Os eventos extremos estão aumentando na Amazônia? Javier Tomasella e José A. Marengo. Centro de Ciência do Sistema Terrestre, INPE

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1 Os eventos extremos estão aumentando na Amazônia? Javier Tomasella e José A. Marengo Centro de Ciência do Sistema Terrestre, INPE Hamburgo, Março 2011

The Amazon Basin River Drainage area (km 2 ) Rainfall (mm y -1 ) Annual mean discharge (m 3 s -1 ) Main Stem Solimões (São 990 780 2900 46 500 Paulo de Olivença) Solimões (Itapeuá) 1 769 000 n/a 85

2 The Amazon Basin River Drainage area (km 2 ) Rainfall (mm y -1 ) Annual mean discharge (m 3 s -1 ) Main Stem Solimões (São Paulo de Olivença) Solimões (Itapeuá) n/a Solimões (Manacapurú) Amazonas (Jatuarana) Amazonas (Óbidos) Northern tributaries Iça Japurá Negro Trombetas Southern tributaries Jutaí Juruá Purus Madeira Tapajós Xingu Whole basin Amazon The Amazon River and its main tributaries. Black triangles indicate the locations of main-stem discharge stations: São Paulo de Olivença SPO; Itapéua ITA; Manacapuru MAN; Jatuarana JAT and Óbidos OBI

3 Why extreme events are so important in Amazonia? Recent studies suggest that the Amazon is highly vulnerable to: global climate change (Cox et al, 2004; Li et al. 2006; Salazar et al. 2007; Cox et al., 2008); deforestation and (Sampaio et al., 2007; Costa el al., 2007); increased forest fires Brown et al 2006; Cardoso et al. 2003; 2009); and has the potential to accelerate those changes by feedback mechanisms (Cox et al 2008; Nobre and Borma 2009). Therefore, a better understanding of how Amazon ecosystems cope with environmental extremes is crucial.

4 El Niño/La Niña Schematics

5 Severe hydrological extremes (drought/floods) in the Amazon have generally been associated to strong El Niño or La Niña events. However, a careful look at the stage record at Manaus harbor, the longest available record of the Amazon (107 years), shows that intense warming/cooling of the Tropical Pacific do not, sometimes, coincide with extreme events.

6 Water level (cm) 3200 Negro River at Manaus Harbour c c c El Niño La Niña Maximum Minimum Extremes El Niño

7 Water level (cm) 3200 Negro River at Manaus Harbour c c c El Niño La Niña Maximum Minimum Almost neutral

8 Water level (cm) Extremes La Niña Negro River at Manaus Harbour c c c El Niño La Niña Maximum Minimum

9 Water level (cm) Almost neutral Negro River at Manaus Harbour c c c El Niño La Niña Maximum Minimum

10 Negro river at Manaus Harbor statistics Source: CPRM (2010)

11 Water level (cm) Negro river at Manaus Harbor, the largest available record in Amazonia 3200 Negro River at Manaus Harbour El Niño La Niña Maximum Minimum 10 Largest floods: 2009, 1953, 1976, 1989, 1922, 1999, 1909, 1971, 1975, 1994

12 Water level (cm) Negro river at Manaus Harbor, the largest available record in Amazonia 3200 Negro River at Manaus Harbour El Niño La Niña Maximum Minimum 10 Largest droughts: 2010, 1963, 1906, 1997, 1916, 1926, 1958,2005, 1936,1998

13 Basic hydrology tells that extreme events are associated to significant rainfall anomalies However, given the sheer size of the Amazon Basin, the main-stem floodwave is the result of highly complex interaction between soils, topography, aquifers, climate regimes and geomorphology Indeed, those factors affect the time of contribution of main-stem tributaries and, consequently, tributaries contribution times which shape the main-stem floodwave.

14 Therefore, extreme hydrological events on the river mainstem do not depend only on the magnitude of rainfall excesses/deficits, but the time of the season when those anomalies occur as well. The most prominent example of such process is the Amazon Negro Madeira rivers flood waves interaction. The Negro river (28400 m 3 s -1 ) is the most important of the northern tributaries, the Madeira river (31200 m 3 s -1 ) is the most important of the Southern tributaries.

