Frequency Of Flood Events Research Articles

A GIS-Cellular Automata-Based Model for Coupling Urban Sprawl and Flood Susceptibility Assessment

In Urban Planning (UP), it is necessary to take under serious consideration the inhibitors of the spread of a settlement in a specific direction. This means that all those parameters for which serious problems may arise in the future should be considered. Among these parameters are geo-hazards, such as floods, landslides, mud movement, etc. This study deals with UP taking into account the possibility of widespread flooding in settlement expansion areas. There is a large flooding history in Greece, which is accompanied by a significant number of disasters in different types of land use/land cover, with a large financial cost of compensation and/or rehabilitation. The study area is the drainage basin of Erasinos River in the Attica Region, where many and frequent flood events have been recorded. The main goal of this study is to determine the flood susceptibility of the study area, taking into account possible factors that are decisive in flood occurrence. Furthermore, the flood susceptibility is also determined, taking into account the scenarios of precipitation and the urban sprawl scenario in the area of reference. The study of flood events uses the Analytic Hierarchy Process (AHP) model and the urban sprawl model SLEUTH, which calibrates historical urban growth, using open and cost-free data and software. Eventually, flood susceptibility maps were overlaid with future urban areas to find the vulnerable areas. Following, three scenarios of flood susceptibility with the corresponding susceptibility maps and vulnerability maps, which measure the flood susceptibility of the current and future urban space of the study area, are presented. The results have shown significant peaks in the moderate class of flood susceptibility, while, in the third scenario, high values of flood susceptibility seem to appear. The proposed methodology and specifically the output maps can serve as a decision support tool to assist urban planners and hazard managers in making informed decisions towards sustainable urban planning.

Grassroots mobilization in Brazil’s urban Amazon: Global investments, persistent floods, and local resistance across political and legal arenas

• We analyze how the urban poor mobilize against floods in the context of a major urban development project in Latin America. • We find a mix of optimism and skepticism regarding the potential changes brought by political and legal mobilization. • The judicialization of flood-related claims in the legal arena coexists with social mobilization in the political arena. • For grassroots movements, litigating against social-ecological injustices is a means to foster better urban governance. By the 1980s, the Brazilian Amazon was already an urbanized forest. A large portion of its population was living in non-rural areas attracted by better service provisioning and economic opportunities in fast-developing urban centers. Located at the Amazon Estuary-Delta, Belém is the Amazon’s largest metropolitan area, marked by informal urban expansion, and serving as an illustrative case of the opportunities and challenges with which urban populations deal in the region. Faced with significant pressures of absent infrastructure, high rates of poverty, precarious settlements, and ever more frequent flood events, already in the 1980s, Belém was home to the biggest urban reform project of its time in Latin America: The Macro-Drainage Project of the Una River Watershed. Costing over 300 million USD, the project was intended to have a multilevel governance system through which the Inter-American Development Bank and local government could coordinate project activities. Yet, due to the combination of poor infrastructure and changing rainfall patterns, about half a million people currently remain vulnerable to flood hazards and property damages. Our analysis uses a socio-legal approach to studying grassroots mobilization against the violation of social and environmental rights aggravated by floods. We also draw on Ostrom’s concepts of action arena and action situation to examine collective action across political and legal arenas within which individuals, grassroots organizations, and the state negotiate/contest flood-related issues. Conducting archival and ethnographic research, we find a story of conflict and cooperation between the civil society and political and legal actors, which accounts for a mix of optimism and skepticism regarding the improvement in the livelihood of the urban poor affected by this developmental program. This interdisciplinary lens contributes to understanding the limits and potentials of collective action to address, whether through political and/or legal mobilization, urban inequalities and social vulnerability to environmental and climate change.

홍수기 농경지 침수 피해 분석

A severe rain storm that occurred on July 16, 2017, caused flooding of paddy fields and rural houses south of Osong Biovalley. To analyze the flood event that occurred in the Cheongju area and to verify its effects on the Osong area, rainfall frequency analysis was evaluated based on the observed hydrological data. The recurrence frequency of flood events was estimated through rainfall frequency analysis, and the effect of flood events on the estimation of probable rainfall was confirmed. The GATE2012 flood simulation program was used to analyze the flood-damaged area. The program simulation was performed by dividing it into the case where the inflow of the generated discharge within the study area was not reflected and the case where it was reflected. In the case of not reflecting the inflow of the generated discharge, it was divided into the non-operational and normal operation of the pumping and drainage station, and in the case of consideration, the generated discharge was changed and the inundation analysis was performed by classifying it into nine cases. Through this study, it is to improve the reliability of the analysis of flood damage in paddy fields during floods and to contribute to the establishment of a flood prevention plan.

