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.

Chapter 5 – Radiation Environment

Abstract: Almost all the energy for physical and biological processes at the earth’s surface comes from the sun. This chapter reviews the quantity and quality of solar (short-wave) radiation reaching the earth and discusses the processes by which it is scattered and absorbed in the atmosphere. Sun-earth geometry, dependent on astronomical factors, determines the major features of radiation at the earth’s surface and their variation over millenia. The spectrum of solar radiation important for environmental physics ranges from the ultra-violet to the infra-red. Wavebands used for vision, photosynthesis, and aspects of plant development (phytochrome absorption) are reviewed. Solar radiation is scattered and absorbed in the atmosphere by molecules, cloud droplets, and particles (aerosol). Spectral aspects of radiation attenuation are discussed. At the ground, solar energy is received as direct or diffuse radiation. The importance of each term and its dependence on cloud and aerosol is reviewed. The ratio of visible to infra-red radiation depends on solar elevation and atmospheric properties. The chapter also discusses terrestrial (long-wave) radiation originating in the atmosphere and emitted from solid surfaces. Expressions describing the long-wave radiation incident at the surface from cloudless and cloudy skies are reviewed. Finally, the topic of the net radiation balance (long- and short-wave radiation) is introduced, and examples of net radiation variation at different time scales and over various natural surfaces are given.

Mass Transfer: (i) Gases and Water Vapor

Abstract: Transfer of water vapor, carbon dioxide, and other trace gases between plants, animals, and the atmosphere takes place by molecular and turbulent diffusion. This chapter uses principles from fluid dynamics to develop methods for relating mass and heat transfer, and applies the methods to analyze mass exchange between leaves and the atmosphere. Mass exchange between the air in greenhouses and similar structures and the atmosphere is also analyzed. Mass diffusion through stomatal pores on leaves is a process limiting photosynthesis, respiration, transpiration, and the uptake of pollutant gases. The concept of stomatal resistance is introduced and measured resistances are compared with theoretical predictions. Water vapor transfer through animal skin, coats, human clothing, and through pores in artificial “breathable” fabric is also analyzed by resistance analogs.

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.