15 Negro-Madeira-Amazon interactions The Madeira river peaks 2-3 months earlier than the Negro, although it encounters the Amazon downstream This peculiar contribution time of the main tributaries causes strong backwater effects (Meade et al. 1991) Amazon at Itacoatiara

16 Two recent examples help to understand those interactions -The drought of 2005 (Marengo et al. 2008, Tomasella et al. 2010) -The floods of 1989, 1999, 2009 (Marengo et al., Submitted to Theoretical and Applied Meteorology)

17 During 2005 the Amazon experienced a severe drought which was not associated to an El Niño event. Unless what usually occurs during strong El Niño events, when negative rainfall anomalies usually affect central and eastern Amazon drainage basin; rainfall deficiencies in the drought of 2005 were spatially constrained to the west and southwest of the basin. Marengo et al. 2008

18 In spite of this, discharge stations at the main stem during 2005 recorded minimum water levels as low as those observed during the basin-wide El Niño related drought. Why an spatially constrained drought caused such severe effects on river discharges, equivalent to strong basin-wide EL Niño droughts?

19 Nov-96 Dec-96 Jan-97 Feb-97 Mar-97 Apr-97 May-97 Jun-97 Jul-97 Aug-97 Sep-97 Oct-97 Nov-97 Dec-97 Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 Discharges variations during 1997 and 2005 droughts along the main stem Main stem Main stem SPO LTM SPO ITA LTM ITA MAN LTM MAN JAT LTM JAT OBI LTM OBI

20 Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 Nov-96 Dec-96 Jan-97 Feb-97 Mar-97 Apr-97 May-97 Jun-97 Jul-97 Aug-97 Sep-97 Oct-97 Nov-97 Dec Northern tributaries Japurá SER MLT SER VBT LTM VBT Northern tributaries Negro Discharges variations during 1997 and 2005 droughts in northern tributaries

21 Nov-96 Dec-96 Jan-97 Feb-97 Mar-97 Apr-97 May-97 Jun-97 Jul-97 Aug-97 Sep-97 Oct-97 Nov-97 Dec-97 Nov-96 Dec-96 Jan-97 Feb-97 Mar-97 Apr-97 May-97 Jun-97 Jul-97 Aug-97 Sep-97 Oct-97 Nov-97 Dec-97 Discharges variations during 1997 and 2005 droughts in southern tributaries Madeira Juruá Purus Southern tributaries Southern tributaries FVA LTM FVA FV FV CAN LTM CAN C C GAV LTM GAV G G

22 During the drought, discharges deficits along the main-stem were controlled most of the time by northern tributaries. In , on the other hand, the discharge in northern tributaries peaked earlier and initiated a rapid recession, accelerating the falling of river stages in the main-stem. During the drought, the signal observed in the main-stem was controlled mostly by the southwestern tributaries.

23 Comparison between both drought revealed that during , the Madeira river at Fazenda Vista Alegre station peaked two months earlier than the Negro river at Serrinha station. During , on the other hand, peak time difference was reduced to a month because the Negro river peaked earlier than normal, and the recession in all tributaries began almost simultaneously

24 An almost coincident recession of northern and southern tributaries during , combined with lower than normal river discharges of southern tributaries affected the gradients along the main-stem The Madeira river peaks 2-3 months earlier than the Negro, although it encounters the Amazon downstream Amazon at Itacoatiara

25 Another example is the flood of 2009, the largest ever recorded in Manaus The flood was compared to two previous floods, 1989 and 1999.

26 Rainfall anomaly (mm day -1 )

27 Discharges variations during 1989, 1999 and 2009 floods along the main stem Nov-88 Dec-88 Jan-89 Feb-89 Mar-89 Apr-89 May-89 Jun-89 Jul-89 Aug-89 Sep-89 Oct-89 Nov-89 Dec-89 Nov-98 Dec-98 Jan-99 Feb-99 Mar-99 Apr-99 May-99 Jun-99 Jul-99 Aug-99 Sep-99 Oct-99 Nov-99 Dec-99 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec Main stem Main stem Main stem SPO LTM SPO ITA LTM ITA MAN LTM MAN JAT LTM JAT OBI LTM OBI SPO LTM SPO ITA LTM ITA MAN LTM MAN JAT LTM JAT OBI LTM OBI SPO LTM SPO ITA LTM ITA MAN LTM MAN JAT LTM JAT OBI LTM OBI 0 0 0

Nov-98 Dec-98 Jan-99 Feb-99 Mar-99 Apr-99 May-99 Jun-99 Jul-99 Aug-99 Sep-99 Oct-99 Nov-99 Dec-99 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09

