## 2 Materials and Methods
### Study Region and Data
Floods are a major problem that can occasionally lead to catastrophic events and can be caused by a high concentration of rainfall within short periods of time or by prolonged sequences of rainy days. These events usually occur in particularly susceptible geological areas (impermeable substrates) such as some tectonic depressions in the interior of Galicia or on the Atlantic coast. Through the study of the daily rainfall series, it is possible to detail the relationships between the duration and the intensity of rainfall. The periods of low duration are in the majority during spring and summer, while the periods of more than 10 days of rain are more characteristic of autumn or winter. The regional government created the MeteoSalicia station network in January 2000, and it has published its data at [[https://www.meteogalicia.es](https://www.meteogalicia.es)]([https://www.meteogalicia.es](https://www.meteogalicia.es)) (accessed on 1 November 2023). Over the years, the network has grown from the initial 14 stations to approximately 150 stations in 2013 (Figure 1). Throughout this time, some stations have been dropped; others have changed their location, and, in other cases, different sensors have been added. The ten-minute data of temperature, humidity, solar radiation, wind, and rainfall have been downloaded in 148 stations, from 1 January 2000 to 31 December 2018, and stored in a PostgreSQL database of more than 400 million records, where more than 90 million correspond to rainfall. Table 1 details the amount of data downloaded for each of these meteorological variables. All stations are equipped with rain gauges to collect rainfall data; however, some of them may lack the corresponding sensors to collect data on other variables. For this study, the rainfall data between 1 January 2000 and 31 December 2006 have been removed because the network of stations was very sparse, and the number of missing data items was very high due to the fact that the first the years stations were in test mode. Regarding the stations selected, only 62 stations were chosen, including those with a registration date before 1 January 2007, and the remaining 86 stations were rejected because their time series data did not reach 10 years, which is the minimum needed to be able to create the intensity-duration-frequency curves. As can be seen in Figure 3, chosen stations have a homogeneous geographical distribution and cover the entire region. Erroneous and missing data are considered imputable data, since we do not have the necessary information to be able to correct them; as well, outliers have also been ruled out. For this reason, it has been necessary to carry out data preprocessing before proceeding to the study. Next, data was analyzed, and it was observed that there were many days with missing data (Figure 4); in the figure below, each row represents one of the 365 days of the year, each column represents a station, the blue cells of the matrix represent the days in which 144 rainfall data items were found to be available, and the red cells represent those days in which at least some missing or erroneous data appeared. It can also be seen how the network of stations has grown from around 70 stations in 2007 to 150 stations in 2018, as well as that, in the first years of operation of the stations, there were many missing data. \begin{table}
\begin{tabular}{c c} \hline \hline Total Data & \(440,250,897\) \\ \hline Mean air temperature & \(79,18,732\) \\ Mean relative humidity & \(79,142,133\) \\ Accumulated global solar radiation & \(61,199,261\) \\ Mean wind speed & \(64,931,543\) \\ Mean wind direction & \(65,299,572\) \\ Accumulated rainfall & \(90,492,656\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Registers stored in the database. By means of algorithms developed ad hoc for the GIS tool, it has been possible to carry out a detailed study observing in which stations a greater number of missing data appeared.