Fluvial processes and landforms

The period 1965-2000 saw a sustained increase in research and publication on fluvial processes and landforms. The trend toward generalisation and/or mechanistic understanding, rather than site-specific history, continued. Research was multi-disciplinary, with important contributions from hydraulic engineers, geologists and physical geographers and from experimental and theoretical approaches as well as geomorphological and sedimentological fieldwork. Rapidly increasing computer power underpinned new measurement methods and greatly increased the scope of data analysis and numerical modelling. There were major advances in understanding the interaction of river process and form at reach scale, with growing recognition of differences between sand-bed and coarse-bed rivers. Field studies outside Europe and North America led to greater awareness of the diversity of river planforms and deposition landforms. Conceptual models of how rivers respond to natural or anthropogenic change in boundary conditions at different timescales were refined, taking advantage of studies of response to land use change, major floods, and volcanic eruptions. Dating of sediments allowed greater appreciation of fluctuations in the incidence of extreme driving events over centuries and thousands of years. Towards the end of the period research on bedrock rivers began to take off.

Low-frequency atmospheric variability patterns and synoptic types linked to large floods in the lower Ebro River basin

This study analyzes the atmospheric variability that caused the largest floods affecting the town of Tortosa in the mouth of the Ebro River (northeast Iberian Peninsula). The Tortosa flood database and flood marks in the nearby town of Xerta are used to define the more relevant flooding episodes (discharges > 2900 m3s−1) of the 1600-2005 period. We explore the atmospheric variability based on low-frequency patterns and synoptic types applying a multivariable analysis to grids at sea-level pressure and geopotential at 500 hPa provided by the 20th Century V3 Reanalysis Project for the instrumental period (since 1836). Output from the Last Millennium Ensemble Project was used to analyze the sea-level pressure over the pre-instrumental period (before 1836). Our analysis includes 33 flood episodes. Four synoptic types are related to floods in Tortosa since 1836, characterized by low-pressure systems that interact with the Mediterranean warm air-mass and promote the atmosphere destabilization. Flooding in Tortosa is related to relative high values of solar activity, positive Northern Hemisphere temperature anomalies and NAO in positive phase. This indicates that the major floods are related to zonal atmospheric circulations (west to east cyclone transfer). During winter, the main impact of the floods is located at the western part of the basin, while the Pyrenean sub-basins are affected during autumn. The major finding is that similar flood behavior is detected since 1600, improving our understanding of past climates, enhancing the knowledge base for some aspects and impacts of climate change and reducing uncertainty about future outcomes.

KESEJAHTERAAN PSIKOLOGI MANGSA BENCANA DI PENEMPATAN SEMULA KOMUNITI MANGSA BENCANA BANJIR

Disasters have had an impact on the psychological well-being of victims for a long period of time. Past research related to the psychological well-being of disaster victims shows the negative and positive psychological well-being experienced by victims even though actions have been taken by certain parties in helping disaster victims. Flooding is a natural disaster that often occurs in Malaysia. Major floods that occurred in 2014 in several states in Malaysia, especially on the east coast, have resulted in certain parties taking action to move disaster victims to new resettlement to avoid repeated tragedies. Thus, the present study was conducted to identify the level of psychological well-being of disaster victims in the relocation area. The study was conducted using a qualitative design where data collection was done through interview methods. A total of 23 informants were interviewed using an interview protocol formed based on previous theories and studies. Data is analyzed using thematic analysis. The results found that stress, sadness and anxiety are elements of negative psychological well-being that informants feel when recalling these events. This negative element is balanced with the positive element of gratitude, acceptance and social support received. This study contributes to the theories of psychological well-being by the addition of acceptance and grateful as a new dimension. The results of this study also contributed to strengthen policies in relation to the importance of intervention from the psychological aspect provided to disaster victims. Keywords: Psychological effects, Natural disaster, Floods, Relocation of flood victims, Qualitative research Abstrak: Bencana mendatangkan kesan terhadap kesejahteraan psikologi mangsa untuk satu tempoh masa yang agak panjang. Penelitian berkaitan kesejahteraan psikologi mangsa bencana menunjukkan kesejahteraan psikologi secara negatif dan positif dialami oleh mangsa meskipun tindakan telah diambil oleh pihak tertentu dalam membantu mangsa bencana. Banjir adalah merupakan bencana alam yang seringkali terjadi di Malaysia. Banjir besar yang dialami pada tahun 2014 di beberapa buah negeri di Malaysia terutama di pantai timur telah mengakibatkan pihak-pihak tertentu mengambil tindakan untuk memindahkan mangsa bencana ke penempatan semula bagi mengelak tragedi ini berulang. Lantaran itu, kajian ini dilakukan bertujuan untuk mengenal pasti tahap kesejahteraan psikologi mangsa bencana di kawasan penempatan semula. Kajian ini dilakukan menggunakan reka bentuk kualitatif iaitu pengumpulan data melalui kaedah temubual. Sejumlah 23 orang informan telah ditemubual menggunakan protokol temubual yang dibentuk berdasarkan teori dan kajian lepas. Data dianalisis menggunakan analisis tematik. Hasil kajian mendapati tekanan, kesedihan dan kebimbangan adalah merupakan elemen kesejahteraan psikologi negatif yang dirasai oleh informan ketika mengenangkan peristiwa berkenaan. Elemen negatif ini diseimbangkan dengan elemen positif iaitu syukur, redha dan sokongan sosial yang diterima. Kajian ini menyumbang kepada teori psikologi iaitu Teori Kesejahteraan Psikologi, Teori Penentuan Diri dan Teori Modal Insan dengan menyumbang kepada penambahan redha dan bersyukur sebagai dimensi baru. Hasil kajian ini turut menyumbang kepada pengukuhan polisi berkaitan dengan kepentingan intervensi dari aspek psikologi diberikan kepada mangsa bencana. Kata kunci: Kesan psikologikal, Bencana alam, Penempatan mangsa banjir, Kajian kualitatif

