Rainfall control on Amazon sediment flux: synthesis from 20 years of monitoring

Armijos, Elisa; Crave, Alain; Espinoza, Jhan Carlo; Filizola, Naziano; Espinoza-Villar, Raúl; Ayes, Irma; Fonseca, Paula Andrea Morelli; Fraizy, Pascal; Gutiérrez, Olga; Vauchel, Philippe; Camenen, B.; Martiinez, J. M.; Santos, André dos; Santini, William; Cochonneau, Gérard; Guyot, Jean‐Loup

doi:10.1088/2515-7620/ab9003

Cited by 34 publications

(18 citation statements)

References 47 publications

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“…Over the savannas and flooded savannas (Figures 8C,D), the discharge variability from June to December is significantly associated with the NDVI variability, considering a time lag of around t-2 to t+2 months. The negative lag is explained by the characteristic rainfall-runoff time of response in the upper Madeira Basin, estimated to be about 60 days at the Porto Velho station (Espinoza et al, 2019b;Armijos et al, 2020).…”

Section: Spatial Patterns Of Rainfall-ndvi Relationships and The Rolementioning

confidence: 99%

On the Hydroclimate-Vegetation Relationship in the Southwestern Amazon During the 2000–2019 Period

Gutierrez-Cori

Espinoza

et al. 2021

Front. Water

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The southern Amazonia is undergoing a major biophysical transition, involving changes in land use and regional climate. This study provides new insights on the relationship between hydroclimatic variables and vegetation conditions in the upper Madeira Basin (~1 × 106 km2). Vegetative dynamics are characterised using the normalized difference vegetation index (NDVI) while hydroclimatic variability is analysed using satellite-based precipitation, observed river discharge, satellite measurements of terrestrial water storage (TWS) and downward shortwave radiation (DSR). We show that the vegetation in this region varies from energy-limited to water-limited throughout the year. During the peak of the wet season (January-February), rainfall, discharge and TWS are negatively correlated with NDVI in February-April (r = −0.48 to −0.65; p < 0.05). In addition, DSR is positively correlated with NDVI (r = 0.47–0.54; p < 0.05), suggesting that the vegetation is mainly energy-limited during this period. Outside this period, these correlations are positive for rainfall, discharge and TWS (r = 0.55–0.88; p < 0.05), and negative for DSR (r = −0.47 to −0.54; p < 0.05), suggesting that vegetation depends mainly on water availability, particularly during the vegetation dry season (VDS; late June to late October). Accordantly, the total rainfall during the dry season explains around 80% of the VDS NDVI interannual variance. Considering the predominant land cover types, differences in the hydroclimate-NDVI relationship are observed. Evergreen forests (531,350 km2) remain energy-limited during the beginning of the dry season, but they become water-limited at the end of the VDS. In savannas and flooded savannas (162,850 km2), water dependence occurs months before the onset of the VDS. These differences are more evident during extreme drought years (2007, 2010, and 2011), where regional impacts on NDVI were stronger in savannas and flooded savannas (55% of the entire surface of savannas) than in evergreen forests (40%). A spatial analysis reveals that two specific areas do not show significant hydroclimatic-NDVI correlations during the dry season: (i) the eastern flank of the Andes, characterised by very wet conditions, therefore the vegetation is not water-limited, and (ii) recent deforested areas (~42,500 km2) that break the natural response in the hydroclimate-vegetation system. These findings are particularly relevant given the increasing rates of deforestation in this region.

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Section: Spatial Patterns Of Rainfall-ndvi Relationships and The Rolementioning

confidence: 99%

On the Hydroclimate-Vegetation Relationship in the Southwestern Amazon During the 2000–2019 Period

Gutierrez-Cori

Espinoza

et al. 2021

Front. Water

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“…SSSC was used to evaluate the possible causes for trends and the 2010 break at Porto Velho, and not the fine suspended sediment concentration (FSC) in the water column as in Ayes et al (2019a). Nevertheless, as Ayes et al (2019a) estimated FSC by multiplying SSSC by a constant value following Armijos et al (2020), clearly both series are fully comparable regarding time variability. Moreover, the relationship of SSSC and FSC has not been evaluated at the Rurrenabaque station, which was also used in this study.…”

