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INTERNATIONAL JOURNAL OF CLIMATOLOGY
Int. J. Climatol. 20: 63–72 (2000)
EL NIN0 O/LA NIN0 A RELATIONSHIP WITH RAINFALL AT
HUANCAYO, IN THE PERUVIAN ANDES
R.P. KANE*
Instituto Nacional de Pesquisas Espacias-INPE, Caixa Postal 515, 12201 -970 -São José dos Campos, SP, Brazil
Recei6ed 29 May 1998
Re6ised 23 March 1999
Accepted 6 April 1999
ABSTRACT
The major rainy season at Huancayo (central Peruvian Andes) is in the months DJFM (December – March). For years
when El Niños were active during these months, two types of effects were noticed. Either there were rainfall deficits
in the DJF months, or there were excess rains in DJ, followed and preceded by deficit rains for a month or two. When
El Niños were active in other months, the non-rainy season rainfall at Huancayo was sometimes far above average.
During years of La Niña (Anti-El Niños), there were often excess rains, in both the rainy and the non-rainy seasons.
In coastal Peru, heavy rainfall is considered as one of the criteria for identifying an El Niño. If true, the rainfall
patterns at Huancayo are different from those of coastal Peru. In the recent El Niño of 1997, southern Peru had
droughts while eastern and northern Peru, Ecuador had floods. The ENSO relationships in different parts of Peru are
probably different and need detailed investigation. Copyright © 2000 Royal Meteorological Society.
KEY WORDS: Huancayo;
Peruvian Andes; El Niño; Southern Oscillation; ENSO; sea-surface temperature; rainfall; drought; flood
1. INTRODUCTION
As described by Quinn (1974, 1992), El Niño refers to the invasion of anomalously warm surface waters
along the southern Ecuadorian and Peruvian coastal regions which are usually under the influence of
cooler waters from coastal upwelling and the northward flowing Peru current. These invasions are
infrequent (spaced 2 – 7 years apart) and generally set in between January and March, coinciding with the
Southern hemisphere summer when sea-surface temperatures (SST) are at a seasonal high. El Niño is
brought about by relaxation from a prolonged period of strong southeast trades and is manifested also
by falling and low Southern Oscillation indices such as Tahiti minus Darwin atmospheric pressure.
Background information on El Niño was provided by Wooster (1960), Idyll (1973) and Miller and Laurs
(1975), monitoring and prediction possibilities were discussed by Quinn (1974) and the relationship with
Southern Oscillation was discussed by Berlage (1957, 1966), Troup (1965) and Quinn (1971, 1976).
Atmospheric teleconnections were investigated by Bjerknes (1966, 1969).
El Niños are at times accompanied by abnormally heavy rainfall over the ordinarily arid coastal region
of Ecuador and Peru, causing mass mortality of indigenous marine life and having a disastrous effect on
Peruvian anchoveta fisheries. Quinn et al. (1978, 1987) have made a determination of the occurrence and
intensity of El Niño events by considering several factors at the Peru and Ecuador coastal regions, such
as (i) disruptions of the anchoveta fishery and marine bird life; (ii) reports of events affecting the coastal
regions; (iii) hydrological data; (iv) SST; (v) coastal rainfall; (vi) characteristics of the Southern Oscillation
Index; (vii) data from only one core of the Southern Oscillation; (viii) SST over the equatorial Pacific; (ix)
rainfall at central and western equatorial Pacific islands. More details are given in Quinn (1992).
