Showing papers in "Meteorological Applications in 2009"

On the use of Standardized Precipitation Index(SPI) for drought intensity assessment

Abstract: Monthly rainfall data from June to October for 39 years were used to compute Standardized Precipitation Index (SPI) values based on two parameter gamma distribution for a low rainfall and a high rainfall districts of Andhra Pradesh state, India. Comparison of SPI with actual rainfall and rainfall deviation from the mean indicated that SPI values under-estimate the intensity of dryness/wetness when the rainfall is very low/very high, respectively. As a result, the SPI in the worst drought years of 2002 and 2006 in the low rainfall district indicated only moderate dryness instead of extreme dryness. SPI values of the high rainfall district showed slightly better stretching in both positive and negative directions, compared to that of the low rainfall district. Further, the SPI values of longer time scales (2, 3 and 4 months) showed an extended range compared to that of 1 month, but the sensitivity in drought years has not improved significantly. Normality tests were conducted based on Shapiro-Wilk statistic, p-values and absolute value of the median to ascertain whether non-normality of SPI is a possible reason. Although the results confirmed normal distribution, the scatter plot indicated deviation of the cumulative probability distribution of SPI from normal probability in the lower and upper ranges. Therefore, it is suggested that SPI as a stand alone indicator needs to be interpreted with caution to assess the intensity of drought. Further investigations should include sensitivity of SPI to the estimated shape and scale at lower and upper bounds of the gamma distribution and use of other distributions, such as Pearson III, to standardize the computational procedures, before using SPI as a substitute to the rainfall deviations from normal, for drought intensity assessment. Copyright © 2009 Royal Meteorological Society

Copula-based drought severity-duration-frequency analysis in Iran

Abstract: Drought is a complex and multi-attribute natural hazard that has worldwide effects. Defined by a commonly used standardized precipitation index (SPI), each drought event is characterized by three correlated attributes: severity, duration and frequency. A probabilistic approach is developed to establish a drought severity-duration-frequency (SDF) relationship. Copulas are employed to construct the joint distribution function of drought severity and duration. Drought frequency, in terms of recurrence interval of drought events, is then related to the copula-based distribution function via a conditional distribution function. The derived analytic drought SDF thus becomes a function of univariate distribution functions of drought severity and duration, a copula function which links the fitted univariate models, and the arrival rate of drought events. In this study, rainfall data for the period of 1954–2003 from two gauge stations in Iran, Abadan in the southwestern semi-arid region and Anzali in the north humid region, are employed as an example to illustrate the proposed approach. From the derived drought SDF, drought severity in Anzali station is greater than those in Abadan station for given drought duration and recurrence interval. The results imply that the drought severity in humid region might be more severe if high rainfall fluctuations exist in that region. Copyright © 2009 Royal Meteorological Society

Understanding and enhancing the public's behavioural response to flood warning information

Abstract: Drawing on evidence from the United Kingdom and elsewhere in Europe, this paper explores how people have responded to flood warning information and how these responses impact upon the effectiveness of a flood warning through saving lives and injuries, and reducing economic damages Methods of flood warning that the public rely upon are discussed alongside empirical evidence of how flood victims prepare for, and respond to, flood warnings in rapid to medium-onset floods The paper investigates why some members of the public fail to act appropriately, or most effectively, to flood warning information, touching on ideas of a lack of understanding, mistrust in authority and a lack of ownership of flood reducing actions The paper examines the styles of public learning about flood warning response which might be most appropriate and effective, and how recent positive steps to increase the public's understanding of effective response might be further enhanced in the United Kingdom Copyright © 2009 Royal Meteorological Society

Extending logistic regression to provide full‐probability‐distribution MOS forecasts

