Model Selection
A hydrological model transforms rainfall into runoff. In the CapTain Rain project, we decided to use the HEC-HMS model based on the following selection criteria:
- The model allows for short-term event modelling of minutes to hours.
- The model can implement natural and urbanized areas, changes in land use, as well as changes in rainfall due to climate change (e.g. Schoener, 2022; Zhang et al., 2019).
- Access is free: Open source model, with user manual (HEC-HMS, 2024).
- The model is often used in semi-arid regions with scarce data (e.g. Schoener, 2022; UN-Habitat, 2020; El Alfy, 2016).
The HEC-HMS model can be set up in various ways in the CapTain Rain project we use the following modules which are suitable for an event based modelling of heavy rainfall events:
Fig.1: Schema of HEC-HMS modules used in CapTain Rain
Data and Methods
The delineation of subbasins and identification of streams is possible in HEC-HMS directly based on a Digital Elevation Model (DEM). For the meteorological model we calculated the gauge weights using the Thiessen polygon function in ArcGIS. The CN for the infiltration module is derived from soil and landuse landcover (LULC) also with ArcGIS. For the different parameters of the transform and routing modules literature values can be found e.g. in USDA (2010). The following table gives an overview about the input data used for the HEC-HMS models for Amman and Wadi Musa respectively.
Tab.1: Input data for the focus areas Amman and Wadi Musa
| Input data | Amman | Wadi Musa |
|---|---|---|
| DEM | 1 m (RJGC) | 2 m (PDTRA) |
| Rainfall | Time series for five stations in/close to our study region in 5 min resolution for the event in Feb. 2019 (JMD, UN-Habitat 2020) | Time series for nine stations in event dependent resolution (PDTRA) and for one station in hourly resolution (MWI) in our study region for the event in Dec. 2022 |
| LULC maps | 1968: CORONA 2021: Sentinel-2 2050: Statistical model & expert interviews |
2021: Sentinel-2 |
| Soil information | HYSOGs250m (Ross et al., 2018) | HYSOGs250m (Ross et al., 2018) |
The different modules can be accessed and adapted via the model’s navigation:
Fig.2: Screenshot of the HEC-HMS model with the Amman catchment
After running the model with a certain setup, as defined in the “Compute” section, the runoff curves at the subbasins outlets as well as the infiltration rates for the different subbasins are available in the “Results” section.
Challenges
Our model results have high uncertainties as they rely on global datasets for information on soil and LULC and local rainfall station data with unknown accuracy. One of the biggest challenges is that there is no runoff data to calibrate and validate the model. Due to this data scarcity we do not trust the calculated runoff values by it self, but focus on the relative changes between different model runs i.e. with past, present and future LULC and possible future rainfall events. These relative changes give the opportunity where to focus and what might happen in the future.
Useful links to access more information:
The latest version of the HEC-HMS model can be downloaded via: https://www.hec.usace.army.mil/software/hec-hms/downloads.aspx
Several manuals are available via: https://www.hec.usace.army.mil/software/hec-hms/documentation.aspx
Also, many tutorial videos are available online e.g. in YouTube
For access to the CapTain Rain HEC-HMS models for Amman and Wadi Musa please contact:
References
- El Alfy, M., 2016: Assessing the impact of arid area urbanization on flash floods using GIS, remote sensing, and HEC-HMS rainfall–runoff modeling. Hydrology Research 47 (6), P. 1142–1160. DOI: 10.2166/nh.2016.133.
- HEC-HMS Hydrological Modeling System of the Hydrologic Engineering Center within the U.S. Army Corps of Engineers (HEC-HMS), www.hec.usace.army.mil/software/hec-hms/ (last excess 03.05.2024).
- Ross, C.W., Prihodko, L., Anchang, J.Y., Kumar, S.S., Ji, W., and Hanan, N.P., 2018: Global Hydrologic Soil Groups (HYSOGs250m) for Curve Number-Based Runoff Modeling. ORNL DAAC, Oak Ridge, Tennessee, USA. https://doi.org/10.3334/ORNLDAAC/1566
- Schoener, G., 2022: Impact of urbanization and stormwater infrastructure on ephemeral channel transmission loss in a semiarid watershed. Journal of Hydrology: Regional Studies, 41, DOI: 10.1016/j.ejrh.2022.101089.
- UN-Habitat, 2020: Developing a Preliminary Design for Flood Mitigation and Performing a Flood Risk Assessment and Flood Hazard Mapping for Downtown Amman, J20112-0100D-RPT-PM-03 REV 0.
- United States Department of Agriculture (USDA), 2010: Natural Resources Conservation Service – Part 630 Hydrology – National Engineering Handbook – Chapter 15 Time of Concentration, https://rashms.com/wp-content/uploads/2021/11/TOC_NRCS-Part-630-Ch-15.pdf.
- Zhang, Y., Wang, Y., Chen, Y., Liang, F., and Liu, H.,2019: Assessment of future flash flood inundations in coastal regions under climate change scenarios-A case study of Hadahe River basin in northeastern China. The Science of the total environment, 693, DOI: 10.1016/j.scitotenv.2019.07.356.