Geospatial Assessment of Flood and Drought on the Chure Region of Western Nepal

Flood troubles people of central chure region and its vicinity almost every year. Besides, the area is also becoming susceptible to the drought currently. In that perspective, it is necessary to assess the vulnerability of floods and drought in the chure region. So this research focused on the assessment of flood and drought geospatially in Butwal city which was the major city and experience flood and drought every year. This study mainly records floods, calculates drought, finds their present condition, studies their trend, and determines drought and flood vulnerable areas within Butwal. Climate data, imagery, soil data, and socioeconomic data, and other relevant information were analyzed and extracted past drought conditions through Temperature and precipitation trend analysis and SPEI model. NDVI, NDDI, NDWI were used to find drought vulnerability status, and AHP and MCDA were used to find flood vulnerability. The city faced extreme drought in 2005, 2011, 2012, and 2013. And, Flood of 1970 and 1981 are the major floods. The area was frequently affected by floods in the past but no flood has been recorded after 2017. About 43% of the area was found high to very highly vulnerable to drought and 68% of the land was found vulnerable to extremely vulnerable to flood. So geospatial vulnerability assessment can enhance the planning decision and effectiveness of activities of the preventive measures by the stakeholders.

Assessing the Impact of Floods Disaster on Soil Erosion Risk Based on the RUSLE-GloSEM Approach in Western Iran

Floods cause great damage to ecosystems and are among the main agents of soil erosion. Given the importance of soils for the functioning of ecosystems and development and improvement of bio-economic conditions, the risk and rate of soil erosion was assessed using the RUSLE model in Iran’s Lorestan province before and after a period of major floods in late 2018 and early 2019. Furthermore, soil erosion was calculated for current and future conditions based on the Global Soil Erosion Modeling Database (GloSEM). The results showed that agricultural development and land use change are the main causes of land degradation in the southern and central parts of the study area. The impact of floods was also significant since our evaluations showed that soil erosion increased from 4.12 t ha-1 yr-1 before the floods to 10.93 t ha-1 yr-1 afterwards. Field surveying using 64 ground control points determined that erodibility varies from 0.17 to 0.49% in the study area. Orchards, farms, rangelands and forests with moderate or low vegetation cover were the most vulnerable land uses to soil erosion. The GloSEM modeling results revealed that climate change is the main cause of change in the rate of soil erosion. Combined land use change-climate change simulation showed that soil erosion will increase considerably in the future under SSP1-RCP2.6, SSP2-RCP4.5, and SSP5-RCP8.5 scenarios. In the study area, both natural factors, i.e. climate change and human factors such as agricultural development, population growth, and overgrazing are the main drivers of soil erosion.