* Correspondence to: Instituto Nacional de Pesquisas Espacias-INPE, Caixa Postal 515, 12201-970-São José dos Campos, SP,
Brazil; e-mail: kane@laser.inpe.br
CCC 0899–8418/2000/010063 – 10$17.50
Copyright © 2000 Royal Meteorological Society
64
R.P. KANE
Though El Niños (warmer waters in the Peru–Ecuador coast) are generally associated with low values
of the Southern Oscillation Index (SOI), represented by the Tahiti minus Darwin pressure difference,
often there is a phase lag or lead. As mentioned in Deser and Wallace (1987), El Niños can occur both
in advance of and subsequent to major SOI negative swings. In addition, the two may occur even
separately. For El Niños and the Pacific Sea surface temperature anomalies, Fu et al. (1986) noticed that
there were at least two distinct patterns. In one, the Pacific was warmer east of the dateline, warmer in
the central Pacific, but slightly below normal west of the dateline (examples 1957, 1965, 1972, 1982). In
another, the Pacific was warmer everywhere (examples 1963, 1969). In cases like 1976, there was a mixture
of the two. These different patterns could have different effects on the world climate. Ward et al. (1994)
sorted out years according to whether these were wet (excess rains) or dry (droughts) in Sahel and India
and their average characteristics were studied in terms of SST anomalies in the Pacific. They found that
years of Type I which were associated with near-global rainfall teleconnections including a tropic-wide
oscillation, had a strong contrast in sea-surface temperature anomalies between the central/eastern
tropical Pacific and western tropical Pacific, leading to a strong perturbation in the longitude of the
maximum in the zonal sea-surface temperature profile at 0–10°S in the western Pacific. Trenberth (1993)
refers to different ‘flavours’ of El Niño. Most of the workers obtain composites lumping together all warm
events, e.g. all El Niños (Rasmusson and Carpenter, 1983), or all SOI minima (Kiladis and Diaz, 1989)
or all warm water events in the Pacific (Mooley and Paolino, 1989). Recently, Kane (1997a,b) attempted
a finer classification in which Unambiguous ENSOW type events were found to be overwhelmingly
associated with droughts in India and southeastern Australia. These were El Niño (EN) years (the list of
Quinn et al., 1978, 1987), during which the SOI (represented by the Tahiti minus Darwin atmospheric
pressure difference T− D) had a minimum (SO) and the equatorial eastern Pacific sea surface temperatures SST had a maximum (W) in the middle of the calendar year. In the present communication, the
behaviour of rainfall at Huancayo, Peru (12°S, 75°W), a location at a high altitude (3313 m) in the central
part of Peruvian Andes, is examined for the various categories of years.
2. DATA
For rainfall, the monthly values (in mm) at Huancayo are used, for 1923 onwards. For commencement
and evolution of the El Niño, the SST (sea-surface temperatures) at Puerto Chicama (Peru coast, 8°S,
80°W) are used. These are available since 1925. Since 1950, CPC (Climate Prediction Center of NOAA’s
National Centers for Environmental Prediction) gives in their monthly Climate Diagnostic Bulletins,
average monthly temperatures in four geographical regions, Niño 1 + 2 near the Peru–Ecuador coast
(0°S–10°S, 90°W– 80°W), Niño 3 at (5°N – 5°S, 150°W–90°W) and Niño 4 at (5°N–5°S, 160°E–150°W).
Among these, Niño 1 +2 region temperature variations match those of Puerto Chicama SST very well,
except that the Puerto Chicama SST anomalies are larger by about a factor of two.
3. FINER CLASSIFICATION OF ENSO EVENTS
In the literature, the term ENSO is used for the general phenomenon of El Niño–Southern Oscillation.
Here, it will be used in the same sense only in general terms; but for specific designation of years, their
literary meaning is used. Thus,
EN =presence of El Niño (warmer waters) at Puerto Chicama (Peru–Ecuador coast) (the list of Quinn
et al., 1978, 1987, and later, visual inspection of the plots).
SO =presence of minima in the SOI, Wright Index or the Tahiti minus Darwin atmospheric pressure
difference (T−D), or maxima in (D− T).
W= presence of maxima (positive anomalies) in the sea-surface temperature (SST) in the eastern
equatorial Pacific (Niño 3 region). Anomaly exceeding 1.0°C.
Copyright © 2000 Royal Meteorological Society
Int. J. Climatol. 20: 63 – 72 (2000)
PERUVIAN ANDES RAINFALL AND EL NIN0 O
65
C= presence of minima (negative anomalies) in the SST in the eastern equatorial Pacific region (Niño
1+ 2 and Niño 3 region). All La Niñas mentioned by various workers are included here.
