Floods are causing massive losses of crops and agricultural infrastructures in many regions across the globe. During the 2018/2019 agricultural year, heavy rains from Cyclone Idai caused flooding in ...Central Mozambique and had the greatest impact on Sofala Province. The main objectives of this study are to map the flooding durations, evaluate how long crops survived the floods, and analyse the dynamics of the affected crops and their recovery following various flooding durations using multi-source satellite data. Our results indicate that Otsu method-based flooding mapping provides reliable flood extents and durations with an overall accuracy higher than 90%, which facilitates the assessment of how long crops can survive floods and their recovery progress. Croplands in both Buzi and Tica administrative units were the most severely impacted among all the regions in Sofala Province, with the largest flooded cropland extent at 23,101.1 ha in Buzi on 20 March 2019 and the most prolonged flooding duration of more than 42 days in Tica and Mafambisse. Major summer crops, including maize and rice, could survive when the fields were inundated for up to 12 days, while all crops died when the flooding duration was longer than 24 days. The recovery of surviving crops to pre-flooding status took a much longer time, from approximately 20 days to as long as one month after flooding. The findings presented herein can assist decision making in developing countries or remote regions for flood monitoring, mitigation and damage assessment.
Display omitted
•Image-dependent threshold method precisely extracts flood extent and duration.•Multi-satellite analysis is feasible to quantify the dynamic flood impacts on crops.•Crops could survive even inundate for 12 days, but recovery was slow.•All crops die with flooding durations longer than 24 days.•The Buzi and Tica regions were severely damaged by the 2019 floods in Mozambique.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Flood duration is a crucial parameter for disaster impact assessment as it can directly influence the degree of economic losses and damage to structures. It also provides an indication of the ...spatio-temporal persistence and the evolution of inundation events. Thus, it helps gain a better understanding of hydrological conditions and surface water availability and provides valuable insights for land-use planning. The objective of this work is to develop an automatic procedure to estimate flood duration and the uncertainty associated with the use of multi-temporal flood extent masks upon which the procedure is based. To ensure sufficiently high observation frequencies, data from multiple satellites, namely Sentinel-1, Sentinel-2, Landsat-8 and TerraSAR-X, are analyzed. Satellite image processing and analysis is carried out in near real-time with an integrated system of dedicated processing chains for the delineation of flood extents from the range of aforementioned sensors. The skill of the proposed method to support satellite-based emergency mapping activities is demonstrated on two cases, namely the 2019 flood in Sofala, Mozambique and the 2017 flood in Bihar, India.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•The control of the hydrological pre-conditions and the meteorological event conditions over distinct flood characteristics is analyzed.•Soil moisture patterns as well as weather patterns are not ...only beneficial to inform on flood occurrence but also on the involved processes and resulting flood characteristics.•Flood-causing soil moisture – weather pattern combinations vary throughout the seasons and show different impacts on flood characteristics.
Flood events can be expressed by a variety of characteristics such as flood magnitude and extent, event duration or incurred loss. Flood estimation and management may benefit from understanding how the different flood characteristics relate to the hydrological catchment conditions preceding the event and to the meteorological conditions throughout the event. In this study, we therefore propose a methodology to investigate the hydro-meteorological controls on different flood characteristics, based on the simulation of the complete flood risk chain from the flood triggering precipitation event, through runoff generation in the catchment, flood routing and possible inundation in the river system and floodplains to flood loss. Conditional cumulative distribution functions and regression tree analysis delineate the seasonal varying flood processes and indicate that the effect of the hydrological pre-conditions, i.e. soil moisture patterns, and of the meteorological conditions, i.e. weather patterns, depends on the considered flood characteristic. The methodology is exemplified for the Elbe catchment. In this catchment, the length of the build-up period, the event duration and the number of gauges undergoing at least a 10-year flood are governed by weather patterns. The affected length and the number of gauges undergoing at least a 2-year flood are however governed by soil moisture patterns. In case of flood severity and loss, the controlling factor is less pronounced. Severity is slightly governed by soil moisture patterns whereas loss is slightly governed by weather patterns. The study highlights that flood magnitude and extent arise from different flood generation processes and concludes that soil moisture patterns as well as weather patterns are not only beneficial to inform on possible flood occurrence but also on the involved flood processes and resulting flood characteristics.