Climatic Hazards and Societal Vulnerability, Resilience and Adaptation in the Flood Zones of Nsanje District, Malawi

This study has assessed societal vulnerability, resilience and adaptation variables to floods in the disaster predisposed Nsanje district, Malawi. The district stands amongst the most affected region by frequent flooding events. This research has deployed quantitative research approach by collecting primary data through self-administered structured questionnaires at the household level. To study the said variables, IPCC’s Livelihood Vulnerability Index (LVI) was deployed for all sub-components of LVI: adaptive capacity, exposure and susceptibility. Also, to determine the influencing factors of livelihood vulnerability, the Ordinary Least Square (OLS) model for regression, where LVI for each household was computed. The other factors hypothesized as influencers of Livelihood Vulnerability were used as explanatory parameters, besides deployment of Stata (SE 14.0) for data analysis. Results declared T/A Ngabu as the most vulnerable area (LVI-IPCC value of 0.027267625), as compared to T/A Tengani (LVI-IPCC value of -0.044597798) in Nsanje district. The regression model estimation output revealed; flood experience, unavailability of warning alert, household proximity to the flooding river, injuries and death, beliefs and altitude, and non-availability of safe living facilities as being the determinants to influence societal exposure to floods in the studied area. The adaptive capacity components were found as being influenced by socio-demographic traits; age, sex, education level, disability, access to credit facilities, government assistance, income diversification, income level, social networking. Societal sensitivity component was established in a significant relationship with; access to health facilities and ability to save seeds, whereas saving food and seeds, irrigation, bank credit, borrowing from family/friends, loan sharks and government assistance were identified as resilience strategies. Lastly, construction of small local dikes and drainage system, elevating the house wall, planting trees in catchment areas and temporary family relocations were remained as the adaptation mechanisms in the area. The study calls for planned relocation, government’s intervention and provision of (non-/tangible) assistance to avoid further societal prey to climatic hazards, exposure and vulnerability in the most affected country side.

Non-stationary Investigation of Extreme Rainfall

Natural or human-induced variability emerged from investigation of the traditional stationary assumption regarding extreme precipitation analyses. The frequency of extreme rainfall occurrence is expected to increase in the future and neglecting these changes will result in the underestimation of extreme events. However, applications of extremes accept the stationarity that assumes no change over time. Thus, non-stationarity of extreme precipitation of 5, 10, 15, and 30 minutes and 1-, 3-, 6-, and 24-hour data of 17 station in the Black Sea region were investigated in this study. Using one stationary and three non-stationary models for every station and storm duration, 136 stationary and 408 non-stationary models were constructed and compared. The results are presented as non-stationarity impact maps across the Black Sea Region to visualize the results, providing information about the spatial variability and the magnitude of impact as a percentage difference. Results revealed that nonstationary (NST) models outperformed the stationary model for almost all precipitation series at the 17 stations. The model in which time dependent location and scale parameter used (Model 1), performed better among the three different time variant non-stationary models (Model 1 as time variant location and scale parameters, Model 2 as time variant location parameter, and Model 3 as time variant scale parameter). Furthermore, non-stationary impacts exhibited site-specific behavior: Higher magnitudes of non-stationary impacts were observed for the eastern Black Sea region and the coastal line. Moreover, the non-stationary impacts were more explicit for the sub-hourly data, such as 5 minutes or 15 minutes, which can be one of the reasons for severe and frequent flooding events across the region. The results of this study indicate the importance of the selected covariate and the inclusion of it for the reliability of the model development. Spatial and temporal distribution of the nonstationary impacts and their magnitude also urges to further investigation of the impact on precipitation regime, intensification, severity. Doi: 10.28991/cej-2021-03091748 Full Text: PDF

