| 1. |
- Emerton, R., et al.
(author)
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Predicting the unprecedented : forecasting the June 2021 Pacific Northwest heatwave
- 2022
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In: Weather. - : John Wiley & Sons. - 0043-1656 .- 1477-8696. ; 77:8, s. 272-279
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Journal article (peer-reviewed)abstract
- In June 2021, an unprecedented extreme heatwave impacted the Pacific Northwest of North America, resulting in more than 1000 excess deaths and affecting infrastructure and wildlife. Predicting such extreme events is key for preparedness and early action, and beyond temperature, it is important to consider biometeorological forecasts, accounting for the effects of the environment on the human body. The performance of ECMWF's (the European Centre for Medium-Range Weather Forecasts) temperature and heat stress (Humidex and the Universal Thermal Climate Index) forecasts during this heatwave is explored, and highlights that several days in advance, an event surpassing the maximum of climatology was predicted with extremely high confidence (100% of ensemble members) – successfully predicting the unprecedented.
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| 2. |
- Mason, David C., et al.
(author)
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Floodwater detection in urban areas using Sentinel-1 and WorldDEM data
- 2021
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In: Journal of Applied Remote Sensing. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 1931-3195. ; 15:3
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Journal article (peer-reviewed)abstract
- Remote sensing using synthetic aperture radar (SAR) is an important tool for emergency flood incident management. At present, operational services are mainly aimed at flood mapping in rural areas, as mapping in urban areas is hampered by the complicated backscattering mechanisms occurring there. A method for detecting flooding at high resolution in urban areas that may contain dense housing is presented. This largely uses remotely sensed data sets that are readily available on a global basis, including open-access Sentinel-1 SAR data, the WorldDEM digital surface model (DSM), and open-accessWorld Settlement Footprint data to identify urban areas. The method is a change detection technique that locally estimates flood levels in urban areas. It searches for increased SAR backscatter in the post-flood image due to double scattering between water (rather than unflooded ground) and adjacent buildings, and reduced SAR backscatter in areas away from high slopes. Areas of urban flooding are detected by comparing an interpolated flood level surface to the DSM. The method was tested on two flood events that occurred in the UK during the storms of Winter 2019-2020. High urban flood detection accuracies were achieved for the event in moderate density housing. The accuracy was reduced for the event in dense housing, when street widths became comparable to the DSM resolution, though it would still be useful for incident management. The method has potential for operational use for detecting urban flooding in near real-time on a global basis. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.
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| 3. |
- Mason, David C., et al.
(author)
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Improving Urban Flood Mapping by Merging Synthetic Aperture Radar-Derived Flood Footprints with Flood Hazard Maps
- 2021
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In: Water. - : MDPI. - 2073-4441. ; 13:11
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Journal article (peer-reviewed)abstract
- Remotely sensed flood extents obtained in near real-time can be used for emergency flood incident management and as observations for assimilation into flood forecasting models. High-resolution synthetic aperture radar (SAR) sensors have the potential to detect flood extents in urban areas through clouds during both day- and night-time. This paper considers a method for detecting flooding in urban areas by merging near real-time SAR flood extents with model-derived flood hazard maps. This allows a two-way symbiosis, whereby currently available SAR urban flood extent improves future model flood predictions, while flood hazard maps obtained after the SAR overpasses improve the SAR estimate of urban flood extents. The method estimates urban flooding using SAR backscatter only in rural areas adjacent to urban ones. It was compared to an existing method using SAR returns in both rural and urban areas. The method using SAR solely in rural areas gave an average flood detection accuracy of 94% and a false positive rate of 9% in the urban areas and was more accurate than the existing method.
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| 4. |
- Mason, David C., et al.
