100-year Return Period Research Articles

Impact of Landuse Change on The Inundations in The Ciberes Watershed

Whenever the rainy season approaches, the Ciberes River always inundates a number of regions. This research was conducted to determine the effect of land use change on the inundation in the Ciberes Watershed, given the aforementioned context. Using land cover change data from 2000 to 2023, a hydrological and hydrodynamic analysis of the Ciberes Watershed is conducted to determine the impact of landuse change. This investigation employs HEC-HMS for hydrological modeling and HEC-RAS for 1D and 2D hydrodynamic modeling. The simulation results demonstrate that the change in CN value is directly proportional to the flood discharge, and the flood discharge is directly proportional to the height of the flood inundation. Based on these findings, it can be concluded that the river’s cross section can accommodate flood discharges with a return period of 50 years, except in coastal areas. whereas the floods that occurred in 2018 and 2022 have a 10-year return period. It can be concluded that the topographical condition of the river in the downstream segment, which has a higher elevation than the surrounding land and flat soil conditions, is the primary cause of inundation in the Ciberes Watershed.

Ciujung river basin flood risk assessment due to climate change and its countermeasure

Ciujung River is experiencing recurrent flooding, which was caused by climate change factor and extensive land use change. Therefore, this study carried out risk assessment in this basin area. First, hydrology analysis was carried out using HEC-HMS software to obtain flood discharge hydrograph, with obtained peak discharge of 3534.3 m3/s for 25-year return period. This hydrograph was then modeled into an inundation map using HEC-RAS two-dimensional model to calculate hazard index. Meanwhile, the vulnerability and capacity index were calculate using the demographic data. Finally, the risk index was calculated by combining hazard, vulnerability, and capacity index using raster calculator on Arc-GIS. Overall, the flood risk analysis shows a medium level. The results shown that hazard index is the most contributing factor in causing a high risk index. Thus, in this study we proposed a structural approach to reduce the hazard index. An embankment with a length of 50.37 km was applied and remodeled to analyze its effectiveness. The modeling results show high effectiveness with a significant reduction in inundation area. The reduction of inundated area reached 39.6%, while the reduction of affected buildings reached 49.9%. Hopefully, the result of this study can provide theoretical support and recommendations for future development.

Design of the Jlantah Reservoir Mini-Hydro Power Plant, Karanganyar Regency, Central Java Province

An increase in the number of electricity users in Jatiyoso District, Central Java, has occurred in the last few years. In 2020 there were 12,773 families using electricity in Jatiyoso District, where there has been an increase of 79 families using electricity compared to 2019. This increase in electricity demand should be balanced with an increase in sources of electrical energy for the community. Therefore, Jlantah Mini-hydro Power Plant is expected to become a source of electrical energy for the local community. The normal water level of the reservoir is planned at an elevation of +691.00 MASL and the elevation of the intake structure at +661.00 MASL. The total dead storage of the reservoir is 1.66 million and the total effective storage is 9.16 million. The powerhouse elevation planning is carried out by analyzing the 100-year return period of flood in the river around the powerhouse. The powerhouse is planned at an elevation of +624.00 MASL. The turbines used in the powerhouse are 2 turbines. Turbine 1 with HLA550-WJ-55 series and turbine 2 with HLA678-WJ-50 series. The average power generated in a normal year (2013) is 516.44 kW with a total energy of 4.47 GWh. The construction cost of the Jlantah PLTM is estimated at IDR 18,795,716,076.00 with normal annual income (2013) of IDR 4,060,935,522. With this income, the NPV value is IDR 4,461,454,224, IRR is 12.96%, BCR is 1.24, and PBP is 12.78 years, so this project is said to be economically feasible.

