Climate extremes and changes in precipitation and wind patterns ( ) 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 Climate Variability and Change? Which were the extreme climate events over the Northern Coast of 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) approaches in order to improve our understanding of past events and projected future 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.

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

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.

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.

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

Mean sea level – Montevideo ( ) 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 (R 2 0.1) was found between river flow and sea level. MSL height (cm) MSL and River Flow River Uruguay flow (m 3 /s) years MSL and SLP MSL height (cm) SLP (hPa) years

(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 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.

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)