The frequency and spatial distributions of precipitation extremes (PEs) and deep convective clouds (DCC) across the Amazon region were assessed using satellite-derived data. For PEs, CHIRPS dataset ...for the period 1981–2018 were used to calculate a set of absolute, threshold, duration, and percentile-based threshold indices defined by the Expert Team on Climate Change Detection and Indices. DCC occurrence was assessed based on the Advanced Microwave Sounding Unit data for the period 2002–2018. In northern Amazon (north of
5
∘
S
) PEs and DCC are more frequent (
≥
60
%
frequency) during February–June. Averaged trends over these months have shown increase in daily rainfall above 20 mm of near 3 days over the 1981–2018 period, and an increase of 2 consecutive wet days (P
≥
1
mm
) in the same period. South of
5
∘
S
prevalence of PEs and DCC is largely observed during November–March (
≥
60
%
frequency), whereas the longest persistence of dry days is observed during June–August. Though all PE trends point to an intensification of rainfall in November–March, only consecutive dry days in winter (JJA) and spring (SON) show significant trends, pointing to an increase of 7 days over the 38-yr winters. Rainfall extremes over the entire Amazon region were found to be moderate to strongly correlated with the mean vertically integrated moisture divergence, and in southern Amazon also to upper level divergence and upward vertical velocity. Increased frequency of DCC were found over the whole basin (
∼
18
%
yr
-
1
), in contrast to decreased convective overshooting (up to
∼
15.4
%
yr
-
1
).
Unprecedented wet conditions are reported in the 2014 summer (December-March) in South-western Amazon, with rainfall about 100% above normal. Discharge in the Madeira River (the main southern Amazon ...tributary) has been 74% higher than normal (58 000 m3 s−1) at Porto Velho and 380% (25 000 m3 s−1) at Rurrenabaque, at the exit of the Andes in summer, while levels of the Rio Negro at Manaus were 29.47 m in June 2014, corresponding to the fifth highest record during the 113 years record of the Rio Negro. While previous floods in Amazonia have been related to La Niña and or warmer than normal tropical South Atlantic, the 2014 rainfall and flood anomalies are associated with warm condition in the western Pacific-Indian Ocean and with an exceptionally warm Subtropical South Atlantic. Our results suggest that the tropical and subtropical South Atlantic SST gradient is a main driver for moisture transport from the Atlantic toward south-western Amazon, and this became exceptionally intense during summer of 2014.
In this work, the authors analyze the origin of the extreme floods in the Peruvian Amazonas River during the 1970–2012 period, focusing on the recent April 2012 flooding (55 400 m³ s−1). Several ...hydrological variables, such as rainfall, terrestrial water storage, and discharge, point out that the unprecedented 2012 flood is mainly related to an early and abundant wet season over the north of the basin. Thus, the peak of the Marañón River, the northern contributor of the Amazonas, occurred sooner than usual (in April instead of May), coinciding with the peak of the Ucayali River, the southern contributor. This concomitance caused a dramatic flood downstream in the Peruvian Amazonas. These results are compared to the amplitude and timing of the three most severe extreme floods (1970–2011). The analysis of the climatic features related to the most important floods (1986, 1993, 1999, and 2012) suggests that they are characterized by a La Niña event, which originates a geopotential height wave train near the ground, with positive anomalies over the subtropical South and North Pacific and Atlantic and over southeastern South America. These patterns contribute to 1) the origin of an abundant humidity transport flux from the tropical North Atlantic and the Caribbean Sea toward the northwestern Amazon and 2) the maintenance of the monsoon flux over this region. They both favor a strong convergence of humidity in the northern Amazonas basin. Finally, the authors suggest that the intensity of floods is more likely related to an early La Niña event (as observed during the 2011/12 season), early rainfall, and simultaneous peaks of both tributaries of the Amazonas River.