Unpacking Adaptive Capacity to Flooding in Urban Environments: Social Capital, Social Vulnerability, and Risk Perception

To effectively cope with the impacts of climate change and increase urban resilience, households and neighborhoods must adapt in ways that reduce vulnerability to climate-related natural hazards. Communities in the United States and elsewhere are exposed to more frequent extreme heat, wildfires, cyclones, extreme precipitation, and flooding events. Whether and how people respond to increased hazard exposure (adaptive behavior) is widely recognized to be driven by their capacity to adapt, perception of the risk, and past experiences. Underlying these important dimensions, however, is social context. In this paper, we examine how social capital and social vulnerability shape risk perception and household flood mitigation actions. The study, based on a metropolitan-wide survey of households in Austin, Texas, USA, suggests that bonding social capital (personal networks, neighborhood cohesion, and trust) is positively related to mitigation behavior and that social vulnerability is negatively related to risk perception. Importantly, our research demonstrates a positive and significant effect of social capital on adaptive behavior even when controlling for social vulnerability of a neighborhood. This suggests that policies and programs that strengthen the social connectedness within neighborhoods can increase adaptive behaviors thus improving community resilience to flood events.

Vertical Distribution of Aerosols during Deep-Convective Event in the Himalaya Using WRF-Chem Model at Convection Permitting Scale

The Himalayan region is facing frequent cloud bursts and flood events during the summer monsoon season. The Kedarnath flooding of 2013 was one of the most devastating recent events, which claimed thousands of human lives, heavy infrastructure, and economic losses. Previous research reported that the combination of fast-moving monsoon, pre-existing westerlies, and orographic uplifting were the major reasons for the observed cloud burst over Kedarnath. Our study illustrates the vertical distribution of aerosols during this event and its possible role using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) simulations. Model performance evaluation shows that simulations can capture the spatial and temporal patterns of observed precipitation during this event. Model simulation at 25 km and 4 km horizontal grid resolution, without any changes in physical parameterization, shows a very minimal difference in precipitation. Simulation at convection-permitting scale shows detailed information related to parcel motion compared to coarser resolution. This indicates that the parameterization at different resolutions needs to be further examined for a better outcome. The modeled result shows changes of up to 20–50% in the rainfall over the area near Kedarnath due to the presence of aerosols. Simulation at both resolutions shows the significant vertical transport of natural (increases by 50%+) and anthropogenic aerosols (increases by 200%+) during the convective event, which leads to significant changes in cloud properties, rain concentration, and ice concentration in the presence of these aerosols. Simulations can detect changes in important instability indices such as convective available potential energy (CAPE), convective inhibition energy (CIN), vorticity, etc., near Kedarnath due to aerosol–radiation feedback.

Identifying and addressing drinking water challenges in well-reliant communities after natural disasters: lessons from a Louisiana flood

BACKGROUND AND AIM: The 2016 Louisiana flood caused extensive structural damage to private drinking water wells, which were submerged under several feet of contaminated surface water for days. Well-reliant communities, which make up 13% of Louisiana’s population, are solely responsible for ensuring the safety of their water. The aims of this study are to evaluate private well user preparedness and recovery, and develop recommendations for flood-prone well-reliant communities. METHODS: A convenience sample of flood-impacted well owners was surveyed and offered free well water testing ten weeks after flood waters subsided (n=106). Surveys collected information to characterize knowledge gaps, risk perceptions, flood impacts, resource accessibility, and well maintenance barriers; while water tests evaluated total coliform and E. coli. RESULTS:Surveyed well owners needed information on well testing labs (90%), water contamination (77%), and water treatment (78%). Of respondents with flooded wells (n=75), one-third resided in low flood risk zones, indicating a need for improved risk determinations. After the flood, over half (57%) of flood-impacted well users (n=75) continued consuming well water after the flood; yet, 26% had water which tested positive for total coliforms. 69% of well users who resumed well water consumption (n=43) disinfected their water, but testing indicated that microbes can continue to regrow or re-enter wells. CONCLUSIONS:Results suggest that well owners lack the knowledge, means, resources, or motivation to protect well water and treat water adequately after floods. In addition, disinfection methods may be either insufficient, will not work due to well system failures, or are conducted incorrectly. Recommendations are made to enhance emergency response communications, and to improve well water surveillance. As the likelihood that more frequent and severe flooding events will increase, officials need to update and enhance technical resources, and provide well user training to facilitate well user preparedness, self-reliance and resilience. KEYWORDS: Flood, private well, well water, disaster preparedness, natural disaster

