Gabriel Katul
Duke University, Nicholas School of the Environment, Faculty Member
- Gabriel G. Katul received his B.E. degree in 1988 at the American University of Beirut (Beirut, Lebanon), his M.S. de... moreGabriel G. Katul received his B.E. degree in 1988 at the American University of Beirut (Beirut, Lebanon), his M.S. degree in 1990 at Oregon State University (Corvallis, OR) and his Ph.D degree in 1993 at the University of California in Davis (Davis, CA). He currently holds a distinguished Professorship in Hydrology and Micrometeorology at the Department of Civil and Environmental Engineering at Duke University (Durham, NC). He was a visiting fellow at University of Virginia (USA) in 1997, the Commonwealth Science and Industrial Research Organization (Australia) in 2002, the University of Helsinki (Finland) in 2009, the FulBright-Italy Distinguished Fellow at Politecnico di Torino (Italy) in 2010, the École polytechnique fédérale de Lausanne (Switzerland) in 2013, Nagoya University (Japan) in 2014, University of Helsinki (Finland) in 2017, the Karlsruher Institute for Technology (Germany) in 2017, Princeton University (USA) in 2020, and CzechGlobe (Brno - Czech Republic) in 2023. He received several honorary awards, including the inspirational teaching award by the students of the School of the Environment at Duke University (in 1994 and 1996), an honorary certificate by La Seccion de Agrofisica de la Sociedad Cubana de Fisica in Habana (in 1998), the Macelwane medal and became thereafter a fellow of the American Geophysical Union (in 2002), the editor’s citation for excellence in refereeing from the American Geophysical Union (in 2008), the Hydrologic Science Award from the American Geophysical Union (in 2012), the John Dalton medal from the European Geosciences Union (in 2018), and the Outstanding Achievements in Biometeorology Award from the American Meteorological Society (in 2021) and later became an elected fellow of the American Meteorological Society (in 2024). Katul was elected to the National Academy of Engineering (in 2023) for his contributions in eco-hydrology and environmental fluid mechanics. He served as the Secretary General for the Hydrologic Science Section at the American Geophysical Union (2006-2008). His research focuses on micro-meteorology and near-surface hydrology with emphasis on heat, momentum, carbon dioxide, water vapor, ozone, particulate matter (including aerosols, pollen, and seeds) and water transport in the soil-plant-atmosphere system as well as their implications to a plethora of hydrological, ecological, atmospheric and climate change related problems.edit
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Causality and Persistence in Ecological Systems: A Nonparametric Spectral Granger Causality Approach,
Research Interests: Environmental Engineering, Civil Engineering, Stochastic Process, Water resources, Applied Economics, and 11 moreWater Cycle, Seasonality, Probability Distribution & Applications, Eddy Covariance, Soil moisture, Evapotranspiration, Tropical rainforest, Tropical rain forest, Probability Density Function, Global Climate Model, and Soil moisture content
The existence of a "-1" power-law scaling at low wavenumbers in the longitudinal velocity spectrum of wall-bounded turbulence was explained by multiple mechanisms; however, experimental support has not been uniform across... more
The existence of a "-1" power-law scaling at low wavenumbers in the longitudinal velocity spectrum of wall-bounded turbulence was explained by multiple mechanisms; however, experimental support has not been uniform across laboratory studies. This letter shows that Heisenberg's eddy viscosity approach can provide a theoretical framework that bridges these multiple mechanisms and explains the elusiveness of the "-1" power law in some experiments. Novel theoretical outcomes are conjectured about the role of intermittency and very-large scale motions in modifying the k⁻¹ scaling.
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Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying underlying frequencies in nonstationary and gap-infested time series, such as eddy-covariance-measured net ecosystem exchange of CO2 (NEE).... more
Orthonormal wavelet transformation (OWT) is a computationally efficient technique for quantifying underlying frequencies in nonstationary and gap-infested time series, such as eddy-covariance-measured net ecosystem exchange of CO2 (NEE). We employed OWT to analyze the frequency characteristics of synchronously measured and modeled NEE at adjacent pine (PP) and hardwood (HW) ecosystems. Wavelet cospectral analysis showed that NEE at PP was more correlated to light and vapor pressure deficit at the daily time scale, and NEE at HW was more correlated to leaf area index (LAI) and temperature, especially soil temperature, at seasonal time scales. Models were required to disentangle the impacts of environmental drivers on the components of NEE, ecosystem carbon assimilation (Ac) and ecosystem respiration (RE). Sensitivity analyses revealed that using air temperature rather than soil temperature in RE models improved the modeled wavelet spectral frequency response on time scales longer tha...
