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Drought Network News (1994-2001) Drought -- National Drought Mitigation Center

July 2000

The Drought in Chile and La Niña

Juan Quintana Direccion Meteorologica de Chile, Santiago, Chile

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Quintana, Juan, "The Drought in Chile and La Niña" (2000). Drought Network News (1994-2001). 71. https://digitalcommons.unl.edu/droughtnetnews/71

This Article is brought to you for free and open access by the Drought -- National Drought Mitigation Center at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Drought Network News (1994-2001) by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. The Drought in Chile and La Niña

La Niña in Chile ber, and it contributes more than 70% of the annual precipitation. Precipitation is one of the climatic elements most affected by the presence of La Niña in Chile. An important precipitation deficit begins during La Niña La Niña conditions events, from latitude 45°S to the north. This deficit In the presence of a La Niña event, the subtropi- prevails most of the year, with winter (April–Sep- cal anticyclone of the southwestern Pacific intensi- tember) being most vulnerable to these anomalies. fies, and its influence is extended to the south. This The central region of Chile (30°S to 40°S) has shift prevents the frontal systems coming from the negative anomalies, with precipitation values 35% to western Pacific from being displaced (as they nor- 100% below the climatologic annual average. These mally are) toward continental mid-latitudes. During rain deficiencies in Chile are determined by the per- La Niña, there is also an intensification of the polar sistence of anomalies of anticyclonal circulation of jet stream and a weakening of the subtropical jet middle and subtropical latititudes and an area of stream, favoring greater frontal activity in southern anomalies of cyclonic circulation in the sub-polar Chile (Figure 1). This condition reduces the fre- latitudes, from a north–south dipole of positive and quency of frontal cloudy bands in central and north- negative anomalies of geopotential height in the mid ern Chile, blocks or weakens the passage of active troposphere. In Chile, La Niña usually produces air fronts to the continent, and inhibits convective activ- temperatures lower than normal, with deviations ity, all essential factors for the generation of precipi- ranging from 0°C to -1°C. The social and economic tation. impacts of La Niña events in Chile are serious. Agriculture, cattle and timber industries, energy, and industrial sectors are the most affected.

Patterns of atmospheric circulation in Chile during La Niña

Normal conditions The atmospheric circulation in Chile is charac- terized by the existence of two meteorological oc- currences: (1) the subtropical anticyclone of the Pa- cific southeast and (2) the circulation of the wester- lies, where the frontal systems and their associated lows are formed and develop. The former corre- sponds to a region where high pressures prevail almost year-round. This high is in northern and cen- tral Chile and migrates from 30–35°S during winter to 35–40°S during summer. The second occurrence that defines the seasonal precipitation cycle in central Chile is the displace- ment of the frontal bands from the west. This dis- Figure 1. Characteristics of atmospheric circulation ob- placement is more frequent from April to Septem- served in Chile during La Niña.

Drought Network News 3 Seasonal precipitation in central Chile, El Niño– Station Precipitation Precipitation La Niña events, and the Southern Oscillation and SST and SOI