Open-access digital elevation model (DEM) selection for flood inundation modelling using HEC-RAS in Capital City of Nusantara

Flood is a classic but complex issue in most regions of Indonesia. Nusantara, the future capital of Indonesia, is now undergoing construction but the site continues to experience flooding due to high intensity rainfall. To overcome this challenge, identification of flood points in those areas needs to be done. Digital Elevation Models (DEM) are the most important component in modeling flood inundation in data-sparse areas. High-accuracy DEMs have been found to give better flood estimation but the availability of such data is very limited. Therefore, open-access DEMs, such as SRTM, DEMNAS, and MERIT-Hydro, are the most common choices used in modeling flood inundation in Indonesia. Each data set may provide varying model outcomes, due to different data processing methods. These results often lead to confusion as to which result should be used in subsequent studies. In this study, flood inundation in Nusantara will be generated using different DEMs and HEC-RAS hydraulic modeling with 25-, 50-, and 100-year return period rainfall events. The return period rainfall was obtained by calibrating Global Precipitation Measurement (GPM) satellite rain data. The results provide various flood inundation conditions, MERIT-Hydro tends to present higher flood depths. Followed by DEMNAS and SRTM which have lower flood depths. On the other hand, the use of return period variation gives a linear increase in flood depth for the DEMNAS model. While a decline in increment occurred in the SRTM and MERIT-Hydro models when the two big year return periods were applied. This research can be considered for the Nusantara development planning.

Evaluating the impacts of climate change and land-use change on future droughts in northeast Thailand

The impacts of climate change (CC) on droughts are well documented, but the effects of land-use change (LUC) are poorly understood. This study compares the projected individual and combined impacts of these stressors on future droughts (2021–2050), with respect to baseline (1981–2010) in one of the major tributaries of the Mekong River. LUC impacts on hydrological droughts are minimal compared to CC, with the latter expected to shorten the recurrence interval of a 20-year return period event to every 14 years. Both CC and LUC have significant impacts on agricultural droughts with heightened sensitivity. ‘Once in a Decade’ agricultural droughts will be 40% (35%) longer and 88% (87%) more severe under the CC (LUC) scenario. Under both stressors, the events occurring every 20 years will be twice as frequent. Results highlight the intensification of future droughts and the urgency for actions to mitigate/adapt to climate change and manage land use. Future policy shall holistically address agricultural water management, sustainable land use management, and crop management to cope with future droughts. We recommend developing resilient agricultural practices, enhanced water resource management strategies, and incorporating drought risk into land-use planning to mitigate the compounded impacts of CC and LUC.

Calculation of Temperature Action of Flat Steel Box Girder of Long-Span Bridges Using a Joint Model of ARMA Mean and GARCH Variance

Using the monitoring temperature field data from the flat steel box girder, the time histories of temperature data and temperature difference data are investigated using the extreme value analysis method. Because the calculation of standard values of temperature action needs massive temperature field data, the simulation of daily extreme values of temperature data and temperature difference data is carried out by virtual of Probability Statistical Method. The seasonal and nonstationary trend terms are described using the weighted sum of a series of basic elementary functions. The random fluctuation term is represented by a joint model of ARMA mean and GARCH variance. Moreover, the yearly extreme values of temperature data and temperature difference data are considered as statistical variables, and their standard values of temperature action with 50-year return period are calculated by means of the general extreme value (GEV) distributive function. The research results can supply references for temperature action of flat steel box girder.

Towards evaluating the conditional probability of waterborne microbial risks associated with critical rainfall events following land application of animal waste — A focus on Irish pastures