Research Interests: Soil, Water, Time Series, Carbon Dioxide, Plant Biology, and 24 moreEcology, Wavelet Analysis, Seasonality, Tree Physiology, Eddy Covariance, Soil moisture, Wavelet Transform, Temperature, Net Ecosystem Exchange, Tree, Trees, Leaf Area Index, Water Use, Soil Temperature, Forestry Sciences, Ecosystem, Air Temperature, Spectrum analysis, Pinus Taeda, Frequency Response, Vapor Pressure Deficit, Plant Leaves, Light Attenuation, and Model Simplification
Research Interests: Environmental Engineering, Civil Engineering, Atmospheric Science, Turbulence, Boundary Layer Meteorology, and 11 moreTime Series, Water resources, Carbon Dioxide, Applied Economics, Atmospheric sciences, Sampling methods, Evapotranspiration, Greenhouse gases, Ozone, Southern California, and Water Vapor
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A scanning water Raman-lidar, designed and constructed to study surface-atmosphere processes with high spatial and temporal resolution is described. It is shown that the lidar is able to measure the absolute water content and then... more
A scanning water Raman-lidar, designed and constructed to study surface-atmosphere processes with high spatial and temporal resolution is described. It is shown that the lidar is able to measure the absolute water content and then calculate evaporative fluxes and other atmospheric parameters quickly over relatively large areas. This capability provides new opportunities for the study of microscale atmospheric processes. Examples
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Over the past three decades, a number of field experiments have suggested that land-cover heterogeneity (LCH) impacts Monin and Obukhov (M–O) scaling, when applied to second-order statistics of temperature (T), water vapor (q), and CO2... more
Over the past three decades, a number of field experiments have suggested that land-cover heterogeneity (LCH) impacts Monin and Obukhov (M–O) scaling, when applied to second-order statistics of temperature (T), water vapor (q), and CO2 (c) fluctuations. To further explore how LCH modifies M–O scaling for second-order statistics, 2 years of atmospheric surface layer (ASL) measurements, conducted above a Mediterranean
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The space-time statistical structure of soil water uptake by oak trees was investigated in a 3.1-m-diameter closed top chamber using a three-dimensional measurement grid of soil moisture and pressure, and measurements of tree... more
The space-time statistical structure of soil water uptake by oak trees was investigated in a 3.1-m-diameter closed top chamber using a three-dimensional measurement grid of soil moisture and pressure, and measurements of tree transpiration. Using the time domain reflectometry (TDR) measured moisture content, resistance block measured soil water pressure, and a compact constant head permeameter measured saturated hydraulic conductivity, the
Research Interests: Environmental Engineering, Civil Engineering, Stochastic Process, Plant Ecology, Monte Carlo Simulation, and 18 moreWater resources, Spatial Statistics, Applied Economics, Soil moisture, Field Experiment, Space Time, First-Order Logic, Coefficient of Variation, Oak, Spatial Variability, Soil Hydraulic Properties, Taylor Series, Statistical Properties, Moisture Content, Three Dimensional, Time Domain Reflectometry, Soil Water, and Unsaturated Zone
Among the fundamental problems in canopy turbulence, particularly near the forest floor, remain the local diabatic effects and linkages between turbulent length scales and the canopy morphology. To progress on these problems, mean and... more
Among the fundamental problems in canopy turbulence, particularly near the forest floor, remain the local diabatic effects and linkages between turbulent length scales and the canopy morphology. To progress on these problems, mean and higher order turbulence statistics are collected in a uniform pine forest across a wide range of atmospheric stability conditions using five 3-D anemometers in the subcanopy.
