Pub Date : 2023-08-25DOI: 10.5194/nhess-23-2857-2023
P. Rivoire, O. Martius, P. Naveau, A. Tuel
Abstract. Heavy precipitation can lead to floods and landslides, resulting in widespread damage and significant casualties. Some of its impacts can be mitigated if reliable forecasts and warnings are available. Of particular interest is the subseasonal-to-seasonal (S2S) prediction timescale. The S2S prediction timescale has received increasing attention in the research community because of its importance for many sectors. However, very few forecast skill assessments of precipitation extremes in S2S forecast data have been conducted. The goal of this article is to assess the forecast skill of rare events, here extreme precipitation, in S2S forecasts, using a metric specifically designed for extremes. We verify extreme precipitation events over Europe in the S2S forecast model from the European Centre for Medium-Range Weather Forecasts. The verification is conducted against ERA5 reanalysis precipitation. Extreme precipitation is defined as daily precipitation accumulations exceeding the seasonal 95th percentile. In addition to the classical Brier score, we use a binary loss index to assess skill. The binary loss index is tailored to assess the skill of rare events. We analyze daily events that are locally and spatially aggregated, as well as 7 d extreme-event counts. Results consistently show a higher skill in winter compared to summer. The regions showing the highest skill are Norway, Portugal and the south of the Alps. Skill increases when aggregating the extremes spatially or temporally. The verification methodology can be adapted and applied to other variables, e.g., temperature extremes or river discharge.
{"title":"Assessment of subseasonal-to-seasonal (S2S) ensemble extreme precipitation forecast skill over Europe","authors":"P. Rivoire, O. Martius, P. Naveau, A. Tuel","doi":"10.5194/nhess-23-2857-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2857-2023","url":null,"abstract":"Abstract. Heavy precipitation can lead to floods and landslides, resulting in widespread damage and significant casualties. Some of its impacts can be mitigated if reliable forecasts and warnings are available. Of particular interest is the subseasonal-to-seasonal (S2S) prediction timescale. The S2S prediction timescale has received increasing attention in the research community because of its importance for many sectors. However, very few forecast skill assessments of precipitation extremes in S2S forecast data have been conducted. The goal of this article is to assess the forecast skill of rare events, here extreme precipitation, in S2S forecasts, using a metric specifically designed for extremes. We verify extreme precipitation events over Europe in the S2S forecast model from the European Centre for Medium-Range Weather Forecasts. The verification is conducted against ERA5 reanalysis precipitation. Extreme precipitation is defined as daily precipitation accumulations exceeding the seasonal 95th percentile. In addition to the classical Brier score, we use a binary loss index to assess skill. The binary loss index is tailored to assess the skill of rare events. We analyze daily events that are locally and spatially aggregated, as well as 7 d extreme-event counts. Results consistently show a higher skill in winter compared to summer. The regions showing the highest skill are Norway, Portugal and the south of the Alps. Skill increases when aggregating the extremes spatially or temporally. The verification methodology can be adapted and applied to other variables, e.g., temperature extremes or river discharge.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46230040","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-24DOI: 10.5194/nhess-23-2841-2023
S. Cusack
Abstract. Traditional insurance has both a great exposure to decadal variations in European storm activity and the ability to adjust its business strategy over these timescales. Hence, the recent development of skilful predictions of multiannual mean European winter climate seems a very welcome addition to the long list of ways that researchers have improved management of windstorm risk. Yet companies do not use these forecasts of mean winter climate to adjust their view of risk. The main reason is the lack of a long, reliable record of losses to understand how forecasted time-mean circulation anomalies relate to the damage from a few, intense storms. This study fills that gap with a European windstorm loss record from 1950 to 2022, based on ERA5 peak near-surface winds per event which were converted to losses using an established damage function. The resulting dataset successfully identifies major storms over the past 70 years and simulates the multidecadal variations from low values in the 1960s up to high levels in the 1980s and 1990s then down to the 2010s. However, it underestimated the steepness of the observed loss decline from the stormy end of the 20th century to the lull over the past 20 years. This was caused by a quite flat trend in ERA5 extreme winds over the period, in contrast to the significant decline in observed peak gusts. Imposing these gust trends on ERA5 peak winds reconciled modelled losses with industry experience over the past few decades. Indices of European winter climate used in long-range forecasting were compared to the new modelled loss dataset. They had correlations of around 0.4 at interannual timescales, rising to about 0.7 for decadal and longer variations. Notably, the climate indices have a similar multidecadal trend as ERA5 extreme winds in modern times, including a less steep decline than found in observed gusts and losses. Further investigation of the modern-day divergence between climate indices and losses may help connect decadal forecasting to insurance.