Abstract: Statistical post-processing of dynamical forecasts, using the Model Output Statistics (MOS) approach, continues to be an essential component of weather forecasting. Even in the current era of ensemble forecasting, ensemble-MOS methods are used to transform raw ensemble forecasts into well-calibrated probability forecasts. Logistic regression has been found to be an especially useful method for this purpose for predictands, such as precipitation amounts, that are distinctly non-Gaussian. However, the usual implementation of logistic regression fits separate forecast equations for different predictand thresholds, yielding finite sets of threshold probabilities rather than full forecast probability distributions. Furthermore, these individual threshold probabilities are not constrained to be mutually consistent, so that negative probabilities may be implied for some ranges of the predictand. In this paper, logistic regressions are extended to yield full continuous, and coherent, probability distribution forecasts by including the predictand threshold itself as an additional predictor in the forecast equation. The procedure is illustrated using 6–10 day precipitation forecasts for a sample of locations in the U.S., drawn from the GFS reforecast dataset. Copyright © 2009 Royal Meteorological Society

Tracking the uncertainty in flood alerts driven by grand ensemble weather predictions

Abstract: The incorporation of numerical weather predictions (NWP) into a flood warning system can increase forecast lead times from a few hours to a few days. A single NWP forecast from a single forecast centre, however, is insufficient as it involves considerable non-predictable uncertainties and can lead to a high number of false or missed warnings. Weather forecasts using multiple NWPs from various weather centres implemented on catchment hydrology can provide significantly improved early flood warning. The availability of global ensemble weather prediction systems through the ‘THORPEX Interactive Grand Global Ensemble’ (TIGGE) offers a new opportunity for the development of state-of-the-art early flood forecasting systems. This paper presents a case study using the TIGGE database for flood warning on a meso-scale catchment (4062 km2) located in the Midlands region of England. For the first time, a research attempt is made to set up a coupled atmospheric-hydrologic-hydraulic cascade system driven by the TIGGE ensemble forecasts. A probabilistic discharge and flood inundation forecast is provided as the end product to study the potential benefits of using the TIGGE database. The study shows that precipitation input uncertainties dominate and propagate through the cascade chain. The current NWPs fall short of representing the spatial precipitation variability on such a comparatively small catchment, which indicates need to improve NWPs resolution and/or disaggregating techniques to narrow down the spatial gap between meteorology and hydrology. The spread of discharge forecasts varies from centre to centre, but it is generally large and implies a significant level of uncertainties. Nevertheless, the results show the TIGGE database is a promising tool to forecast flood inundation, comparable with that driven by raingauge observation. Copyright © 2009 Royal Meteorological Society

Use of high-resolution NWP rainfall and river flow forecasts for advance warning of the Carlisle flood, north-west England

Abstract: On the 8 January 2005 the city of Carlisle in north-west England was severely flooded following 2 days of almost continuous rain over the nearby hills. Orographic enhancement of the rain through the seeder–feeder mechanism led to the very high rainfall totals. This paper shows the impact of running the Met Office Unified Model (UM) with a grid spacing of 4 and 1 km compared to the 12 km available at the time of the event. These forecasts, and forecasts from the Nimrod nowcasting system, were fed into the Probability Distributed Model (PDM) to predict river flow at the outlets of two catchments important for flood warning. The results show the benefit of increased resolution in the UM, the benefit of coupling the high-resolution rainfall forecasts to the PDM and the improvement in timeliness of flood warning that might have been possible. Copyright © 2008 Royal Meteorological Society

Flash flood warning in ungauged basins by use of the flash flood guidance and model-based runoff thresholds

Abstract: This paper investigates the use of the Flash Flood Guidance (FFG) method and a method of model-based threshold runoff computation to improve the accuracy of flash flood forecasts at ungauged locations. The methodology proposed in this paper requires running a lumped hydrological model to derive flood frequencies at the outlet of the ungauged basin under consideration, and then to derive the threshold runoff from these model-based discharges. The study examines the potential of this method to account for the hydrological model's uncertainty and for biases originated by lack of model calibration, which is the typical condition in ungauged basins. Experiments to validate this approach involve the implementation of a semi-distributed continuous rainfall-runoff model and the operation of the FFG method over four basins located in the central-eastern Italian Alps and ranging in size from 75.2 to 213.7 km2. The model is calibrated on two larger basins and the model parameters are transposed to the other two basins to simulate operations in ungauged basins. The FFG method is applied by using the 2 year discharge as the threshold runoff. The threshold runoff is derived both by using local discharge statistics and the model-based approach advocated here. Examination of the results obtained by this comparison shows that the use of model-based threshold leads to improvements in both gauged and ungauged situations. Overall, the Critical Success Index (CSI) increases by 12% for gauged basins and by 31% for ungauged basins by using the model-based threshold with respect to use of local data. As expected, the increase of CSI is more remarkable for ungauged basins, due to lack of local model calibration and the greater likelihood of occurrence of a simulation bias in model application over these basins. This shows that the method of threshold runoff computation provides an inherent bias correction to reduce systematic errors in model applications to ungauged (and gauged) basins. Copyright © 2009 Royal Meteorological Society