Section: Water Discharge and Sediment Datamentioning

confidence: 99%

“…Changes in the spatiotemporal rainfall variability over the Andes-Amazon transition region as reported by Espinoza et al (2019a) and Segura et al (2020) has been related to large scale atmospheric conditions and could modify the sediment dynamics as well over different temporal scales. Indeed, Armijos et al (2020) found that the temporal rainfall variability is well-related (R 2 = 0.89) to the fine suspended sediment concentration (FSC; >0.45 µm and <63 µm) at Porto Velho, while the coarse sediment (>63 µm) is better related to the water discharge.…”

Section: Introductionmentioning

confidence: 99%

The Role of the Rainfall Variability in the Decline of the Surface Suspended Sediment in the Upper Madeira Basin (2003–2017)

et al. 2021

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The Madeira River rises in the Andes, draining the southwestern Amazon basin and contributing up to 50% of the Amazon River sediment load. The Porto Velho station monitors the Upper Madeira basin and is located just downstream of the Jirau and Santo Antonio hydropower dams. At this station, decreasing trend (p < 0.10) of the surface suspended sediment concentration (SSSC) has been documented during the sediment peak season (December to February) for the 2003–2017 period. This study aims to evaluate the role of the rainfall variability on this documented decreasing trend. For this purpose, we applied correlation and trend analysis in water discharge, SSSC and rainfall time series over the main tributaries of the Upper Madeira basin. The decline of SSSC in December is attributed to the reduction of rainfall in the Madre de Dios sub-basin from the start of the rainy season in October. However, the SSSC negative trend (p < 0.10) in January and February is associated with a shift in the magnitude of rainfall during these months in the Andean region after 2008, and the dilution associated with base flow. These results reveal that the decline of SSSC in the Madeira River should not be evaluated just on the basis of the data downstream from the dams, but also of the processes upstream in the Andean part of the basin. In a context of drastic anthropogenic climate and environmental changes, understanding the combined influence of regional hydroclimate variability and human actions on erosion and sediment transport remains a critical issue for the conservation of the Amazon-Andes system.

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“…This causes a strong orographic effect that interacts with regional atmospheric circulation to produce an exceptional spatial rainfall contrast (Chavez and Takahashi 2017;Junquas et al 2018). There, high precipitation rates lead to large values of runoff per unit area (Moquet et al 2011), providing most of the sediment load to Amazon rivers (Vauchel et al 2017;Armijos et al 2020). Consequently, extreme hydrological events over this region can impact the whole basin downstream (Espinoza et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Deforestation Impacts on Amazon-Andes Hydroclimatic Connectivity

Sierra

Junquas

Espinoza

et al. 2021

Preprint

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Amazonian deforestation has accelerated during the last decade, threatening an ecosystem where almost one third of the regional rainfall is transpired by the local rainforest. Due to the precipitation recycling, the southwestern Amazon, including the Amazon-Andes transition region, is particularly sensitive to forest loss. This study evaluates the impacts of Amazonian deforestation in the hydro-climatic connectivity between the Amazon and the eastern tropical Andes during the austral summer (December-January-February) in terms of hydrological and energetic balances. Using 10-year high-resolution simulations (2001–2011) with the Weather Research and Forecasting Model, we analyze control and deforestation scenario simulations. Regionally, deforestation leads to a reduction in the surface net radiation, evaporation, moisture convergence and precipitation (~ 20%) over the entire Amazon basin. In addition, during this season, deforestation increases the atmospheric subsidence over the southern Amazon and weakens the regional Hadley cell. Atmospheric stability increases over the western Amazon and the tropical Andes inhibiting convection in these areas. Consequently, major deforestation impacts are observed over the hydro-climate of the Amazon-Andes transition region. At local scale, nighttime precipitation decreases in Bolivian valleys (~ 20–30%) due to a strong reduction in the humidity transport from the Amazon plains toward Andes linked to the South American low-level jet. Over these valleys, a weakening of the daytime upslope winds is caused by local deforestation, which reduces the turbulent fluxes at lowlands. These alterations in rainfall and atmospheric circulation could impact the rich Andean ecosystems and its tropical glaciers.

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Rainfall control on Amazon sediment flux: synthesis from 20 years of monitoring

Cited by 34 publications

References 47 publications

On the Hydroclimate-Vegetation Relationship in the Southwestern Amazon During the 2000–2019 Period

On the Hydroclimate-Vegetation Relationship in the Southwestern Amazon During the 2000–2019 Period

The Role of the Rainfall Variability in the Decline of the Surface Suspended Sediment in the Upper Madeira Basin (2003–2017)

Deforestation Impacts on Amazon-Andes Hydroclimatic Connectivity

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