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The linkages between soil moisture dynamics and convection triggers, defined here as the first crossing between the boundary layer height (hBL) and lifting condensation level (hLCL), are complicated by a large number of interacting... more
The linkages between soil moisture dynamics and convection triggers, defined here as the first crossing between the boundary layer height (hBL) and lifting condensation level (hLCL), are complicated by a large number of interacting processes occurring over a wide range of space and time scales. To progress on this problem, a soil-plant hydrodynamics model was coupled to a simplified ABL
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High elevation snow-melt runoff represents one of the main sources of freshwater in many different regions of the world, e.g. Western North America, where as much as 75% of water supplies are delivered from snowmelt. This resource is... more
High elevation snow-melt runoff represents one of the main sources of freshwater in many different regions of the world, e.g. Western North America, where as much as 75% of water supplies are delivered from snowmelt. This resource is sensitive to climatic fluctuations, as changes in the precipitation regime have been proven to affect both the total runoff volume and the
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A central topic in rainfall research is to determine whether rainfall variability at a given space-time scale is caused by dynamics acting at some other scales. Random multiplicative cascades (RMCs) are standard approaches for describing... more
A central topic in rainfall research is to determine whether rainfall variability at a given space-time scale is caused by dynamics acting at some other scales. Random multiplicative cascades (RMCs) are standard approaches for describing rainfall variability across a wide range of time scales. Their popularity stems from their ability to reproduce rainfall self-similarity and long-range correlations as well as
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Rainfall variability occurs over a wide range of time scales owing to processes initiated by cloud microphysics and sustained by atmospheric circulation. A central topic in rainfall research is to determine whether rainfall variability at... more
Rainfall variability occurs over a wide range of time scales owing to processes initiated by cloud microphysics and sustained by atmospheric circulation. A central topic in rainfall research is to determine whether rainfall variability at a given scale is caused by dynamics acting at some other scales. Random multiplicative cascades (RMCs) are standard approaches for describing rainfall variability across such
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Long-distance seed dispersal is an important topic in ecology, but notoriously difficult to quantify. Previous modeling approaches have failed to simulate long-distance dispersal, and it has remained unclear which mechanisms determine... more
Long-distance seed dispersal is an important topic in ecology, but notoriously difficult to quantify. Previous modeling approaches have failed to simulate long-distance dispersal, and it has remained unclear which mechanisms determine long-distance dispersal and what their relative importance is. We simulated wind dispersal of grassland plant seeds with four mechanistic models of increasing complexity and realism to assess which pro-
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Predicted changes in precipitation and air temperature patterns can lead to major alterations in timing and volume of mountain snowmelt runoff with a possible increased incidence of catastrophic events such as flooding and summer... more
Predicted changes in precipitation and air temperature patterns can lead to major alterations in timing and volume of mountain snowmelt runoff with a possible increased incidence of catastrophic events such as flooding and summer droughts. Here, the role of the temperature seasonal cycle and the relative duration of cold and warm seasons on the partitioning of precipitation into snow and
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Global climate models predict decreases in leaf stomatal conductance and transpiration due to increases in atmospheric CO2. The consequences of these reductions are increases in soil moisture availability and continental scale run-off at... more
Global climate models predict decreases in leaf stomatal conductance and transpiration due to increases in atmospheric CO2. The consequences of these reductions are increases in soil moisture availability and continental scale run-off at decadal time-scales. Thus, a theory explaining the differential sensitivity of stomata to changing atmospheric CO2 and other environmental conditions must be identified. Here, these responses are investigated using optimality theory applied to stomatal conductance. An analytical model for stomatal conductance is proposed based on: (a) Fickian mass transfer of CO2 and H2O through stomata; (b) a biochemical photosynthesis model that relates intercellular CO2 to net photosynthesis; and (c) a stomatal model based on optimization for maximizing carbon gains when water losses represent a cost. Comparisons between the optimization-based model and empirical relationships widely used in climate models were made using an extensive gas exchange dataset collect...
Research Interests: Mass Transfer, Carbon Dioxide, Photosynthesis, Plant Biology, Ecology, and 15 moreOptimality Theory, Atmosphere, Water use efficiency, Soil moisture, Climate Model, Water Loss, Theoretical Models, Pinus, Environmental Conditions, Analytical Model, Pinus Taeda, Global Climate Model, Gas Exchange, Plant Leaves, and Stomatal Conductance
C4 photosynthesis evolved independently numerous times, probably in response to declining atmospheric CO2 concentrations, but also to high temperatures and aridity, which enhance water losses through transpiration. Here, the environmental... more
C4 photosynthesis evolved independently numerous times, probably in response to declining atmospheric CO2 concentrations, but also to high temperatures and aridity, which enhance water losses through transpiration. Here, the environmental factors controlling stomatal behaviour of leaf-level carbon and water exchange were examined across the evolutionary continuum from C3 to C4 photosynthesis at current (400 μmol mol(-1)) and low (280 μmol mol(-1)) atmospheric CO2 conditions. To this aim, a stomatal optimization model was further developed to describe the evolutionary continuum from C3 to C4 species within a unified framework. Data on C3, three categories of C3-C4 intermediates, and C4 Flaveria species were used to parameterize the stomatal model, including parameters for the marginal water use efficiency and the efficiency of the CO2-concentrating mechanism (or C4 pump); these two parameters are interpreted as traits reflecting the stomatal and photosynthetic adjustments during the ...