Quantifying the effects of high summer temperatures due to climate change on buckling and rail related delays in south-east United Kingdom

Abstract: Extreme high temperatures are associated with increased incidences of rail buckles. Climate change is predicted to alter the temperature profile in the United Kingdom with extreme high temperatures becoming an increasingly frequent occurrence. The result is that the number of buckles, and therefore delays, expected per year will increase if the track is maintained to the current standard. This paper uses a combination of analogue techniques and a weather generator to quantify the increase in the number of buckles and rail related delays in the south-east of the United Kingdom. The paper concludes by assigning a cost to the resultant rise in delays and damage before making recommendations on how these effects can be mitigated. Copyright © 2008 Royal Meteorological Society

Long lead time flood warnings: reality or fantasy?

Abstract: This paper reviews recent advances in weather forecasting capability in the United Kingdom and their implications for increasing the lead time with which flood warnings can be issued. The events of summer 2007 have highlighted the vulnerability of parts of the United Kingdom to flooding and the need for long lead time flood warnings to enable the protection of people and critical infrastructure. Historically, computer weather forecasting models have been unable to forecast at the scales of importance for flood warning, and so the warning processes have been forced to rely on measurements on the ground. Examples are presented to demonstrate that new forecasting technologies, currently being implemented, enable warnings to be produced much earlier, provided they are couched in probabilistic terms and interpreted appropriately. Crown Copyright © 2009. Reproduced with the permission of the Controller of HMSO. Published by John Wiley & Sons, Ltd

Simulation of mesoscale features associated with intense western disturbances over western Himalayas

Abstract: North India is comprised, in parts, of complex Himalayan mountain ranges having different altitudes and orientations all along this region. Due to the highly variable altitude and orientation of orographic barriers the prevailing weather conditions over the region are complex. The winter season over this region is frequented by eastward-moving low pressure synoptic weather systems called Western Disturbances (WDs). Advance information of these WDs are important for organizations where men and machines are employed to operate in the open, for example, for defence purpose, agriculture, tourism and transport. Future projection of meteorological variables is important during the winter in assessment of cold wave conditions, avalanche release and a critical human comfort index. Therefore, a non-hydrostatic version of the Penn State University/National Center for Atmospheric Research, US, (PSU/NCAR) mesoscale model is used to simulate the characteristic features of the Western Disturbances (WDs) occurring over the Indian region during a winter season. For this study, four cases of active WDs are selected. The model is integrated with 60 km horizontal resolution to simulate the WD features. The model simulations with 60 km horizontal resolution are compared with the National Center for Environmental Prediction/National Center for Atmospheric Research, US, (NCEP/NCAR) reanalyses. It is seen that in all the cases the rate of movement of the system is, in general, a little slower in the simulations. Examining the differences between the predicted and analysed zonal component of the wind reveal that the model simulated zonal winds are generally weaker/under-estimated in the location of the upper trough at 500 hPa or aloft and even in the position of the WDs at lower levels. These results suggest that the model has a systematic easterly bias, though the magnitude is small. In other words the advection simulated in the model is not strong enough to advect the system with the observed speed. Copyright  2009 Royal Meteorological Society

Detection and climatology of fronts in a high-resolution model reanalysis over the Alps

