John L. Monteith

Bio: John L. Monteith is an academic researcher from International Crops Research Institute for the Semi-Arid Tropics. The author has contributed to research in topics: Atmosphere & Transpiration. The author has an hindex of 58, co-authored 138 publications receiving 30024 citations. Previous affiliations of John L. Monteith include Goddard Space Flight Center & University of Nottingham.

Transport of Heat, Mass, and Momentum

Abstract: This chapter introduces some of the major concepts and principles on which environmental physics depends. It considers how the transport of entities such as heat, mass, and momentum is determined by the state of the atmosphere and the corresponding state of the surface involved in the exchange, whether soil, vegetation, the coat of an animal, or the integument of an insect or seed. A simple general equation can be derived for transport within a gas by “carriers”, which may be molecules, particles or eddies. A carrier can “unload” its excess of property P at a point where the local value is less than that at the starting point. This relation provides the “eddy covariance” method of measuring vertical fluxes. All three forms of transfer (heat, mass and momentum) are the direct consequence of molecular agitation, as they are described by similar relationships. Because the same process of molecular agitation is responsible for all the three types, the diffusion coefficients for momentum, heat, water vapor, and other gases are similar in size and in their dependence on temperature.

Microclimatology of Radiation: (iii) Interception by Plant Canopies and Animal Coats

Abstract: Building on the principles of Chapter 7 , this chapter is concerned with estimating the radiation interception of vegetation canopies and animal coats. The interaction of radiation with canopies is approached first by considering idealized canopies of leaves that absorb fully at all wavelengths (“black leaves”). Expressions for estimating interception are derived for canopies with assumed leaf angle distributions (horizontal, vertical, ellipsoidal, conical), and for direct and diffuse radiation separately. Then the principles are extended for canopies of leaves with spectral properties, using Kubelka-Munk equations. The chapter continues with discussion of the absorption of photosynthetically active radiation (PAR), known to correlate well with crop productivity. Principles behind remote sensing of vegetation from satellites and aircraft are discussed. Interception of radiation by animal coats depends on the radiative properties of hair and skin, and on the depth and density of the coat, analogous to the roles of leaf and soil properties and canopy density in determining radiation interception by canopies. The chapter concludes with discussion of modeling and measuring the net radiation absorbed by canopies, leaves, and animals.

Micrometeorology: (ii) Interpretation of Flux Measurements

Abstract: This chapter is concerned with describing the principles of methods used for interpreting micrometeorological fluxes, and illustrating these principles with examples from agricultural and forest science. Flux measurements are most useful to biologists, hydrologists, and environmental scientists if they are interpreted to reveal how the canopy or surface controlled or responded to the measured flux. Resistance analogs serve this purpose. Canopy (or surface) resistance to water vapor or carbon dioxide transfer is a parameter comparable to the stomatal resistance of single leaves, but with several important caveats that are explained. Methods of deriving canopy resistance and aerodynamic resistance for momentum are reviewed. An additional resistance is needed to parameterize aerodynamic heat and mass transfer, and measurements and models of this resistance are discussed. Fluxes of pollutant gases and particles to canopies can be interpreted similarly, and the relation between canopy resistance and surface depostion velocity for pollutants is explained. Examples are given of flux interpretation for water vapor and transpiration, carbon dioxide, and crop and forest growth, and pollutant gas uptake to crops and natural vegetation. Finally there is discussion of measurement and interpretation of fluxes within vegetation canopies.

Crop evapotranspiration : guidelines for computing crop water requirements

Abstract: (First edition: 1998, this reprint: 2004). This publication presents an updated procedure for calculating reference and crop evapotranspiration from meteorological data and crop coefficients. The procedure, first presented in FAO Irrigation and Drainage Paper No. 24, Crop water requirements, in 1977, allows estimation of the amount of water used by a crop, taking into account the effect of the climate and the crop characteristics. The publication incorporates advances in research and more accurate procedures for determining crop water use as recommended by a panel of high-level experts organised by FAO in May 1990. The first part of the guidelines includes procedures for determining reference crop evapotranspiration according to the FAO Penman-Monteith method. These are followed by updated procedures for estimating the evapotranspiration of different crops for different growth stages and ecological conditions.

Large Area Hydrologic Modeling and Assessment Part i: Model Development

Abstract: A conceptual, continuous time model called SWAT (Soil and Water Assessment Tool) was developed to assist water resource managers in assessing the impact of management on water supplies and nonpoint source pollution in watersheds and large river basins. The model is currently being utilized in several large area projects by EPA, NOAA, NRCS and others to estimate the off-site impacts of climate and management on water use, nonpoint source loadings, and pesticide contamination. Model development, operation, limitations, and assumptions are discussed and components of the model are described. In Part II, a GIS input/output interface is presented along with model validation on three basins within the Upper Trinity basin in Texas.

Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components

Abstract: Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.

Correction of flux measurements for density effects due to heat and water vapour transfer

Abstract: When the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived. If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre-dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required. If the constituent's density fluctuations or mean gradients are measured directly in the air in situ, then corrections arising from both heat and water vapour fluxes are required. These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.