{"title":"A long record of European windstorm losses and its comparison to standard climate indices","authors":"S. Cusack","doi":"10.5194/nhess-23-2841-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2841-2023","url":null,"abstract":"Abstract. Traditional insurance has both a great exposure to decadal variations in\u0000European storm activity and the ability to adjust its business strategy\u0000over these timescales. Hence, the recent development of skilful predictions\u0000of multiannual mean European winter climate seems a very welcome addition to\u0000the long list of ways that researchers have improved management of windstorm\u0000risk. Yet companies do not use these forecasts of mean winter climate to\u0000adjust their view of risk. The main reason is the lack of a long, reliable\u0000record of losses to understand how forecasted time-mean circulation\u0000anomalies relate to the damage from a few, intense storms. This study fills\u0000that gap with a European windstorm loss record from 1950 to 2022, based on\u0000ERA5 peak near-surface winds per event which were converted to losses using\u0000an established damage function. The resulting dataset successfully\u0000identifies major storms over the past 70 years and simulates the\u0000multidecadal variations from low values in the 1960s up to high levels in\u0000the 1980s and 1990s then down to the 2010s. However, it underestimated the\u0000steepness of the observed loss decline from the stormy end of the 20th\u0000century to the lull over the past 20 years. This was caused by a quite flat\u0000trend in ERA5 extreme winds over the period, in contrast to the significant\u0000decline in observed peak gusts. Imposing these gust trends on ERA5 peak\u0000winds reconciled modelled losses with industry experience over the past few\u0000decades. Indices of European winter climate used in long-range forecasting were\u0000compared to the new modelled loss dataset. They had correlations of around\u00000.4 at interannual timescales, rising to about 0.7 for decadal and longer\u0000variations. Notably, the climate indices have a similar multidecadal trend\u0000as ERA5 extreme winds in modern times, including a less steep decline than\u0000found in observed gusts and losses. Further investigation of the modern-day\u0000divergence between climate indices and losses may help connect decadal\u0000forecasting to insurance.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42953773","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-18DOI: 10.5194/nhess-23-2821-2023
Felix Erdmann, O. Caumont, E. Defer
Abstract. This study develops a lightning data assimilation (LDA) scheme for the regional, convection-permitting numerical weather prediction (NWP) model AROME-France. The LDA scheme intends to assimilate total lightning, i.e., cloud-to-ground (CG) and inter- and intra-cloud (IC), of the future Meteosat Third Generation (MTG) Lightning Imager (LI; MTG-LI). MTG-LI proxy data are created, and flash extent density (FED) fields are derived. An FED forward observation operator (FFO) is trained based on modeled, column-integrated graupel mass from 24 storm days in 2018. The FFO is successfully verified for 2 independent storm days. With the FFO, the LDA adapts a 1-dimensional Bayesian (1DBay) retrieval followed by a 3-dimensional variational (3DVar) assimilation approach that is currently run operationally in AROME-France for radar reflectivity data. The 1DBay retrieval derives relative humidity profiles from the background by comparing the FED observations to the FED inferred from the background. Retrieved relative humidity profiles are assimilated as sounding data. The evaluation of the LDA comprises different LDA experiments and four case studies. It is found that all LDA experiments can increase the background integrated water vapor (IWV) in regions where the observed FED exceeds the FED inferred from AROME-France outputs. In addition, IWV can be reduced where spurious FED is modeled. A qualitative analysis of 6 h accumulated rainfall fields reveals that the LDA is capable of locating and initiating some local precipitation fields better than a radar data assimilation (RDA) experiment. However, the LDA also leads to rainfall accumulations that are too high at some locations. Fractions skill scores (FSSs) of 6 h accumulated rainfall are overall similar for the developed LDA and RDA experiments. An approach aiming at mitigating effects due to differences in the optical extents of lightning flashes and the area of the corresponding cloud was developed and included in the LDA; however, it does not always improve the FSS.
