Session 3: Case studies Low flows and floods – Amazon Basin Jean Loup GUYOT – IRD Lima – - UPS Toulouse ANA Brasília UnB Brasília UFF Niteroí UFRJ Rio de Janeiro INAMHI Quito SENAMHI Lima UNALM Lima SENAMHI La Paz UMSA La Paz

Amazon Drainage Basin the largest basin of the world (Area : km²) ≈ 5% of continental areas ≈ 20% of fresh water discharge 7 countries Mean discharge : m³.s -1

Rainfall Data

Rainfall stations from : ANA (Brazil), SENAMHI (Bolivia and Peru), INAMHI (Ecuador) IDEAM (Colombia

This methodology consists in assuming that for the same climatic zone under the same rainfall regime, the annual pluviometric totals are pseudo proportional, with a little random variation every year due to rain distribution in the zone. To calculate this “Vector” station, the RVM applies the concept of extended average rainfall to the work period, which is an estimation of the average possible value that would have been obtained through continuous observations during the study period. Based on the above mentioned, the Least Squares Method is applied to find the Regional Annual Pluviometric Regional Indexes Zi and the extended average rainfall Pj. This may be calculated by minimizing the sum of the formula (1), where i is the year index, j is the station index, N is the number of years, and M is the number of stations. Pij is the annual rainfall in the station j, the year i; Pj is the extended average rainfall to the period of N years; and finally, Zi is the regional pluviometric index of the year i. The series of the chronological indexes Zi is called “Regional Annual Pluviometric Indexes Vector”. Regional Vector Method - RVM Hiez (1977) & Brunet-Moret (1979)

25 vectors (homogenous areas) : 16 in the Andean Countries, 9 in Brazil Espinoza et al. (submitted). n = 1446 (756) 1964/2003

50W55W60W65W70W75W 80W 05N 00 05S 15S 10S 20S Km 300mm Mean annual rainfall

W55W60W65W70W75W 80W 05N 00 05S 15S 10S 20S Purus Juruá Madeira Tapajós Xingu Negro Branco Amazonas Marañón Ucayali Seasonal Variability Coefficient (sVC)

05N 00 05S 15S 10S 20S 50W55W60W65W70W75W 80W Interannual Variability Coefficient (iVC)

W55W60W65W70W75W 80W 05N 00 05S 15S 10S 20S Interannual VC / Seasonal VC

Espinoza et al. (submitted) % / year Mean annual rainfall trend (Óbidos)

TAMSHIYACU Espinoza et al. (2006). Mean annual rainfall trend (Tamshiyacu) % / year

Callède et al. (2004). n = /1999

Callède et al. (submitted). n = /2003 No trend

Discharge Data

Gauging stations from : ANA (Brazil), SENAMHI (Bolivia), INAMHI (Ecuador), HYBAM (Bolivia, Peru and Ecuador) Óbidos Tamshiyacu

Reconstructing / Correcting Water Level Data

ADCP Discharge Measure (Tamshiyacu gauging station, Peru)

Rating curve (Tamshiyacu gauging station, Peru)

ADCP Discharge Data (Óbidos gauging station, Brazil)

Historical Gauging Data (Óbidos gauging station, Brazil)

TAM SAI ACA SER CAR G-L PVE FVA MAN OBI ALT Peru Ecuador Colombia Venezuela Bolivia Brasil Km ITA

The trend analysis is made based on the calculation of the correlation coefficients, which are applied for evaluating the series trend. The correlation coefficients applied are: Pearson coefficient, which is parametric and measures the lineal correlation among variables, Spearman is non-parametric based on the range, and Kendall, also non-parametric based on the range and probability of the data occurrence order. Trend analysis

Annual Discharge Data (Óbidos gauging station, Brazil) Mean (no trend) Max Min Nine events with runoff higher than m3/s occurred between 1970 and 2005, while four have been observed since the beginning of the century,

Annual Discharge Data (Tamshiyacu gauging station, Peru) -0.81% / year Espinoza et al. (2006). IAHS Publ. 308,

TAM SAI ACA SER CAR MAN G-L PVE FVA ITA ALT OBI Mean annual discharge trend

TAM SAI ACA SER CAR MAN G-L PVE FVA ITA ALT OBI Max annual discharge trend

TAM SAI ACA SER CAR MAN G-L PVE FVA ITA ALT OBI Min annual discharge trend

One long observed time serie : Negro River at Manaus ( today) Due to backwater effects, Negro River water levels are controlled by the Amazon river near the confluence, like all majors tributaries of the Amazon basin. Meade et al. (1991). Environ. Geol. Water Sci. 18(2),

Richey et al. (1989). Science. 246, > No trend, links with ENSO events Milly et al. (2002). Nature, 415: > increasing floods

One long reconstructed time serie : Amazon River at Óbidos ( today)

2 observed periods without nivel correction. The rating curve for the recent Period can not be used for the whole period. -> be careful with published discharge data (UNESCO)

Callède et al. (2004). Max, Mean and Min annual discharges : Amazon River at Óbidos ( )

The breaks and changes in the series are evaluated through different methods, using Kronostat software: the Buishand method, of Bayesian nature, based on changes of the series average. The Pettitt method is a non-parametric test based on changes in the average and the range of the series. Lee and Heghinian test are also used, which is other Bayesian method that uses the average as an indicator of change. Finally, Hubert segmentation is applied based on the significant difference of the average and the standard deviation among periods; for the search of multiple changes in the series. Breaks analysis Callède et al. (2004).

Callède et al. (submitted). Runoff coefficient : Amazon River at Óbidos ( )

Using Wavelet analyses to detect changes

Conclusion Main results for the 1902 – 1999 period at Obidos are : i)increasing trends for annual mean discharge and annual flood discharge, ii)no tendency for low flows, and iii)a significant break for the maximum and mean time series in Using the HYBAM dataset for the whole Amazon basin, a first study has been realized for 30 years ( ). Mean annual rainfall over the Óbidos drainage basin presents a decreasing trend of 0.32%/year, while mean annual discharge is stable. This difference between rainfall estimation and discharge can be the consequence of: rainfall under estimation, mainly in the equatorial region (north Peru, Colombia) were rainfall data is rare, impact of the deforestation : with the same rainfall, there is more runoff, etc… and/or change in the rainfall regime, with higher intensity, i.e. more runoff. For the same period ( ), annual flood discharges are increasing, while annual low flows are decreasing, traducing an increasing amplitude of discharge at the Óbidos station. The study of these tendencies in the different sub basins should allow us to understand better the impact of the climatic variability in the Amazon basin. => More data is required, => We have to help the Andean countries in this way

HYBAM Observatory

Suspended Sediment Yield : Amazon River at Óbidos ( today) Guyot et al. (in press). IAHS