Three representative stations were selected from La Serena 0.54 -0.41 Santiago 0.64 -0.64 central Chile: La Serena (30°S), Santiago (33°S), and Concepción 0.31 -0.38 Concepción (37°S). In the central zone, precipitation occurring during April–September represents more Table 1. Linear correlation of precipitation, SST, and SOI values. than 70% of the annual total. Precipitation totals (April–September) for every year of the period 1950– phase between the amount of precipitation registered in 98 were correlated with (1) anomalies of the sea sur- central Chile and the atmospheric pressure (Tahiti– face temperature (SST) observed in the area of El Darwin) defined by the SOI (Table 1). Niño 3—the central equatorial Pacific, whose coordi- In summary, in central Chile, precipitation between nates are 5°N–5°S, 150°W–90°W; and (2) the April and September correlates with the heating of the Southern Oscillation Index (SOI), expressed in stan- sea surface in the central equatorial Pacific (positive dardizing anomalies. The arithmetic averages of the anomalies of Niño 3–SST) and the reduction in the anomalies observed between April and September in surface pressures (negative SOI). When SST sur- both SST and SOI were used in the correlation analy- passes the average by more than 0.5°C and pressures sis. The results show a significant statistical relationship decrease (-1.0 standard deviation), precipitation be- (P < 0.05) between winter precipitation (April–Sep- tween La Serena and Concepción tends to increase. tember) in central Chile and the El Niño–La Niña Actual precipitation is usually twice the climatologic events and the Southern Oscillation. value. However, if SST is 0.5°C or more below the Precipitation at Santiago’s station responds well average and the atmospheric pressure at the surface (r = 0.64) to changes in the thermal condition of the (SOI) is more than 1.0 standard deviation above aver- equatorial Pacific (Figure 2). The other two selected age, significant precipitation deficits are more likely to stations, although statistically significant, had lower occur during the rainy season. The close relationship correlation coefficients (Table 1). Precipitation in cen- between precipitation, SST, and SOI is demonstrated tral Chile and the SOI are inversely correlated, and the by the results of linear correlation, which reached their highest value (r = 64) was obtained for Santiago (Fig- greatest magnitude for Santiago at 64% for SST and ure 3). In other words, there is a statistically significant -64% for the SOI.

) 800 m m (

600

n SST in the central equatorial Pacific, atmospheric o i t 400 a t

i pressure in Antofagasta, and rainfall in Santiago p i 200 c e r P 0 The rain regime in central Chile in 1997 and 1998 -2.0 -1.0 0.0 1.0 2.0 3.0 SST Anomalies C shows sharp contrasts (Figure 4). In Santiago, precipi- Figure 2. Precipitation for Santiago correlated with anoma- tation in 1997 surpassed the climatological mean lies of the SST (Niño 3), April–September 1950–98. (312.5 mm) by 403 mm (positive anomaly). June was the rainiest month, with 188.6 mm above normal for the

) 800

m month. But during May–October 1998, a deficit or m

( 600

n negative anomaly was registered—less than 234.1 mm o i 400 t a

t below normal (286.4 mm). July 1998 was one of the i 200 p i th c driest months of the 20 century, with only 0.2 mm of e

r 0 P -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 rainfall (normal rainfall is 86.6 mm). This rainfall deficit Standardized Anomalies persisted during 1999. Santiago displayed a negative Figure 3. Precipitation for Santiago correlated with anoma- anomaly of -117 mm below the cumulative normal lies of the SOI, April–September 1950–98. value between January 1 and July 27, a deficit of more

4 Vol. 12, No. 2, Summer 2000 4 200

3 150 )

C 2 100 ° (

) n o m i 50

t 1 a m i (

v n e 0

0 o D i t a d i r v a

-1 -50 e d D n

a t

S -2 -100

-3 -150

-4 -200 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J

1997 1998 1999

Precipitation Niño 3.4 Atmos.Pressure, SOI Monthly SOI Monthly Value, for Santiago Antofagasta Value Antofogasta Figure 4. Sea surface temperature in the central equatorial Pacific, atmospheric pressure in Antofagasta, and precipitation in Santiago, January 1997–July 1999.

than 50%. The first half of winter 1999 was character- precipitation values for Santiago. The annual average ized by a low frequency of frontal systems in central precipitation in Santiago during La Niña years was 210 Chile (30°S to 36°S), with precipitation below normal. mm. The standardized anomalies of the Southern Oscil- The analysis selected 25 years as El Niño years. lation represent the atmospheric component of this For these years, Santiago had an annual mean of 494 cycle. In Chile, the most prominent of these anomalies mm. In 71 years considered as normal (an absence of are observed in the atmospheric pressure at sea level in La Niña or El Niño), the annual precipitation mean was Antofagasta (23°S), with negative anomalies during 340 mm. 1997 and positive anomalies in 1998, a product of the Figure 5 shows the histogram of relative frequen- weakening and later intensification of the semiperma- cies of annual precipitation for Santiago for the period nent anticyclone of the eastern South Pacific. The in- 1877–1998. The impact of La Niña on the annual crease in precipitation during the rainy season (April– cycle of precipitation in Santiago is clear, with a distri- September) in 1997, and significant deficits in 1998 and part of 1999, are another clear signal. 50

