Abstract
Climate change is considered as one of the main factors controlling sediment fluxes in mountain belts. However, the effect of El Niño, which represents the primary cause of inter-annual climate variability in the South Pacific, on river erosion and sediment transport in the Western Andes remains unclear. Using an unpublished dataset of Suspended Sediment Yield (SSY) in Peru (1968–2012), we show that the annual SSY increases by 3–60 times during Extreme El Niño Events (EENE) compared to normal years. During EENE, 82% to 97% of the annual SSY occurs from January to April. We explain this effect by a sharp increase in river water discharge due to high precipitation rates and transport capacity during EENE. Indeed, sediments accumulate in the mountain and piedmont areas during dry normal years, and are then rapidly mobilized during EENE years. The effect of EENE on SSY depends on the topography, as it is maximum for catchments located in the North of Peru (3–7°S), exhibiting a concave up hypsometric curve, and minimum for catchments in the South (7–18°S), with a concave down hypsometric curve. These findings highlight how the sediment transport of different topographies can respond in very different ways to large climate variability.
Highlights
Numerous studies on erosion mass balance at global, regional or local scales highlight the control of geological[1,2], climatic[3,4] and anthropical[5,6,7] constrains on erosion rates
To characterize statistics of river hydrology during Extreme El Niño Events (EENE) and normal periods, we rely our analysis on the use of cumulated density function (CDF) of daily river discharge from long-term time series (Fig. 2a)
During normal periods about 90% of daily discharge events occur for Q/Qmean < 2.5 for all the catchments, while during EENE periods, 90% of daily discharge events occur 1) for Q/Qmean < 12 or 8 when considering the Ardilla and El Tigre stations, respectively; or 2) for Q/Qmean < 4 when considering the Socsi, Condorcerro and La Balsa stations
Summary
Numerous studies on erosion mass balance at global, regional or local scales highlight the control of geological[1,2], climatic[3,4] and anthropical[5,6,7] constrains on erosion rates. Some of the highest recorded erosion rates occur in tropical mountain ranges, where large magnitude earthquakes and rainfall events are frequent[8,9] This observation questions the impact of such extreme events, relatively to average conditions, on the source to sink mass balance of mountains belts. The western Peruvian Andes (3–18°S) are located in a region where frequent floods and recurrent large earthquakes occur[10], which in turn influence sediment fluxes in this mountainous region[11,12] It is an area where extreme hydrological and climatological processes occur, partly driven by the irregularly periodical ENSO, which is characterized by changes in atmospheric pressure and sea surface temperature around the Pacific Ocean.
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