Floods in Argentina: identification of daily rainfall thresholds and their relationship with intraseasonal variability

FEDERICO ARIEL ROBLEDO; MARIANO ALVAREZ; CAROLINA VERA

Brasilia

Workshop; 2nd CLIMAX General Meeting; 2017

Instituto Nacional de Pesquisas Espaciais (INPE), Brasil

There are different statistical techniques to identify events of extreme daily rainfall (Extreme Values Theory, daily percentiles, etc.). These techniques only contemplate rain above a statistical threshold, without evaluating whether this threshold effectively covers all situations of social or economic impact in a territory. This work defines daily rainfall thresholds taking the impact of floods in La Matanza, a locality with 2 million people, located in the Metropolitan area of Buenos Aires, Argentina. In addition, the relationship with the SIS pattern of intra-seasonal variability is analyzed.Extreme daily rainfall thresholds were calculated with the 75th and 95th percentile, with rainfall data from the National Meteorological Service closest to the locality (7km, Ezeiza Station) in the 1982-2015 period. In addition, the daily rainfall threshold was estimated from the 71 flood dates recorded between 1982 and 2015 of the impact database provided by the Ministry of Science. Flood dates are associated with a sequence of 4 to 6 rainy days (not necessarily consecutive) with a mean daily intensity of 30 (23) mm/day in summer (spring). This value is lower than that given by P95 which in summer (spring) is 40 (37) mm/day. The relationship between flooding and intra-seasonal variability was analyzed using the SIS pattern. This pattern of climatic variability acts in periods of several days-weeks, altering the conditions of temperature and rain mainly in the central-east of Argentina, Uruguay, Paraguay and south-southeast of Brazil. In La Matanza, 50% of the floods occurred in the positive phase of the SIS pattern, and 15% in the negative phase.