Abstract: The identification of low-level thermal fronts is particularly challenging in high-resolution model fields over complex terrain. Firstly, direct model output often contains numerical noise which spuriously influences the high-frequency variability of thermal parameters. Secondly, the boundary layer interferes via convection and consequently leaves its thermal marks on low levels. Here, an automated objective method for the detection of frontal lines is introduced which is designed to be insusceptible to consequences of small grid spacings. To this end, existing algorithms are readopted and combined in a novel way. The overall technique subdivides into a basic detection of fronts and a supplemental division into local fronts and synoptic fronts. The fundamental parts of the detection are: (1) a smoothing of the initial fields, (2) a definition of the frontal strength, and, (3) a localisation with the thermal front parameter. The local fronts are identified by means of a classification of open and closed thermal contours. The resulting data comprise the spatial outline of the frontal structures in a binary field as well as their type and movement. The novel methodology is applied to a 3 year high-resolution reanalysis over central Europe computed with the COSMO model using a grid spacing of 7 km. Grid-point based climatologies are derived for the Alpine region. Frequencies of occurrence and characteristics of motion are analysed for different frontal types. The novel climatology also provides quantitative evidence of dynamical properties such as the retardation of cold fronts ahead of mountains and the dissolution of warm fronts over mountains. Copyright © 2009 Royal Meteorological Society

Recent developments in operational flood forecasting in England, Wales and Scotland

Abstract: This paper discusses developments in the last five to six years in the provision of operational flood forecasting in England, Wales, and Scotland. Before the formation of the Environment Agency (EA) in England and Wales and the Scottish Environment Protection Agency (SEPA), flood forecasting capabilities were fragmented. Just over a decade ago both organisations received governmental mandates for the provision of flood forecasting and warning nationally, and have as a result in recent years established systems providing national coverage: the National Flood Forecasting System, and Flood Early Warning System (FEWS) Scotland. These have facilitated a rapid expansion of catchments for which forecasts are provided, and the common framework used has enabled a more rapid introduction of scientific advances in forecasting techniques. This paper gives an overview of some of these recent developments, as well as providing an outlook to further developments to be undertaken in the near future. Copyright © 2009 Royal Meteorological Society

Catchment dynamics and social response during flash floods: the potential of radar rainfall monitoring for warning procedures

Abstract: The objective of this paper is to examine how the current techniques for flash-flood monitoring and forecasting can meet the requirements of the population at risk to evaluate the severity of the flood and anticipate its danger. To this end, we identify the social response time for different social actions in the course of two well studied flash flood events which occurred in France and Italy. We introduce a broad characterization of the event management activities into three types according to their main objective (information, organisation and protection). The activities are also classified into three other types according to the scale and nature of the human group involved (individuals, communities and institutions). The conclusions reached relate to i) the characterisation of the social responses according to watershed scale and to the information available, and ii) to the appropriateness of the existing surveillance and forecasting tools to support the social responses. Our results suggest that representing the dynamics of the social response with just one number representing the average time for warning a population is an oversimplification. It appears that the social response time exhibits a parallel with the hydrological response time, by diminishing in time with decreasing size of the relevant watershed. A second result is that the human groups have different capabilities of anticipation apparently based on the nature of information they use. Comparing watershed response times and social response times shows clearly that at scales of less than 100 km2, a number of actions were taken with response times comparable to the catchment response time. The implications for adapting the warning processes to social scales (individual or organisational scales) are considerable. At small scales and for the implied anticipation times, the reliable and high-resolution description of the actual rainfall field becomes the major source of information for decision-making processes such as deciding between evacuations or advising to stay home. This points to the need to improve the accuracy and quality control of real time radar rainfall data, especially for extreme flash flood generating storms.

Monthly-, Medium-, and Short-Range Flood Warning: Testing the Limits of Predictability

Abstract: This paper describes a case study that explores the limits of the predictability of floods, by combining forecasts with multiple spatial and temporal resolutions. Monthly, medium- and short range numerical weather prediction (NWP) data are input to the European Flood Alert System for a flood event that affected rivers in Romania in October 2007. The NWP data comprise ensembles and deterministic forecasts of different spatial resolutions and lead times from different weather prediction models. Results are explored in terms of the individual NWP components as well as the ensemble. In this case study, ensembles of monthly weather forecasts contribute only marginally to the early warning, although some indication is given as early as 3 weeks before the event. The 15-day medium-range weather forecasts produce early flood warning information 9 to 11 days in advance. As the event draws nearer and is in range to be captured by the higher resolution ensemble forecasts, the spatial extent of the event is forecast with much more precision than with the medium-range. A novel post-processing method for the calculation of river discharge is applied to those stations where observations are available, and is able to correct for time-shifts and to improve the quantitative forecast. The study illustrates how a combination of forecasts and post-processing improves the lead time for early flood warnings by 2 to 3 days, while remaining reliable also in the short-range. Copyright © 2009 Royal Meteorological Society

