Abstract

PAREDES-TREJO, Franklin; GUEVARA-PEREZ, Edilberto; BARBOSA-ALVES, Humberto  and  UZCATEGUI-BRICENO, Carlos. Seasonal Trend of the Rainfall and the Influence of El Niño-Southern Oscillation on the Occurrence of Extreme Rainfalls at the Watershed of Valencia's Lake, Venezuela. Tecnol. cienc. agua [online]. 2015, vol.6, n.6, pp.33-48. ISSN 2007-2422.

The Valencia lake basin is the endorheic watershed larger of Venezuela (VLB). VLB is densely populated and industrialized; therefore the extreme climate events can cause severe impacts. In the Venezuelan territory, it is known that ENSO (El Niño-Southern Oscillation) can modulate the rainfalls, however no has been explored in detail as ENSO can affect the rainfalls on VLB. This study analyzes the spatio-temporal trends of the seasonal rainfalls and explores the association between the occurrence of extreme rainfall months and the phases of ENSO (El Niño, La Niña and Neutral) on VLB. Eight stations were selected by the quality control of their registers. We considered two periods for our analysis: 1934-2005 (local scale) and 1966-1992 (regional-local scale). In addition, were identified the months of occurrence of the rainy and dry seasons. The accumulated rainfall by season in each station was calculated and after was explored the occurrence of a long-term trend by Mann-Kendall test. Seasonal precipitation in each station and season was categorized in extreme dry, extreme-no, or extreme wet (ED, EN and EW) using the 10th and 90th percentiles as threshold. The likelihood of occurrence of a month ED, EN or EW at local scale according to season and phase of ENSO was estimated. The association between these categorical variables was analyzed by chi-square test for independence. The results more remarkable were: there is no evidence of a long-term trend at local scale on seasonal precipitation; the Niño/Niña episodes are partially associated with the occurrence of extreme rainfall at seasonal scale; a high-proportion of the extreme rainfall events could have been driven by local factors which were not evaluated here.

Keywords : Valencia's Lake; El Niño-Southern Oscillation; climate change; extreme rainfall.

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