Spatio‐temporal rainfall variability in the Amazon basin countries (Brazil, Peru, Bolivia, Colombia, and Ecuador)

Abstract

Rainfall variability in the Amazon basin (AB) is analysed for the 1964-2003 period. It is based on 756 pluviometric stations distributed throughout the AB countries. For the first time it includes data from Bolivia, Peru, Ecuador, and Colombia. In particular, the recent availability of rainfall data from the Andean countries makes it possible to complete previous studies. The impact of mountain ranges on rainfall is pointed out. The highest rainfall in the AB is observed in low windward regions, and low rainfall is measured in leeward and elevated stations. Additionally, rainfall regimes are more diversified in the Andean regions than in the lowlands. Rainfall spatio-temporal variability is studied based on a varimax-rotated principal component analysis (PCA). Long-term variability with a decreasing rainfall since the 1980s prevails in June-July-August (JJA) and September-October-November (SON). During the rainiest seasons, i.e. December-January-February (DJF) and March-April-May (MAM), the main variability is at decadal and interannual time scales. Interdecadal variability is related to long-term changes in the Pacific Ocean, whereas decadal variability, opposing the northwest and the south of the AB, is associated with changes in the strength of the low-level jet (LLJ) along the Andes. Interannual variability characterizes more specifically the northeast of the basin and the southern tropical Andes. It is related to El Niño-Southern Oscillation (ENSO) and to the sea surface temperature (SST) gradient over the tropical Atlantic. Mean rainfall in the basin decreases during the 1975-2003 period at an annual rate estimated to be −0.32%. Break tests show that this decrease has been particularly important since 1982. Further insights into this phenomenon will permit to identify the impact of climate on the hydrology of the AB.

<strong>New insights on land surface-atmosphere feedbacks over tropical South America at interannual timescales</strong>

“…On the other hand, the process variables (PRC and EVP) are the most complex in the region HPREC= 0.76 and HEVP= 0.71. This result confirms the diversity of factors that make part of the hydro-climatic variance at interannual timescale, thus reflecting the implicit complexity of the linkages between these two processes over TropSA [44,46,59,[70][71][72]. The high entropy of EVP can be also explained in terms of the multivariate influence of water and energy fluxes in TropSA [22,47,73].…”

Seasonal variability in methane and nitrous oxide fluxes from tropical peatlands in the western Amazon basin

“…River discharge varies by season, with the lowest discharge between the dry season months of August and September. Peak discharge from the wet season flood pulse occurs between April and May, as recorded at the Tamshiyacu River gauging station (Espinoza Villar et al, 2009b). Householder et al (2012) and Lahteenoja et al (2009a, b).…”

Climate variability and extreme drought in the upper Solimões River (western Amazon Basin): Understanding the exceptional 2010 drought

“…In Tamshiyacu station (Figure 1a), discharge values are extended to the 1970-2010 period using their correlation with the water level data measured in the nearby Iquitos hydrometric station [Espinoza et al, 2006]. Requena on the Ucayali River and San Regis on the Marañón River, which permit analysis of the southern and northern rivers contributions (Figure 1a [Espinoza et al, 2009a].…”

“…They cause inundations, as in 1999, 2006 and 2009, or very low water stages, as in 1998, 2005 and 2010, which are harmful to people living nearby the watercourse and damaging for agriculture and ecosystems [e.g., Saleska et al, 2007;Phillips et al, 2009;Asner and Alencar, 2010;Lewis et al, 2011;Xu et al, 2011]. While interannual rainfall and discharge variability are related to the El Niño Southern Oscillation (ENSO) in the northeastern Amazon [e.g., Marengo et al, 1998;Uvo et al, 1998;Williams et al, 2005], no clear ENSO impact is documented in the western part of the basin [Ronchail et al, 2002;Poveda et al, 2006;Espinoza et al, 2009aEspinoza et al, , 2009b. However, high Tropical North Atlantic (TNA) SST, which are associated with an anomalous northward position of ITCZ, cause dry conditions in the southern and western Amazon [Marengo, 1992;Uvo et al, 2000], which are particularly severe during austral winter and spring [Ronchail et al, 2002;Espinoza et al, 2009b;Yoon and Zeng, 2010].…”