{"title":"Assimilation of Meteosat Third Generation (MTG) Lightning Imager (LI) pseudo-observations in AROME-France – proof of concept","authors":"Felix Erdmann, O. Caumont, E. Defer","doi":"10.5194/nhess-23-2821-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2821-2023","url":null,"abstract":"Abstract. This study develops a lightning data assimilation (LDA) scheme for the regional, convection-permitting numerical weather prediction (NWP) model AROME-France. The LDA scheme intends to assimilate total lightning, i.e., cloud-to-ground (CG) and inter- and intra-cloud (IC), of the future Meteosat Third Generation (MTG) Lightning Imager (LI; MTG-LI). MTG-LI proxy data are created, and flash extent density (FED) fields are derived.\u0000An FED forward observation operator (FFO) is trained based on modeled, column-integrated graupel mass from 24 storm days in 2018. The FFO is successfully verified for 2 independent storm days.\u0000With the FFO, the LDA adapts a 1-dimensional Bayesian (1DBay) retrieval followed by a 3-dimensional variational (3DVar) assimilation approach that is currently run operationally in AROME-France for radar reflectivity data. The 1DBay retrieval derives relative humidity profiles from the background by comparing the FED observations to the FED inferred from the background. Retrieved relative humidity profiles are assimilated as sounding data.\u0000The evaluation of the LDA comprises different LDA experiments and four case studies. It is found that all LDA experiments can increase the background integrated water vapor (IWV) in regions where the observed FED exceeds the FED inferred from AROME-France outputs. In addition, IWV can be reduced where spurious FED is modeled. A qualitative analysis of 6 h accumulated rainfall fields reveals that the LDA is capable of locating and initiating some local precipitation fields better than a radar data assimilation (RDA) experiment. However, the LDA also leads to rainfall accumulations that are too high at some locations. Fractions skill scores (FSSs) of 6 h accumulated rainfall are overall similar for the developed LDA and RDA experiments. An approach aiming at mitigating effects due to differences in the optical extents of lightning flashes and the area of the corresponding cloud was developed and included in the LDA; however, it does not always improve the FSS.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48713492","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. The super cyclonic storm Amphan originated in the central Bay of Bengal (BoB) in May 2020, and a phytoplankton bloom occurred in the upper ocean that was devoid of background nutrients. The dynamic mechanism of the chlorophyll a (Chl a) bloom was researched based on reanalysis data, remote sensing and Argo float data. During the passage of Amphan, an inertial oscillation with a 2 d period appeared in the thermocline and lasted for approximately 2 weeks. After the passage of Amphan, a cyclonic eddy with a maximum vorticity of approximately 0.36 s−1 formed in the study area (Box A). Additionally, horizontal transport of Chl a also occurred when the maximum inlet fluxes through the western and northern sides of Box A were 0.304 and −0.199 mg m−2 s−1, respectively. With the weakened thermocline and thinner barrier layer thickness (BLT), nitrate and Chl a were uplifted to the upper ocean by upwelling. Then, with the high photosynthetically available radiation (PAR) in the upper ocean, a phytoplankton bloom occurred. This study provides new insights into the biological responses in the BoB during the passage of tropical cyclones (TCs).
