scholarly journals Evapotranspiration seasonality across the Amazon basin

2017 ◽  
Author(s):  
Eduardo Eiji Maeda ◽  
Xuanlong Ma ◽  
Fabien Wagner ◽  
Hyungjun Kim ◽  
Taikan Oki ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Regional Climate ◽  
Root Water Uptake ◽  
Environmental Drivers ◽  
Seasonal Patterns ◽  
Wet Season ◽  
Important Indicator ◽  
Seasonally Dry ◽  
Basin Scale ◽  
Terrestrial Water

Abstract. Evapotranspiration (ET) of Amazon forests is a main driver of regional climate patterns and an important indicator of ecosystem functioning. Despite its importance, the seasonal variability of ET over Amazon forests, and its relationship with environmental drivers, is still poorly understood. In this study, we carry out a water balance approach to analyse seasonal patterns in ET and their relationships with water and energy drivers over five sub-basins across the Amazon basin. We used in-situ measurements of river discharge, and remotely sensed estimates of terrestrial water storage, rainfall, and solar radiation. We show that the characteristics of ET seasonality in all sub-basins differ in timing and magnitude. The highest mean annual ET was found in the northern Rio Negro basin (~ 1497 mm year−1) and the lowest values in the Solimões River basin (~ 986 mm year−1). For the first time in a basin-scale study, using observational data, we show that factors limiting ET vary across climatic gradients in the Amazon, confirming local-scale eddy covariance studies. Both annual mean and seasonality in ET are driven by a combination of energy and water availability, as neither rainfall nor radiation alone could explain patterns in ET. In southern basins, despite seasonal rainfall deficits, deep root water uptake allows increasing rates of ET during the dry season, when radiation is usually higher than in the wet season. We demonstrate contrasting ET seasonality with satellite greenness across Amazon forests, with strong asynchronous relationships in ever-wet watersheds, and positive correlations observed in seasonally dry watersheds. Finally, we compared our results with estimates obtained by two ET models, and we conclude that neither of the two tested models could provide a consistent representation of ET seasonal patterns across the Amazon.

scholarly journals Evapotranspiration seasonality across the Amazon Basin

2017 ◽  
Vol 8 (2) ◽  
pp. 439-454 ◽  
Author(s):  
Eduardo Eiji Maeda ◽  
Xuanlong Ma ◽  
Fabien Hubert Wagner ◽  
Hyungjun Kim ◽  
Taikan Oki ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Regional Climate ◽  
Root Water Uptake ◽  
Environmental Drivers ◽  
Seasonal Patterns ◽  
Wet Season ◽  
Important Indicator ◽  
Seasonally Dry ◽  
Basin Scale ◽  
Terrestrial Water

Abstract. Evapotranspiration (ET) of Amazon forests is a main driver of regional climate patterns and an important indicator of ecosystem functioning. Despite its importance, the seasonal variability of ET over Amazon forests, and its relationship with environmental drivers, is still poorly understood. In this study, we carry out a water balance approach to analyse seasonal patterns in ET and their relationships with water and energy drivers over five sub-basins across the Amazon Basin. We used in situ measurements of river discharge, and remotely sensed estimates of terrestrial water storage, rainfall, and solar radiation. We show that the characteristics of ET seasonality in all sub-basins differ in timing and magnitude. The highest mean annual ET was found in the northern Rio Negro basin (∼ 1497 mm year−1) and the lowest values in the Solimões River basin (∼ 986 mm year−1). For the first time in a basin-scale study, using observational data, we show that factors limiting ET vary across climatic gradients in the Amazon, confirming local-scale eddy covariance studies. Both annual mean and seasonality in ET are driven by a combination of energy and water availability, as neither rainfall nor radiation alone could explain patterns in ET. In southern basins, despite seasonal rainfall deficits, deep root water uptake allows increasing rates of ET during the dry season, when radiation is usually higher than in the wet season. We demonstrate contrasting ET seasonality with satellite greenness across Amazon forests, with strong asynchronous relationships in ever-wet watersheds, and positive correlations observed in seasonally dry watersheds. Finally, we compared our results with estimates obtained by two ET models, and we conclude that neither of the two tested models could provide a consistent representation of ET seasonal patterns across the Amazon.