ABSTRACT Modelling surface runoff and infiltration in an agricultural watershed is essential for understanding the nutrient cycle and water quality management. This research evaluates the critical rainfall events causing maximum surface runoff and infiltration. Empirical models such as Soil Conservation Service (SCS) curve number and Explicit Green-Ampt (EGA) were analysed for different soil hydraulic conditions and storm events with specific return periods. The present study forecasted the maximum daily rainfall and intensity as 113.6 mm and 19.9 cm h–1, respectively, considering a 100-year return period storm. The deterministic part of the model calculates the daily maximum surface runoff as 5.51 cm (from the SCS model). The EGA model revealed that the rainfall intensity of 0.143, 0.163, 0.175, 0.179, 0.181, 0.182, and 0.182 cm h−1 (duration of 24 h) was found critical for 1, 2, 5, 10, 25, 50, 100 year return period of the storm, respectively in different soil texture classes (sand, loamy sand, sandy loam, loam, silt loam, sandy clay loam, clay loam, silty clay soils). Exceptions imply for three occasions where the intensity of 0.407 cm h−1 and duration of 18 h produced maximum infiltration for silty clay loam, and intensity of 0.352 and 0.354 cm h−1 with 9 h rainfall (each) produced maximum infiltration for clay. The probabilistic model revealed that a daily storm event probability of 2.74 × 10–5 is associated with a simulated mean runoff depth of 0.69 cm and infiltration of 20.7 cm. Critical rainfall probabilities calculated in this study can be multiplied with the overall microbial/pollutant human health risk assessment framework to calculate conditional probability and better estimate microbial risk through the drinking water pathway. This study is very relevant for the wet climatic condition of Ireland, where most land use is pastures.

Evaluating barrier beach protection with numerical modelling. A practical case

Embryonic dunes, continuous dunes and classical beach nourishment are tested as soft coastal protection measures in the vulnerable Trabucador barrier beach located in the NW Mediterranean Sea against different storm conditions. The beach was impacted by severe breaching events during past storms. Evaluation of the performance of the dunes and nourishment as coastal protection measures for the barrier beach is carried out using XBeach model for three different storm events: Storm Isaak being a mid-tier double peak storm, Storm Filomena a typical larger storm of the region and Storm Gloria the largest ever storm to hit the region, with 7, 12 and 60 years of return period respectively. The model showed embryonic dunes and shoreface nourishment systems greatly protect the beach against Storm Isaak and Storm Filomena but did not withstand Storm Gloria considering it being almost 1.5 times larger than the second-highest storm in terms of significant wave height. The study aids in assessing the effectiveness of various mitigation actions for barrier beaches, with the aim of implementing them in practical field applications.

STRATEGI MITIGASI BANJIR BERDASARKAN KAPASITAS SALURAN DRAINASE DI KELURAHAN JAGALAN

<p><em>Flood mitigation is an important step in maintaining the sustainability and safety of urban environments. One key factor that affects the capacity of drainage channels is the flow rate of water through the channels. Therefore, this research aims to assess flood mitigation strategies based on the flow rate in drainage channels using the HSS SCS method. The study was conducted in Jagalan Sub-District, which frequently experiences flooding due to inadequate drainage channel capacity. The HSS SCS method was used to estimate the maximum flow rate that can be accommodated by the drainage channels. Hydrological and topographic data of the study area were collected and analyzed to identify relevant hydrological characteristics and physical parameters.</em></p><p><em>The analysis results showed the planned flood discharge values in Jagalan Sub-District through the Kali Boro Watershed, which were 3.1154 mm3/dt for a 2-year return period, 3.8297 mm3/dt for a 5-year return period, 4.3025 mm3/dt for a 10-year return period, and 4.7501 mm3/dt for a 20-year return period. The existing discharge values were 14.5243 mm3/dt for Surya Road, 19.1823 mm3/dt for Rejosari Road, 8.7376 mm3/dt for Kali Kepunton Road, 66.0338 mm3/dt for Kali Simpang Road, 21.7882 mm3/dt for Bororejo Road, and 42.2077 mm3/dt for Ir. Juanda Road. From these values, it can be concluded that the drainage channels in Jagalan Sub-District have sufficient capacity to accommodate the maximum flow rate during high-intensity rainfall. </em></p>

Frequency-Based Flood Risk Assessment and Mapping of a Densely Populated Kano City in Sub-Saharan Africa Using MOVE Framework