Probability or frequency? Expressing forecast uncertainty in public weather forecasts

Abstract: Is uncertainty expressed as frequency easier for non-experts to understand than uncertainty expressed as probability? The experiment reported here compared participants' responses to the same wind speed forecast expressed several different ways. Three different uncertainty expressions were tested (90%, 9 times in 10, or 90 out of 100%). Also tested was whether understanding was improved by including a short phrase explaining, in lay terms, how the forecast was derived (adding a reference class). Results suggested that, contrary to prior research, participants better understood the forecast when it was presented in a probability format rather than a frequency format. Furthermore, specifying a reference class did not facilitate understanding. Copyright © 2009 Royal Meteorological Society

Quantification of climate for tourism in the northwest of Iran

Abstract: Tourism as a major sector of the global economy is influenced by weather and climate. At several travel destinations, climate represents a natural resource on which the tourism industry is predicated. Data covering the period 1985–2005 and from a dense network of 15 meteorological stations was used to compute the Physiologically Equivalent Temperature (PET) and ‘tourism climate index’ (TCI) in Northwest of Iran. The cities Maku, Ahar, Ardabil, Takab, Khoy, Ourimeh and Sarab have a summer peak distribution. Each of these locations has at least 1 month with a TCI score above 80: this level can be classified to be an ‘excellent’ tourism climate. The cities Maku, Ardabli and Takab have TCI above 90, an ‘ideal’ tourism climate for the summer months. Among these cities, Ardabil has the most favourable climatic conditions for tourist attractiveness in the summer. The cities Mahabad, Jolfa, Marageh, Sagez and Parsabad have a bimodal-shoulder peak distribution. In addition, based on calculations of PET in Ourmieh Lake coast it is shown that the months June, July and August are lying in the comfortable class representing the most suitable months for tourism and tourist activities. Copyright © 2009 Royal Meteorological Society

Simulation of the mean urban heat island using 2D surface parameters: empirical modelling, verification and extension

Abstract: The spatial distribution of the annual mean urban heat island (UHI) intensity was simulated applying empirical models based on datasets from urban areas of Szeged and Debrecen, using simple and easily determinable urban surface cover variables. These two cities are situated on the Alf¨ old (Great Hungarian Plain) and have similar topographic and climatic conditions. Temperature field measurements were carried out, Landsat satellite images were evaluated, and then one- and multiple variable models were constructed using linear regression techniques. The selected multiple-parameter models were verified using independent datasets from three urban settlements. In order to obtain some impression of the mean UHI patterns in other cities with no temperature measurements available, the better model was extended to urban areas of four other cities situated in geographical environments similar to Szeged and Debrecen. The main shortcoming of typical empirical models, namely that they are often restricted to a specific location, is overcome by the obtained model since it is not entirely site but more region specific, and valid in a large and densely populated area with several settlements. Copyright  2009 Royal Meteorological Society

Communicating the value of probabilistic forecasts with weather roulette

Abstract: In times of ever increasing financial constraints on public weather services it is of growing importance to communicate the value of their forecasts and products. While many diagnostic tools exist to evaluate forecast systems, intuitive diagnostics for communicating the skill of probabilistic forecasts are few. When the goal is communication with a non-expert audience it can be helpful to compare performance in more everyday terms than ‘bits of information’. Ideally, of course, the method of presentation will be directly related to specific skill scores with known strengths and weaknesses. This paper introduces Weather Roulette, a conceptual framework for evaluating probabilistic predictions where skill is quantified using an effective daily interest rate; it is straightforward to deploy, comes with a simple storyline and importantly is comprehensible and plausible for a non-expert audience. Two variants of Weather Roulette are presented, one of which directly reflects proper local skill scores. Weather Roulette contrasts the performance of two forecasting systems, one of which may be climatology. Several examples of its application to ECMWF forecasts are discussed illustrating this new tool as useful addition to the suite of available probabilistic scoring metrics. Copyright © 2008 Royal Meteorological Society