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Possible linkages between climatic fluctuations in rainfall at low frequencies and local intensity fluctuations within single storms is now receiving significant attention in climate change research. To progress on a narrower scope of... more
Possible linkages between climatic fluctuations in rainfall at low frequencies and local intensity fluctuations within single storms is now receiving significant attention in climate change research. To progress on a narrower scope of this problem, the cross-scale probabilistic structure of rainfall intensity records collected over time scales ranging from hours to decades at sites dominated by either convective or frontal
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Nocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, reflecting the common assumption that plant stomata close at night to prevent water loss from transpiration. However, recent evidence across a... more
Nocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, reflecting the common assumption that plant stomata close at night to prevent water loss from transpiration. However, recent evidence across a wide range of species and climate conditions suggests that significant transpiration occurs at night, frustrating efforts to estimate total annual evapotranspiration (ET) from conventional methods such as
Research Interests: Applied Mathematics, Earth Sciences, Modeling, Biometeorology, Biological Sciences, and 20 moreModels, Eddy Covariance, Evapotranspiration, Missing Data, Measurement Error, Transpiration, Nocturnal, Water Use, Qualitative Analysis, Water Loss, Forest ecosystem, Ecosystem, Multiple Imputation, Flux, Night, Early Terrestrial Ecosystems, Wind Speed, Southeast, Vapor Pressure Deficit, and Non linear regression
Orthonormal wavelet expansions are applied to atmospheric surface layer velocity measurements. The effect of intermittent events on the energy spectrum of the inertial subrange is investigated through analysis of wavelet coefficients. The... more
Orthonormal wavelet expansions are applied to atmospheric surface layer velocity measurements. The effect of intermittent events on the energy spectrum of the inertial subrange is investigated through analysis of wavelet coefficients. The local nature of the orthonormal wavelet transform in physical space makes it possible to identify a relationship between the inertial subrange slope of the local wavelet spectrum and
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A new, parameter-free method, based on orthonormal wavelet expansions is proposed for calculating the principal time scale of coherent structures in atmospheric surface layer measurements. These organized events play an important role in... more
A new, parameter-free method, based on orthonormal wavelet expansions is proposed for calculating the principal time scale of coherent structures in atmospheric surface layer measurements. These organized events play an important role in the exchange of heat, mass, and momentum between the land and the atmosphere. This global technique decomposes the energy contribution at each scale into organized and random
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Research Interests: Pharmacology, Biochemistry, Bioinformatics, Evolutionary Biology, Genetics, and 57 moreMarine Biology, Neuroscience, Environmental Science, Geophysics, Physics, Materials Science, Quantum Physics, Developmental Biology, Immunology, Climate Change, Water, Molecular Biology, Structural Biology, Genomics, RNA, Computational Biology, Transcriptomics, Carbon Dioxide, Carbon, Biotechnology, Systems Biology, Biomass, Cancer, Biology, Metabolomics, Cell Cycle, Proteomics, Ecology, Drug Discovery, Evolution, Carbon Sequestration, Nanotechnology, Astrophysics, Neurobiology, Medicine, Multidisciplinary, Palaeobiology, Functional Genomics, Nature, Signal Transduction, Astronomy, DNA, Atmosphere, Cell Signalling, Medical Research, Nitrogen deposition, Nitrogen, Nutrient Limitation, Trees, Gymnosperms, Soil Fertility, Tree growth, Forest ecosystem, Ecosystem, Transient Stability, Earth Science, and Carbon Sink
The conceptual framework for modeling the inertial subrange is strongly influenced by the Kolmogorov cascade phenomena, which is nowadays the subject of significant reinterpretation. It has been argued that the effects of boundary... more
The conceptual framework for modeling the inertial subrange is strongly influenced by the Kolmogorov cascade phenomena, which is nowadays the subject of significant reinterpretation. It has been argued that the effects of boundary conditions influence large-scale motion and direct interaction between large and small scales is possible by means other than passing sequentially through the full cascade. Using longitudinal (u)
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In stably stratified turbulent flows, the mixing efficiency associated with eddy diffusivity for heat, or equivalently the turbulent Prandtl number (Pr(t)), is fraught with complex dynamics originating from the scalewise interplay between... more
In stably stratified turbulent flows, the mixing efficiency associated with eddy diffusivity for heat, or equivalently the turbulent Prandtl number (Pr(t)), is fraught with complex dynamics originating from the scalewise interplay between shear generation of turbulence and its dissipation by density gradients. A large corpus of data and numerical simulations agree on a near-universal relation between Pr(t) and the Richardson number (R(i)), which encodes the relative importance of buoyancy dissipation to mechanical production of turbulent kinetic energy. The Pr(t)-R(i) relation is shown to be derivable solely from the cospectral budgets for momentum and heat fluxes if a Rotta-like return to isotropy closure for the pressure-strain effects and Kolmogorov's theory for turbulent cascade are invoked. The ratio of the Kolmogorov to the Kolmogorov-Obukhov-Corrsin phenomenological constants, and a constant associated with isotropization of the production whose value (= 3/5) has been pre...