In the last four decades, the Southern Amazon (south of 8°S) has shown changes in the spatial and temporal patterns of its hydro‐climatic components, leading to drier conditions. Due to climate and ...land‐use changes, this region is considered as a zone under biophysical transition processes. Previous studies have documented a complex interaction between climate and deforestation either on a large‐scale or based on limited in situ data, typically covering the Brazilian Amazon. In this study, we analyse the relationships between hydro‐climate, the surface water‐energy partitioning and an index of regional forest cover change for the period 1981–2018. Additionally, we discretized three regions covering the Bolivian Amazon and the southern portions of the Peruvian and Brazilian Amazon due to their differences in the evolution of land use. In the Bolivian region, a high ratio of forest cover change, exceeding 40–50%, is related to a significant tendency to become water‐limited. This change is associated with decreased rainfall, increased potential evapotranspiration and decreased actual evapotranspiration. Regardless of the region analysed, those that are characterized by a high ratio of forest cover change (>40–50%) show growing imbalance between increasing potential and decreasing actual evapotranspiration. However, in the Peruvian and Brazilian regions, hydro‐climatic conditions remain energy‐limited due to minor rainfall changes. The observed differences in surface water‐energy partitioning behaviour evidence a complex dependence of both sub‐regional (i.e., land cover changes) and large‐scale (i.e., strengthening of the Walker and Hadley circulations) conditions. Our findings indicate a clear link between hydro‐climatic changes and deforestation, providing a new perspective on their spatial variability on a sub‐regional scale.
Schematic distribution of increased (large icon with “+”), decreased (small icon with “‐”) and non‐trend (medium icon with “0”) for precipitation (cloud), potential evapotranspiration (red arrow), actual evapotranspiration (purple arrow) and dryness index (gold arrow), for areas displaying the most significant variations, over 1981‐2018. The percentage of non‐forest vegetation areas as for 2018, is represented by the green‐red color bar.
In 2023 Amazonia experienced both historical drought and warm conditions. On October 26th 2023 the water levels at the port of Manaus reached its lowest record since 1902 (12.70 m). In this region, ...October monthly maximum and minimum temperature anomalies also surpassed previous record values registered in 2015 (+ 3 °C above the normal considering the 1981-2020 average). Here we show that this historical dry and warm situation in Amazonia is associated with two main atmospheric mechanisms: (i) the November 2022-February 2023 southern anomaly of vertical integrated moisture flux (VIMF), related to VIMF divergence and extreme rainfall deficit over southwestern Amazonia, and (ii) the June-August 2023 downward motion over northern Amazonia related to extreme rainfall deficit and warm conditions over this region. Anomalies of both atmospheric mechanisms reached record values during this event. The first mechanism is significantly correlated to negative sea surface temperature (SST) anomalies in the equatorial Pacific (November-February La Niña events). The second mechanism is significantly correlated to positive SST anomalies in the equatorial Pacific, related to the impacts of June-September El Niño on the Walker Circulation. While previous extreme droughts were linked to El Niño (warmer North Tropical Atlantic SST) during the austral summer (winter and spring), the transition from La Niña 2022-23 to El Niño 2023 appears to be a key climatic driver in this record-breaking dry and warm situation, combined to a widespread anomalous warming over the worldwide ocean.
This work provides an initial overview of climate features and their related hydrological impacts during the recent extreme droughts (1995, 1998, 2005 and 2010) in the upper Solimões River (western ...Amazon), using comprehensive in situ discharge and rainfall datasets. The droughts are generally associated with positive SST anomalies in the tropical North Atlantic and weak trade winds and water vapor transport toward the upper Solimões, which, in association with increased subsidence over central and southern Amazon, explain the lack of rainfall and very low discharge values. But in 1998, toward the end of the 1997–98 El Niño event, the drought is more likely related to an anomalous divergence of water vapor in the western Amazon that is characteristic of a warm event in the Pacific. During the austral spring and winter of 2010, the most severe drought since the seventies has been registered in the upper Solimões. Its intensity and its length, when compared to the 2005 drought, can be explained by the addition of an El Niño in austral summer and a very warm episode in the Atlantic in boreal spring and summer. As in 2005, the lack of water in 2010 was more important in the southern tropical tributaries of the upper Solimões than in the northern ones.
