El Niño and La Niña influence on mean river flows of southern South America in the 20th century

Figures & data

Table 1. River flow gauge stations used, listed from north to south, with upstream drainage area (km²), long-term maximum and minimum monthly mean discharge (m³ s⁻¹), period of analysis and data source. SHR: Secretary of Hydric Resources of Argentina; GWD: General Water Directorate of Chile.

River	Gauge station	Drainage (km^2)	Monthly discharge (m^3 s^−1)		Period of analysis	Data source
			Max	Min
Colorado	Pichi Mahuida	22 300	274	73	1919–2003	SHR
Neuquén	Paso de Indios	30 843	608	93	1904–2003	SHR
Limay	Paso Limay	26 400	1031	258	1904–1989	SHR
Cautin	Rari Ruca	1365	175	42	1930–2006	GWD
Tolten	Villarica	2880	440	131	1930–2006	GWD
Pilmaiquén	San Pablo	2680	298	84	1930–2006	GWD
Manso	Los Alerces	750	61	20	1952–2003	SHR
Futaleufú	Balsa Garzón	4608	351	164	1949–2001	SHR
Chubut	Los Altares	16 400	86	10	1944–2003	SHR
Santa Cruz	Charles Fuhr	15 550	1273	281	1957–2002	SHR
Grande	Tierra del Fuego	2725	48	11	1982–2006	SHR
San Juan	Desembocadura	860	32	7	1981–2006	GWD

Figure 1. Geographical distribution of the river basins in the southern extreme of South America, and long-term monthly mean river flows (m³ s⁻¹).

Figure 2. Oceanic Niño Index (ONI) average of El Niño (red) and La Niña (blue) events for the period 1950–2003. Values are 3-month running means of SST anomalies (°C) in the Niño3.4 region (5°N–5°S, 120°W–170°W), from February of the year when the ENSO event starts (o) until November of the following year (+).

Table 2. List of warm (El Niño) and cold (La Niña) ENSO events considered in the study.

Warm ENSO (El Niño) events	Cold ENSO (La Niña) events
1902/03, 1905/06, 1911/12	1904/05, 1908/09
1914/15, 1918/19, 1923/24	1910/11, 1916/17
1925/26, 1930/31, 1932/33	1924/25, 1928/29
1939/40, 1941/42, 1951/52, 1953/54, 1957/58, 1958/59	1938/39, 1954/55 1955/56, 1964/65
1963/64, 1965/66, 1968/69	1970/71, 1971/72
1969/70, 1972/73, 1976/77	1973/74, 1974/75
1977/78, 1979/80, 1982/83 1986/87, 1987/88, 1991/92 1992/93, 1994/95, 1997/98 2002/03, 2004/05	1975/76, 1983/84 1984/85, 1988/89 1995/96, 1998/99 1999/00, 2000/01

Figure 3. Monthly mean river flows (m³ s⁻¹) of El Niño (red) and La Niña (blue) composites, and long-term monthly mean river flows (black), with geographical reference of the basins. The 24-month period runs from January of the year when the ENSO event starts (o) until December of the following year (+), both years separated by a vertical line.

Table 3. Differences between El Niño and long-term monthly mean river flows. The red scale boxes indicate positive differences and the blue scale boxes negative differences. The colour scale indicates that the result of Student’s t test of the difference in means is significant at 99%, 95% and <95% confidence levels, respectively. White boxes indicate no difference between monthly mean river flows. The vertical black line divides year(o) when the ENSO event begins and the following year(+). The rivers are listed from north to south and the horizontal thick lines separate groups of rivers (see text for the details).

Table 4. Differences between La Niña and long-term monthly mean river flows. See Table 3 for explanation.

Figure 4. Time series of annual mean river flows (m³ s⁻¹) of the (a) Colorado, (b) Chubut and (c) Santa Cruz rivers for the whole available period of each river.