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Missing data is a ubiquitous problem in evaluating long-term experimental measurements, such as those associated with the FluxNet project, due to the equipment failures, system maintenance, power-failure, and lightning strikes among other... more
Missing data is a ubiquitous problem in evaluating long-term experimental measurements, such as those associated with the FluxNet project, due to the equipment failures, system maintenance, power-failure, and lightning strikes among other things. To estimate annual values of net ecosystem carbon exchange (NEE), latent heat flux (LE) and sensible heat flux (H), such gaps in the measured data must be
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Microtopography, consisting of small-scale excursions in the elevation of the land surface on millimeter to centimeter scales, is ubiquitous on hillslopes, but its effects are rarely incorporated into hydrological analyses of... more
Microtopography, consisting of small-scale excursions in the elevation of the land surface on millimeter to centimeter scales, is ubiquitous on hillslopes, but its effects are rarely incorporated into hydrological analyses of rainfall-runoff partitioning. To progress toward a hydrological theory that accounts for microtopography, two research questions are considered: (1) Does microtopography change the partitioning of rainfall into runoff and infiltration
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Page 1. Role of biomass spread in vegetation pattern formation within arid ecosystems Sally Thompson,1 Gabriel Katul,1 and Sean M. McMahon1 Received 12 February 2008; revised 10 June 2008; accepted 6 August 2008; published 29 October... more
Page 1. Role of biomass spread in vegetation pattern formation within arid ecosystems Sally Thompson,1 Gabriel Katul,1 and Sean M. McMahon1 Received 12 February 2008; revised 10 June 2008; accepted 6 August 2008; published 29 October 2008. ...
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Using long-term (1948-1996) pan evaporation measurements, a 6% increase in warm-season (May-October) actual evapotranspiration (ET) is computed over the conterminous United States between 1949 and 1996 via the complementary hypothesis.... more
Using long-term (1948-1996) pan evaporation measurements, a 6% increase in warm-season (May-October) actual evapotranspiration (ET) is computed over the conterminous United States between 1949 and 1996 via the complementary hypothesis. This predicted increase in ET is in agreement with the measured precipitation increase for the same period if long-term wet-surface ET is assumed to be constant. Long-term relative humidity and
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Longitudinal velocity and temperature measurements above a uniform dry lakebed were used to investigate sources of eddy-motion anisotropy within the inertial subrange. Rather than simply test the adequacy of locally isotropic relations,... more
Longitudinal velocity and temperature measurements above a uniform dry lakebed were used to investigate sources of eddy-motion anisotropy within the inertial subrange. Rather than simply test the adequacy of locally isotropic relations, we investigated directly the sources of anisotropy. These sources, in a daytime desert-like climate, include: (1) direct interaction between the large-scale and small-scale eddy motion, and (2) thermal
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The existence of universal power laws at low wavenumbers (K) in the energy spectrum (Eu) of the turbulent longitudinal velocity (u) is examined theoretically and experimentally for the near-neutral atmospheric surface layer. Newly derived... more
The existence of universal power laws at low wavenumbers (K) in the energy spectrum (Eu) of the turbulent longitudinal velocity (u) is examined theoretically and experimentally for the near-neutral atmospheric surface layer. Newly derived power-law solutions to Tchen's approximate integral spectral budget equation are tested for strong- and weak-interaction cases between the mean flow and turbulent vorticity fields. To verify
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The Janzen–Connell (JC) effect, which hypothesizes that recruitment and growth of seedlings is positively correlated to the distance from the parent tree, is shown to generate highly organized vegetation biomass spatial patterns when... more
The Janzen–Connell (JC) effect, which hypothesizes that recruitment and growth of seedlings is positively correlated to the distance from the parent tree, is shown to generate highly organized vegetation biomass spatial patterns when coupled to a revised Fisher–Kolmogorov (FK) equation. Spatial organization arises through a novel mechanism of non-local activation and local inhibition. Over a single generation, the revised FK model calculations predict a “hen and chicks” dynamic pattern with mature trees surrounded by new seedlings growing at characteristic spatial distances in agreement with field data. Over longer timescales, the importance of stochastic dynamics, such as those associated with randomly occurring light gaps, increase thereby causing a substantial deviation between predictions from the deterministic FK model and its stochastic counterpart derived to account for such random disturbances. At still longer timescales, however, statistical measures of the spatial organiza...