Heterogeneous distribution of rainfall and discharge regimes in the Ecuadorian Amazon basin

Abstract : The hydrology of the Ecuadorian Amazon basin is still poorly documented. The research developed between the Institute for Research and Development (IRD) and the National Institute of Meteorology and Hydrology (INAMHI) of Ecuador takes advantage of a newly available rainfall and discharge dataset to explore spatial distribution and regimes in this region (135 600 km2). Forty-seven rainfall and 27 discharge stations were retained over a 30-yr period (1965-94). A new annual isoyets map is proposed for the Amazon basin of Ecuador. The most striking result is a high spatial regime variability, to the extent that out-of-phase regimes are found in nearby stations. Indeed, in high intra-Andean basins there is a marked bimodal rainfall regime, with maxima in March-April and in October and a minimum from June to August. On the contrary, as moisture transport reaches a maximum in June, a rainfall peak can also be observed at the same time on slopes to the east due to the moist easterlies. In the lowlands, a bimodal regime is observed as in the intra-Andean basin; as water vapor is abundant, seasonal variability is not as strong as in the Andes. Discharge regimes are related to rainfall regimes. However, even if no delay is observed between maximum rainfall and maximum discharge in the inner Andean basins, a delay varying from one to two months is observed in larger basins. Soil conditions also affect the discharge regime in the upper and inner Andes: paramo soils (a kind of tundra formation) release water, in particular after the March-April rainfall peak, and sustain the dry season runoff.
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Alain Laraque, Josyane Ronchail, Gérard Cochonneau, Rodrigo Pombosa, Jean Loup Guyot. Heterogeneous distribution of rainfall and discharge regimes in the Ecuadorian Amazon basin. Journal of Hydrometeorology, American Meteorological Society, 2007, 8 (6), pp.1364-1381. ⟨10.1175/2007JHM784.1⟩. ⟨ird-00555542⟩

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