[Lcefiec] COLOQUIO:"The impact of rainfall-extreme events on sediment-transport and erosion processes in the south-central Andes of NW Argentina"

[coloquios]

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Coloquio del Departamento de Ciencias de la Atmósfera y los Océanos
(DCAO)/
Centro de Investigaciones del Mar y la Atmósfera (CIMA)

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Jueves 22 de Marzo, 13hs, 2º Piso, DCAO, SALA DE REUNIONES

COLOQUIO
"The impact of rainfall-extreme events on sediment-transport and 
erosion processes in
the south-central Andes of NW Argentina – PhD research proposal"

Fabiana Castino
Universität Potsdam, Germany
castino at geo.uni-potsdam.de


Resumen:

Erosion processes, sediment transport, and deposition-aggradation 
cycles are
primarily controlled by rainfall and river discharge. In order to 
understand how rainfall, and in
particular hydrometeorological extreme events (> 90th percentile) 
modulate erosive
processes in tectonically active mountain belts, my proposed study 
focuses on the southern
Central Andes of NW Argentina. This region is a climatic threshold 
area, characterized by
pronounced relief contrasts and a steep rainfall gradient, which is 
fundamentally affected by
climate variability on different time scales.

In a traverse perpendicular to the orogen the southern Central Andes 
comprise a
pronounced topographic gradient involving a change from 500m elevation 
in the undeformed
foreland to >1500m in the intermontane basins of the Eastern 
Cordillera, and >3500m
elevation in the internally drained Puna Plateau. These basins receive 
large quantities of
sediment from the flanks of mountain ranges that reach >5000m elevation 
and either
transiently store or route sediment to the foreland regions. The 
topographic contrasts of this
region are accompanied by a transition from humid sectors along the 
eastern flanks of the
mountain ranges to arid basins in the orogen interior, and an E-W 
decrease in the erosional
efficiency of fluvial systems. The tectonic evolution of the region has 
provided corridors for
moisture transport from the eastern lowland to the semi-arid to arid 
intermontane basins to
the west, which offers favourable conditions for enhancing rainfall and 
erosion processes in
the orogen interior during times of increased moisture availability.

Spatiotemporal variability of rainfall in this part of South America is 
fundamentally
influenced by the El Niño Southern Oscillation (ENSO). During negative 
ENSO phases (La
Niña), frequent and intense rainfall events occur along the eastern 
flank of the Andes,
creating high positive rainfall anomalies and a penetration of moisture 
into the orogen. During
these events the resulting sediment-transport processes transfer large 
volumes of sediment
from the hillslopes through the fluvial system to the foreland, 
although sediments may be
transiently stored in intermontane basins. Currently, it can be 
observed that many fluvial
systems in this region are forced to alluviate due to high sediment 
availability, affecting
infrastructure and socioeconomic activities in these areas.

In order to evaluate the link between rainfall, runoff, and sediment 
transport,
hydrological time series from several surface stations were collected 
in this region. I
analyzed the observed rainfall data, in terms of normal mean and 
extreme values. In a
follow-up study, due to a pronounced decrease in surface-station 
density during the last
decades especially in the orogen interior, I will integrate the 
available observed time series
using satellite and nested climate-modelling approaches. The 
characteristics of modern
rainfall patterns will be evaluated applying Empirical Orthogonal 
Function (EOF) analysis to
the integrated time series with particular emphasis on extreme values. 
Furthermore, the rate
of mass removal will be determined using discharge and suspended 
sediment-load data
available from gauging stations. This analysis will be extended to 
those basins and fluvial
systems for which a poor database exists, applying runoff and specific 
stream power
modelling approaches. Additional information on the spatial 
distribution of eroded sediments
will be obtained by exploiting recognition techniques using time series 
of remote sensing
imagery. Finally, I will integrate the outcomes of the previous 
analyses to evaluate how
extreme rainfall events impact erosive and sediment transport processes 
in order to define
under which conditions surface processes are most efficient. Thus far, 
a test case relevant to
an extreme event in the study area has been analyzed, both using 
observed rainfall data and
applying a regional climate model. Comparison between the observations 
and the simulated
rainfall field shows encouraging results, rendering this a promising 
approach for further work.

Lugar: SALA DE REUNIONES, DCAO, 2º Piso
Pabellón 2,
Ciudad Universitaria.

Los esperamos a todos!

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Grupo Coloquios
Departamento de Ciencias de la Atmosfera y los Oceanos (FCEN-UBA)
Centro de Investigaciones del Mar y la Atmosfera (CONICET-UBA)
Ciudad Universitaria, 2do piso.
email: coloquios at at.fcen.uba.ar
http://www.at.fcen.uba.ar/charlas_not.php
http://www.cima.fcen.uba.ar/espanol/index.htm
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