Climate Change Impacts on Rice Cultivation: A Comparative Study of the Tonle Sap and Mekong River

Climate change is unequivocal. Farmers are increasingly vulnerable to floods and drought. In this article, the negative impact of climate hazards on rice cultivation in the Tonle Sap and Mekong River influenced by climatic variability between 1994 and 2018 are analyzed. A cohort of 536 households from four Cambodian districts participated in household surveys designed to consider how various vulnerability factors interacted across this time series. It was found that: (i) The major climate hazards affecting rice production between 1994 and 2018 were frequent and extreme flood and drought events caused by rainfall variability; (ii) In 2018, extreme flood and drought occurred in the same rice cultivation cycle. The impact caused by each hazard across each region were similar; (iii) An empirical model was used to demonstrate that drought events tend to limit access to irrigation, impact rice production, and result in an increased prevalence of water-borne diseases. Flood events cause reduced rice production, damage to housing, and impede children from accessing education. The impact of drought events on rice production was found to be more severe than flood events; however, each climatic hazard caused physical, economic, social, and environmental vulnerabilities. It is recommended that sufficient human and financial resources are distributed to local authorities to implement adaptation measures that prepare rice farmers for flood and drought events and promote equitable access to water resources.

Cytotoxicity analysis of pre- and post-hurricane harvey soil samples collected from greater houston bayous

Rapid urbanization, anthropogenic pollution and frequent flooding events are affecting the soil and water quality along the streams and bayous of Houston. Soil acts as sink and reservoir of heavy metals and nutrients affecting human and animal health. The objectives of the study are 1) to analyze the effects of the metal and nutrient concentration of bayou flood plain surface soil samples on the gut cell cytotoxicity and 2) to evaluate the spatial and temporal difference in soil contamination on cell viability of colon cancer (HT-29) and normal colon epithelial (CCD 841 CoN) cell lines. To evaluate soil contamination between pre- and post-hurricane (Summer and Fall) conditions in six Bayous (Brays, Buffalo, Halls, Hunting, Greens and White Oak Bayous) of Harris County, Texas, in vitro bioassay analysis was applied to soil extracts. The MTT assay determined that, with increase in concentration of Bayou soil from 12.5% to 100%, the viability of CCD 841 CoN and HT-29 cells decreased significantly, across all sampling locations during both summer and fall seasons. Among all the bayous, the viability of CCD 841 CoN cells in summer and fall followed the pattern of White Oak > Greens > Halls > Brays Bayou, where the viability of cells exposed to White Oak soils was 3–4 times higher than cells exposed to Brays Bayou soil at 100% soil concentration. The viability of HT-29 cells in both seasons followed the pattern of Greens > White Oak > Halls > Brays Bayou, where the viability of cells exposed to Greens Bayou soil was more than 3–4 times higher than the cells exposed to Brays Bayou soil at 100% concentration. The higher concentration of metals and nutrients such as P, Zn, Cd, and Cu might have contributed to the significant cell lethality in Brays Bayou samples compared to other locations.

The Delphi method to identify attributes for a valuation approach for residential property exposed to flood risk

PurposeThis study is aimed to identify the attributes for a valuation approach of flood risk exposure, in particular for residential property. With frequent flood events in Malaysia, there is a need for valuation methods to evolve and represent the increased risk of natural disasters.Design/methodology/approachThis study employed the Delphi method which is a systematic and interactive research technique in obtaining variables for a valuation approach for residential property exposed to flood risk.FindingsResults from the Delphi method revealed four categories of attributes, namely environmental, locational, structural and economical.Originality/valueThe findings from this research will transform the valuation approach in Malaysia to identify the value of residential property exposed to flood risk. The determination of variables will represent the current risk in valuations, especially for residential property in flood-prone areas.