Various combinations of these were seen. Of major interest are events of type ENSOW, where El Niño
(EN) existed (the list of Quinn et al., 1978, 1987), SOI minima (SO) also existed and, eastern equatorial
Pacific SST was warmer (W). The SOI and SST plots of monthly values are often erratic. But their
12-monthly running means are smooth and show distinct maxima and minima, as seen in the various plots
in Kane (1997a,b). These were used to check whether the SOI minima or SST maxima occurred in the
middle of the calendar year (May – Aug.). If so, the events were termed as ENSOW-U, i.e. Unambiguous
ENSOW. If the extremes were in the earlier or later part of the year (not in the middle), the events were
termed as ENSOW-A, i.e. Ambiguous ENSOW. As shown in Kane (1997a,b), the Unambiguous ENSOW
were overwhelmingly associated with droughts in India and southeastern Australia. Other combinations
were ENSO, ENW, in which El Niño existed at Puerto Chicama, but either SOI minima or W existed, not
both (dephasing mentioned by Deser and Wallace, 1987). Other combinations not involving El Niños
were: (i) SOW which means SOI minima (SO) existed, equatorial eastern Pacific temperature was warmer
(W), but there was no El Niño mentioned in the Quinn et al. list; (ii) SO, only SOI minima existed; (iii)
W, only central Pacific was warmer; (iv) years having neither an EN nor SO nor W nor C, are termed as
non-e6ents.
Some years are designated as SOC or ENC. This looks contradictory as SO or EN are warm events
while C is a cold event and these cannot exist at the same time. What is implied is that in these years, SO
or EN existed in the early part of the year and C in the later part. These events could have been considered
as non-events, but are used as other types of El Niños, mainly to increase the size of the sample, hoping
that these could reveal El Niño effects on rainfall in the early part of the year. One event (1973) was
actually an extension of the 1972 event and could have been considered as an Ambiguous ENSOW, S
1973 II. But the event was very short lived (January–February 1973) and has been mentioned by some
workers as a La Niña (Philander, 1990). Hence, it is designated as ENC, as a special case. However, this
is not of any consequence, because, in the present communication, the ENC and SOC e6ents are not used
in obtaining composites, to avoid complication.
These designations are somewhat subjective and some borderline cases may throw some small events
into another category. Thus, in the Kane (1997a,b) listing, 1927 may be ENC rather than C; 1929 may
be EN rather than a non-event; 1960, 1961, 1962 should be C rather than non-events; 1976 is probably
an Ambiguous ENSOW rather than an Unambiguous ENSOW. In the present paper, these changes are
incorporated. But most of the major events are clearly defined and are as in Kane (1997a,b). Similar
designations are available for 1871 – 1924 also, before the availability of Puerto Chicama data. For these,
the Wright SST Index (Wright, 1984) was used. For the period 1900–1990, the classification used is as
shown in Table I.
4. AVERAGE PATTERNS AND PROCEDURE OF ANALYSIS
Figure 1(a) (top plot) shows the SST at Puerto Chicama for two successive years. The thick line is the
average pattern for 1950 – 1979 (Deser and Wallace, 1987, repeated twice), showing temperature (°C)
maxima during the southern summer (JFMA months). The crosses are values for two successive years
1972–1973. For 1972, the values are above average, indicating the presence of a strong El Niño in 1972
(Quinn et al., 1978, 1987), which continued up to January–February 1973 and fizzled out thereafter. The
second plot in Figure 1 is the anomaly (actual monthly values minus average). The excess temperature
anomalies (exceeding 1.0°C) in 1972 are shaded and the temperatures below average in 1973 are shown
hatched. The third plot is for the SOI, the Tahiti minus Darwin standardized atmospheric pressure, and
shows prominent minima during the middle of 1972. Hence, 1972 was designated as Unambiguous
ENSOW (ENSOW-U). The year 1973 is also considered an El Niño year. It should have been an
Ambiguous ENSOW (ENSOW-A), but the SST anomaly was positive only during January–February,
followed by a cold event. Hence, it is designated as ENC, useful as an El Niño for the early part of 1973.
Copyright © 2000 Royal Meteorological Society
Int. J. Climatol. 20: 63 – 72 (2000)
66
R.P. KANE
Figure 1(b) shows similar plots for the rainfall at Huancayo. The thick line in the top plot shows the
average rainfall (1922 – 1997) in mm. The major rainfall is during DJFM months. The crosses show the
actual rainfall in 1972 and 1973. The second plot shows the anomalies (deviations from the average
pattern, in mm) and shows excess rains in April 1972 and from December 1972 to April 1973 and again
in July and October 1973, often exceeding 50 mm. (Results for other El Niño years are discussed further
later.) The third plot in Figure 1(b) shows the rainfall anomaly values of the second plot, but expressed
as fractions of the standard deviation of each month (standardized values). The second and third plots are
similar except that abnormal rains in non-season periods get accentuated in the standardized values of the
third plot.