scholarly journals Carbon monoxide and related trace gases and aerosols over the Amazon Basin during the wet and dry seasons

2012 ◽  
Vol 12 (13) ◽  
pp. 6041-6065 ◽  
Author(s):  
M. O. Andreae ◽  
P. Artaxo ◽  
V. Beck ◽  
M. Bela ◽  
S. Freitas ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Southern Hemisphere ◽  
Biomass Burning ◽  
Large Scale ◽  
Amazon Basin ◽  
Photochemical Degradation ◽  
Wet Season ◽  
Biomass Smoke ◽  
Airborne Measurements ◽  
Basin Scale

Abstract. We present the results of airborne measurements of carbon monoxide (CO) and aerosol particle number concentration (CN) made during the Balanço Atmosférico Regional de Carbono na Amazônia (BARCA) program. The primary goal of BARCA is to address the question of basin-scale sources and sinks of CO2 and other atmospheric carbon species, a central issue of the Large-scale Biosphere-Atmosphere (LBA) program. The experiment consisted of two aircraft campaigns during November–December 2008 (BARCA-A) and May–June 2009 (BARCA-B), which covered the altitude range from the surface up to about 4500 m, and spanned most of the Amazon Basin. Based on meteorological analysis and measurements of the tracer, SF6, we found that airmasses over the Amazon Basin during the late dry season (BARCA-A, November 2008) originated predominantly from the Southern Hemisphere, while during the late wet season (BARCA-B, May 2009) low-level airmasses were dominated by northern-hemispheric inflow and mid-tropospheric airmasses were of mixed origin. In BARCA-A we found strong influence of biomass burning emissions on the composition of the atmosphere over much of the Amazon Basin, with CO enhancements up to 300 ppb and CN concentrations approaching 10 000 cm−3; the highest values were in the southern part of the Basin at altitudes of 1–3 km. The ΔCN/ΔCO ratios were diagnostic for biomass burning emissions, and were lower in aged than in fresh smoke. Fresh emissions indicated CO/CO2 and CN/CO emission ratios in good agreement with previous work, but our results also highlight the need to consider the residual smoldering combustion that takes place after the active flaming phase of deforestation fires. During the late wet season, in contrast, there was little evidence for a significant presence of biomass smoke. Low CN concentrations (300–500 cm−3) prevailed basinwide, and CO mixing ratios were enhanced by only ~10 ppb above the mixing line between Northern and Southern Hemisphere air. There was no detectable trend in CO with distance from the coast, but there was a small enhancement of CO in the boundary layer suggesting diffuse biogenic sources from photochemical degradation of biogenic volatile organic compounds or direct biological emission. Simulations of CO distributions during BARCA-A using a range of models yielded general agreement in spatial distribution and confirm the important contribution from biomass burning emissions, but the models evidence some systematic quantitative differences compared to observed CO concentrations. These mismatches appear to be related to problems with the accuracy of the global background fields, the role of vertical transport and biomass smoke injection height, the choice of model resolution, and reliability and temporal resolution of the emissions data base.

scholarly journals Carbon, nitrogen and sulfur (CNS) status and dynamics in Amazon basin upland soils, Brazil

2019 ◽  
Author(s):  
Jörg Matschullat ◽  
Roberval Monteiro Bezerra de Lima ◽  
Sophie F. von Fromm ◽  
Solveig Pospiech ◽  
Andrea M. Ramos ◽  
...  
Keyword(s):  
Climate Change ◽  
Amazon Basin ◽  
Forest Canopy ◽  
Regional Climate ◽  
Mineral Soil ◽  
Regional Climate Change ◽  
Wet Season ◽  
N Losses ◽  
Carbon And Nitrogen ◽  
C And N

