Calibration and evaluation of a flood forecasting system: Utility of numerical weather prediction model, data assimilation and satellite-based rainfall

Two new approaches are proposed and developed for making time and space dependent, quantitative short-term forecasts of lightning threat, and a blend of these approaches is devised that capitalizes on the strengths of each. The new methods are distinctive in that they are based entirely on the ice-phase hydrometeor fields generated by regional cloud-resolving numerical simulations, such as those produced by the WRF model. These methods are justified by established observational evidence linking aspects of the precipitating ice hydrometeor fields to total flash rates. The methods are straightforward and easy to implement, and offer an effective near-term alternative to the incorporation of complex and costly cloud electrification schemes into numerical models. One method is based on upward fluxes of precipitating ice hydrometeors in the mixed phase region at the-15 C level, while the second method is based on the vertically integrated amounts of ice hydrometeors in each model grid column. Each method can be calibrated by comparing domain-wide statistics of the peak values of simulated flash rate proxy fields against domain-wide peak total lightning flash rate density data from observations. Tests show that the first method is able to capture much of the temporal variability of the lightning threat, while the second method does a better job of depicting the areal coverage of the threat. Our blended solution is designed to retain most of the temporal sensitivity of the first method, while adding the improved spatial coverage of the second. Exploratory tests for selected North Alabama cases show that, because WRF can distinguish the general character of most convective events, our methods show promise as a means of generating quantitatively realistic fields of lightning threat. However, because the models tend to have more difficulty in predicting the instantaneous placement of storms, forecasts of the detailed location of the lightning threat based on single simulations can be in error. Although these model shortcomings presently limit the precision of lightning threat forecasts from individual runs of current generation models,the techniques proposed herein should continue to be applicable as newer and more accurate physically-based model versions, physical parameterizations, initialization techniques and ensembles of forecasts become available.

Forecasting lightning threat using cloud- resolving model simulations

[1] The rainfall-elevation relationship in the central Himalayan region (CHR) for premonsoon and monsoon seasons is analyzed utilizing the 11-year (1998–2008) high-spatialresolution TRMM PR 2A25 near-surface rainfall data. The results indicate a strong relationship between rainfall and elevation during both seasons. The investigation reveals a relatively large amount of rainfall over higher elevations during pre-monsoon season. Interestingly, two significant rainfall peaks appear over the southern slope of the Himalayas during summer monsoon season. The first primary peak appears along the Sub-Himalayas (� 500–700 m above MSL), while the second appears along the Lesser Himalayas (� 2,000–2,200 m above MSL). The former rainfall peak is attributed to fewer heavy rainfall events, and the latter to frequent, weak, but persistent rainfall. It is suggested that the atmosphere is insufficiently moist to trigger convections during the pre-monsoon season, and sufficiently moist during summer monsoon season. The convections over the Sub-Himalayas may moisten the middle layer, and the water vapor in the atmosphere condenses because of the forced lifting along the slope, forming the second rainfall band. The total rain amount is primarily determined by the frequency of rain. The rainconditioned rain rate along the slope monotonically decreases with elevation. This shows that the precipitation occurs because of forced lifting. In addition, our results show that seasonal variation of rainfall is rather similar to the variation of rainfall characteristics observed during active and break periods.

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Spatiotemporal variation of rainfall over the central Himalayan region revealed by TRMM Precipitation Radar

Regional analysis was used to improve estimates of the probabilities of extreme precipi- tation events in the Czech Republic. The delimitation of 4 homogeneous regions was based on statisti- cal procedures (cluster analysis of site characteristics and subsequent tests for regional homogeneity). The regions also reflect climatological differences in precipitation regimes and synoptic patterns that cause heavy precipitation. The Generalized Extreme Value (GEV) distribution was identified as the most suitable distribution for modelling maximum annual 1 to 7 d precipitation amounts according to the L-moment ratio diagram and goodness-of-fit tests. Only in the northeast region (which is most prone to the occurrence of extremely high precipitation totals) was the Generalized Logistic (GLO) dis- tribution preferred. The regional approach considerably lessened the between-site variation of esti- mates of the shape parameter of the GEV/GLO distribution compared to at-site procedures, and the estimates of high quantiles (e.g. 50 yr return values) were more reliable and climatologically consistent in individual regions. Different growth curve shapes are characteristic of the 4 regions, the between- region variability being larger for multi-day than 1 d events. Particularly noteworthy is the heavy tail of distributions of 5 and 7 d annual maxima in the northeast region, reflected also in the inapplicability of the general 4-parameter kappa distribution in regional homogeneity tests. A nonparametric statistical test on the value of the tail index supports a hypothesis that data in this flood-prone area may be drawn from a distribution with a very heavy tail for which L-moments do not exist.

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Regional growth curves and improved design value estimates of extreme precipitation events in the Czech Republic

A new satellite-based monthly precipitation downscaling algorithm with non-stationary relationship between precipitation and land surface characteristics

Areal distribution and precipitation–altitude relationship of heavy short-term precipitation in the Czech Republic in the warm part of the year

Assimilation of extrapolated radar reflectivity into a NWP model and its impact on a precipitation forecast at high resolution

Effects of an assimilation of radar and satellite data on a very-short range forecast of heavy convective rainfalls

Radar-based rainfall information has been widely used in hydrological and meteorological applications, as it provides data with a high spatial and temporal resolution that improve rainfall representation. However, the broad diversity of studies makes it difficult to gather a condensed overview of the usefulness and limitations of radar technology and its application in particular situations. In this paper, a comprehensive review through a categorization of radar-related topics aims to provide a general picture of the current state of radar research. First, the importance and impact of the high temporal resolution of weather radar is discussed, followed by the description of quantitative precipitation estimation strategies. Afterwards, the use of radar data in rainfall nowcasting as well as its role in preparation of initial conditions for numerical weather predictions by assimilation is reviewed. Furthermore, the value of radar data in rainfall-runoff models with a focus on flash flood forecasting is documented. Finally, based on this review, conclusions of the most relevant challenges that need to be addressed and recommendations for further research are presented. This review paper supports the exploitation of radar data in its full capacity by providing key insights regarding the possibilities of including radar data in hydrological and meteorological applications.

https://www.mdpi.com/2072-4292/13/3/351/pdf

Zbyněk Sokol

Papers

Areal distribution and precipitation–altitude relationship of heavy short-term precipitation in the Czech Republic in the warm part of the year

Assimilation of extrapolated radar reflectivity into a NWP model and its impact on a precipitation forecast at high resolution

Effects of an assimilation of radar and satellite data on a very-short range forecast of heavy convective rainfalls

The Role of Weather Radar in Rainfall Estimation and Its Application in Meteorological and Hydrological Modelling—A Review

A comparison of the flood precipitation episode in August 2002 with historic extreme precipitation events on the Czech territory