{"title":"A phytoplankton bloom caused by the super cyclonic storm Amphan in the central Bay of Bengal","authors":"Haojie Huang, Linfei Bai, Haoyun Shen, Xiaoqi Ding, Rui Wang, Haibin Lü","doi":"10.5194/nhess-23-2807-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2807-2023","url":null,"abstract":"Abstract. The super cyclonic storm Amphan originated in the central Bay of Bengal (BoB) in May 2020, and a phytoplankton bloom occurred in the upper ocean that was devoid of background nutrients. The dynamic mechanism of the chlorophyll a (Chl a) bloom was researched based on reanalysis data,\u0000remote sensing and Argo float data. During the passage of Amphan, an inertial oscillation with a 2 d period appeared in the thermocline and\u0000lasted for approximately 2 weeks. After the passage of Amphan, a cyclonic\u0000eddy with a maximum vorticity of approximately 0.36 s−1 formed in the\u0000study area (Box A). Additionally, horizontal transport of Chl a also\u0000occurred when the maximum inlet fluxes through the western and northern\u0000sides of Box A were 0.304 and −0.199 mg m−2 s−1, respectively. With the weakened thermocline and thinner barrier layer thickness (BLT), nitrate and Chl a were uplifted to the upper ocean by upwelling. Then, with the high photosynthetically available radiation (PAR) in the upper ocean, a phytoplankton bloom occurred. This study provides new insights into the biological responses in the BoB during the passage of tropical cyclones (TCs).\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43775006","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-15DOI: 10.5194/nhess-23-2787-2023
Lisa Köhler, Torsten Masson, Sabrina Köhler, C. Kuhlicke
Abstract. To better understand factors shaping adaptive behavior and resilience is crucial in designing policy strategies to prepare people for future flooding. The central question of our paper is how frequent flood experience (FFE) impacts adaptive behavior and self-reported resilience. The applied empirical methods are binary logistic and linear regression models using data from a panel dataset including 2462 residents (Germany, state of Saxony). Four main conclusions from the investigations can be drawn. First, more flood-experienced respondents are statistically significantly more likely to have taken precautionary measures in the past. Second, FFE has a statistically significant negative impact on self-reported resilience. Third, the impact of FFE on the capacity to recover and the capacity to resist is statistically significantly non-linear. Fourth, putting together these results reveals the paradox of more flood-experienced respondents being better prepared but feeling less resilient at the same time. It can be concluded that more research is needed to obtain deeper insights into the drivers behind self-reported resilience and that this study can be seen as a piece of the puzzle, taking frequent flood experience as the primary entry point.
{"title":"Better prepared but less resilient: the paradoxical impact of frequent flood experience on adaptive behavior and resilience","authors":"Lisa Köhler, Torsten Masson, Sabrina Köhler, C. Kuhlicke","doi":"10.5194/nhess-23-2787-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2787-2023","url":null,"abstract":"Abstract. To better understand factors shaping adaptive behavior\u0000and resilience is crucial in designing policy strategies to prepare people\u0000for future flooding. The central question of our paper is how frequent flood\u0000experience (FFE) impacts adaptive behavior and self-reported resilience. The\u0000applied empirical methods are binary logistic and linear regression models\u0000using data from a panel dataset including 2462 residents (Germany, state of\u0000Saxony). Four main conclusions from the investigations can be drawn. First,\u0000more flood-experienced respondents are statistically significantly more\u0000likely to have taken precautionary measures in the past. Second, FFE has a\u0000statistically significant negative impact on self-reported resilience.\u0000Third, the impact of FFE on the capacity to recover and the capacity to\u0000resist is statistically significantly non-linear. Fourth, putting together\u0000these results reveals the paradox of more flood-experienced respondents\u0000being better prepared but feeling less resilient at the same time. It can be\u0000concluded that more research is needed to obtain deeper insights into the\u0000drivers behind self-reported resilience and that this study can be seen as a\u0000piece of the puzzle, taking frequent flood experience as the primary entry\u0000point.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45286544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-10DOI: 10.5194/nhess-23-2769-2023
Helen Hooker, S. Dance, D. Mason, J. Bevington, K. Shelton
Abstract. An ensemble of forecast flood inundation maps has the potential to represent the uncertainty in the flood forecast and provide a location-specific likelihood of flooding. Ensemble flood map forecasts provide probabilistic information to flood forecasters, flood risk managers and insurers and will ultimately benefit people living in flood-prone areas. Spatial verification of the ensemble flood map forecast against remotely observed flooding is important to understand both the skill of the ensemble forecast and the uncertainty represented in the variation or spread of the individual ensemble-member flood maps. In atmospheric sciences, a scale-selective approach has been used to evaluate a convective precipitation ensemble forecast. This determines a skilful scale (agreement scale) of ensemble performance by locally computing a skill metric across a range of length scales. By extending this approach through a new application, we evaluate the spatial predictability and the spatial spread–skill of an ensemble flood forecast across a domain of interest. The spatial spread–skill method computes an agreement scale at every grid cell between each unique pair of ensemble flood maps (ensemble spatial spread) and between each ensemble flood map with a SAR-derived flood map (ensemble spatial skill; SAR: synthetic aperture radar). These two are compared to produce the final spatial spread–skill performance. These methods are applied to the August 2017 flood event on the Brahmaputra River in the Assam region of India. Both the spatial skill and spread–skill relationship vary with location and can be linked to the physical characteristics of the flooding event such as the location of heavy precipitation. During monitoring of flood inundation accuracy in operational forecasting systems, validation and mapping of the spatial spread–skill relationship would allow better quantification of forecast systematic biases and uncertainties. This would be particularly useful for ungauged catchments where forecast streamflows are uncalibrated and would enable targeted model improvements to be made across different parts of the forecast chain.