5. AVERAGE RAINFALLS FOR THE VARIOUS CATEGORIES OF YEARS
For studying the average response in each category (ENSOW-U, etc.), three successive years were
considered, where the middle year corresponded to the e6ent. Thus, for the Unambiguous ENSOW
(ENSOW-U) of 1972, the 36 monthly normalized rainfalls from January 1971 to December 1973 were
considered. To obtain composites, values for the same month for all ENSOW-U events were averaged.
Table I. Distribution of the years 1900–1990 in various categories
Unambiguous
ENSOW
Ambiguous
ENSOW
Other El Niños
SOW, etc.
Non-events
C La Niña
M 1902 RKP
M 1905 R P
S 1911 RKP
S 1918 I RKP
M 1930 I RKP
S 1941 II R P
M 1951 RKP
S 1957 I RKP
M 1965 RKP
S 1972 I RKP
S 1982 KP
M 1987
12 events
M 1914 R
M 1919 II
M 1923 RK
S 1925 I RKP
S 1926 II
M 1931 II K*
S 1940 I P
W 1948 P
M 1953 RK
S 1958 II
W 1963 KP
W 1969 RKP
M 1976 RKP
S 1983 II P*
14 events
S 1912 ENSO
M 1929 EN
S 1932 EN
M 1939 EN
M 1943 EN
M 1907 ENC
S 1917 ENC
S 1927 ENC
S 1973 ENC
9 events
1904 SOW KP
1913 SOW KP
1944 SOW
1977 SOW
1979 SOW
1920 W K*
1968 W P
1986 W K
1959 SO
1974 SO
1935 SOC
1936 SOC
1946 SOC P*
1949 SOC K*
14 events
1901
1915
1937
1945
1947
1952
1966
1978
1980
1981
1984
1985
1989
1990
14 events
1903 K*P*
1906 K*P*
1908 K*P*
1909
1910
1916 K*P*
1921
1922
1924 K*
1928 K*
1933
1934
1938 K*
1942 K*
1950
1954 K*
1955 P*
1956
1960
1961
1962
1964 K*P*
1967 P*
1970 K*P*
1971
1975 K*
1988
27 events
Symbols S (strong), M (moderate), W (weak) indicate the strengths of the El Niños involved. I and II indicate first and second
years of double events (1957–1958, etc.). R, K, P indicate that these were selected as warm events by Rasmusson and Carpenter
(1983), Kiladis and Diaz (1989) and Mooley and Paolino (1989). K* and P* indicate that these were selected as cold events by
Kiladis and Diaz (1989) and Mooley and Paolino (1989).
Copyright © 2000 Royal Meteorological Society
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PERUVIAN ANDES RAINFALL AND EL NIN0 O
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Figure 1. Plots of monthly means (crosses) for the two consecutive years 1972, 1973 for: (a) first plot: Puerto Chicama SST
(sea-surface temperatures, crosses) and the average temperatures (superposed thick line); second plot: SST anomalies (deviations
from the average, positive are shaded, negative shown hatched); third plot: Southern Oscillation (SO) Index represented by the
Tahiti minus Darwin atmospheric pressure difference (T − D), monthly values (crosses and dashes) and 12-month running means
(thick curve), negative values shown hatched. (b) Similar plots for Huancayo rainfall. The second and third plots are rainfall
anomalies (deviations from average) in mm and normalized units, respectively
The 36 average values obtained for the eight events of the type Unambiguous ENSOW (ENSOW-U,
years 1930, 1941, 1951, 1957, 1965, 1972, 1982, 1987) are shown in the top plot, Figure 2(a), as crosses.