Major Floods and Tropical Cyclones over Bangladesh: Clustering from ENSO Timescales

The present study analyzed major floods and tropical cyclones (TCs) over Bangladesh on El Niño-Southern Oscillation (ENSO) timescales. The geographical location, low and almost flat topography have introduced Bangladesh as one of the most vulnerable countries of the world. Bangladesh is highly vulnerable to the extreme hazard events like floods and cyclones which are impacted by ENSO. ENSO is mainly a tropical event, but its impact is global. El Niño (La Niña) represents the warm (cold) phase of the ENSO cycle. Rainfall and cyclonic disturbances data have been used for the period of 70 years (1948–2017) and compared with the corresponding observations of the Southern Oscillation Index. Result shows that major flood events occurred during the monsoon period, and most of them are during the La Niña condition, consistent with the historical archives of flood events in Bangladesh. Synoptic conditions of these events are well matched during La Niña condition. On the other hand, the major TC cases are in the period of either pre-monsoon or post-monsoon season. The pre-monsoon cases are under neutral (developing La Niña) or El Niño and the post-monsoon cases are under La Niña, consistent with climatology studies that La Niña is favorable to have more intense TCs over the Bay of Bengal.

Flood forecasting system for Brahmaputra river basin

<p>Assam has always been India’s most flood prone state due to the presence of Brahmaputra river, which is very unstable in terms of its flow direction witnessing 12 major floods from 1950 to 2012. Flooding in the basin has affected around 2.75 million of people and 0.27 million hectares of agricultural land on an average causing catastrophic damage to human life and infrastructure. In this study, we analysed all the major floods across the Brahmaputra river in the past 70 years and established the dependency within discharge and atmospheric parameters. Variable Infiltration Capacity (VIC) model was set up to simulate the flow at two stations namely Yangcun, China and Bahadurabad, Bangladesh. We  used near surface meteorological data for driving land surface modelling systems from 1901 to 2016 as input parameters to the VIC model. To avoid the discontinuity of data after 2016, we used ECMWF reanalysis (ERA5) data for the period of 2016 to 2020. After obtaining the continuous simulated discharge for 120 years, we established the relationship between the observed and simulated discharge data for which the R-squared and Nash Sutcliffe coefficient values were 0.83 and 0.78 respectively. Comparing the simulated discharge with the observed extreme discharge at various locations on the river, we apply the model to address future flood situations.</p>

Multitemporal geomorphological analysis to predict flash flood impacts: its contribution to inform flood risk management

<p>The 2016 implementation of the EU Flood Directive in Spain defines within the flood-prone zones the Preferential Flow Zone (Zona de Flujo Preferente, ZFP). This zone includes a) broadly, the area where the floods flow is concentrated; b) for the 100 years return period flood, the intensive drainage waterway and the zone dangerous to persons. The ZFP is usually defined for the 100 years flood applying hydraulic modelling. However, the calculation of the 100 years flood poses multiple limitations. For instance, different probability distributions produce different results for the same data series, or for rainfall and discharge data, depending on the time interval considered in the calculation, the results are also different. Regarding rainfall, the meteorological radar data are still too new to extrapolate to 100 years. The destruction of meteorological and gauging stations during storms and floods is not rare; hence, a lack of data on major events in the data series can deeply affect the calculations. Furthermore, similar rainfall can produce different discharges due to differences in the antecedent conditions or to land use changes. All the above and the climate change, question the hypothesis of stationarity at the base of the floods return period concept<sup>1</sup> and, thus, its calculation reliability.</p><p>Since the middle of the 20<sup>th</sup> century, significant socio-economic and land use changes occurred in the western Mediterranean region, resulting in changes in the morphology of rivers (e.g., reduced channel section, entrenchment). The record of these morphological changes, including the effects of major floods, can provide insights to define the high-energy flow zone or ZFP. This work contributes to determine the flash flood effects and, therefore, to define the ZPF, through multitemporal geomorphological analysis applied to a case study of the upper basin of the Francolí river in Catalonia, Spain. It was affected by several major floods in 1874, 1930, 1994 and 2019, where the first and the last events were the largest and of quite similar, centenial magnitude. Different reaches of the river are studied and compared to validate the analysis: reaches where 1994 and 2019 flood were similar and reaches where these floods were of very different magnitude; reaches where all the basic dataset is available (1946, 1956, 1995 post flood, pre and post 2019 orthophotos; 2003 detailed DTM; stereo photographs, post 2019 flood field data and GNSS-RTK data of river cross sections) and reaches with lack of some data (especially of the 1995 post flood image). Historical information (water levels attained by the past floods and the calculated discharges) are also used to complement and validate the geomorphological analysis results.</p><p>With this work we test whether the main geomorphic effects of the 2019 flood could have been predicted using the multitemporal geomorphological analysis. The ZFP can be reasonably determined for major floods in this Mediterranean river. This multitemporal geomorphological analysis appears as a good complementary tool to inform flood risk.</p><p><sup>1</sup> Sofia, G., E. I. Nikolopoulos, L. Slater (2020), It’s time to revise estimates of river flood hazards, Eos, 101, https://doi.org/10.1029/2020EO141499. 16 March 2020.</p>