AGENCIES' MANAGEMENT PREPARATIONS AND PROPOSED EVACUATION ROUTES FOR FLOOD DISASTER: A CASE STUDY OF MELAKA

The research focuses on the flooding event in Melaka. Flooding has been occurring so frequently in Melaka that assessing the management and preparation for flooding needs to be undertaken. Alor Gajah, Melaka has been selected as a case study because frequent flooding events in the district affected many people. Using FGD as a data collection method, the result showed there is no management structure of flooding events beyond the district level and a proper training for the community is required before the structure can be developed. The original hierarchy and functions under Directive 20 should be maintained. This research suggested a proper institutionalisation of flood management and flood rehabilitation structure for Alor Gajah's district.

Urban Flood Management through Urban Land Use Optimization Using LID Techniques, City of Addis Ababa, Ethiopia

In recent years, many urban areas in Ethiopia have experienced frequent flood events as a result of climate change and urban sprawl. Unplanned and unsustainable poor urban storm water management strategies will aggravate the impact and frequency of flood occurrence. In this study, impacts of urbanization and climate change on generated flood magnitude are analyzed using the urban hydrological model of Storm Water Management Model (SWMM) and Low Impact Development (LID) sustainable land use optimization techniques. Three rainfall distribution patterns (TS1, TS2 and TS3) in combination with rainfall duration periods of 10, 30 and 60 min and a pessimistic climate change scenario of RCP 4.5 compared to RCP 8.5 are used for the analysis purpose for selected infiltration and storage LID techniques (Bio-Retention Cell, Infiltration Trench and Rain Barrel). The study results showed that combined LID techniques have a significant impact on urban flood reduction of up to 75%. This significant amount of flood reduction is greater than the amount of excess flood magnitude which occurred as a result of climate change using the most pessimistic climate change scenario. The study results also confirmed that rainfall patterns have a significant impact on peak discharge for shorter rainfall durations. This study highly recommends using cost effective, easy and environmental adaptive and sustainable LID techniques for urban flood management in addition to existing drainage structures.

Source, transport and fate of terrestrial organic carbon from Yangtze River during a large flood event: Insights from multiple-isotopes (δ13C, δ15N, Δ14C) and geochemical tracers

Climate change-triggered episodic and intensive flood events are increasing in frequency globally; these events play a disproportionate role in the carbon cycle at land-ocean interfaces by influencing the delivery of terrestrial organic matter to the sea. However, the transport and burial of flood-driven terrestrial organic carbon (Corg) in river-dominated marginal seas remains poorly understood. Here, water column particles (surface, intermediate, and bottom layers) and surface sediments from the Yangtze River estuary system were collected during a large flooding event (>60,000 m3 s−1) for a multiproxy geochemical study. We analyzed N/C, δ13Corg, δ15N, F14C, grain size, and elemental (Al and Si) to characterize the sources, ages, and alterations of particulate organic carbon (POC) and sedimentary Corg from the river channel to the estuarine mixing zone to the continental shelf and fingerprint the fate of Corg burial in marine sediments.We found that terrestrial POC delivered by the Yangtze flood is characterized by low F14C (0.625 ± 0.002; Δ14C = −379.8 ± 2.3‰, 14C age = 4,135 yr before present (BP)) and δ13Corg (−27.1 ± 0.5‰) values and high δ15N (3.9 ± 0.6‰), and N/C (0.15 ± 0.01) values, and was adsorbed on fine-grained particles. Using a Bayesian-Monte Carlo simulation approach, we estimated that terrestrial POC is dominated by C3 plant detritus (42 ± 16% on average), followed by petrogenic organic carbon (33 ± 7%), and soil (26 ± 22%). Moving offshore, hydrodynamic sorting of lithogenic particles exerts first-order control on POC by selecting particles with unique signatures. Petrogenic organic carbon and aged plant debris associated with coarse-sized particles preferentially accumulated within the proximal delta, whereas POC derived from catchment soil and adsorbed on fine-grained particles was transported offshore along the sediment dispersion system. We estimated that, on average, 76 ± 18% of POC initially present in the water column is oxidized at the water column-seabed interface during seaward transport and constitutes a source of atmospheric carbon dioxide. In contrast, the stable form of the organic matter-aluminosilicate mineral association controls the preservation of the sedimentary Corg. Our results suggest that frequent flooding events in the near future will likely increase lithospheric Corg delivery to marine sediments and have the potential to promote petrogenic Corg burial efficiency in the river-dominated marginal seas and accelerate biospheric POC oxidation and CO2 release, thus generating a positive feedback to global warming.