Flooding is a major environmental problem facing urban cities, causing varying degrees of damage to properties and disruption to socio-economic activities. Nigeria is the most populous African country and Kano metropolis is the second largest urban center in Nigeria, and the most populated in Northern Nigeria. The aim of the paper was to conduct a flood risk assessment of Kano metropolis. The city is divided into two hydrological basins: the Challawa and Jakara basins. Flood frequency analyses for 2 to 100-year return periods were carried out for both the basins using a Log-Pearson Type III distribution and flood inundation and hazard mapping was carried out. The social vulnerability to flooding of both basins was assessed using the method for the improvement of vulnerability assessment in Europe (MOVE) framework. Flood risk was determined as a product of flood hazard and flood vulnerability. The results showed that areas of 50.91 and 40.56 km2 were vulnerable to a 100-year flood. The flood risk map for the two basins showed that 10.50 km2 and 14.23 km2 of land in Challawa and Jakara basins, respectively, was affected by the risk of a 100-year flood, out of which 11.48 km2 covers built-up areas. As the city is densely populated, with a population density of well over 20,000 persons per square kilometer in the highly built-up locations, this means that much more than 230,000 persons will be affected by the flood risk in the two basins.

Flood Risk Assessment for an Irrigation Project in Odissa, India

Objectives: Flood risk assessment is a fundamental aspect of disaster management, particularly in regions heavily reliant on irrigation infrastructure for agriculture. This study employs advanced hydrological and hydraulic modeling techniques to evaluate flood risk for the Lower Suktel region in Odisha, India. Methods: The methodology integrates Intensity-Duration-Frequency (IDF) curves, Isopluvial maps, and the Hydrologic Engineering Center-River Analysis System (HEC-RAS) to comprehensively analyze flood risk and its implications. Findings: IDF curves further reveal that the design rainfall intensity for a one-hour duration with a 100-year return period is 152 mm/h, aiding in characterizing rainfall intensity for specific return periods. Model simulation identifies the pump house's susceptibility to flooding, with maximum flood depths ranging from 0 to 2 meters. These findings underscore the significance of employing advanced modeling techniques and Isopluvial maps for precise flood risk assessment. Novelty: The novelty of this paper lies in its pioneering effort to introduce a comprehensive flood risk assessment in an area where it has not been previously conducted. The integration of advanced modeling techniques and spatial analysis tools contributes to the novelty of the research, making it a valuable and innovative contribution to the field of flood risk management. Understanding extreme rainfall events, hydraulic behavior, and potential flood depths is imperative for developing effective flood mitigation strategies. Keywords: Flood risk assessment, Irrigation infrastructure, IDF curves, Hydrological modeling, Hydraulic modeling, GIS

Sediment connectivity as a key to understand geomorphic effects of the Storm Alex in two mountain catchments of the Mediterranean Alps (Italy)

The occurrence of extreme rainfall events over mountain catchments is likely to trigger mass failure processes on hillslopes and sediment transport within the channel network. Understanding the degree of linkage between the sediment sources and transfer pathways downstream is essential in those catchments where settlements are affected by hydro-geomorphic processes, in order to plan suitable interventions for risk mitigation. A recent storm (October 2020) named “Alex”, estimated to be an extratropical cyclone with a more than 100-year return period, hit the Mediterranean Alps at the border between Italy and France, triggering deadly landslides and flooding processes. This work focuses on two adjacent mountain catchments located in the Liguria region (Italy) which share the same outlet, where a small village was damaged by high-magnitude sediment transport and deposition processes during the storm. In order to analyze sediment dynamics at the catchment scale leading to severe damage to the urban settlements at the outlet, an integrated approach was used. Very high resolution (0.5 m) satellite imagery was employed to map the mass failure processes on the hillslopes with a visual interpretation. This dataset was then compared with a map of the Index of Connectivity created using the SedInConnect 2.3 software to characterize the pre-event structural connectivity in both catchments. The integration of these two datasets permitted understanding that debris slides evolving into debris flows downstream supplied most of the sediments to the channel network. These processes concentrated mainly in a specific catchment where hillslopes have the highest connectivity with the valley bottom. This outcome provided a clear evidence that inventory maps developed soon after an extreme event, coupled with sediment connectivity datasets, can provide relevant information for future land management and risk mitigation strategies. These can be exploited to prioritize structural interventions in specific areas, to reduce the connectivity or disconnect inhabited areas from the hydro-geomorphic systems and avoid future damage.