(author)
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Toward improved urban flood detection using Sentinel-1 : dependence of the ratio of post- to preflood double scattering cross sections on building orientation
- 2023
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In: Journal of Applied Remote Sensing. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 1931-3195. ; 17:1
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Journal article (peer-reviewed)abstract
- High-resolution synthetic aperture radar (SAR) sensors are now commonly used for flood detection. Automated detection tends to be limited to rural areas owing to the complicated backscattering mechanisms occurring in urban areas. Flooding can be identified in urban areas by searching for increased SAR backscatter in a postflood image due to double scattering between water and adjacent buildings, compared with a preflood image where double scattering is between unflooded ground and buildings. For co-polarized data, if f is the angle between the building wall and the satellite direction of travel, double scattering is strongest for f = 0 deg and falls off as f increases. Theoretical studies estimating the ratio of flooded-to-unflooded double scatterer (DS) radar cross section (RCS) using X-band SAR data, found that the ratio was high at f = 0 deg but only small at f > 10 deg. Ostensibly, this implies that few DSs might be detected in an urban area. However, experiments on real images have called into question the veracity of the modeling. We describe an empirical study to examine the relationship between the flooded-to-unflooded DS RCS ratio and f in Sentinel-1 (S-1) C-band data. We use high-resolution light detection and ranging and aerial photographs so that f can be measured accurately and is based on S-1 images from flood events that occurred in the United Kingdom during the storms of winter 2019 to 2020. Results indicate that vertical-vertical polarization is better than vertical-horizontal at distinguishing flooded from unflooded DS; that the theoretical model used underestimates the number of DS with high RCS ratios in the f range 10 deg to 30 deg; and that sufficient DS ground heights can be determined to estimate an accurate local average flood level, although in high density housing there are less of these due to the presence of adjacent buildings.
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| 5. |
- Matthews, Gwyneth, et al.
(author)
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Evaluating the impact of post-processing medium-range ensemble streamflow forecasts from the European Flood Awareness System
- 2022
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In: Hydrology and Earth System Sciences. - : Copernicus Publications. - 1027-5606 .- 1607-7938. ; 26:11, s. 2939-2968
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Journal article (peer-reviewed)abstract
- Streamflow forecasts provide vital information to aid emergency response preparedness and disaster risk reduction. Medium-range forecasts are created by forcing a hydrological model with output from numerical weather prediction systems. Uncertainties are unavoidably introduced throughout the system and can reduce the skill of the streamflow forecasts. Post-processing is a method used to quantify and reduce the overall uncertainties in order to improve the usefulness of the forecasts. The post-processing method that is used within the operational European Flood Awareness System is based on the model conditional processor and the ensemble model output statistics method. Using 2 years of reforecasts with daily timesteps, this method is evaluated for 522 stations across Europe. Post-processing was found to increase the skill of the forecasts at the majority of stations in terms of both the accuracy of the forecast median and the reliability of the forecast probability distribution. This improvement is seen at all lead times (up to 15 d) but is largest at short lead times. The greatest improvement was seen in low-lying, large catchments with long response times, whereas for catchments at high elevation and with very short response times the forecasts often failed to capture the magnitude of peak flows. Additionally, the quality and length of the observational time series used in the offline calibration of the method were found to be important. This evaluation of the post-processing method, and specifically the new information provided on characteristics that affect the performance of the method, will aid end users in making more informed decisions. It also highlights the potential issues that may be encountered when developing new post-processing methods.
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| 6. |
- Titley, Helen A., et al.
(author)
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A global evaluation of multi-model ensemble tropical cyclone track probability forecasts
- 2020
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In: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 146:726, s. 531-545
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Journal article (peer-reviewed)abstract
- At the Met Office, dynamic ensemble forecasts from the Met Office Global and Regional Ensemble Prediction System (MOGREPS-G), the European Centre for Medium-Range Weather Forecasts Ensemble (ECMWFENS) and National Centers for Environmental Prediction Global Ensemble Forecast System (NCEP GEFS) global ensemble forecast models are post-processed to identify and track tropical cyclones. The ensemble members from each model are also combined into a 108-member multi-model ensemble. Track probability forecasts are produced for named tropical cyclones showing the probability of a location being within 120 km of a named tropical cyclone at any point in the next 7 days, and also broken down into each 24-hour forecast period. This study presents the verification of these named-storm track probabilities over a two-year period across all global tropical cyclone basins, and compares the results from basin to basin. The combined multi-model ensemble is found to increase the skill and value of the track probability forecasts over the best-performing individual ensemble (ECMWF ENS), for both overall 7-day track probability forecasts and 24-hour track probabilities. Basin-based and storm-based verification illustrates that the best performing individual ensemble can change from basin to basin and from storm to storm, but that the multi-model ensemble adds skill in every basin, and is also able to match the best performing individual ensemble in terms of overall probabilistic forecast skill in several high-profile case-studies. This study helps to illustrate the potential value and skill to be gained if operational tropical cyclone forecasting can continue to migrate away from a deterministic-focused forecasting environment to one where the probabilistic situation-based uncertainty information provided by the dynamic multi-model ensembles can be incorporated into operational forecasts and warnings.
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| 7. |
- Wagener, Thorsten, et al.