{"title":"Assessing the spatial spread–skill of ensemble flood maps with remote-sensing observations","authors":"Helen Hooker, S. Dance, D. Mason, J. Bevington, K. Shelton","doi":"10.5194/nhess-23-2769-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2769-2023","url":null,"abstract":"Abstract. An ensemble of forecast flood inundation maps has the potential to represent the uncertainty in the flood forecast and provide a location-specific likelihood of flooding. Ensemble flood map forecasts provide probabilistic information to flood forecasters, flood risk managers and insurers and will ultimately benefit people living in flood-prone areas. Spatial verification of the ensemble flood map forecast against remotely observed flooding is important to understand both the skill of the ensemble forecast and the uncertainty represented in the variation or spread of the individual ensemble-member flood maps. In atmospheric sciences, a scale-selective approach has been used to evaluate a convective precipitation ensemble forecast. This determines a skilful scale (agreement scale) of ensemble performance by locally computing a skill metric across a range of length scales. By extending this approach through a new application, we evaluate the spatial predictability and the spatial spread–skill of an ensemble flood forecast across a domain of interest. The spatial spread–skill method computes an agreement scale at every grid cell between each unique pair of ensemble flood maps (ensemble spatial spread) and between each ensemble flood map with a SAR-derived flood map (ensemble spatial skill; SAR: synthetic aperture radar). These two are compared to produce the final spatial spread–skill performance. These methods are applied to the August 2017 flood event on the Brahmaputra River in the Assam region of India. Both the spatial skill and spread–skill relationship vary with location and can be linked to the physical characteristics of the flooding event such as the location of heavy precipitation. During monitoring of flood inundation accuracy in operational forecasting systems, validation and mapping of the spatial spread–skill relationship would allow better quantification of forecast systematic biases and uncertainties. This would be particularly useful for ungauged catchments where forecast streamflows are uncalibrated and would enable targeted model improvements to be made across different parts of the forecast chain.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47551326","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-09DOI: 10.5194/nhess-23-2749-2023
K. Haslinger, W. Schöner, J. Abermann, G. Laaha, K. Andre, M. Olefs, R. Koch
Abstract. In this paper future changes of surface water availability in Austria are investigated. We use an ensemble of downscaled and bias-corrected regional climate model simulations of the EURO-CORDEX initiative under moderate mitigation (RCP4.5) and Paris Agreement (RCP2.6) emission scenarios. The climatic water balance and its components (rainfall, snow melt, glacier melt and atmospheric evaporative demand) are used as indicators of surface water availability, and we focus on different altitudinal classes (lowland, mountainous and high alpine) to depict a variety of processes in complex terrain. Apart from analysing the mean changes of these components, we also pursue a hazard risk approach by estimating future changes in return periods of meteorological drought events of a given magnitude as observed in the reference period. The results show, in general, wetter conditions over the course of the 21st century over Austria on an annual basis compared to the reference period 1981–2010 (e.g. RCP4.5 +107 mm, RCP2.6 +63 mm for the period 2071–2100). Considering seasonal differences, winter and spring are getting wetter due to an increase in precipitation and a higher fraction of rainfall as a consequence of rising temperatures. In summer only little changes in the mean of the climatic water balance conditions are visible across the model ensemble (e.g. RCP4.5 ±0 mm, RCP2.6 −2 mm for the period 2071–2100). On the contrary, by analysing changes in return periods of drought events, an increasing risk of moderate and extreme drought events during summer is apparent, a signal emerging within the climate system along with increasing warming.