Extreme precipitation trends in Northeast China based on a non-stationary generalized extreme value model

AbstractNortheast China is the main food production base of China. Extreme precipitation (EP) events can seriously impact agricultural production and socioeconomics, but the understanding of EP in Northeast China is still limited. In this study, using the non-stationary generalized extreme value (GEV) model, we investigate the trend and potential risk of EP in Northeast China during 1959–2017, especially in early and mid-summer (periods of high frequency of EP). Then, the relationships between EP and large-scale circulation over Northeast China in early and mid-summer are analyzed separately. The EP in Northeast China mainly presents positive trends in early summer but negative trends in mid-summer. Meanwhile, the EP with all the return periods presents apparently increasing trends in early summer, corresponding to more frequent EP events. Nevertheless, in mid-summer, the EP with 2-year return period decreases with location parameter, and the EP with 20-year, 50-year, and 100-year return periods slightly increases with scale parameter. The EP with 2-year return period occurs frequently in Liaoning Province, while the EP with 100-year return period is more likely to occur in Jilin Province and Heilongjiang Province. Moreover, the increase of the EP in early summer is mainly influenced by the northeast cold vortex; the effect of cold air on the EP is stronger in mid-summer, giving a clear explanation why the EP in mid-summer does not increase significantly. Overall, the outcomes of this study would be beneficial for the disaster prevention and mitigation in Northeast China.

Theoretical Boundaries of Annual Flood Risk for Single-Family Homes Within the 100-Year Floodplain

Special flood hazard areas (SFHAs), defined as having an annual probability of occurrence of 1 percent or above, are used by U.S. Federal Emergency Management Agency (FEMA) to demarcate areas within which flood insurance purchase is required to secure a mortgage. However, quantifying flood risk within SFHAs can be challenging due to the lack of modeled flood depth data for all return periods. To address this issue, this research quantifies flood risk indicated by average annual loss (AAL) within the A Zone—the subset of the SFHA where wave heights can potentially range from 0 to 3 feet. The methodology resolves the Gumbel quantile function for four distinct flooding cases (i.e., locations flooded at return periods exceeding 1.58-, 10-, 25-, and 50-year return period events) and generates synthetic flood hazard parameters for these cases within the 100-year floodplain, as well as with additional elevation above the base flood elevation (BFE), known as freeboard, for single-family homes with different attributes. The results indicate that for single-family homes in the A Zone, with the lowest floor elevated to the BFE, the AAL ranges from 0.3 to 1 percent of the building replacement cost value. Adding one foot of freeboard reduces flood risk by over 90% if the annual flood risk is between the minimum and 25th percentiles and the 100-year flood depth is less than two feet. The demonstrated approach helps enhance flood resilience in the A Zone, demonstrating the feasibility of proactive measures to protect communities.

Simulation of the Hydraulic Model HEC-RAS Coupled with GIS and Remote Sensing to Study the Effect of River Cross-section Width in Detecting Flood-prone Areas