Abstract. Given the dimensions of the Amazon basin (7.5 million km2), its internal dynamics, increasing anthropogenic strain on this large biome, and its global role as one of two continental biospheric tipping elements, it appears crucial to have data-based knowledge on carbon and nitrogen concentrations and pools as well as on possible intra-annual dynamics. We quantified carbon (Ct, Corg), nitrogen (N) and sulfur (S) concentrations in litter (ORG) and mineral soil material (TOP 0–20 cm, BOT 30–50 cm) of upland (terra firme) oxisols across Amazonas state and present a first pool calculation. Data are based on triplicate seasonal sampling at 29 sites (forest and post-forest) within the binational project EcoRespira-Amazon (ERA). Repeated sampling increased data accuracy and allows for interpreting intra-annual (seasonal) and climate-change related dynamics. Extreme conditions between the dry season in 2016 and the subsequent wet season (ENSO-related) show differences more clearly. Median CNS in the Amazon basin TOP soils (Ct 1.9, Corg 1.6, N 0.15, S 0.03 wt-% under forest canopy) as well as Corg / N ratios show concentrations similar to European soils (FOREGS, GEMAS). TOP Ct concentrations ranged from 1.02 to 3.29 wt-% (medianForest 2.17 wt-%; medianPost-Forest 1.75 wt-%), N from 0.088 to 0.233 wt-% (medianForest 0.17 wt-%; medianPost-Forest 0.09 wt-%) and S from 0.012 to 0.051 wt.-% (medianForest 0.03 wt.-%; medianPost-Forest 0.02 wt-%). Corg / N ratios ranged from 6 to 14 (median 10). A first pool calculation (hectare-based) illustrates forest versus post-forest changes. The elements are unevenly distributed in the basin with generally higher CNS values in the central part (Amazonas graben) as compared to the southern part of the basin. Deforestation and drought conditions lead to C and N losses – within 50 years after deforestation, C and N losses average 10 to 15 %. Regional climate change with increased drought will likely speed up carbon and nitrogen losses.

scholarly journals The Major Floods in the Amazonas River and Tributaries (Western Amazon Basin) during the 1970–2012 Period: A Focus on the 2012 Flood*

2013 ◽  
Vol 14 (3) ◽  
pp. 1000-1008 ◽  
Author(s):  
Jhan Carlo Espinoza ◽  
Josyane Ronchail ◽  
Frédéric Frappart ◽  
Waldo Lavado ◽  
William Santini ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Wave Train ◽  
La Niña ◽  
Wet Season ◽  
Extreme Floods ◽  
The North ◽  
La Nina ◽  
Terrestrial Water ◽  
Major Floods ◽  
La Nina Event

Abstract 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.

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

2021 ◽  
Vol 3 ◽  
Author(s):  
Omar Gutierrez-Cori ◽  
Jhan Carlo Espinoza ◽  
Laurent Z. X. Li ◽  
Sly Wongchuig ◽  
Paola A. Arias ◽  
...  
Keyword(s):  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Regional Climate ◽  
Dry Season ◽  
Shortwave Radiation ◽  
Wet Season ◽  
Evergreen Forests ◽  
Terrestrial Water ◽  
Southern Amazonia ◽  
Hydroclimatic Variability

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.

scholarly journals Physiographic and floristic gradients across topography in transitional seasonally dry evergreen forests of southeast Pará, Brazil

2006 ◽  
Vol 36 (4) ◽  
pp. 483-496 ◽  
Author(s):  
James Grogan ◽  
Jurandir Galvão
Keyword(s):  
Amazon Basin ◽  
Nutrient Status ◽  
Dry Season ◽  
Wet Season ◽  
Moisture Retention ◽  
Deep Soil ◽  
Forest Canopies ◽  
Seasonally Dry ◽  
Evergreen Forests ◽  
South Central

