Trend and uncertainty in spatial‐temporal patterns of hydrological droughts in the Amazon basin

Lopes, A. V.; Chiang, John C. H.; Thompson, Sally; Dracup, John A.

doi:10.1002/2016gl067738

Cited by 52 publications

(36 citation statements)

References 54 publications

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“…For instance, the Granger test results show robust influence of ENSO and PDO on the dry/wet conditions over the southwestern North America and the southern Great Plains, which is consistent with the results from the Climate Variability and Predictability drought experiments [ Schubert et al ., ; Mo et al ., ]. EOF analyses have revealed teleconnections between the ENSO signal and climate variability in southeast China [ Zhang and Zhou , ], Australia, and the Amazon [ Lewis et al ., ; Lopes et al ., ], similar to the results from the Granger test. We believe that the Granger causality test is reliable and easier to use for large‐scale studies.…”

Section: Discussionmentioning

confidence: 99%

Century‐scale causal relationships between global dry/wet conditions and the state of the Pacific and Atlantic Oceans

Sun

Miao

AghaKouchak

et al. 2016

Geophysical Research Letters

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The Granger causality test is used to examine the effects of the El Niño–Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the North Atlantic Oscillation (NAO) on global dry/wet conditions. The results show robust relationships between dry/wet conditions and the ocean states, as assessed through a multi‐index (standardized precipitation evapotranspiration index and standardized precipitation index) and multiscale (3 months and 12 months) evaluation. The influence of ENSO events is widespread, dominating about 38% of the global land surface (excluding Antarctica). Southern and western North America, northern South America, and eastern Russia are influenced by the PDO. The NAO influences not only dry/wet conditions in Europe but also dry/wet conditions in northern Africa. Similarly, climate variability in southern Europe and northern Africa may be due to the concurrence of the ENSO and the NAO. Knowledge of the spatial influence of ocean states on global dry/wet conditions is valuable for improving drought and flood forecasting.

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Section: Discussionmentioning

confidence: 99%

Century‐scale causal relationships between global dry/wet conditions and the state of the Pacific and Atlantic Oceans

Sun

Miao

AghaKouchak

et al. 2016

Geophysical Research Letters

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“…Future possible changes of Amazonian precipitation that bear direct consequences on Amazon ecosystems56 and carbon storage789 are of great concern10. Analysis of observational data demonstrated a strong dependence of western Amazonian precipitation (e.g., the 2005 drought) on the Atlantic meridional sea surface temperature (SST) gradient11, but equatorial Pacific climate anomalies have also been related to Amazonian droughts and floods1213. Potential decreases in the strength (by ca.…”

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confidence: 99%

Equatorial Pacific forcing of western Amazonian precipitation during Heinrich Stadial 1

Zhang¹,

Xu²,

Chiessi³

et al. 2016

Sci Rep

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Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet conditions during Heinrich Stadial 1 (HS1, 18–15 ka), a cold period in the high latitudes of the North Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient. However, the physical viability of this mechanism has never been rigorously tested. We address this issue by combining a thorough compilation of tropical South American paleorecords and a set of atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone, although leading to dry conditions in northern South America and wet conditions in northeastern Brazil, cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1. Instead, an eastern equatorial Pacific SST increase (i.e., 0.5–1.5 °C), in response to the slowdown of the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central Amazonia towards the Andes.

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“…El Niño events bring periods of low rainfall and reduced cloud cover to tropical rainforests that are typically supplied with plentiful water (Lopes et al 2016), but the responses of tropical rain forests to these events remain poorly understood. The Southern Oscillations responsible for El Niño events have occurred for at least 130 000 years (Tudhop et al 2001) suggesting ample opportunity for natural selection to enhance the capability of trees to tolerate irregular drought events (Harrison 2000, Detto et al 2018.…”

Section: Introductionmentioning

confidence: 99%

“…reduced cloud cover) by up-regulating photosynthetic and protective pigments (Saleska et al 2007, Saleska et al 2016. An alternative explanation is that greening during dry periods is related to the flush of new leaves (Lopes et al 2016, Wagner et al 2017. However, interpretation of remotely sensed data is challenging and there is continued debate over tropical forest responses to variability in temperature, irradiance and precipitation (Samanta et al 2010, Morton et al 2014, Bi et al 2015.…”

Section: Introductionmentioning

confidence: 99%

Changes in leaf functional traits of rainforest canopy trees associated with an El Niño event in Borneo

Nunes

Both

Bongalov

et al. 2019

Environ. Res. Lett.

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El Niño events generate periods of relatively low precipitation, low cloud cover and high temperature over the rainforests of Southeast Asia, but their impact on tree physiology remains poorly understood. Here we use remote sensing and functional trait approaches-commonly used to understand plant acclimation to environmental fluctuations-to evaluate rainforest responses to an El Niño event at a site in northern Borneo. Spaceborne measurements (i.e. normalised difference vegetation index calculated from Moderate Resolution Imaging Spectroradiometer data) show the rainforest canopy greened throughout 2015, coinciding with a strengthening of the El Niño event in Sabah, Malaysia, then lost greenness in early 2016, when the El Niño was at its peak. Leaf chemical and structural traits measured for mature leaves of 65 species (104 branches from 99 tree canopies), during and after this El Niño event revealed that chlorophyll and carotenoid concentrations were 35% higher in mid 2015 than in mid 2016. Foliar concentrations of the nutrients N, P, K and Mg did not vary, suggesting the mineralisation and transportation processes were unaffected by the El Niño event. Leaves contained more phenolics, tannins and cellulose but less Ca and lignin during the El Niño event, with concentration shifts varying strongly among species. These changes in functional traits were also apparent in hyperspectral reflectance data collected using a field spectrometer, particularly in the shortwave infrared region. Leaf-level acclimation and leaf turnover could have driven the trait changes observed. We argue that trees were not water limited in the initial phase of the El Niño event, and responded by flushing new leaves, seen in the canopy greening trend and higher pigment concentrations (associated with young leaves); we argue that high evaporative demand and depleted soil water eventually caused leaves to drop in 2016. However, further studies are needed to confirm these ideas. Time-series of vegetation dynamics obtained from space can only be understood if changes in functional traits, as well as the quantity of leaves in canopies, are monitored on the ground.

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Trend and uncertainty in spatial‐temporal patterns of hydrological droughts in the Amazon basin

Cited by 52 publications

References 54 publications

Century‐scale causal relationships between global dry/wet conditions and the state of the Pacific and Atlantic Oceans

Century‐scale causal relationships between global dry/wet conditions and the state of the Pacific and Atlantic Oceans

Equatorial Pacific forcing of western Amazonian precipitation during Heinrich Stadial 1

Changes in leaf functional traits of rainforest canopy trees associated with an El Niño event in Borneo

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