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Flood-duration–frequency (QdF) analysis is becoming a popular tool for estimating the severity of flood events as an integrated function of return period and flood duration. QdF models are often ...applied in regional flood studies, leading to regional QdF relations derived for hydrologically homogeneous regions. Regional QdF models can be used to estimate flood quantiles for a given return period and flood duration at any ungaged site of a homogeneous region. By combining the information on sampling variability from hydrologically similar neighboring sites, the regional approach to QdF modeling also decreases the estimation uncertainty at gaged sites of the region. Regional QdF models have been developed for stable environmental conditions. Nevertheless, recent studies on stationarity of hydrologic records conducted in different parts of the world have identified significant changes in the statistical parameters of the analyzed records. Changing environmental conditions call for new flood estimation methods that can take into account the nonstationary character of hydrologic records and that can deal with time-dependent parameters of flood frequency distributions. This study defines the key concepts of a nonstationary approach to regional QdF modeling. The proposed approach uses regional trend analysis to identify time-dependent parameters of the model, and to estimate and predict flood quantiles for the present and near future time horizons. The model can be flexibly applied to various scenarios of nonstationarity at both local and regional scales. The approach is illustrated on a set of data from a hydrologically homogeneous region in Québec, Canada. A split-sample experiment is used to compare the performance of the proposed model with the traditional stationary regional QdF model. The case study results demonstrate that ignoring statistically significant nonstationarity of hydrologic records can seriously bias flood quantiles estimated for the near future.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Flooding dynamics across a medium‐size (Janauaca Lake, 786 km2) floodplain system along the Amazon/Solimoes River over a 9‐year period (2006–2015) is studied through integration of remote sensing and ...limited in situ data in hydrologic‐hydrodynamic modelling based on Telemac‐2D model. Model accuracy varies through the hydrological year. We focus on seasonal and interannual spatial variability of water circulation and inundation duration. We highlight strong heterogeneities in water velocity magnitude between the different morphological domains of the floodplain, the highest velocities being encountered in the river‐floodplain channel. In addition to topography, we emphasize the importance of the main channel and the local runoff in controlling the water circulation, at least during part of the hydrological year. From low water to early rising period, local runoff constrains the river incursion across the floodplain, while the rates of main channel rising/receding controls the flood duration. The comparison of several hydrological years highlights the interannual changes of these hydraulic controls and also the influence exerted by prior inundation conditions. While we observed few changes in water velocity distribution among hydrological years, the inundation duration is highly variable. Usually defined by maximum water level, extreme flood events may paradoxically induce positive (up to 40 days) but also negative (up to −20 days) anomalies of inundation duration.
Key Points
Interannual 2‐D water circulation variations are controlled by main channel rising/receding rates, local runoff, and prior inundation condition
Extreme floods induce positive (up to 40 days) or negative (up to −20 days) anomalies of inundation duration
Extreme floods only slightly modify velocity intensity and spatial distribution patterns
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Flooding is a major natural hazard that can cause significant damage to socioeconomic and ecological systems. This study presents an approach to producing the maximum flood inundation and flood ...duration maps over the Chao Phraya River Basin (CPRB), Thailand. An integrated numerical model and spatial analysis tool were utilized in this study. The Rainfall-Runoff-Inundation (RRI) model was first used to simulate both river discharge and inundation depth. Then, the maximum flood inundation and flood duration maps with different return periods were estimated using a Geographical Information System (GIS) tool. The results illustrate that the flood inundation areas were spread out, starting from Nakhon Sawan Province, which is located in the central part of the basin. The maximum flood inundation depth could reach up to approximately 7.71, 8.28, and 8.78 m for the flood return periods of 50, 100, and 200 years, respectively. The results also indicate that the inundation areas over the CPRB could cover approximately 21,837, 23,392, and 24,533 km
2
for flood return periods of 50, 100, and 200 years, respectively. The longest flood durations for return periods of 50, 100, and 200 years were approximately 159, 177, and 198 days, respectively. The longest flood duration occurred in the vicinity of the Nakhon Sawan. This study suggests that flood inundation areas and duration mapping could provide supporting information regarding the impacts caused by varying degrees of flood hazards and can be used to enhance comprehensive disaster risk management planning.