28 Nov-98 Dec-98 Jan-99 Feb-99 Mar-99 Apr-99 May-99 Jun-99 Jul-99 Aug-99 Sep-99 Oct-99 Nov-99 Dec-99 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Nov-88 Dec-88 Jan-89 Feb-89 Mar-89 Apr-89 May-89 Jun-89 Jul-89 Aug-89 Sep-89 Oct-89 Nov-89 Dec-89 Discharges variations during 1989, 1999 and 2009 floods in northern tributaries Northern tributaries SER MLT SER VBT LTM VBT Japurá Negro Northern tributaries Northern tributaries SER LTM SER VBT LTM VBT SER MLT SER VBT LTM VBT 0 0

drought in 2010, both events with a recurrence time of

29 Back to the recent extremes It is intriguing that the largest flood was recorded in 2009, and the largest drought in 2010, both events with a recurrence time of more than 100 years! ( assuming that the record is stationary)

30 Water level (cm) The questions is whether the extremes are increasing. Is Manaus series stationary? No trend! MAX MIN DIF

31 Water level (cm) However, if we constrain the analysis of the series from ~ NS *SS *SS MAX MIN DIF

32 Unfortunately, Manaus Harbor suffers strong backwater effects, so discharge series are not available (since the ratio curve is not bi-univocal). Manaus Harbor is influenced not only by Negro river water levels, but most of the time by the Solimões - Amazon water stages Is it the trend that appear in Manaus Harbor record a pure local process? Is it the trend in Manaus series a result of changes in the river cross section?

33 Looking at key stations with longest (possible) record available SER MAN OBI SPO FVA São Paulo de Olivença SPO; Manaus MAN; Serrinha SER; Fazenda Vista Alegre - FVA and Óbidos OBI

34 Height ASL (m) Stage data: Daily Maximum SER MAN OBI SPO 40 FVA Negro at MAN Madeira at FVA Amazonas at OBI Negro at SER Solimões at SPO Although the series in SPO, FVA, MAN and OBI show a slight increase after the seventies, no significant statistical trend can be detected

35 Height ASL (m) Stage data: Daily Minimum SPO SER MAN FVA OBI Negro at MAN Madeira at FVA Amazonas at OBI Negro at SER Solimões at SPO Data suggests that there is signal in discharges due to tributaries of the southern part of the Amazon basin 0

36 Previous studies (Cox et al. 2008) have shown that reduction of dry season (July October) rainfall in western Amazonia correlates well with an index of the north south SST gradient across the equatorial Atlantic (the Atlantic N S gradient ).

37 Relationship between rainfall in western Amazonia and the index of the north south SST gradient across the equatorial Atlantic (Cox et al. 2008)

38 Therefore, it is possible to assume that minimum water level at Manaus might be related to the reduction of rainfall in western Amazonia Consequently, minimum water levels at Manaus were compared to SST at the north and south tropical Atlantic.

1920 1923 1926 1929 1932 1935 1938 1941 1944 1947 1950 1953 1956 1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992

8-2 o C 1.8 2 1.6 1.4 1.2 0.8 1 0.6 0.4 0.2-0.2 0-0.4-0.6-0.8-1.2-1 -1.4-1.6-1.

39 cm o C o C Anomaly SST (North Atlantic) Anomaly SST (South Atlantic) DJF MAM JJA SON DJF MAM JJA SON Minimum water levels of the Negro River at Manaus

40 Conclusions Floods and droughts in the Amazon river are not only related to positive/negative rainfall anomalies, but more importantly the timing when those extreme rainfall events occurred. If the onset of the wet season in the northern and southern part of the basin is such that put in phase river discharges of northern and southern tributaries of the main-stem, the damping effect produced by the differences in contributions time of northern and southern tributaries is suppressed, and such conditions generally result in extreme discharges (either floods or droughts) in the main-stem.

41 Conclusions Manaus stage record indicate a negative trend beginning in the 1970s This trend is associated to the increase frequency of extremes in Amazonia, particularly droughts The minimum stage levels recorded in Manaus seems to be related to the dipole of the Tropical Atlantic Further investigation are needed to understand if this relationship is spurious or there are physical mechanisms involved.

42 OBRIGADO!!! Acknowledgements Daniel Andrés Rodriguez Lincoln Muniz Alves Wagner Soares

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