(author)
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Knowledge gaps in our perceptual model of Great Britain's hydrology
- 2021
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In: Hydrological Processes. - : John Wiley & Sons. - 0885-6087 .- 1099-1085. ; 35:7
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Journal article (peer-reviewed)abstract
- There is a no lack of significant open questions in the field of hydrology. How will hydrological connectivity between freshwater bodies be altered by future human alterations to the hydrological cycle? Where does water go when it rains? Or what is the future space-time variability of flood and drought events? However, the answers to these questions will vary with location due to the specific and often poorly understood local boundary conditions and system properties that control the functional behaviour of a catchment or any other hydrologic control volume. We suggest that an open, shared and evolving perceptual model of a region's hydrology is critical to tailor our science questions, as it would be for any other study domain from the plot to the continental scale. In this opinion piece, we begin to discuss the elements of and point out some knowledge gaps in the perceptual model of the terrestrial water cycle of Great Britain. We discuss six major knowledge gaps and propose four key ways to reduce them. While the specific knowledge gaps in our perceptual model do not necessarily transfer to other places, we believe that the development of such perceptual models should be at the core of the debate for all hydrologic communities, and we encourage others to have a similar debate for their hydrologic domain.
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| 8. |
- Brimicombe, Chloe, et al.
(author)
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Borderless Heat Hazards With Bordered Impacts
- 2021
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In: Earth's Future. - : American Geophysical Union (AGU). - 2328-4277. ; 9:9
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Journal article (peer-reviewed)abstract
- Heatwaves are increasing in frequency, duration, and intensity due to climate change. They are associated with high mortality rates and cross-sectional impacts including a reduction in crop yield and power outages. Here we demonstrate that there are large deficiencies in reporting of heatwave impacts in international disasters databases, international organization reports, and climate bulletins. We characterize the distribution of heat stress across the world focusing on August in the Northern Hemisphere, when notably heatwaves have taken place (i.e., 2003, 2010, and 2020) for the last 20 years using the ERA5-HEAT reanalysis of the Universal Thermal Comfort Index and establish heat stress has grown larger in extent, more so during a heatwave. Comparison of heat stress against the emergency events impacts database and climate reports reveals underreporting of heatwave-related impacts. This work suggests an internationally agreed protocol should be put in place for impact reporting by organizations and national government, facilitating implementation of preparedness measures, and early warning systems.
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| 9. |
- Brimicombe, Chloe, et al.
(author)
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Heatwaves : An invisible risk in UK policy and research
- 2021
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In: Environmental Science and Policy. - : Elsevier. - 1462-9011 .- 1873-6416. ; 116, s. 1-7
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Journal article (peer-reviewed)abstract
- In 2019, a heatwave - an unusual extended period of hot weather - broke the UK's highest recorded temperature of 38.7 degrees C set in 2003. Of concern is that for summer 2019, this resulted in 892 excess deaths. With the intensity and frequency of UK heatwaves projected to increase, and summer temperatures predicted to be 5 degrees C hotter by 2070, urgent action is needed to prepare for, and adapt to, the changes now and to come. Yet it remains unclear what actions are needed and by whom. In response, a systematic literature review of UK heatwaves peer reviewed publications, inclusive of keyword criteria (total papers returned = 183), was conducted to understand what lessons have been learnt and what needs to happen next. Our research shows that heatwaves remain largely an invisible risk in the UK. Communication over what UK residents should do, the support needed to make changes, and their capacity to enact those changes, is often lacking. In turn, there is an inherent bias where research focuses too narrowly on the health and building sectors over other critical sectors, such as agriculture. An increased amount of action and leadership is therefore necessary from the UK government to address this.
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| 10. |
- Brimicombe, Chloe, et al.
(author)
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Thermofeel : A python thermal comfort indices library
- 2022
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In: SoftwareX. - : Elsevier. - 2352-7110. ; 18
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Journal article (peer-reviewed)abstract
- Here the development of the python library thermofeel is described. thermofeel was developed so that prominent internationally used thermal indices (i.e. Universal Thermal Climate Index and Wet Bulb Globe Temperature) could be implemented into operational weather forecasting systems (i.e. the European Centre for Medium Range Weather Forecasts) whilst also adhering to open research practices. This library will be of benefit to many sectors including meteorology, sport, health and social care, hygiene, agriculture and building. In addition, it could be used in heat early warning systems which, with the right preparedness measures, has the potential to save lives from thermal extremes.
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