On the propagation of uncertainty in weather radar estimates of rainfall through hydrological models

Abstract: The generation of flow forecasts using rainfall inputs to hydrological models has been developed over many years. Unfortunately, errors in input data to models may vary considerably depending upon the different sources of data such as raingauges, radar and high resolution Numerical Weather Prediction (NWP) models. This has hampered the operational use of radar for quantitative flow forecasting. The manner with which radar rainfall input and model parametric uncertainty influence the character of the flow simulation uncertainty in hydrological models has been investigated by several authors. In this paper an approach to this problem based upon a stochastic hydrological model is considered. The errors in the input data, although they may be constrained, do propagate through the model to the flow predictions. Previous work on this error propagation through a fully distributed model is described, and a similar analysis for a stochastic hydrological model implemented in a mixed rural and urban area in north-west England carried out. Results are compared with those previously published for an American catchment. A possible approach to selecting flow forecast ensemble members is proposed. Copyright  2009 Royal Meteorological Society

Understanding the Value of Radar Rainfall Nowcasts in Flood Forecasting and Warning in Flashy Catchments

Abstract: Providing flood forecasts in flashy catchments poses significant challenges to the hydrologist. This is particularly the case when the prediction of high intensity rainfall at small spatial scales is difficult. Radar rainfall nowcasts, such as those provided by the Met Office Nimrod system, provide short range predictions at these spatial scales, and can be used as an input to hydrological models for the prediction of flood flows. Such short term forecasts are, however, considerably uncertain, and this uncertainty will influence the reliability of hydrological forecasts used in flood warning and forecasting. In this paper the value and benefit of the use of radar rainfall nowcasts in three small catchments in central Scotland is assessed through the evaluation of a large sample of forecasts. Both the reliability of the catchment rainfall predictions and the forecast flows are assessed. Whilst it is demonstrated that the rainfall predictions provided by Nimrod are uncertain and at times biased, it is also shown that there is considerable benefit in their use for flood forecasting when compared to the alternative of using no future prediction of rainfall. To deal with the uncertainty in the forecast, a method is shown that can help the hydrologist and forecaster to understand the structure of the uncertainties, allowing them to use the guidance provided by the forecasts more effectively in the provision of flood warnings. Copyright © 2009 Royal Meteorological Society

Towards the provision of site specific flood warnings using wireless sensor networks

Abstract: An important aspect of flood risk management is the issuing of timely flood alerts. The spatial, as well as temporal, scale of these warnings is important. In many situations efficient risk management may be aided by the provision of local flood predictions at a high spatial resolution. Examples of such situations include issuing warnings for small groups of outlying houses or key infrastructure locations Such as power sub-stations. In this paper a methodology for providing automated, detailed and location specific warnings which are computed ‘on-site’ is presented. Copyright (C) 2009 Royal Meteorological Society

Artificial neural network models for forecasting intermittent monthly precipitation in arid regions

Abstract: Forecasting monthly precipitation in arid regions is investigated by means of feed forward back propagation (FFBP) artificial neural networks (ANNs) and compared to the linear regression technique with multiple inputs (MLR). Four meteorological stations from different geographical regions in Jordan are selected. The ANNs and MLR processes are analysed based on the mean square error, relative/absolute error, determination coefficient as well as the central statistical moments such as mean, standard deviation, and minimum and maximum values. It is found that whilst on one hand the ANNs are slightly better than the MLR in forecasting the monthly total precipitation, on the other hand, both are found with to have limitations which should be improved by means of either changing the type and architecture of the ANNs or incorporating modelling tools such as Markov chains into the forecast model. Copyright © 2009 Royal Meteorological Society

A comparison of the rainfall patterns between stations on the East and the West coasts of Peninsular Malaysia using the smoothing model of rainfall amounts.

