Prйsentation PowerPoint

1
HYDROCLIMATIC VARIABILITY IN THE ANDEAN REGION OF
THE AMAZON BASIN
ESPINOZA VILLAR Jhan Carlo1,2,3, GUYOT Jean
Loup1,2, RONCHAIL Josyane1,3,4, CHAVARRI
Eduardo1,2, FRAIZY Pascal1,2, GUYOMARD Marine1,5,
NORIEGA Luis1,6, de OLIVEIRA Eurides1,9, ORDÓÑEZ
Juan Julio1,7, POMBOSA Rodrigo1,8, VAUCHEL
Philippe1,2,6.
INTRODUCTION
The Amazon Basin (AB) is the major hydrological
basin in the world (6.106Km2, Molinier et al.,
1996). Discharge variability has been studied in
the main stream (Richey et al., 1989 Costa and
Foley, 1999) and a strong variability since the
1970s has been put in evidence by Callède et al.
(2004) and Labat et al. (2005). Few studies
analyzed the regional hydroclimatic variability
(Rocha et al., 1989 Marengo et al., 1998
Ronchail et al., 2006 Espinoza et al., 2006),
though strong runoff events occurred lately, as
the dramatic low flow in the western basins in
2005 (Zeng et al., 2007). Nevertheless, what is
the main runoff variability in the Andean rivers
of the AB? Is the evolution of mean values the
same than for extreme values?
DATA
The rainfall and runoff annual cycle in TAM, PVE
and OBI show a strong seasonality in the tropical
PVE basin, but is more regular in TAM and OBI
because they drain tropical and equatorial
regions (Fig. 3A, B and C).
RESULTS AND DISCUTIONS
Trend tests (parametric Pearson and
non-parametric and rank based Spearman and
Kendall coefficients) are applied. The
interannual rainfall and runoff evolutions reveal
a strong diminution in TAM and PVE and no trend
in OBI, during the 1974 2004 period (Fig. 4A B
and C). A Qmean and Qmin diminution in TAM and
PVE (significant at the 99 level), and no trend
in Qmax is observed for the 1974 2004 period
(Figure 5 A, B and C, and Table 2). OBI do not
display any significant trend during this period.
In Andean rivers sub basins, strong trends are
detected for the 1990 2005 period (Figures 5 D,
E and F and Table 2). Inside PVE, trends are
negative, strong in GUA and weak in CAE. Toward
north, a strong diminution is observed in REQ,
but trend is positive and strong in SRE (in Qmax
and Qmean principally). In BOR no significant
trend is observed.
FIGURE 5
CONCLUSIONS AND PERSPECTIVES
Strong runoff trends are noticed in the Andean
rivers of the AB during the 1974 2004 period.
An opposition is put in evidence between a
negative trend in many shouthern tropical basins
specially in Qmin and Qmean and a positive trend
in a small northern equatorial basin, especially
in Qmax. These trends are consistent with
rainfall variability (Espinoza et al., 2007a).
The resultant runoff diminution in the Andean
rivers of the AB and the absence of trend in the
mean stream at Obidos, suggest that the Andean
rivers of AB cause extreme low stage values in
OBI and that increasing high flow values should
be registered in other basins. So, what is the
trend in the other Amazon sub basins (Espinoza et
al., 2007b)? Any way, what is the origin of these
trends regional and/or global climate changes or
human impacts as deforestation?
1 HYBAM. 2IRD/UNALM-PERU. 3LOCEAN/IPSL-FRANCE.
4UNIVERSITÉ PARIS 7-FRANCE. 5 ENS-FRANCE.
6SENAMHI BOLIVIA. 7SENAMHI PERU. 8INAMHI ECUADOR.
9ANA BRAZIL. Correspondence to ESPINOZA VILLAR
J.C. LOCEAN. Boite 100, 4 Place Jussieu, 75252.
Paris Cedex 05, France. jhan-carlo.espinoza_at_locean
-ipsl.upmc.fr.