Characterization of extreme precipitation and temperature events during El Niño Southern Oscillation in the Colombian Andes

Extreme precipitation and temperature events (EPTE) cause devastating impacts to ecosystems and society. The diversity of climates around the world does not allow a single definition of extreme events given the multiplicity of conditions in which each event develops. In regions of complex topography, interactions with vegetation have as a result numerous atmospheric circulation patterns and the existence of various phenomena at different spatial and temporal scales, which impedes homogeneity of distribution, frequency, and intensity of extreme events. It is known that El Niño Southern Oscillation (ENSO) influences the interannual variability of precipitation and temperature in different regions around the world. However, it is not clear how this phenomenon interacts with the frequency and intensity of EPTE in regions with complex topography gradient and a diversity of climates. Here we focus on the Colombian Andes mountain range in northern South America because it occupies a quarter of the territory, gathers most of the socio-economic development, and concentrates the majority of the country´s population. In this context, we use statistical analysis to characterize EPTE during La Niña, El Niño, and neutral years. In this work, we also compare the frequency and intensity of EPTE between La Niña and neutral years and El Niño and neutral years. Unlike other studies, we want to know if there is any pattern of increase or decrease of EPTE when an ENSO phase is active. We discuss the months in which there is an increase or decrease in EPTE according to the interannual variability of precipitation and temperature, as well as the months in which there is a significant relationship between the sea surface temperature of the Niño 3.4 region with precipitation and temperature. Our results show that the highest intensities of extreme precipitation events occur in the rainy seasons March-April-May and September-October-November. Also, the highest frequency of extreme precipitation events occurs between December and March for both the 95th and 99th percentile. The difference analysis showed that during El Niño and La Niña periods, extreme precipitation events are more intense than in neutral years. Additionally, the frequency of events is higher during El Niño, but their localization is variable in time and space. The behavior of temperature extremes is more marked since the most intense events occur during El Niño from February to September, and the highest frequency of extreme events occurs between April and September and varies throughout the year in the Andes region according to the active phase of ENSO. These results provide a basis for the design of adaptation and mitigation policies in the face natural variability and climate change, and for improving hydrometeorological forecasts.