Abstract Flooding is one of the extreme hydrological phenomena. It is a recurring natural disaster that causes loss of life and property in many parts of the world, particularly during the monsoon season. It is important to address such issues for local government and policymakers to manage the flood properly. One such flood management activity is to develop a flood-prone area that depicts the spatial and temporal extent of flood accurately. The integration of the Hydrologic Engineering Centre - River Analysis System (HEC-RAS) model and geospatial tools have emerged as a crucial approach for identifying and mapping flood-prone areas. The successful application of the HEC-RAS model generally depends on the topographical data, which represents the channel and floodplain geometry. In floodplain geometry, discrete cross-sections play a vital role to develop the floodplain map, particularly in the flat topographical region. To extract these data it needs a high-quality digital elevation model (DEM), such as light detection and ranging (LiDAR). However, due to a lack of high-resolution topographical data, flood hazard mapping in developing countries is rare. In common practice, the centerline of the river is considered the flow path for the channel. The orientation of the cross-sections is perpendicular to this line and extends to reach the limits of the floodplain. But, it is difficult to define the limits and it may depend on the magnitude of the flood. Hence, in this study, the HEC RAS model coupled with ArcGIS has been applied to the Ganga River, which traverses through the Bihar state of India to study the effect of cross-sectional width to define the floodplain. The Bihar state is facing substantial hardships from annual flooding events with approximately 16.5% of India’s flood-prone area. The extreme flood values for 5, 10, and 25 years of return period have been determined and the influence of the three different cross-sectional widths to mapping the floodplain has been investigated. This novel perspective adds dimension to the understanding of flood dynamics and its implications for flood risk assessment. In this analysis, it has been observed that, with an increase in the width of the cross-section, the floodplain area also getting increased. In this topographical region, keeping a fixed flow path will underestimate the flood-prone area. The width of the flow path depends on the topography of the region and the river flow. The outcomes of this analysis provide valuable insights into the flood-inundated areas for the specified return periods, enabling the identification and prioritization of flood-prone zones.

Evaluation of wind-induced turbulence around offshore platforms in different wind speeds and directions, along with safety assessment of helicopter operation and helideck’s air-gap optimization

The demand for helicopter transportation has increased as offshore activity has expanded into more remote waters. In this situation, safe takeoffs, approaches, and landings on the platform's helidecks require understanding wind behavior. This study simulates the effect of a helideck air gap on wind turbulence around an offshore platform. The simulations are carried out using a validated computational fluid dynamics model based on the Reynolds-averaged Navier-Stokes k-equations. Five wind directions (with intervals of 45°), two wind speeds (5, 15, and 35 m/s, respectively, for winds with 7-days, 1-year, and 100-year return periods), and six air gap sizes (0–6 m) were assumed to calculate the induced turbulence. The Norsok C-004 standard, two speed-base, and one energy-based criterion were used to identify the turbulence conditions that allow helicopter operations. Wind-induced turbulence was significantly generated by the interaction of the wind with the crane and equipment placed on the highest level, limiting helicopter operation, particularly in most cases where the wind blows from the southwest. According to the findings, a minimum 4-m air gap is nedded to reduce turbulence caused by wind contact with equipment. Although no upward or downward flows (with ±2 m/s) have formed on the helipad, they have formed strongly around the helipad structure and in the direction of the helicopter approach.

Potential deformation assessment of Semantok Main Dam in North Nganjuk Region at East Java Indonesia

Semantok Dam was constructed using a zone l embankment type and required safety measures for deformation control. This study aims to understand material specifications, geological conditions, and deformation behavior. The results of the material specifications indicate that the core material and fine filter material meet the design criteria. The geological conditions comprise sand, sandstone, and claystone. The rock’s bearing capacity and settlement in the core zone are considered safe. The elastic vertical deformation of the foundation, analyzed using a flexible foundation approach by Lord, is estimated to be between 4.36 and 6.10 cm. Dynamic analysis is also performed using the Plaxis 8.6 version software to estimate deformation. The software input includes soil properties from the borrow and quarry areas surrounding the dam site. Earthquake design criteria are based on the Operating Basis Earthquake (OBE) with a 100-year return period and the Maximum Design Earthquake (MDE) with a 10,000-year return period. The dynamic analysis results indicate that the maximum deformation during a 100-year return period earthquake is 7.37 cm (horizontal deformation) and 12.68 cm (vertical deformation). In the case of a 10,000-year return period earthquake, the maximum deformation is 83.41 cm (horizontal deformation) and 175 cm (vertical deformation) during rapid drawdown.