AbstractPrevious literature has shown unsatisfactory validation of the existing equations predicting pier-scour depth with laboratory and field data. In an attempt to find the reasons for the ...unsatisfactory comparisons, we examined the performance of the Chinese equations with several other equations through in-depth analyses of the errors and explored the possible error-causing factors both in field measurement data and the proper use of parameters. Results show that the Chinese equations underpredicted scour depth for all the laboratory data and for field data under clear-water conditions. The Chinese equations performed better for field data under live-bed conditions compared to the other (i.e., laboratory, or clear-water field) conditions. The other equations overpredicted scour depth for both laboratory and field data. Uncertainty of the field data associated with measurement accuracy results in large errors, especially when scour depth is less than 1 m. The flood duration in the field is usually far shorter than what is needed to reach the equilibrium scour depth that the equations are attempting to predict for safe design, which contributes to the larger predicted scour depth than measurements. The effect of some parameters (e.g., sediment size, pier width, and incipient velocity for local pier scour) should be modified in the Chinese equations under fine-sediment and/or wide-pier conditions.
The scarcity of model input and calibration data has limited efforts in reconstructing scenarios of past floods in many regions globally. Recently, the number of studies that use distributed ...post-flood observation data collected throughout flood-affected communities (e.g. face-to-face interviews) are increasing. However, a systematic method that applies such data for hydrodynamic modelling of past floods in locations without hydrological data is lacking. In this study, we developed a method for reconstructing plausible scenarios of past flood events in data-scarce regions by applying flood observation data collected through field interviews to a hydrodynamic model (CAESAR-Lisflood). We tested the method using 300 spatially distributed flood depths and duration data collected using questionnaires on five river reaches after the 2017 flood event in Suleja and Tafa region, Nigeria. A stepwise process that aims to minimize the error between modelled and observed flood depth and duration at the locations of interviewed households was implemented. Results from the reconstructed flood depth scenario produced an error of ± 0.61 m for all observed and modelled locations and lie in the range of error produced by studies using comparable hydrodynamic models. The study demonstrates the potential of utilizing interview data for hydrodynamic modelling applications in data-scarce regions to support regional flood risk assessment. Furthermore, the method can provide flow depths and durations at houses without observations, which is useful input data for physical vulnerability assessment to complement disaster risk reduction efforts.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The relationship between hydrological variation and the habitat use of waterbirds in wetland complexes is a significant field of ecological research. Quantification of the relationships between ...wetland hydrological attributes and waterbirds distribution is critical for the success of waterbird conservation. In this study, flood duration (FD) derived from synthetic aperture radar (SAR) imagery was combined with geese GPS tracking data to quantify the optimal FD thresholds for identifying geese habitats. Based on the thresholds, we defined the suitable habitats of wintering geese and investigated the difference in the spatial distribution pattern of habitat from 2018 to 2020 in Poyang Lake, China. We also considered the role of sub-lakes in habitat protection. The results showed that the area of suitable habitats for wintering geese decreased in both dry and wet years, and the range of optimal FD threshold was wider in normal years than in both dry and wet years. The proportion of suitable habitats per unit area was greater in the sub-lakes than in the whole Poyang Lake. We concluded that FD indices extracted from SAR data are valuable for reflecting the influence of the pattern of hydrological variation on waterbird distribution and for the protection and rational use of wetland ecosystems.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Vegetation condition has declined along many regulated river systems globally due to alteration of flow regimes via flow regulation. Understanding how plants respond to inundation is critical for ...managing regulated river flows to improve riparian vegetation condition. We experimentally tested the effects of inundation duration on the survival and growth of six tufted grass species commonly found in riparian zones in south-eastern Australia. We conducted three nursery-based experiments in late winter/early spring, corresponding with natural temperate flow peaks and managed flows, with inundation treatments on: (1) established plants, up to 35 days inundation; (2) seedlings, up to 25 days inundation; and (3) established plants, up to 53 days inundation including additional shaded treatments. Plant survival, height and biomass growth, and onset of flowering were recorded for established plants, and, for seedlings, survival only. Plant height and biomass growth declined with longer inundation duration across all species, although surprisingly few established plants died. Unexpectedly, grass seedlings were generally tolerant of inundation also, although there was some evidence of increased mortality for the longest treatment (25 days inundation). Shading did not result in increased mortality or reduced height growth of inundated plants. Inundation effects on the onset of flowering were modest and varied between species ranging from earlier to delayed onset. Our results suggest that tufted grasses are tolerant of cool-season inundation. Given that mortality of these species has been observed in the field and experimentally under shorter inundation periods in warmer conditions (late spring and summer), we suggest that seasonal timing of inundation is critical in determining plant responses to inundation.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
PDF
