Climate extremes and changes in precipitation and wind patterns (1971-2002) in the vicinities of Montevideo,

Uruguay

V Pshennikov, M Bidegain, F Blixen, EA Forbes, JJ Lagomarsino and GJ Nagy

Research questions

Are extreme events useful for a better understanding of ClimateVariability and Change?

Which were the extreme climate events over the Northern Coastof the Rio de la Plata?

How do we make use of short time extreme events analysis in our projected scenarios?

Goal

To make use of synoptic (1-10 days time-scale analysis) approachesin order to improve our understanding of past events and projectedfuture scenarios

Definition of Extreme Event

• Events that exceed, at critical level, the natural climate variability (Simple events, R. Jones)

• Combining multiple variables (geophysical and socioeconomic) for specific location (Complex events, R. Jones)

• Depending on the socioeconomic and environmental sector involved.

ANNUAL PRECIPITATION MONTEVIDEO 1948-2001

0200400600800

100012001400160018002000

1948 1951 1954 1957 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

YEARS

PREC

IPIT

ATI

ON

(mm

)

• Increased annual totals of precipitation from 1050 to 1200 mm

• Positive precipitation cycles were observed during the 50’s and from late 70’s to mid 90’s in Montevideo

SPRING PRECIPITATION (OCT-NOV-DEC) MONTEVIDEO 1948-2001

0

100

200

300

400

500

600

1948 1951 1954 1957 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

YEARS

PRE

CIP

ITA

TIO

N (m

m)

• A strong trend in spring precipitation (from 210 to 350 mm) was observed in Montevideo (Uruguay) over the last 50 years.

• A remarkable hydroclimatic shift ocurred around mid-70’s.

• There exists a possible link with El Niño (warm events), that partially could explain the observed precipitation increase.

MONTHLY MEAN WIND VELOCITY (km/h)1961 - 2002

MONTEVIDEO (BLACK) AND COLONIA (RED)

0

5

10

15

20

25

30

35

1961 1963 1965 1968 1970 1972 1975 1977 1979 1982 1984 1986 1989 1991 1993 1996 1998 2000

Mea

n V

eloc

ity (k

m/h

)

M o nte vid e o

Punta d e l Este

Río d e la Pla ta

Bu e no s A ire s

C o lo nia

Re p úb lic a O rie nta l d e l Urug ua y

Re p úb lic a A rg e ntina

C a rra sc o

Ro c h aPra d o

Eze iza

D o n To rc u a to

Ae ro p a rq ue

• A negative trend in wind velocity was observed in Montevideo and Colonia (Uruguay) over the last 40 years.

• There exists a change in the atmospheric circulation in the region, that could explain the observed wind velocity decrease.

Zonal Circulation Index at 57°W(between 33°S and 37°S)

-3,0

-2,0

-1,0

0,0

1,0

2,0

3,0

1948 1950 1953 1955 1958 1960 1963 1966 1968 1971 1973 1976 1979 1981 1984 1986 1989 1991 1994 1997 1999 2002

• A Zonal Circulation Index (based on SLP) shows a trend change and a shift around 1994-95 (decrease) in the zonal circulation (east wind) in the mouth of Rio de la Plata

Mean sea level – Montevideo (1902-2000)cm

years

• The rate of increase is 0.93 mm y-1

• SLP decreased 1.3 hPa.• River Uruguay flow increased by > 35% since the mid-40’s.

• A slight correlation (R2 0.1) was found between river flow and sea level.

MSL

hei

ght (

cm)

MSL and River Flow

Riv

er U

rugu

ay fl

ow (m

3 /s)

years

MSL and SLP

MSL

hei

ght (

cm)

SLP

(hPa

)

years

Maximum (hourly data) tide height (1971-2002) at Montevideo

180

200

220

240

260

280

300

320

1970 1978 1986 1994 2002

years

heig

ht (c

m)

(wind-induced events)

• Since 1971, the three meter threshold was reached only twice, whereas before 1950 it was reached seven times, two of them > 350 cm.

• Wind-induced events always reach a minimum of 220 cm since 1902.

• Maximum for 2001 was the first below two meters.

• Maximum water height recorded at Montevideo in the last 25 years during the extreme event ocurred from Feb 6 to Feb 9, 1993.

Tide heights 6-9 February 1993 Montevideo Harbour

-50

0

50

100

150

200

250

300

350

6 7 8 9

days

heig

hs (c

m)

• Precipitation over Santa Lucia river basin during the extreme event (6 –10 Feb-93).

• This period was the maximum “5-days “ precipitation (245 mm) event recorded since 1948.

• Baric system at sea level pressure (Feb 7, 1993)