Considerable fluctuations are seen, often with large deviations only for single months. To smooth erratic
single values, running averages over three consecutive months were evaluated and are shown as
superposed thick lines. Even these show considerable fluctuations, even in the (− 1) year, i.e. the year
preceding to the event. Kiladis and Diaz (1989) mention that the years preceding the warm events (El
Niño years) are generally cold events, mainly due to the biennial component of ENSO (Meehl, 1987).
However, in the present case, the preceding years were 1929 (EN), 1940 (ENSOW-A), 1950 (C), 1956 (C),
1964 (C), 1971 (C), 1981 (Non-event), 1986 (W). Thus, only four are C events and others may have El
Niño characteristics. Thus, the values for the ( − 1) year do not belong to any particular group and hence,
will not be taken into consideration. In the event year (0), excess rains (shaded) occur in the months
JFMAMJ and then again in OND, followed by deficit rains (shown hatched) in the next (+ 1) year.
Figure 2(b) shows results for the average for eight events of the type Ambiguous ENSOW (ENSOW-A,
years 1923, 1925, 1940, 1948, 1953, 1963, 1969, 1976). (In Table I, there are many more events; but many
of these are II year events, 1958 in 1957 – 1958, etc. and are omitted from the analysis, because their effect
is already seen at the end of the first year.) For the (0) year, fluctuations are small; but D month shows
Copyright © 2000 Royal Meteorological Society
Int. J. Climatol. 20: 63 – 72 (2000)
68
R.P. KANE
excess rains, followed by deficit rains in JF months. In year (+1), large excess rains occur. The pattern
in Figure 2(b) is different from that for Figure 2(a).
Figure 2(c) refers to six events of the type Other EN (years 1927, 1929, 1932, 1939, 1943, 1973). (The
ENC events are not considered for analysis, to avoid complications.) Excess rains occur in the middle of
year (0) and the beginning of year ( +1), followed by deficit rains in the middle of year ( + 1), a pattern
opposite to that in (b).
Figure 2(d) refers to all El Niños ((a), (b) and (c) combined, total 22 events, ENC not considered) and
shows small fluctuations, because of the dissimilarity of (a), (b) and (c).
Figure 2(e) refers to ten events of the type SO, SOW, etc., where no El Niños were reported, but Pacific
SST was warmer and SO Index was smaller than average. (SOC events are not considered.) Excess rains
occur in the (0) year and deficit rains in the (+ 1) year.
Figure 2(f) refers to nine non-events. (When there were events in successive years, only the first one was
used for analysis.) Here, no large fluctuations are expected; but the (0) year shows deficit rains and the
( + 1) year shows excess rains. This raises doubts about the credibility of the fluctuations seen in Figure
2(a), (b) and (c).
Figure 2. Plots of averages of monthly rainfalls at Huancayo for 36 consecutive months (crosses) and running averages over three
consecutive monthly values (thick lines), for events of different types: (a) ENSOW-U; (b) ENSOW-A; (c) Other EN; (d) All EN
(a + b+ c); (e) SOW, etc.; (f) Non-events; (g) C (cold SST, La Niña). Positive anomalies (excess rains) are shaded and deficit rains
are shown hatched. Years used in each category are marked. The events are: the middle year (0), the preceding year ( − 1) and the
succeeding year ( + 1)
Copyright © 2000 Royal Meteorological Society
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PERUVIAN ANDES RAINFALL AND EL NIN0 O
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Figure 3. Evolution of El Niños (Puerto Chicama SST anomalies) and Huancayo rainfall, for several individual events: (a)
1925 – 1926, 1927 – 1928, 1930–1931, 1940–1941; (b) 1949–1950, 1952 – 1953, 1957 – 1958, 1965 – 1966. In each case, the previous year
is also considered (total 3 years). Positive anomalies are shaded, negative anomalies are shown hatched
Figure 2(g) refers to 15 events of type C (Anti-El Niños, La Niñas). (When there were events in
successive years, only the first one was used for analysis.) These events are expected to show results
opposite to those for El Niño events. However, El Niño effects are not alike for all types (a), (b) and (c)
and hence, one does not know what to expect for C events. Very small fluctuations are seen, except excess
rains in the beginning of year ( +1), opposite to the deficit rains for these months seen in (a), (b) and (e)
but not in (c).