{"title":"Apparent contradiction in the projected climatic water balance for Austria: wetter conditions on average versus higher probability of meteorological droughts","authors":"K. Haslinger, W. Schöner, J. Abermann, G. Laaha, K. Andre, M. Olefs, R. Koch","doi":"10.5194/nhess-23-2749-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2749-2023","url":null,"abstract":"Abstract. In this paper future changes of surface water availability in Austria are investigated. We use an ensemble of downscaled and bias-corrected regional climate model simulations of the EURO-CORDEX initiative under moderate mitigation (RCP4.5) and Paris Agreement (RCP2.6) emission scenarios. The climatic water balance and its components (rainfall, snow melt, glacier melt and atmospheric evaporative demand) are used as indicators of surface water availability, and we focus on different altitudinal classes (lowland, mountainous and high alpine) to depict a variety of processes in complex terrain. Apart from analysing the mean changes of these components, we also pursue a hazard risk approach by estimating future changes in return periods of meteorological drought events of a given magnitude as observed in the reference period. The results show, in general, wetter conditions over the course of the 21st century over Austria on an annual basis compared to the reference period 1981–2010 (e.g. RCP4.5 +107 mm, RCP2.6 +63 mm for the period 2071–2100). Considering seasonal differences, winter and spring are getting wetter due to an increase in precipitation and a higher fraction of rainfall as a consequence of rising temperatures. In summer only little changes in the mean of the climatic water balance conditions are visible across the model ensemble (e.g. RCP4.5 ±0 mm, RCP2.6 −2 mm for the period 2071–2100). On the contrary, by analysing changes in return periods of drought events, an increasing risk of moderate and extreme drought events during summer is apparent, a signal emerging within the climate system along with increasing warming.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49475774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-03DOI: 10.5194/nhess-23-2737-2023
K. Nissen, M. Wilde, Thomas M. Kreuzer, A. Wohlers, B. Damm, U. Ulbrich
Abstract. The effect of climate change on rockfalls in the German low mountain regions is investigated following two different approaches. The first approach uses a logistic regression model that describes the combined effect of precipitation, freeze–thaw cycles, and fissure water on rockfall probability. The climate change signal for the past 6 decades is analysed by applying the model to meteorological observations. The possible effect of climate change until the end of the century is explored by applying the statistical model to the output of a multi-model ensemble of 23 regional climate scenario simulations. It is found that the number of days per year exhibiting an above-average probability for rockfalls has mostly been decreasing during the last few decades. Statistical significance is, however, present at only a few sites. A robust and statistically significant decrease can be seen in the Representative Concentration Pathway (RCP) climate scenario 8.5 (RCP8.5) simulations for Germany and neighbouring regions, locally falling below −10 % when comparing the last 30 years of the 20th century to the last 30 years of the 21st century. The most important factor determining the projected decrease in rockfall probability is a reduction in the number of freeze–thaw cycles expected under future climate conditions. For the second approach four large-scale meteorological patterns that are associated with enhanced rockfall probability are identified from reanalysis data. The frequency of all four patterns exhibits a seasonal cycle that maximises in the cold half of the year (winter and spring). Trends in the number of days that can be assigned to these patterns are determined both in meteorological reanalysis data and in climate simulations. In the reanalysis no statistically significant trend is found. For the future scenario simulations all climate models show a statistically significant decrease in the number of rockfall-promoting weather situations.