The assessment of flood hazard in Pondok Keumuning village of Langsa City, Aceh due to heavy rain in 2020

Langsa faces the recurring threat of floods every year, primarily caused by high rainfall resulting in surface runoff in the Langsa Watershed. However, there is uncertainty regarding the specific causes of flooding in the city. This research discusses the flood hazards generated by Langsa River due to high rainfall in Keumuning Village, Langsa City, in 2020. The data utilized in this study includes daily rainfall data obtained from PTPN I Langsa, specifically from the Kebun Lama (KLM), Kebun Baru (KBR), and Tualang Sawit (TWS) stations. Additionally, observed water level data is collected from the Keumuning water gauge station operated by the Aceh Irrigation Agency. Since there is no river discharge record at the Keumuning water gauge station, the Nreca method is used to analyze the direct runoff from the Langsa Watershed due to rainfall, linking it to the water level at Keumuning. Historical flood event data is compiled from the Regional Disaster Management Agency of Langsa City, online media sources, and interviews with flood-affected communities. The research findings indicate that floods in Keumuning Village, Langsa, are triggered by high rainfall, leading to increased river discharge as a result of heavy rainfall at the TWS station (located upstream in the Langsa Watershed) with a 2-year return period. This can result in flooding for the villages around the Langsa River. Similarly, suppose rainfall reaches a 2-year return period at the KLM and KBR stations situated within the middle and downstream of the Langsa Watershed. In that case, it poses a flood threat to the upstream villages along the estuary branches. However, further studies are necessary to assess compound floods triggered by tidal water levels, rainfall, and river discharge in the vicinity of these estuary branches.

Risk assessment of wave hazard in Guangdong Province

In order to improve the prediction ability of wave hazard levels in the ocean under the jurisdiction of Guangdong Province, this paper uses the wave simulation data to evaluate the wave hazard index of the ocean under the jurisdiction of Guangdong Province, and analyses the risk assessment analysis of wave hazards in the Guangdong Province, which provides data support for future wave disaster prevention and mitigation, coastal development, and spatial planning in Guangdong Province. The significant wave height of the 50-year return period in the coastal areas of Guangdong Province is generally distributed within 9 meters of the territorial sea baseline. The intensity of the return period gradually increases with the distance from the mainland and decreases with the decrease of water depth. In the past 30 years, the sea areas under the jurisdiction of the Guangdong Province are mainly dominated by class III and IV wave heights, with class IV being higher than class III. The frequency of Class IV wave heights in the mainly marine area is more than 90%. The risk level of wave disasters in the coastal waters of Guangdong Province is mainly level IV. However, the risk level of wave disasters in the waters under the jurisdiction of Guangdong Province is mainly Level I.

Impact of climate change on Kupang River flow and hydrological extremes in Greater Pekalongan, Indonesia

Located downstream the Kupang Catchment in Indonesia, Pekalongan faces significant land subsidence issues, leading to severe coastal flooding. This study aimed to assess the impact of climate change on future flow regimes and hydrological extremes to inform long-term water resources management strategies for the Kupang Catchment. Utilizing precipitation and air temperature data from general circulation models in the Coupled Model Intercomparison Project 6 (CMIP6) and employing bias correction techniques, the Soil and Water Assessment Tool (SWAT) hydrological model was employed to analyze climate-induced changes in hydrological fluxes, specifically streamflow. Results indicated a consistent increase in monthly streamflow during the wet season, with a substantial rise of 22.8%, alongside a slight decrease of 18.0% during the dry season. Moreover, both the frequency and severity of extremely low and high flows were projected to intensify by approximately 50% and 70%, respectively, for a 20-year return period, suggesting heightened flood and drought risks in the future. The observed declining trend in low flow, by up to 11%, indicated the potential for long-term groundwater depletion exacerbating the threat of land subsidence and coastal flooding, especially in areas with inadequate surface water management policies and infrastructure.