It seems, therefore, that the El Niño effects are different for the three types (a), (b) and (c) which seem
to represent different ‘flavours’ (Trenberth, 1993). However, non-events show considerable fluctuations,
indicating that some effects may not be related to the ENSO phenomenon at all, but may be due to other
causes (local circulations, etc.).
Since the variations in (a), (b) and (c) are very different from each other, it is necessary to check
whether these three types are homegeneous, i.e. individual events in the same group show similar
characteristics. Also, the commencement and duration of the El Niños involved could be important.
Figure 3(a) and (b) and Figure 4(a) and (b) show the evolution of major El Niño events (monthly
temperature anomalies at Puerto Chicama) and the accompanying rainfall anomalies (deviations from
mean in mm of Huancayo monthly rainfall). In each frame, the upper part shows temperature anomalies
and the lower part, the rainfall anomalies. In each frame, the monthly means for three consecutive years
are shown and the middle year certainly has an El Niño (excess temperatures, shaded), though the
previous and/or next year could also be an El Niño year, at least partially. In Figure 4(b), frame 2, both
SST Puerto Chicama and Niño 1 +2 temperature anomalies are plotted. As can be seen, these are similar
except that Puerto Chicama anomalies are double in magnitude. As data for Puerto Chicama SST were
Copyright © 2000 Royal Meteorological Society
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R.P. KANE
available only up to 1995, the temperatures plotted in Figure 4(b), frame 3, are of Niño 1 + 2 region. The
following may be noted.
5.1. The year ( − 1)
The year (− 1) was generally quiet, except in 1929, 1948, 1951 (Figure 3(a) frame 3; (b) frame 1, frame
2) and 1993 (Figure 4(b) frame 2), when there were positive temperature anomalies. From these, 1929 and
1993 were associated with excess rains at Huancayo, while 1948 and 1951 were associated with small
excess and deficit rains. Years 1964, 1975, 1981, 1985, 1996 had negative temperature anomalies and can
be termed as La Niñas. Except for 1996, the rainfalls were mostly excess, indicating that La Niñas, in
general, could be associated with excess rains at Huancayo. However, some excess rainfalls (or deficit
rainfalls) occurred in single months and were not associated with either El Niño or La Niña activities
(examples: excess rains: April 1926, March 1939, August 1971, September 1985, June 1990; deficit rains:
January 1927, February – March 1940, December 1948, October 1976). Thus, a random component is
indicated.
5.2. The year (0) and (+1)
Most of the El Niños are in these years. Some were operative almost throughout the year, some in the
first half of year (0), some in the latter half, overflowing into year ( + 1). Since the major rainfall at
Huancayo occurs in the DJFM months, let us consider El Niños active in different (calendar) months
separately.
Figure 4. Evolution of El Niños (Puerto Chicama SST anomalies) and Huancayo rainfall, for several individual events: (a)
1972 – 1973, 1976 – 1977, 1982–1983, 1986–1987; (b) 1991 – 1992, 1994 – 1995, 1997 – 1998. In each case, the previous year is also
considered (total 3 years). Positive anomalies are shaded, negative anomalies are shown hatched
Copyright © 2000 Royal Meteorological Society
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(i) During 1925, 1930,1940 (Figure 3(a) frames 1, 3, 4), 1957, 1965 (Figure 3(b) frames 3, 4), 1972, 1976,
1982, 1986 (Figure 4(a) frames 1, 2, 3, 4), 1991, 1994, 1997 (Figure 4(b) frames 1, 2, 3), the
temperature anomalies were positive (El Niños active) in the end part (also) of the calendar year and
coincided with the main rainfall season (DJFM) at Huancayo. From these, in 1925 (A), 1940 (A),
1957 (U), 1976 (A), 1986 (W) and probably 1997 (A) (recent El Niño, rainfall data for 1998 not yet
fully available), the main season rainfalls were mixed, i.e. excess for a month or two, followed by
deficits in the next month or two, or 6ice-6ersa. Note that four events were Ambiguous ENSOW and
one was Unambiguous ENSOW. In 1930 (U), 1965 (U), 1982 (U), 1991 (A), 1994 (A), the rainfalls
were all deficits. Note that three events were Unambiguous ENSOW and two were Ambiguous
ENSOW. U and A are distinguished by whether the Pacific SST and SO Index reached extremes in
the middle or in the end of the year. In the present case, what mattered is whether the El Niño (U
or A) lasted up to the year end, to coincide with the main rainy season. Only in 1972 (U), the main
season rainfall was excess. (Thus, the example of 1972–1973 shown in Figure 1 to illustrate the
procedure of analysis, was of an exceptional rain pattern.) In general, if an El Niño was active in the
latter part of an year (and continuing in the first few months of the next year), the rainfall at
Huancayo was either deficit, or excess followed and preceded by a deficit.
