Detected and projected changes in precipitation

The IPCC Third Assessment Report (IPPC, 2001) has shown no clear signs of negative trends in Amazonia due to increased deforestation as one would expect (Section 9.2.3). Section 9.2.5 describes trends and long-term variability in observed mean seasonal and annual rainfall and discharges. The magnitude and size of the trends depend on rainfall data sets, length of records, etc. and the uncertainty is high since

Ccsr Nies Uncertainty

Figure 9.7. Air temperatures in the Amazon region as simulated by five IPCC models: R30 (GFDL, U.S.A.), CCCMa (Canada), HadCM3 (U.K.), CSIRO (Australia), CCSR/NIES (Japan). Anomalies are in °C from the 1961-1990 long-term mean. Observations are from the CRU rainfall data set for the 1903-1998 period. Air temperatures are for the A2 SRES.

Figure 9.7. Air temperatures in the Amazon region as simulated by five IPCC models: R30 (GFDL, U.S.A.), CCCMa (Canada), HadCM3 (U.K.), CSIRO (Australia), CCSR/NIES (Japan). Anomalies are in °C from the 1961-1990 long-term mean. Observations are from the CRU rainfall data set for the 1903-1998 period. Air temperatures are for the A2 SRES.

various studies (Section 9.2.4) found trends that vary in direction when different length periods are used. What is clear is the presence of decadal-scale rainfall variability, with wetter periods during 1945-76 and relatively drier periods during 19772000 in northern Amazonia. Analysis of extreme rainfall events in Amazonia (Haylock et al., 2006) has also shown this, with some degree of spatial coherence and uncertainty due to the reduced number of stations used for the region. Using the records at Manaus and Belem, since 1961 an increase in rainfall exceeding the 99th and 95th percentiles has been detected, suggesting a tendency for more intense and extreme events during the last 40 years, even though the annual totals may have not exhibited a significant positive trend.

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