Seasonally dry evergreen forests in southeast Pará, Brazil are transitional between taller closed forests of the interior Amazon Basin and woodland savannas (cerrados) of Brazil's south-central plains. We describe abiotic and biotic gradients in this region near the frontier town of Redenção where forest structure and composition grade subtly across barely undulating topography. Annual precipitation averaged 1859 mm between 1995-2001, with nearly zero rainfall during the dry season months of June August. Annual vertical migrations of deep-soil water caused by seasonal rainfall underlie edaphic and floristic differences between high- and low-ground terrain. Low-ground soils are hydromorphic, shaped by perching water tables during the wet season, pale gray, brown, or white in color, with coarse texture, low moisture retention during the dry season, and relatively high macro-nutrient status in the surface horizons. Forest canopies on low ground are highly irregular, especially along seasonal streams, while overstory community composition differs demonstrably from that on high ground. High-ground soils are dystrophic, well-drained through the wet season, brown or red-yellow in color, with finer texture, higher moisture retention, and low macro-nutrient status in the surface horizons compared to low-ground soils. Forest canopies are, on average, taller, more regular, and more closed on high ground. Low-ground areas can be envisioned as energy and nutrient sinks, where, because of hydrologic cycles, canopy disturbance likely occurs more frequently than at high-ground positions if not necessarily at larger scales.

The hydroclimate-vegetation relationship in the Amazon basin during the last 20 years: an analysis focused on the southwestern region

2021 ◽  
Author(s):  
Omar Gutierrez-Cori ◽  
Jhan Carlo Espinoza ◽  
Laurent Z X Li ◽  
Sly Wongchuig-Correa ◽  
Paola A. Arias ◽  
...  
Keyword(s):  
Land Cover ◽  
Amazon Basin ◽  
Land Use Changes ◽  
The Other ◽  
Wet Season ◽  
Deep Soil ◽  
Evergreen Forests ◽  
Terrestrial Water ◽  
Hydroclimatic Variability ◽  
Hydroclimatic Variables

<p>The relationship between multiple hydroclimatic variables and vegetation conditions in the upper Madeira Basin (southwestern Amazon) has been analyzed. Vegetative dynamics are characterized using NDVI dataset as an indicator of the photosynthetic capacities of vegetation. Hydroclimatic variability is analyzed using satellite-based precipitation datasets, observed river discharge, and satellite measurements of terrestrial water storage (TWS). Our results show that the vegetation in the Basin varies from energy- to water-limited. During the peak of the wet season (January-February), rainfall, discharge, and TWS are negatively correlated with NDVI (r=-0.48 to -0.65), suggesting that during this period the vegetation is mainly energy-dependent. Outside this period, these correlations are positive (r=0.55 to 0.9), suggesting that vegetation depends mainly on water availability. This higher water dependence is more noticeable during the vegetation dry season (VDS; June-October). Considering the predominant land cover types, differences in the hydroclimate-NDVI relationship are observed. Evergreen forests remain energy-limited during the beginning of the VDS, but they become water-dependent almost at the end. Savannas show a different behavior, where water dependence occurs months before the onset of the VDS. On the other hand, unlike the other variables, the TWS better explains the NDVI in evergreen forests during the VDS (r=0.7 to 0.85). This is probably because evergreen forests are more dependent on deep soil water. A spatial analysis between hydroclimatic variables and the NDVI shows the predominance of positive correlations in most of the basin. However, specific areas do not show significant correlations. The weak relationship in these areas is explained by two factors i) very wet conditions during most of the year in the "rainfall hotspot" regions, where the vegetation is not water-limited, and ii) recent land-use changes (deforestation) that break the natural response in the hydroclimate-vegetation system. These findings provide new evidence on the impacts of the land cover changes on the natural relationship between vegetation and hydroclimatic variability, which is particularly relevant given the increasing rates of deforestation in this region during recent years.</p>

scholarly journals Carbon monoxide and related trace gases and aerosols over the Amazon Basin during the wet and dry seasons

