# Development of Open-Source Tools for Event-Based Hydrological Modelling Using GIS and Python
## 2 Materials and Methods
### Case Study  
We selected a set of 29 small-sized catchments at the Spanish Ebro River basin (see Figure 3). The Ebro River basin, located in Northeastern Spain, is the country's largest river basin, covering approximately 85,000 km\({}^{2}\). Hydrologically, the Ebro River flows over 910 km from its headquarters in the Cantabrian Mountains to its delta on the Mediterranean Sea, with a complex network of tributaries exhibiting diverse flow regimes influenced by snowmelt, rainfall and groundwater contributions. Geologically, the basin is characterised by a combination of the Pyrenean ranges to the north, the Iberian System to the south, and the Ebro Depression in the central sector, which is filled with Tertiary and Quaternary sedimentary deposits, mainly clays, marls, and limestones, influencing infiltration rates and groundwater dynamics. Climatologically, the basin exhibits high variability, with Atlantic influences in the headwaters, a continental semi-arid climate in the central depression, and Mediterranean influences near the delta. The average annual precipitation rangesfrom over 1200 mm in the Pyrenean headwaters to less than 400 mm in the central valley, while average temperatures vary significantly, with cold winters and hot, dry summers dominating the lower basin.  
We selected pilot catchments with high latency precipitation and water level records at the downstream end point, featuring homogeneous land uses and potential for easy parametrisation to apply hydrological models. Table 2 presents the main catchments characteristics.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Catchment** & **z Max** & **z Min** & **Channel** & **Catchment** \\  & **(masl)** & **(masl)** & **Length** & **Area** \\ \hline Aragon at Canfranc & 2160.03 & 1041.91 & 18,987.66 & 18,254,694 \\ Bailin at Sabinanigo & 1078.86 & 743.675 & 4651.442 & 4,508,212 \\ Cidacos at Arnedillo & 1607.32 & 647.671 & 28,141.38 & 176,407,587 \\ Cidacos at Yanguas & 1607.32 & 943.343 & 26,049.78 & 230,120,488 \\ Deza at EmbidDeAriza & 1091.97 & 780.169 & 40,193.02 & 207,366,324 \\ Flamisell at Cabella & 2670.56 & 1275.38 & 17,336.71 & 72,034,834 \\ Garona at Bossost & 2577.25 & 710.235 & 47,696.3 & 440,715,489 \\ Isuela at Trasobares & 1580.56 & 636.852 & 28,743.83 & 116,994,476 \\ Izalzu at Anduña & 1501.12 & 796.684 & 12,066.23 & 47,171,880 \\ Larraun at Iribas & 697.602 & 560.652 & 3067.464 & 5,825,444 \\ Nela at Villarcayo & 1495.34 & 1065.76 & 16,309.96 & 105,146,261 \\ Linares at & & & & \\ SanPedroManrique & 947.97 & 593.783 & 51,586.01 & 254,733,836 \\ Oca at Oña & 1235.93 & 572.718 & 90,988.14 & 1,038,283,932 \\ Oja at Azurrulla & 1895.08 & 919.251 & 14,463.59 & 73,822,908 \\ Omecillo at Berengueda & 940.005 & 477.69 & 37,291.6 & 342,161,356 \\ Oroncillo at Oron & 1031.87 & 477.678 & 39,005.88 & 215,597,179 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Main properties of the selected catchments.  
Figure 3: Area of study representing the selected catchments in the Ebro River basin (images retrieved from the Spanish national mapping provider, Instituto Geografico Nacional at [[https://centrodedescargas.cnig.es/CentroDescargas/index.jsp#](https://centrodedescargas.cnig.es/CentroDescargas/index.jsp#)]([https://centrodedescargas.cnig.es/CentroDescargas/index.jsp#](https://centrodedescargas.cnig.es/CentroDescargas/index.jsp#)), accessed on 16 May 2025).  
Table 3 presents a summary of the GIS data sources used in this study, along with their respective spatial resolutions.