Seasonal variations in vegetation water content retrieved from microwave remote sensing over Amazon intact forests

Wang, Huan; Wigneron, Jean‐Pierre; Ciais, Philippe; Yao, Yitong; Fan, Lei; Liu, Xiangzhuo; Li, Xiaojun; Green, Julia K.; Tian, Feng; Tao, Shengli; Li, Wei; Frappart, Frédéric; Albergel, Clément; Wang, Mengjia; Li, Shuangcheng

doi:10.1016/j.rse.2022.113409

Cited by 27 publications

(10 citation statements)

References 118 publications

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“…Second, we treated the VOD model coefficients ( a , b , and c ) and the scattering albedo ω as constant over time. However, in many ecosystems the scattering albedo van vary significantly over time with seasonal and interannual changes in vegetation structure (Baur et al., 2021; Konings et al., 2016; H. Wang et al., 2023). Third, we treated the effect of soil roughness on brightness temperature at our site as known a priori, when it varies spatially.…”

Section: Discussionmentioning

confidence: 99%

“…More physically detailed parametrizations of the VWC-VOD relationship have recently been proposed (Fink et al, 2018; Second, we treated the VOD model coefficients (a, b, and c) and the scattering albedo ω as constant over time. However, in many ecosystems the scattering albedo van vary significantly over time with seasonal and interannual changes in vegetation structure (Baur et al, 2021;Konings et al, 2016;H. Wang et al, 2023).…”

Section: Limitations Of This Studymentioning

confidence: 99%

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Constraining Plant Hydraulics With Microwave Radiometry in a Land Surface Model: Impacts of Temporal Resolution

Holtzman,

Wang,

Wood

et al. 2023

Water Resources Research

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Vegetation water content (VWC) plays a key role in transpiration, plant mortality, and wildfire risk. Although land surface models now often contain plant hydraulics schemes, there are few direct VWC measurements to constrain these models at global scale. One proposed solution to this data gap is passive microwave remote sensing, which is sensitive to temporal changes in VWC. Here, we test that approach by using synthetic microwave observations to constrain VWC and surface soil moisture within the Climate Modeling Alliance Land model. We further investigate the possible utility of sub‐daily observations of VWC, which could be obtained through a satellite in geostationary orbit or combinations of multiple satellites. These high‐temporal‐resolution observations could allow for improved determination of ecosystem parameters, carbon and water fluxes, and subsurface hydraulics, relative to the currently available twice‐daily sun‐synchronous observational patterns. We find that incorporating observations at four different times in the diurnal cycle (such as could be available from two sun‐synchronous satellites) provides a significantly better constraint on water and carbon fluxes than twice‐daily observations do. For example, the root mean square error of projected evapotranspiration and gross primary productivity during drought periods was reduced by approximately 40%, when using four‐times‐daily relative to twice‐daily observations. Adding hourly observations of the entire diurnal cycle did not further improve the inferred parameters and fluxes. Our comparison of observational strategies may be informative in the design of future satellite missions to study plant hydraulics, as well as when using existing remotely sensed data to study vegetation water stress response.

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Section: Discussionmentioning

confidence: 99%

Section: Limitations Of This Studymentioning

confidence: 99%

Constraining Plant Hydraulics With Microwave Radiometry in a Land Surface Model: Impacts of Temporal Resolution

Holtzman,

Wang,

Wood

et al. 2023

Water Resources Research

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“…VOD is sensitive to both woody and leafy biomass (Wang et al., 2023), thus the empirically derived recovery rates from VOD represent better a return of vegetation to its actual previous state than optical remote sensing observations, which are mostly sensitive to leafy biomass, for example, leaf area index (LAI) and NDVI. In this study, we applied the daily AMSR‐E/2‐IB C‐VOD products at 0.25° spatial resolution during 2002–2020 (corresponding to the available time range of C‐VOD) as a proxy of canopy water mass to calculate resilience, indicated by lag‐1 month temporal autocorrelation (TAC).…”

Section: Methodsmentioning

confidence: 99%

“…VOD is sensitive to both woody and leafy biomass (Wang et al, 2023), thus the empirically derived recovery rates from VOD represent better a return of vegetation to its actual previous state than optical remote sensing observations, which are mostly sensitive to leafy biomass, for example, leaf area index (LAI) and NDVI.…”

Section: C-band Amsr-e/2 Ib-vodmentioning

confidence: 99%

“…We calculated TAC using a 4‐year rolling window, following Boulton et al., 2022 and Forzieri et al., 2022, during 2002–2020 based on a recent C‐band VOD datasets (the retrieval algorithms of C‐VOD can be found in Wang, Fan, et al., 2021). Compared with Ku‐band VOD, which is mainly sensitive to the temporal variations of top‐of‐canopy water content, C‐band VOD measured at a lower frequency is less limited by saturation effects in dense canopy and better represents the whole canopy water mass (Wang et al., 2023, Figure S1).…”

Section: Introductionmentioning

confidence: 99%

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Anthropogenic disturbance exacerbates resilience loss in the Amazon rainforests

Wang,

Ciais,

Sitch

et al. 2023

Global Change Biology

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Uncovering the mechanisms that lead to Amazon forest resilience variations is crucial to predict the impact of future climatic and anthropogenic disturbances. Here, we apply a previously used empirical resilience metrics, lag‐1 month temporal autocorrelation (TAC), to vegetation optical depth data in C‐band (a good proxy of the whole canopy water content) in order to explore how forest resilience variations are impacted by human disturbances and environmental drivers in the Brazilian Amazon. We found that human disturbances significantly increase the risk of critical transitions, and that the median TAC value is ~2.4 times higher in human‐disturbed forests than that in intact forests, suggesting a much lower resilience in disturbed forests. Additionally, human‐disturbed forests are less resilient to land surface heat stress and atmospheric water stress than intact forests. Among human‐disturbed forests, forests with a more closed and thicker canopy structure, which is linked to a higher forest cover and a lower disturbance fraction, are comparably more resilient. These results further emphasize the urgent need to limit deforestation and degradation through policy intervention to maintain the resilience of the Amazon rainforests.

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Asymmetric response of primary productivity to precipitation anomalies in Southwest China

Dong

Fan

Fensholt

et al. 2023

Agricultural and Forest Meteorology

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Seasonal variations in vegetation water content retrieved from microwave remote sensing over Amazon intact forests

Cited by 27 publications

References 118 publications

Constraining Plant Hydraulics With Microwave Radiometry in a Land Surface Model: Impacts of Temporal Resolution

Constraining Plant Hydraulics With Microwave Radiometry in a Land Surface Model: Impacts of Temporal Resolution

Anthropogenic disturbance exacerbates resilience loss in the Amazon rainforests

Asymmetric response of primary productivity to precipitation anomalies in Southwest China

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