{"title":"A decrease in rockfall probability under climate change conditions in Germany","authors":"K. Nissen, M. Wilde, Thomas M. Kreuzer, A. Wohlers, B. Damm, U. Ulbrich","doi":"10.5194/nhess-23-2737-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2737-2023","url":null,"abstract":"Abstract. The effect of climate change on rockfalls in the German low mountain regions is investigated following two different approaches. The first approach uses a logistic regression model that describes the combined effect of precipitation, freeze–thaw cycles, and fissure water on rockfall probability. The climate change signal for the past 6 decades is analysed by applying the model to meteorological observations. The possible effect of climate change until the end of the century is explored by applying the statistical model to the output of a multi-model ensemble of 23 regional climate scenario simulations. It is found that the number of days per year exhibiting an above-average probability for rockfalls has mostly been decreasing during the last few decades. Statistical significance is, however, present at only a few sites. A robust and statistically significant decrease can be seen in the Representative Concentration Pathway (RCP) climate scenario 8.5 (RCP8.5) simulations for Germany and neighbouring regions, locally falling below −10 % when comparing the last 30 years of the 20th century to the last 30 years of the 21st century. The most important factor determining the projected decrease in rockfall probability is a reduction in the number of freeze–thaw cycles expected under future climate conditions. For the second approach four large-scale meteorological patterns that are associated with enhanced rockfall probability are identified from reanalysis data. The frequency of all four patterns exhibits a seasonal cycle that maximises in the cold half of the year (winter and spring). Trends in the number of days that can be assigned to these patterns are determined both in meteorological reanalysis data and in climate simulations. In the reanalysis no statistically significant trend is found. For the future scenario simulations all climate models show a statistically significant decrease in the number of rockfall-promoting weather situations.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46283256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-02DOI: 10.5194/nhess-23-2719-2023
G. Romano, M. Antonellini, D. Patella, A. Siniscalchi, A. Tallarico, Simona Tripaldi, A. Piombo
Abstract. Mud volcanoes are fluid escape structures allowing for surface venting of hydrocarbons (mostly gas but also liquid condensates and oils) and water–sediment slurries. For a better understanding of mud volcano dynamics, the characterization of the fluid dynamics within mud volcano conduits; the presence, extent, and depth of the fluid reservoirs; and the connection among aquifers, conduits, and mud reservoirs play a key role. To this aim, we performed a geoelectrical survey in the Nirano Salse Regional Nature Reserve, located at the edge of the northern Apennines (Fiorano Modenese, Italy), an area characterized by several active mud fluid vents. This study, for the first time, images the resistivity structure of the subsoil along two perpendicular cross sections down to a depth of 250 m. The electrical models show a clear difference between the northern and southern sectors of the area, where the latter hosts the main discontinuities. Shallow reservoirs, where fluid muds accumulate, are spatially associated with the main fault/fracture controlling the migration routes associated with surface venting and converge at depth towards a common clayey horizon. There is no evidence of a shallow mud caldera below the Nirano area. These findings represent a step forward in the comprehension of the Nirano Salse plumbing system and in pinpointing local site hazards, which promotes safer tourist access to the area along restricted routes.
{"title":"Fluid conduits and shallow-reservoir structure defined by geoelectrical tomography at the Nirano Salse (Italy)","authors":"G. Romano, M. Antonellini, D. Patella, A. Siniscalchi, A. Tallarico, Simona Tripaldi, A. Piombo","doi":"10.5194/nhess-23-2719-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2719-2023","url":null,"abstract":"Abstract. Mud volcanoes are fluid escape structures allowing for surface venting of hydrocarbons (mostly gas but also liquid condensates and oils) and water–sediment slurries. For a better understanding of mud volcano dynamics, the characterization of the fluid dynamics within mud volcano conduits; the presence, extent, and depth of the fluid reservoirs; and the connection among aquifers, conduits, and mud reservoirs play a key role. To this aim, we performed a geoelectrical survey in the Nirano Salse Regional Nature Reserve, located at the edge of the northern Apennines (Fiorano Modenese, Italy), an area characterized by several active mud fluid