Key Points
Climate features related to extreme droughts in Solimões River
Hydrological impacts of the extreme droughts in the upper Solimões River
Hydrology of the Solimões River is documented and analyzed using a new data set
Knowledge and studies on precipitation in the Amazon Basin (AB) are determinant for environmental aspects such as hydrology, ecology, as well as for social aspects like agriculture, food security, or ...health issues. Availability of rainfall data at high spatio-temporal resolution is thus crucial for these purposes. Remote sensing techniques provide extensive spatial coverage compared to ground-based rainfall data but it is imperative to assess the quality of the estimates. Previous studies underline at regional scale in the AB, and for some years, the efficiency of the Tropical Rainfall Measurement Mission (TRMM) 3B42 Version 7 (V7) (hereafter 3B42) daily product data, to provide a good view of the rainfall time variability which is important to understand the impacts of El Nino Southern Oscilation. Then our study aims to enhance the knowledge about the quality of this product on the entire AB and provide a useful understanding about his capacity to reproduce the annual rainfall regimes. For that purpose we compared 3B42 against 205 quality-controlled rain gauge measurements for the period from March 1998 to July 2013, with the aim to know whether 3B42 is reliable for climate studies. Analysis of quantitative (Bias, Relative RMSE) and categorical statistics (POD, FAR) for the whole period show a more accurate spatial distribution of mean daily rainfall estimations in the lowlands than in the Andean regions. In the latter, the location of a rain gauge and its exposure seem to be more relevant to explain mismatches with 3B42 rather than its elevation. In general, a good agreement is observed between rain gauge derived regimes and those from 3B42; however, performance is better in the rainy period. Finally, an original way to validate the estimations is by taking into account the interannual variability of rainfall regimes (i.e., the presence of sub-regimes): four sub-regimes in the northeast AB defined from rain gauges and 3B42 were found to be in good agreement. Furthermore, this work examined whether TRMM 3B42 V7 rainfall estimates for all the grid points in the AB, outgoing longwave radiation (OLR) and water vapor flux patterns are consistent in the northeast of AB.
Former hydrological studies in the Amazon Basin generally describe annual discharge variability on the main stem. However, the downstream Amazon River only represents the mean state of the Amazonian ...hydrological system. This study therefore uses a new data set including daily discharge in 18 sub-basins to analyze the variability of regional extremes in the Amazon basin, after recalling the diversity of the hydrological annual cycles within the Amazon basin. Several statistical tests are applied in order to detect trends and breaks in the time series. We show that during the 1974–2004 period, the stability of the mean discharge on the main stem in Óbidos is explained by opposite regional features that principally involve Andean rivers: a decrease in the low stage runoff, particularly important in the southern regions, and an increase in the high stage runoff in the northwestern region. Both features are observed from the beginning of the nineties. These features are also observed in smaller meridian sub-basins in Peru and Bolivia. Moreover we show that the changes in discharge extremes are related to the regional pluriannual rainfall variability and the associated atmospheric circulation as well as to tropical large-scale climatic indicators.
•Runoff coefficient and evapotranspiration decrease in the upper Madeira (1982–2017).•Rainfall decrease in the southern Madeira explains the decrease of runoff coefficient.•Rainfall increases in the ...northern upper Madeira Results suggest changes in the atmosphere and land surface interactions since the 1990s.
Upper Madeira Basin (975,500 km2) in Southern Amazonia, which is suffering a biophysical transition, involving deforestation and changes in rainfall regime.
The evolution of the runoff coefficient (Rc: runoff/rainfall) is examined as an indicator of the environmental changes (1982–2017).
At an annual scale, the Rc at Porto Velho station declines while neither the basin-averaged rainfall nor the runoff change. During the low-water period Rc and runoff diminish while no changes are observed in rainfall. This cannot be explained by increase of evapotranspiration since the basin-averaged actual evapotranspiration decreases. To explain the decrease of Rc, a regional analysis is undertaken. While the characteristic rainfall-runoff time-lag (CT) at Porto Velho basin is estimated to 60 days, CT is higher (65–75 days) in the south and lower (50 days) over the Amazon-Andes transition regions. It is found that 1) the southern basin (south of 14 °S) best explains low-level Porto Velho runoff, 2) in the south, rainfall diminishes and the frequency of dry days increases. Both features explain the diminution of the runoff and the Rc in Porto Velho. Moreover, the increasing dryness in the south compensates for the rainfall and frequency of wet days (>10 mm) increase north of 14 °S and explains the lack of basin-averaged rainfall trends of the upper Madeira basin.
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