Abstract: The aim of this study is to model rainfall amounts on a daily basis by fitting a smooth curve to the mean rainfall per rainy day. The rainfall amounts are described as gamma distributions with smoothing parameters. The smoothing technique used is the approach of the Fourier series. Six rain gauge stations with the daily rainfall series covering the same period (1975-2004) are examined. Different rainfall patterns are observed among the stations, particularly between the east and the west. The stations in the western area have a bimodal pattern of rainfall and are best described with two harmonics, while four harmonics are required for the stations in the eastern area which exhibit a unimodal pattern of rainfall. The resulting curves with fitted smoothing parameters provide a good summary of statistics and useful information for describing the rainfall patterns and climate of the studied stations.

A laboratory-based study of understanding of uncertainty in 5-day site-specific temperature forecasts

Abstract: The impact of presenting uncertainty in 5-day location-specific temperature forecasts on the decision making of non-specialists was tested in an experimental economics laboratory. Undergraduate students studying a range of disciplines were asked to select which of two criteria involving temperature would be most likely to occur based on a given 5-day forecast. If they selected a criterion that was subsequently satisfied they were given a small cash reward. It was found that students presented with uncertainty information (the 50th and 90th percentile confidence intervals) in addition to the expected temperature were more likely to select the most probable criterion. This was true irrespective of the academic subject the participants were studying. Copyright © Royal Meteorological Society and Crown Copyright, 2008

Regional daily maximum rainfall estimation for Cekerek Watershed by L‐moments

Abstract: The estimation of maximum daily rainfall (PDmax) is usually required for the estimation of design flood (the maximum flood that any hydraulic structure can safely pass). However, PDmax estimation is usually required for watersheds where rainfall data are either not available or only available in short periods from various sites and so are unsuitable for maximum daily rainfall estimation. In this study, the regional PDmax of the Cekerek watershed in Turkey is estimated using the method of l-moments using 17 rainfall stations in the region. The discordant test for outlier stations showed no discordant station in the region. Applying the homogeneity measure, Hi, the homogeneous region was identified. To find the best regional distribution, the ZDIST goodness-of-fit test was applied. This test introduced two distributions as the candidates for regional parent distributions; Generalized Extreme Values (GEV) and 3-parameter Log Normal (LOGN3) distributions. The LOGN3 distribution was selected as the best regional distribution as it has the smaller absolute value of the statistics (ZDIST) based on the goodness-of-fit-test. Copyright © 2009 Royal Meteorological Society

Cloud-radar observations of insects in the UK convective boundary layer

Abstract: Radar has been applied to the study of insect migration for almost 40 years, but most entomological radars operate at X-band (9.4 GHz, 3.2 cm wavelength), and can only detect individuals of relatively large species, such as migratory gras shoppers and noctuid moths, over all of their flight altitudes. Many insec ts (including economically important species) are much smaller than this, but development of the requisite higher power and/or higher frequency radar systems to detect these species is often prohibitively expensive. In this paper, attention is focussed upon the uses of some recently-deployed meteorological sensing devices to investigate insect migratory flight behaviour, and especially its inter actions with boundary layer processes. Records were examined from the vertically-pointing 35 GHz 'Copernicus' and 94 GHz ' Galileo' cloud radars at Chilbolton (Hampshire, England) for 12 clo udless and convective occasions in summer 2003, and one of these occasions (13 July) is presented in detail. Insects were freque ntly found at heights above aerosol particles, which represent passiv e tracers, indicating active insect movement. It was found that insect flight above the convective boundary layer occurs most often during the morning. The maximum radar-reflectivity (an indicator of aerial insect biomass) was found to be positively correlated with maximum screen temperature. Copyright c 0000 Royal Meteorological Society