vents. This study, for the first time, images the resistivity structure of the subsoil along two perpendicular cross sections down to a depth of 250 m. The electrical models show a clear difference between the northern and southern sectors of the area, where the latter hosts the main discontinuities. Shallow reservoirs, where fluid muds accumulate, are spatially associated with the main fault/fracture controlling the migration routes associated with surface venting and converge at depth towards a common clayey horizon. There is no evidence of a shallow mud caldera below the Nirano area. These findings represent a step forward in the comprehension of the Nirano Salse plumbing system and in pinpointing local site hazards, which promotes safer tourist access to the area along restricted routes.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48944296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-01DOI: 10.5194/nhess-23-2649-2023
Yimei Huang
Abstract. The data of debris-flow events between 2004 and 2021 in the Shenmu area Taiwan are presented and discussed in this paper. A total of 20 debris-flow events were observed in 18 years. Debris flows in the Shenmu area usually occurred in the Aiyuzi Stream during the rainy season, May to September, and about once per year between 2009 and 2017. The rainfall thresholds from the observed data are proposed to be Imax (maximum hourly rainfall), R24 (24 h accumulated rainfall), and Rt (effective accumulated rainfall) of 9, 23, and 67.8 mm, respectively. The rainfall data also imply that the trend curves of intensity–duration (I–D) were different before and after 2009, which is due to the extreme rainfall event of Typhoon Morakot in 2009. The I–D curve obtained from the post-2009 data is proposed as the baseline of the debris-flow I–D relationship in the study area. The extreme rainfall event also influenced the flow speed (average 14.3 m s−1 before 2010 and 4.46 m s−1 after 2010) and the occurrence frequency of debris flows (1.83 times per year before 2009 and 0.75 times after 2009). Recent findings have indicated that the ground surface vibrational signals of debris flows are potentially useful for debris-flow early warning in terms of accumulated energy, and the characteristic frequency of debris flows in the study area was below 40 Hz. The dataset and the rainfall thresholds in this study permit comparison with other monitored catchments and are useful for global debris-flow datasets.
摘要本文介绍并讨论了台湾神木地区2004～2021年的泥石流资料。在18年中总共观测到20次泥石流事件。神木地区的泥石流通常发生在5月至9月的雨季，大约在2009年至2017年间每年发生一次。观测数据中的降雨量阈值建议为Imax （最大小时降雨量），R24（24 h累积降雨量），Rt（有效累积降雨量）分别为9、23和67.8 mm。降雨数据还表明，2009年前后强度-持续时间（I–D）的趋势曲线有所不同，这是由于2009年莫拉克台风的极端降雨事件。从2009年后的数据中获得的I–D曲线被提议作为研究区域泥石流I–D关系的基线。极端降雨事件也影响了流速（平均14.3 m 2010年之前的s−1和4.46 m s−1）和泥石流发生频率（2009年前每年1.83次，2009年后每年0.75次）。最近的研究结果表明，泥石流的地表振动信号在累积能量方面有可能用于泥石流预警，研究区域的泥石流特征频率低于40 赫兹。本研究中的数据集和降雨量阈值允许与其他监测流域进行比较，并可用于全球泥石流数据集。
{"title":"Characteristics of debris flows recorded in the Shenmu area of central Taiwan between 2004 and 2021","authors":"Yimei Huang","doi":"10.5194/nhess-23-2649-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-2649-2023","url":null,"abstract":"Abstract. The data of debris-flow events between 2004 and 2021 in\u0000the Shenmu area Taiwan are presented and discussed in this paper. A total of\u000020 debris-flow events were observed in 18 years. Debris flows in\u0000the Shenmu area usually occurred in the Aiyuzi Stream during the rainy\u0000season, May to September, and about once per year between 2009 and 2017. The rainfall thresholds from the observed data are proposed to be Imax (maximum hourly rainfall),\u0000R24 (24 h accumulated rainfall), and Rt (effective accumulated rainfall) of 9, 23, and 67.8 mm, respectively. The rainfall data also imply that the trend curves of intensity–duration (I–D) were different before and after 2009, which is due to the extreme rainfall event of Typhoon Morakot in 2009. The I–D curve obtained from the post-2009 data is proposed as the baseline of the debris-flow I–D relationship in the study area. The extreme rainfall event also influenced the flow speed (average 14.3 m s−1 before 2010 and 4.46 m s−1 after 2010) and the occurrence frequency of debris flows (1.83 times per year before 2009 and 0.75 times after 2009). Recent findings have\u0000indicated that the ground surface vibrational signals of debris flows are\u0000potentially useful for debris-flow early warning in terms of accumulated\u0000energy, and the characteristic frequency of debris flows in the study area\u0000was below 40 Hz. The dataset and the rainfall thresholds in this study\u0000permit comparison with other monitored catchments and are useful for\u0000global debris-flow datasets.\u0000","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":4.6,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44347983","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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