y 40 c n

e 30 u

q 20 e r

Precipitation in Santiago during La Niña events F 10 0 Between 1877 and 1999, twenty-six years show 0 100 200 300 400 500 600 700 800 900 negative anomalies equal to or smaller than -0.5°C for Precipitation (mm) three or more consecutive months in the central equa- El Niño years La Niña years Normal years torial Pacific during April to September. These years Figure 5. Relative frequencies of annual precipitation for are shown in Table 2, with their respective annual Santiago, 1877–1998.

Drought Network News 5 Year Total Year Total La Serena Lat.: 30°S 200

(mm) (mm) )

m 160 m (

n 120 o i

1879 166.0 1938 202.0 t a t i

p 80 1886 126.0 1942 402.7 i c e r

1889 230.0 1950 292.7 P 40

1890 222.0 1954 316.2 0 1892 123.0 1955 193.8 J F M A M J J A S O N D 1893 238.0 1964 186.4 1998 1999 Normal (1961–90) 1903 194.0 1970 327.7 Santiago Lat.: 33°S 1908 202.0 1973 172.1 500

1909 184.0 1975 184.3 ) m 400 m (

1910 270.0 1985 186.2 n 300 o i t

1916 225.3 1988 139.6 a t i

p 200 i

1924 66.3 1998 89.7 c e r 1933 316.4 P 100 0 Table 2. Precipitation in Santiago during La Niña years J F M A M J J A S O N D during the period 1877–1999. 1998 1999 Normal (1961–90)

Puerto Montt Lat.: 41°S bution centered on the 200 mm annual precipitation 2000 ) and a frequency of 43%. For El Niño years, the annual m 1600 m (

n

o 1200 distribution of precipitation in Santiago shows a greater i t a t i 800 p variability (700 mm) and a smaller frequency (28%). i c e r 400 P

J F M A M J J A S O N D

La Niña 1998/99’s impact on Chile’s precipitation 1998 1999 Normal (1961–90)

Punta Arenas Lat.: 53°S The rapid change of SSTs in the equatorial Pacific 600 ) 500 altered atmospheric circulation patterns worldwide. m m ( 400 Conditions went from very warm in the first months of n o i t 300 a t 1998 (January–April)—associated with El Niño—to a i p i 200 c e characteristic cold condition of La Niña during the r

P 100 second quarter of 1998. In Chile, the subtropical high 0 was an almost permanent feature that reached 40°S to J F M A M J J A S O N D 1998 1999 Normal (1961–90) 45°S during May and July 1998, reducing precipitation during the rainy season in the central part of the country Figure 6. Accumulated precipitation for 1998 and 1999, in both 1998 and 1999. compared to the normal, for four locations in Chile. The atmospheric blocking observed during most of the period between May 1998 and July 1999 pre- 1999, the region with the greatest deficits was the vented the normal displacement and development of central zone, from 36°S to the north, with values oscil- frontal systems in central and northern Chile. This lating between 0% and 80% lower than average. Fig- blocking caused the driest year of the 20th century ure 6 shows accumulated precipitation for 1998 and between 30°S and 36°S. Between 37°S and 45°S, the 1999 versus the climatologic value for four locations in precipitation deficit reached 30–50%. Only the austral Chile. region (Punta Arenas) had a surplus (near 40%). During the first half of 1999, meteorological condi- Juan Quintana tions in Chile were similar to those of the previous year, Direccion Meteorologica de Chile with a precipitation deficit in almost the entire country, Santiago, Chile but of a lesser magnitude than in 1998. Up to July e-mail: [email protected]

6 Vol. 12, No. 2, Summer 2000