Flood Risk Assessment for the Kävlinge River for Present and Future Climate Scenarios using HEC-RAS Rain-on-Grid

Abstract (Swedish)

Extrema klimathändelser, såsom betydande översvämningar, utgör en risk för naturkatastrofer. På grund av klimatförändringarnas effekter förväntas södra Sverige få fler betydande regnväder som kan orsaka översvämningar i allt högre grad med mängden utsläpp. I denna studie undersöks dagens och framtidens översvämningsrisk i ett litet område i denna region, inom Kävlinges avrinningsområde. I det framtida klimatscenariot används den Intergovernmental Panel on Climate Change (IPCC) RCP (Representative Concentration Pathway) 8,5-scenario för år 2100.

Översvämningsrisken bestäms med hjälp av skärningspunkten mellan översvämningsrisk och sårbarhet. Nuvarande och framtida risknivåer baseras på översvämningsdjup som beräknas med en kalibrerad och validerad hydraulisk-hydrodynamisk modell som kallas HEC-RAS rain-on-grid. De prestationsmått som användes i kalibrerings- och valideringsprocessen var Nash-Sutcliffe Efficiency (NSE), Coefficient of Determination (R2) och Percent Bias (PBIAS). Sårbarheten fastställs med hjälp av en analytisk hierarkiprocess som viktar och kombinerar marktäcke, transportinfrastruktur, skolor, befolkningens ålder och skörhet, kommunala byggnader och kulturmiljöer.

Området visar sig mestadels ha relativt låg sårbarhet, med några måttligt sårbara områden nära städerna. HEC-RAS rain-on-grid-modellens NSE, R2 och PBIAS låg inom tillfredsställande intervall och återspeglade goda prestanda för modellen, vilket innebär en korrekt representation av översvämningssimuleringarna. Översvämningsrisken i det här området är måttlig längs floden och mycket låg eller låg risknivå på vissa ställen i hela området. Skärningspunkten mellan sårbarhet och risk visar på måttliga och stora risker längs floden och särskilt nära städerna. Andra områden, främst jordbruksområden, uppvisar en låg eller måttlig risknivå. Skillnaden mellan dagens översvämningar och översvämningarna i klimatscenariot är liten men viktig, med tanke på städernas närhet till klimatscenariots ökade översvämningar och därmed ökade risker.

Begränsningarna, som främst beror på tidsbegränsningar, diskuteras tillsammans med potentiella ytterligare överväganden eller förbättringar av riskbedömningen. De aktuella resultaten kan dock vara användbara för att planera för nuvarande och framtida översvämningar i denna region.

Abstract

Extreme climate events, such as significant flooding, pose a natural disaster risk. Due to climate change effects, the southern region of Sweden is anticipated to receive more significant rainstorms that could cause flooding increasingly with the quantity of emissions. This study examines the present-day and future climate’s flooding risk in a small area in this region, within the Kävlinge Watershed. The future climate scenario uses the Intergovernmental Panel on Climate Change’s (IPCC) Representative Concentration Pathway (RCP) 8.5 scenario in the year 2100.

The flooding risk is determined using the intersection of flooding hazard and vulnerability. Present-day and future hazard levels are based on flooding depth as calculated by a calibrated and validated hydraulic-hydrodynamic model called HEC-RAS rain-on-grid. The performance metrics used in the calibration and validation process were the Nash-Sutcliffe Efficiency (NSE), Coefficient of Determination (R2), and Percent Bias (PBIAS). Vulnerability is found using an analytic hierarchy process weighting and combination of land cover, transportation infrastructure, schools, age and fragility of the population, municipal buildings, and cultural sites.

The area is shown to have mostly relatively low vulnerability, with a few moderately vulnerable areas close to towns. The HEC-RAS rain-on-grid model’s NSE, R2, and PBIAS were within satisfactory ranges and reflected good performance of the model, which signifies an accurate representation of the flooding simulations. The hazard of the flooding in this area is moderate along the river, and very low or low levels of hazard in spots throughout the area. The intersection of the vulnerability and the hazard show moderate and major risks along the river and particularly close to the towns. Other areas, mostly agricultural, show a low or moderate level of risk. The difference between the present-day and climate scenario flooding is small but important, given the close proximity of the towns to the climate scenario’s increased flooding and therefore increased risk.

The limitations, mostly due to time-constraints, are discussed, along with potential additional considerations or improvements to the risk assessment. However, the current results may be useful for planning for present and future flooding in this region.

Popular Abstract

Extreme climate events, such as significant flooding, pose a natural disaster risk. Due to climate change effects, the southern region of Sweden is anticipated to receive more significant rainstorms and flooding. This study examines the present and future climate’s flooding risk of the last 23.6 kilometers of the Kävlinge River.

Risk is made up of two components, hazard and vulnerability. Present and future climate hazard is determined by finding peak flood depth using a software program called HEC-RAS. The vulnerability is found by combining several factors including population demographics, land use, and different types of infrastructure. The two hazard maps are then combined with the vulnerability map to create risk maps of present and future climate.

The first step was to test the HEC-RAS model, which performed well. In the last 23.6 kilometers, the hazard maps for present and future climate (year 2100) showed relatively similar results, with hazardous areas along the Kävlinge River, especially in the towns of Kävlinge and Löddeköpinge and some agricultural areas. However, the future climate scenario model showed a slight increase in both covered area and flood depth, particularly in the town of Kävlinge.

The results of the vulnerability map showed that in the last 23.6 kilometers of the river, the most vulnerable area was the town of Kävlinge. In addition, this area had a generally elevated vulnerability in comparison to the rest of the watershed.

The risk maps created by the combination of hazard and vulnerablity maps, highlighted the higher vulnerability and higher hazard in the town of Kävlinge, for present climate, and even more so for the future climate. Similar results were seen for the town of Löddeköpinge. The risk maps showed that with the exception of the towns, the relative risk is not severe in the study area, and that the area is generally well adaped for the given levels of hazard and agricultural areas are under a low level of risk.

These results have implications for use in budgeting, zoning, policies, and infrastructure projects. It can also be useful for local forums as a discussion point, to aide in discussions, or facilitate two-way communication. Particularly pertinent is the ability to plan in advance for future flooding, which has been proven to be more severe due to the changing climate.

• author: Roosli, Josephine
• supervisor: Zheng Duan
• organization: Dept of Physical Geography and Ecosystem Science
• course: GISM01 20242
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: Geography, GIS, hydrology, hydraulics, risk, hazard, vulnerability
• publication/series: Master Thesis in Geographical Information Science
• report number: 183
• language: English
• id: 9177985
• date added to LUP: 2024-11-18 10:34:49
• date last changed: 2024-11-18 10:34:49