 °C isotherm is above 2000 m. For summer and fall events, which are those leading to the most remarkable floods in the region, the radar provides undeniable added value. Data merging by kriging with external drift can effectively combine the qualities of the two observation systems, i.e. the spatial and temporal resolution of the radar and direct measurements of raingauges. For these episodes, the gain provided by the radar is more pronounced at the smallest spatial and temporal scales.The quantification of estimation errors is a fundamental aspect of this work, discussed in the context of geostatistics. francaisCet article decrit une methodologie d'estimation des precipitations s'appuyant sur les donnees pluviographiques et radar operationnelles de la region Cevennes-Vivarais. Appliquee a l'annee 2008, cette approche est destinee a la production de re-analyses pluviometriques de longue duree pour des applications hydrologiques. La mosaique radar et le reseau pluviographique sont « mis en competition » par l'application de trois methodes d'estimation reposant sur chaque systeme d'observation separement et sur leur fusion. On montre que l'apport du radar n'est effectif que pour les episodes pluvieux pour lesquels l'isotherme 0 °C est a une altitude superieure a 2000 m. Pour les episodes d'ete et d'automne, qui sont ceux conduisant aux phenomenes de crues marquees dans la region, le radar apporte une indeniable plus-value et la fusion radar-pluviographes par krigeage avec derive externe permet de combiner efficacement les qualites des deux systemes d'observation (resolution spatio-temporelle du radar et mesure directe des pluviographes). Pour ces episodes, le gain apporte par le radar est d'autant plus marque que les echelles spatiales et temporelles sont fines. La quantification des erreurs d'estimation est un aspect fondamental de ce travail, aborde dans le cadre de la geostatistique.

Dominique Faure

Papers

Use of a weather radar for the hydrology of a mountainous area. Part I: radar measurement interpretation

Geostatistical radar–raingauge merging: A novel method for the quantification of rain estimation accuracy

Bollène-2002 Experiment: Radar Quantitative Precipitation Estimation in the Cévennes–Vivarais Region, France.

Impact of the Altitudinal Gradients of Precipitation on the Radar QPE Bias in the French Alps

Prototype de ré-analyses pluviométriques pour la région Cévennes-Vivarais