Climate change and variability awareness and livelihood adaptive strategies among smallholder farmers in semi-arid northern Ghana

This study examined smallholder farmers' observation of climate change and variability, its effect on agricultural output, and the livelihood adaptive strategies being used in response to such dynamic changes. A total of 121 smallholder farmers were randomly selected from three vulnerable rural farming communities in northern Ghana through a mixed methodological approach involving household surveys, interviews and focus group discussions. Data were analysed using descriptive and binary logistic regression with the help of IBM SPSS statistical software package integrated with qualitative thematic analysis involving transcription, categorization and interconnecting. The results show that majority (95.9%) of the smallholders have observed climatic changes in their local ecology with manifestations involving protracted drought (95.9%), unpredictable rainfall pattern (94.2%), high temperature (99.2%), strong winds (66.9%) and frequent flood events (99.2%). As a consequence, smallholders have observed that changes in temperature (99.2%) and rainfall patterns (97.5%) result in decreased agricultural output. In resolving the impacts, these smallholders employ preferred livelihood adaptive strategies involving non-farm diversification (51.2%), crop diversification (75.2%), changes in farm location (76.9%) and agrochemical application (100%) with moderate or high levels of effectiveness across space. The logistic regression results revealed that factors such as age, gender and access to credit significantly influenced smallholder farmers’ observation and adaptation to climate change and variability. The findings suggest the need for a location-specific climate adaptation policy. By this, the local knowledge, adaptive capacity and resilience of smallholder farmers could be built upon to mitigate their vulnerability to food insecurity and poverty.

\u201cListening to the Sounds of the Water\u201d: Bringing Together Local Knowledge and Biophysical Data to Understand Climate-Related Hazard Dynamics

Integrating local knowledge and scientific information can aid in co-developing locally relevant approaches for climate change adaptation and disaster risk reduction. Communities along the Mekong River have adapted to variability in temperature, rainfall, and flooding patterns over time. Rapid environmental change in the Mekong Basin presents a new set of challenges related to drought, altered seasonal rainfall, more frequent high-flow flood events, and water withdrawals for hydropower and irrigation. We present a multi-method approach to understand how local knowledge of the spatial and temporal patterns of floods, droughts, and rainfall can be integrated with scientific information along a flood-prone section of the lower Mekong River in Kratie Province, Cambodia. Participatory hazard mapping of community members’ knowledge of the movement of floodwaters through the landscape enabled interpretation of flood extent mapping using Synthetic Aperture Radar images from the Sentinel-1A satellite. Seasonal calendars of weather patterns and livelihood activities, together with local indicators of flooding, rainfall, and drought were compared with trends in 35 years of rainfall data, and highlighted “pressure points” at the beginning and end of the rainy season where agriculture may be particularly impacted by climate change. We discuss potential applications of our findings for adaptation and hazard planning.

Evaluation and comparison of morphometric parameters of Savitri watershed, India

The morphometric assessment has proved to be effective in recognizing and analyzing the neotectonic signatures governing a particular drainage basin. Studies on morphometric properties involving the linear, areal, and relief aspects are vital as it aids in evaluating the hydrological response and prioritization of watersheds. The present research attempts to investigate and compare the morphometric parameters of the Savitri watershed considering two datasets, i.e., topographical sheet and digital elevation model over two time periods. The Savitri is designated as a seventh-order basin with a dendritic pattern covering a total area of 1966.34 km2. The average bifurcation ratio is 3.8 which confirms that the network of the drainage in the basin is not regulated by the underlying rock structure. Moreover, the drainage density and stream frequency values have shown marked changes that might be attributed to both natural and injudicious human activities, thus affecting the nature of the basin. The relief analysis of the basin indicates that most of the areas of the basin have gentle to flat gradient favoring frequent flood events.