Deterministic and fuzzy verification methods for a hierarchy of numerical models

Abstract: Deterministic and fuzzy verification methods are compared to assess the Quantitative Precipitation Forecasts (QPF) performance of an hierarchy of models run at Meteo-France: two operational models (ARPEGE and ALADIN) and a prototype version of the high resolution model AROME. The reference data are 24-h accumulated rainfall values measured by the French climatological network of rain gauges. The deterministic forecasts are converted to frequencies of threshold exceedence in a neighbourhood in order to apply a fuzzy verification method, able to determine the influence of the double penalty. Local and regional versions of the Brier skill score (BSS) are computed and persistence is the selected reference system. An optimal size of the neighbourhood can be determined from the local version of the BSS. The regional version of the BSS increases with the size of the neighbourhood and provides useful information on the reduction of the error for large scales. All the scores show that the ALADIN 3DVAR implementation improves the quality of the ALADIN QPF in comparison to the ARPEGE QPF. Deterministic verification methods show that AROME improves the QPF for weak precipitation but produces too many false alarms for heavy rain. Moreover, the fuzzy approach removes more substantially the double penalty for the heavy rain forecasts of AROME than for the light precipitation of ALADIN. After recalibration the ALADIN QPF have better deterministic scores than the AROME QPF. Nevertheless, fuzzy verification methods prove the contrary: for scales larger than 50 km, the AROME scores exceed the ALADIN scores, but not significantly. Copyright © 2008 Royal Meteorological Society

Analysis of extreme rainfall in Barcelona using a microscale rain gauge network

Abstract: Extreme storms registered by the urban rain gauge network installed and supported by CLABSA (Clavegueram de Barcelona S. A.) in Barcelona in the period 1994–2001 have been investigated. Eleven rain events presenting intensities for durations between 5 min and 24 h with return periods equal to or larger than 5 years for any of the network gauges have been found. A cluster analysis has yielded four main classes of extreme rainfall events in this area, related to the meteorological scales involved: local (18%), mesoscale (37%) and synoptic storms (27%), as well as more complex rain events originated by multiscale mechanisms acting together (18%). An intensity index to classify extreme rainfall events in order to their complexity and severity, taking into account the contribution of the different scales implied in the rainfall processes, has been calculated. The frequency distribution of the intensity index values obtained for the urban network has resulted very similar to that calculated for rain data recorded by the Jard´i gauge of the Observatory Fabra of Barcelona during 1927–1992 inclusive.

Benefits and value of meteorological information services—the case of the Finnish Meteorological Institute

Abstract: The benefits of meteorological information services have been widely studied, but a coherent view of the impacts of these services remains elusive. Meteorological information services must be seen primarily to have potential positive impacts on the functions of society: only in that light will their true worth emerge. This paper looks at the value of the services for society as a whole. In addition to their methodological contribution to the value assessment of meteorological services in general, the services of the Finnish Meteorological Institute represent an empirical case. Evidently the value of information is set to play an increasing role as societies grow increasingly information intensive. The results of the empirical case were explicit. The total value of benefits generated each year by the Institute's services exceeded the annual budget of the Institute many times over. Copyright © 2009 Royal Meteorological Society

Observational verification of urban surface roughness parameters derived from morphological models

Abstract: This study focuses on how to verify the aerodynamic roughness parameters in an urban area by using observational data collected in the roughness sub-layer. Anemometrical observations were made in the downtown area of Nanjing, China, in summer and winter. Data were collected using both slow and fast response anemometers mounted on a 36 m tower. The friction velocity was observed just above the top of the urban canopy layer, which is at the height of 19.7 m, while the mean wind speed was observed at a relatively low level that is generally thought to be in the roughness sub-layer, of which the top usually ranges from 2 to 5 times the height of the urban canopy layer. The results of the measurements show that the dimensionless friction velocities (normalized by the mean wind speed at an upper level) maintain approximately a constant (0.20) and the fluctuations are small ( ± 0.02) in a period of 21 days. The results imply that the similarity relation for the mean wind profile is still valid and that the effect of stratification is negligibly small in the urban roughness sub-layer. Based on the measurement results, the logarithmic wind profile was applied to verify the aerodynamic roughness parameters empirically derived from four morphological models: the rule of thumb (Rt) method, the Bottema (Ba) method, the Macdonald (Ma) method and the Raupach (Ra) method. The results show that they are not very different from each other. The good performance of the Rt method may be due to the fact that the distribution of buildings in the study area is regular. The Ba and Ra methods are likely to be better since they can give reasonable estimates of roughness parameters. Evidence indicates that the Ma method underestimates the roughness length. Copyright © 2008 Royal Meteorological Society