Statistical modelling of floods is among others used for estimating design floods (e.g. the 200-year flood) required for dam safety, area planning, and infrastructure design. Robust and reliable models are needed. Statistical modelling faces several challenges including data quality, sample size, and prediction in ungauged locations.
The Norwegian Water Resources and Energy Directorate (NVE) is responsible for the national recommendation for design flood estimation and providing data and tools for such estimates (e.g. nevina.nve.no). Results from master projects can form the basis for improving guidelines or provide recommendations for best practices.
Example projects:
- Project 1: Consistent Design Flood Estimates Along River Networks
Many practical flood risk assessments require design flood values (e.g., the 100-year flood) to be estimated at multiple locations along a river network. Because most locations of interest are ungauged, these estimates must be transferred in space using regionalization methods.
A key challenge is ensuring that the resulting set of flood estimates is physically consistent, for example by preserving expected downstream increases in flow between calculation points. Achieving this can be difficult due to the extensive extrapolation involved, and inconsistencies can arise when estimates are derived independently at different locations. In operational practice, such inconsistencies are typically addressed through manual adjustment or post-processing corrections, increasing the workload for the practitioner.
This master's project will investigate methods for producing sets of design flood estimates that are consistent across calculation points within a single basin. The work will evaluate strategies for incorporating spatial and hydrological constraints into existing flood estimation frameworks. The ultimate goal is to improve the efficiency of operational flood frequency analysis for ungauged sites.
- Project 2: Catchment Similarity Methods to Support Design Flood Analysis
Society relies on estimates of design flood values, such as the 100-year flood, for flood hazard mapping, infrastructure design, and risk assessment. As part of the modeling chain used to obtain these estimates, hydrologists often identify hydrologically similar catchments to serve as comparison sites in the analysis of a target catchment. The selection of appropriate comparison catchments is therefore an important step in producing reliable flood estimates.
This master's project will investigate methods for identifying hydrologically similar catchments with an eye towards the existing datasets and workflow for flood calculation at NVE. The work will compare approaches based on similarity in catchment descriptors, such as climate, topography, and land use, with approaches based on similarity in observed flow and flood characteristics.
The project may also explore ways of combining multiple sources of information to improve catchment selection. The ultimate goal is to support the existing operational workflow for design flood values.
- Project 3: Analysis of widespread floods - Analyzing and improving of the co-occurence of floods at multiple locations is critical for handling flood risk since it allows us to assess how large areas can be affected.
We suggest to build on methods developed by Brunner et al. (2020) and Jiang et al. (2020). In Brunner et al. (2020) a methodology for creating an event occurrence matrix across locations is suggested, and it is possible to estimate this matrix for floods of different return periods. Jiang et et al. (2020) propose an analysis similar to principal component analysis (PCA) for extremes that allows us to look at patterns describing the spatial co-occurrence of extremes.
For the analysis both observed flood data and simulated flood data from a hydrological model can be used to analyse widespread floods along a linear infrastructure or within specific areas and assess how frequently a flood of specific return periods might occur depending on the length of the infrastructure or size of a region.
REFERENCES
- Brunner, M L, S Papalexiou, M P Clark and E Gilleland (2020): How probable is widespread flooding in the United States? Water Resources Research, 56: e2020WR028096.
- Jiang, Y, D Cooley and M F Wehner (2020): Principal component analysis for extremes and application to U.S. precipitation. Journal of Climate, 33: 6441-6451. hb.