Seven decades of hydrogeomorphological changes in a near‐natural (Sense River) and a hydropower‐regulated (Sarine River) pre‐Alpine river floodplain in Western Switzerland

ABSTRACTHydropower alteration of the natural flow and sediment regime can severely degrade hydromorphology, thereby threatening biodiversity and overall ecosystem processes of rivers and their floodplains. Using sequences of aerial images, we quantified seven decades (1938/1942–2013) of spatiotemporal changes in channel and floodplain morphology, as well as changes in the physical habitats, of three floodplain river reaches of the Swiss pre‐Alps, two hydropower‐regulated and one near‐natural. In the Sarine River floodplain, within the first decades of hydropower impairment, the magnitude and frequency of flood events (Q2, Q10, Q30) decreased substantially. As a result, the area of pioneer floodplain habitats that depend on flood activity and sediment dynamic, such as bare sediments, decreased dramatically by approximately 95%. However, by 2013 vegetated areas had generally increased in comparison to the pre‐regulation period in 1943, indicating general vegetative colonization. Between 1943 and 2013, the active channel underwent essential narrowing (up to 62% width reduction in the residual flow reach) and habitat turnover rates were very low (5% of the total floodplain area changed habitat type five to six times). In contrast, from the 1950s onwards, the near‐natural floodplain of the Sense River experienced recurrent narrowing and widening, and frequent changes between bare and vegetated areas, reflecting the shifting habitat mosaic concept typical for natural floodplains. In the three reaches investigated, we found that the active floodplain width and erosion of vegetated areas were primarily controlled by medium to large floods (Q10, Q30), which combined with reduced time intervals between ordinary floods ≥ Q2 most likely mobilized streambed sediments and limited the ability of vegetation to establish itself on bare gravel bars within the parafluvial zone. These findings can contribute to restoration action plans such as controlled flooding and sediment replenishments in the Sarine and other floodplain rivers of the Alps. © 2020 John Wiley & Sons, Ltd.

Intensification of Summer Rainfall Extremes over Nigeria during Recent Decades

Rainfall extremes can cause a significant loss of lives and economic losses in Nigeria. This study aims to investigate the trends of summer rainfall extremes over Nigeria with daily station datasets from 1975 to 2013. Using the rainfall extreme indices recommended by the Expert Team on Climate Change Detection Monitoring Indices (ETCCDMI), it is found that regionally averaged summer total wet-day rainfall amount (PRCPTOT), maximum consecutive 5-day rainfall amount (RX5day), and wet-day rainfall intensity (SDII) have increased in the three climatic regions of Nigeria namely Guinea coast, Sub-Sahel, and the Sahel regions. Meanwhile, heavy rainfall days (R20mm) increased significantly over the Guinea coast and sub-Sahel regions, while the wet-day frequency (RR1) only increased slightly. The increase in PRCPTOT over the two regions is mainly resulting from the increasing intensity and frequency of rainfall extremes. However, the Nigerian Sahel is characterized by a decreasing wet-day frequency, which demonstrates that a large proportion of the increasing PRCPTOT in the region is more associated with intense rainfall than its frequency. These characteristic increasing trends of rainfall extremes may explain the frequent flood events over Nigeria and as such this study may give guidance to stakeholders on how best to cope with it in the future.

Vegetation dynamics and Fire History in Färnebofjärden National Park, Central Sweden

Palaeoecological studies can identify past trends in vegetation communities and processes over long time scales. Pollen, plant macrofossils and charcoal analyses are used to reconstruct vegetation over the last 6400 years and provide information about former human impact and disturbance regimes in Färnebofjärden National Park, Central Sweden. Three specific conservation planning topics were addressed: (1) the changing ratio of conifers to broadleaved trees; (2) the origin and history of the river meadows and the biodiverse Populus tremula meadows; (3) the role of fire in the maintenance of biological values. Early diverse mixed broadleaved forest assemblages with pine were followed by significant declines of the more thermophilic forest elements prior to the expansion of spruce in the Iron Age. The rise to dominance of spruce was a ‘natural’ process that has been exaggerated by anthropogenic disturbance to artificially high levels today. The initial river meadow communities were facilitated by fire and frequent flooding events, but subsequent dynamics have more definitely been supported by human activities. Rural abandonment during the last 100 years has led to woody successions. Fire has been a continual disturbance factor with an influence on conservation issues such as Picea abies dominance and the maintenance of diverse, non-forest communities. Present occurrence of fire is unusually low, but natural fire frequencies are increasing in the region.