2012 ◽  
Vol 12 (3) ◽  
pp. 8107-8168 ◽  
Author(s):  
M. O. Andreae ◽  
P. Artaxo ◽  
V. Beck ◽  
M. Bela ◽  
S. Freitas ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Southern Hemisphere ◽  
Biomass Burning ◽  
Large Scale ◽  
Amazon Basin ◽  
Photochemical Degradation ◽  
Wet Season ◽  
Biomass Smoke ◽  
Airborne Measurements ◽  
Basin Scale

Abstract. We present the results of airborne measurements of carbon monoxide (CO) and aerosol particle number concentration (CN) made during the Balanço Atmosférico Regional de Carbono na Amazônia (BARCA) program. The primary goal of BARCA is to address the question of basin-scale sources and sinks of CO2 and other atmospheric carbon species, a central issue of the Large-scale Biosphere-Atmosphere (LBA) program. The experiment consisted of two aircraft campaigns during November–December 2008 (BARCA-A) and May 2009 (BARCA-B), which covered the altitude range from the surface up to about 4500 m, and spanned most of the Amazon Basin. Based on meteorological analysis and measurements of the tracer, SF6, we found that airmasses over the Amazon Basin during the late dry season (BARCA-A, November 2008) originated predominantly from the Southern Hemisphere, while during the late wet season (BARCA-B, May 2009) low-level airmasses were dominated by northern-hemispheric inflow, and mid-tropospheric airmasses were of mixed origin. In BARCA-A we found strong influence of biomass burning emissions on the composition of the atmosphere over much of the Amazon Basin, with CO enhancements up to 300 ppb and CN concentrations approaching 10 000 cm−3; the highest values were in the southern part of the Basin at altitudes of 1–3 km. The ΔCN/ΔCO ratios were diagnostic for biomass burning emissions, and were lower in aged than in fresh smoke. Fresh emissions indicated CO/CO2 and CN/CO emission ratios in good agreement with previous work, but our results also highlight the need to consider the residual smoldering combustion that takes place after the active flaming phase of deforestation fires. During the late wet season, in contrast, there was little evidence for a significant presence of biomass smoke. Low CN concentrations (300–500 cm−3) prevailed basinwide, and CO mixing ratios were enhanced by only ~10 ppb above the mixing line between Northern and Southern Hemisphere air. There was no detectable trend in CO with distance from the coast, but there was a small enhancement of CO in the boundary layer suggesting diffuse biogenic sources from photochemical degradation of biogenic volatile organic compounds or direct biological emission. Simulations of CO distributions during BARCA-A using a range of models yielded general agreement in spatial distribution and confirm the important contribution from biomass burning emissions, but the models evidence some systematic quantitative differences compared to observed CO concentrations. These mismatches appear to be related to problems with the accuracy of the global background fields, the role of vertical transport and biomass smoke injection height, the choice of model resolution, and reliability and temporal resolution of the emissions data base.

scholarly journals Assessing evapotranspiration drivers and patterns at multiple scale in the Amazon basin

2020 ◽  
Author(s):  
Adriana Aparecida Moreira ◽  
Anderson Luis Ruhoff
Keyword(s):  
Remote Sensing ◽  
Tropical Forest ◽  
Amazon Basin ◽  
Vegetation Index ◽  
Dry Season ◽  
Limiting Factors ◽  
Net Radiation ◽  
Wet Season ◽  
Basin Scale ◽  
The Tropics

