Climate Variability and Its Effect on Flood Risk Through Dynamic Modeling in the Quigushuaycu Stream

Every year in the rainy season, Quito's ravines generate intense floods with considerable human and economic losses. Water is crucial for human development, the environment, and the economy. The water infiltrating the soil depends on the degree of salinity in it. This can generate adverse effects such as flooding. In the last decade, the Conocoto parish in the south of Quito city, Ecuador's capital, has gained importance. It has become a highly populated area where agricultural, industrial, and residential activities occur. This study evaluated the impact of the Sodium Adsorption Ratio (SAR) index on the risks of infiltration in the Quigushuaycu stream in the Conocoto parish. With the help of HEC-RAS modeling, it is determined that 4.7% of the stream has a potential risk of heavy flooding. A representative sample of water from the creek was taken, and the concentration of calcium, magnesium, and sodium and electrical conductivity were measured. It is worth mentioning that the best time to take the sample is in the rainy season because there is a more significant amount of water in the stream there. The sodium adsorption ratio index is calculated, with a value of 0.74 meq/L and an electrical conductivity of 410 µS/cm. When applying the Relative Reduction Diagram of infiltration caused by salinity and RAS, water with medium salinity and low sodium from the creek fell into the severe and light-moderate reduction categories. Regarding the anomalies of the accumulated annual rainfall, they presented a significant interannual variability associated with the occurrence of the phenomenon “El Niño Southern Oscillation.”