(ii) In 1925, 1929, 1930, 1941, 1951, 1953, 1957, 1965, 1972 and 1976, El Niños were active in the middle
part of the year, outside the main rainy season. In 1925, 1929, 1930, 1941, 1957, 1965 and 1972,
Huancayo showed excess rains in these pre- or post-rainy season months. Only 1951, 1953 and 1976
showed very little fluctuations or slightly deficit rains. Thus, El Niños active during the months of
normally little rains seem to cause excess rains. Incidentally, this is in contradiction with the results
in (i) above, where La Niñas also gave excess rains in the non-season months. Thus, such rains could
be random.
(iii) El Niños active in the early part of the year are generally continuations of El Niños which lasted up
to the end of the previous calendar year and are considered in (i).
6. CONCLUSIONS
A comparison was made of the evolution of El Niños (sea-surface temperature anomalies at Puerto
Chicama, Peru coast) and the rainfall anomalies at Huancayo, a high altitude location in the central part
of Peruvian Andes, for the period 1923 – 1997. The following was observed:
(i) The main rainy season at Huancayo is the DJFM months. If El Niños were active in these months,
the rainfalls were either deficit (1925 – 1926, 1930–1931, 1965–1966, 1976–1977, 1982–1983, 1991–
1992, 1994–1995) or were mixed, i.e. excess in December–January, followed and preceded by deficits
(1940–1941, 1952 – 1953, 1957 – 1958, 1972–1973, 1986–1987, 1997–1998). Data for the coastal
regions of Peru and Ecuador are not available for comparison; but Quinn et al. (1978, 1987) use
coastal rainfall as one of the criteria to evaluate the characteristics of El Niños. Thus, heavy rainfall
in the coastal regions during strong El Niños is implied. If true, the patterns seen at Huancayo are
somewhat different from those in the coastal regions.
(ii) When El Niños are active during the non-season rainfall months at Huancayo, often excess rainfall
occurs in these non-season months. However, similar excess rainfall occurs during La Niña events
also. Hence, a random cause is suspected. Often, such excess rainfalls seem to occur in single months
and are not associated with El Niño or La Niña activity in or near those months.
(iii) The uncertainties in the rainfall patterns (sometimes deficit, sometimes mixed) do not seem to be
related to the strength of the El Niños. In the five strongest El Niños during the last few decades,
1925 was associated with excess rains in ND, followed by deficit rains in the JFM months, 1972 with
excess rains in DJFMA, 1982 with deficit rains in DJFMA, 1991 with deficit rains in DJFMAM and
1997 with deficit rains in O, followed by excess rains in ND, 1997 and J, 1998 (so far).
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If El Niños are assumed to be associated with excess rainfall in coastal Peru, the different patterns in
the Andes (deficits, or excesses followed and preceded by deficits) are intriguing. The circulation patterns
associated with these patterns need investigation. Also, rainfall patterns seem to differ considerably in
different parts of Peru. For the recent El Niño of 1997–1998, reports say that southern Peru had droughts
while eastern and northern Peru, Ecuador had floods. As such, ENSO relationships in different parts of
Peru–Ecuador are probably different and need to be investigated. Only some data are available for the
recent two to three decades but interesting features could be revealed as some of the largest El Niño
events have occurred in the last few decades. Work in this direction is in progress.
ACKNOWLEDGEMENTS
Thanks are due to Mr. Hugo Trigoso Avilés, Director of the Observatory of Huancayo ‘J.A. Fleming’,
Geophysical Institute of Peru (IGP), for providing the Huancayo rainfall data. This work was partially
supported by FNDCT Brazil under contract FINEP-531/CT.
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Copyright © 2000 Royal Meteorological Society
Int. J. Climatol. 20: 63 – 72 (2000)
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