Changes in the South American Monsoon and potential regional impacts L. Carvalho, C. Jones, B. Bookhagan, D. Lopez-Carr UCSB, USA A.Posadas, R. Quiroz CIP, Peru B. Liebmann CIRES/NOAA, USA

The presence of a monsoonal type of circulation and precipitation is the most important climatic feature in the tropical Americas Agriculture and water management are among human activities that are strongly tied to the seasonal migration of the monsoons. Changes in the onset, duration and total monsoonal precipitation have significant impact for the economy of countries in South, Central and North Americas

Objectives of this talk Examine the recent (60yrs) variations in SAMS Investigate mechanisms and links with global warming Discuss possible impacts in the Andean region and the importance of regional analysis of climate variability and change Importance of an interdisciplinary approach to understand human-natural systems inter- relationships and feedbacks

Large Scale Index for South America Monsoon (LISAM) ( Silva and Carvalho 2007 ) SAMS is characterized by seasonal changes in:  Circulation anomalies  Precipitation  Moisture  Temperature LISAM index was designed to characterize the ONSET, DEMISE, DURATION, AMPLITUDE, BREAKS AND ACTIVE PHASES of SAMS based in all variables above. 4

5 LISAM (Silva and Carvalho 2007) o Precipitation: Global Precipitation Climatology Project - GPCP (2.5 o resolution) o Zonal (U850) and meridional (V850) winds, Specific Humidity (Q850) and temperature (T850) at 850hPa from NCEP/NCAR reanalysis were used in this case. o (5 days average) pentads ; subtract only long-term mean o Method applied to obtain the INDEX: Combined Empirical Orthogonal Function o Use first two modes (LISAM1, LISAM2)

6 Precipitation Specific humidity Zonal wind Meridional wind Air temperature First CEOF Mode - LISAM 6 Correlation between LISAM and all variables used in the CEOF Westerlies Easterlies Northerly

7 7 Precipitation Specific humidity Zonal wind Meridional wind Air temperature Second CEOF Mode – South Atlantic Convergence Zone (SACZ) Westerlies Easterlies Northerly Southerly Correlation between LISAM and all variables used in the CEOF

There is a clear distinction between the oceanic (SACZ) and continental activity (LISAM) associated with SAMS Precipitation (LISAM) Precipitation (SACZ) 8

LISAM and SACZ time coefficients Period (pentads) Spectral Density LISAM days ~ days Annual cycle removed SACZ Period (pentads) days ~15-25 days 9

Does LISAM capture active and break phases of SAMS? Differences wet and dry events (defined as indices upper quartile – lower quartile during summer – after removing the annual cycle) Wet events=123 Dry events=94 Difference Precipitation (Wet – Dry) Difference U850 (Wet – Dry) Westerlies 10

Liebmann and Dallured 2005)

Multi-annual to decadal variations To extend the analysis to the period of reanalysis ( ) LISAM was obtained using the same set of variables BUT EXCLUDING PRECIPITATION (since all daily precipitation datasets have problems during this period) Patterns of wind, temperature, specific humidity are very similar (First and second CEOF) and will not be shown here

Definition of Amplitude Amplitude of SAMS was defined as the integral of positive values of LISAM index (which are indicative of enhanced monsoonal activity over central eastern Brazil)

LISAM with GPCP

Amplitude of the second C-EOF (SACZ) obtained as the integral from the onset-demise of the positive values (SACZ in its climatological position during the wet season).

The 18 o C isotherm at 850hPa extends over the continents year round: a good metrics to evaluate impacts of global warming

Interannual extent of the 18 o C at 850hPa – Note its migration towards tropical regions in the last decades Interannual variation of the extent of the 15oC isotherm. Note the warming of tropical oceans in the last decades OCTOBER: onset SAMS

Trends in SAMS amplitude (blue) and trends in the T18 o C area in November(Red) Change point for both indices: 1977 (climate shift)

Changes in patterns of temperature indicate fast rates over the Brazilian Altiplano (east Brazil): these changes may have intensified temperature gradients and monsoon circulations in the region.

Difference in the integrated moisture fluxes (from surface up to 400hPa): ( ) minus ( ) (From Carvalho et al 2010). Note the increase in the moisture flow over central Brazil from the Atlantic Ocean Note also changes in moisture flow over Northern Peru after the climate shift

Regional impacts There are non uniform impacts of SAMS in South America: Northern Amazonian Peru and Southern Peru and Bolivia are anti-correlated. ENSO is important for water balance and glaciers over Western Andes but SAMS may play a significant over eastern Andes

Peruvian glaciers are located on the catchment boundary between the Atlantic and Pacific drainage divide, have moderate relief and lower elevations than Bolivian glaciers, which generally have higher relief and higher elevations and are located on the eastern flanks of the internally-drained Altiplano-Puna Plateau

ENSO effect in the Andes: 12 yrs TRMM (Bookhagan and Strecker 2010)

Conclusions Regional impacts are complex as they involve natural factors and human dimensions. Assessing regional impacts require appropriate methods and improvement in datasets (climate and social variables) and modeling Interdisciplinary approaches, additional local measurements, international efforts are crucial to evaluate vulnerability, feedbacks, and prevent further impacts