<p>Evapotranspiration (ET) is a key variable to terrestrial climate system, transferring water from the surface to the atmosphere, regulating air temperature and carbon exchanges, thus, linking the water, carbon and water cycles. Despite its great importance, ET patterns in tropical biomes are not fully understood yet. Studies with eddy covariance (EC) ET measurements and remote sensing models demonstrated a huge importance over ET drivers and limiting factors. In this context, this study aimed to assess the ET process in the tropics, from local to basin scale, using EC measurements (from the LBA project) and remote sensing models (MOD16 and GLEAM). At local scale, measurements and estimates were evaluated against net radiation, precipitation and vegetation index (EVI), in order to assess how these drivers control ET patterns. Then, a Budyko approach was applied at basin scale to calculate how water and energy constrain ET in large basins, including Amazon, Solimões, Purus, Medeira, Tapajós, and Xingu rivers. Our results demonstrated disagreements between models to represent maximum and minimum ET rates at tropical forest vegetation (at K43, K67 and K83 sites), with ET measurements peaking during the dry season, in a pattern coincident with annual net radiation cycle. Moreover, deep rooting of well-established rainforests, available soil moisture and increased solar radiation allow ET processes to be maintained during the dry season. ET estimates from MOD16 algorithm agree with these patterns, however, estimates from GLEAM indicates maximum ET rates during the rainy season. At cropland/pasture vegetation (at K77 site), also located in central Amazon, EC measurements showed moderate negative agreement with net radiation (R² = -0.48) and positive with precipitation (R² = 0.53), with decreasing ET rates during the dry season. GLEAM showed ET rates reduction in dry months, but also showed a peak in during wet season, while increasing ET estimates are observed for MOD16, both presented similar behavior as in tropical forest sites. Furthermore, measurements in the southwest part (RJA and FNS sites) did not show clear seasonal patterns, and both MOD16 and GLEAM algorithms, agree with decreasing ET rates during the dry season, showing a significant relationship with precipitation and vegetation indices. Results based on the Budyko approach indicated agreement between the models, indicating a predominant energy-limited condition when evaluated whole basin (at Óbidos station), or basins located in the northern and western parts of Amazon (in Amazon, Purus, and Negro basins), which corroborates with other studies, where ET has limited energy availability. However, our results also demonstrated disagreements in basins located in the southern and eastern parts (in Madeira, Tapajós and Xingu basins), where MOD16 showed some water-limited conditions, whilst it was not observed for GLEAM algorithm. Whether the models agree in terms of seasonality and water and energy limitations, they also disagree between them and ground measurements. This study highlighted the importance to understand limitations of multi-models and multi-scale ET processes for hydroclimatological studies in the tropics.</p>

scholarly journals What Controls Evapotranspiration in the Amazon Basin?

2007 ◽  
Vol 8 (3) ◽  
pp. 380-395 ◽  
Author(s):  
Natalia Hasler ◽  
Roni Avissar
Keyword(s):  
Water Stress ◽  
Large Scale ◽  
Amazon Basin ◽  
Climate Models ◽  
Global Climate ◽  
Regional Climate ◽  
Dry Season ◽  
Global Climate Models ◽  
Net Radiation ◽  
Wet Season

Abstract Global climate models (GCMs) and regional climate models (RCMs) generally show a decrease in the dry season evapotranspiration (ET) rate over the entire Amazon basin. Based on anecdotal observations, it has been suggested that they probably overestimate tropical rain forest water stress. In this study, eddy covariance flux measurements from eight different towers of the Large-Scale Biosphere–Atmosphere Experiment in Amazonia (LBA) were used to provide a first look at the spatial variability and temporal cycle of ET throughout the basin. Results show strong seasonality in ET for stations near the equator (2°–3°S), with ET increasing during the dry season (June–September) and decreasing during the wet season (December–March), both correlated (0.75 to 0.94) and in phase with the net radiation annual cycle. In stations located farther south (9°–11°S) no clear seasonality could be identified in either net radiation or ET. For these more southerly stations, net radiation and ET are still correlated (0.76–0.92) in the wet season, but correlations decrease in the dry season (0–0.71), which is likely associated with water stress. For both pasture sites, located in southern Amazonia, ET decreases during the second half of the dry season, indicating progressively increased water stress. GCMs and RCMs indeed tend to overestimate dry season water stress in the Amazon basin and, therefore, should be revised to better simulate this region, which has a key role in the global hydrometeorology.

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