Branislava Lalic

An Empirical Relation Describing Leaf-Area Density inside the Forest for Environmental Modeling

Abstract The spatial distribution of the leaf-area density is a key parameter in describing the forest canopy characteristics, which has a strong impact on its radiation balance and the mass and energy exchange with the atmosphere as well. The objective of this short study is to define an empirical relation describing the vertical distribution of leaf-area density that can be used for an improved estimation of the turbulent transfer coefficient inside the forest as well as above it. To check the validity of the method proposed, the calculated values are compared with the observations using datasets from eight observational sites located in four different types of forest, covering a broad range of mean values of leaf-area indices between 2 and 18.

Sensitivity of soil surface temperature in a force‐restore equation to heat fluxes and deep soil temperature

The ‘force-restore’ approach is commonly used in order to calculate the surface temperature in atmospheric models. A critical point in this method is how to calculate the deep soil temperature which appears in the restore term of the ‘force-restore’ equation. If the prognostic equation for calculating the deep soil temperature is used, some errors in surface temperature calculation and consequently in partitioning the surface energy and land surface water can be introduced. Usually, these errors should appear as a result of incorrect parameterization of surface energy terms in the prognostic equation based on ‘force-restore’ approach. In this paper, the sensitivity of the ‘force-restore’ model for surface temperature to the: (a) changes of soil heat flux; (b) variations of deep soil temperature and (c) changes in soil water evaporation is examined. In addition, the impact of the deep soil temperature variations on partitioning the surface energy and land surface water is discussed. Finally, a new procedure for calculating the deep soil temperature based, on climatological data of soil temperature and its exponential attenuation in the deep soil layers is suggested. All numerical experiments with the LAPS land surface scheme were performed using two data sets, obtained from the micrometeorological measurements over a bare soil at Rimski Sancevi (Yugoslavia), RS, and Caumont (France), HAPEX. Copyright

Wind profile within the forest canopy and in the transition layer above it

Abstract The forest as an underlying surface has to be considered in atmospheric models of different scales. Experimental evidence shows that there can be a significant variation of the wind profile within the forest and in the so-called transition layer above it. Experimentally observed wind speed is often found below as indicated by the wind speed profile obtained by: (a) the logarithmic relationship in the transition layer and (b) K theory within the forest. This situation can seriously disturb the real physical picture concerning the transfer of momentum, heat and water vapour from the surface into the atmosphere. In order to minimise the foregoing problems, we have suggested an empirical expression for the wind profile in the transition layer above the forest as well as the expressions for the wind profile and turbulent momentum transfer coefficient within the forest canopy layer. Additionally, for the proposed wind profiles, the expressions for the displacement height, roughness length and parameters are determined as functions of the forest structural characteristics using continuity conditions and a simple mass conservation hypothesis. The validity of the proposed expressions was checked using the micrometeorological measurements from the experimental sites in the Thetford Scots pine forest in Norfolk, United Kingdom and in the Ponderosa pine forest at the Shasta Experimental Forest, California, USA.

Turbulent Transfer Coefficients and Calculation of Air Temperature inside Tall Grass Canopies in Land–Atmosphere Schemes for Environmental Modeling

Abstract A method for estimating profiles of turbulent transfer coefficients inside a vegetation canopy and their use in calculating the air temperature inside tall grass canopies in land surface schemes for environmental modeling is presented. The proposed method, based on K theory, is assessed using data measured in a maize canopy. The air temperature inside the canopy is determined diagnostically by a method based on detailed consideration of 1) calculations of turbulent fluxes, 2) the shape of the wind and turbulent transfer coefficient profiles, and 3) calculation of the aerodynamic resistances inside tall grass canopies. An expression for calculating the turbulent transfer coefficient inside sparse tall grass canopies is also suggested, including modification of the corresponding equation for the wind profile inside the canopy. The proposed calculations of K-theory parameters are tested using the Land–Air Parameterization Scheme (LAPS). Model outputs of air temperature inside the canopy for 8–17 Jul...

A study on the effects of subgrid-scale representation of land use on the boundary layer evolution using a 1-D model

Abstract A soil–vegetation–atmosphere transfer scheme based on a one-dimensional boundary layer model has been developed to study the sensitivity of boundary layer growth on the surface temperature fields and land-use types. Full interaction between the surface and atmosphere is achieved by representing the surface and turbulent mixing processes by using a Land Air Parameterization Scheme (LAPS) and the Blackadars local closure PBL scheme. Sensitivity tests are performed by simulating planetary boundary layer structures over different underlying surfaces, soil textures and soil moisture contents using the meteorological data for July 17, 1999 in Philadelphia, PA. Also, a simpler surface parameterization used in the MM5 model results in a significantly higher surface temperature as well as the PBL depth over the urban area than those obtained by the LAPS parameterization in which a new method, including a combination of aggregated fluxes and parameters in calculating the surface temperature, is applied.

Simulation of air temperature inside the canopy by the LAPS surface scheme

Abstract A land–air parameterization scheme (LAPS) describes water vapour, heat and momentum transfer between the land surface and the atmosphere. The scheme is designed as a software package, which can be run as part of an atmospheric, hydrological or ecological model, or as a stand-alone model that operates with seven prognostic variables and 16 morphological and physiological input parameters. Such large number of parameters provides reliable simulation of diurnal courses of meteorological elements inside the crop. In this paper, for simulating the diurnal course of air temperature inside a sunflower field, the LAPS scheme has been used. The results obtained are compared with the results of micrometeorological measurements of a sunflower experimental field of the Oil Crops Department at Rimski Sancevi (Yugoslavia) using data sets from 18 July to 24 July, 1998. The LAPS scheme was compared with two other surface schemes using canopy air temperature data derived from measured air temperature above a maize field at an experimental site in De Sinderhoeve (The Netherlands) for 18 August, 8 September, and 4 October 1988.

An Approach for Calculation of Turbulent Transfer Coefficient for Momentum inside Vegetation Canopies

Abstract A method for calculating the profile of turbulent transfer coefficient for momentum inside a vegetation canopy for use in land surface schemes is presented. It is done through the following steps. First, an equation for the turbulent transfer coefficient for momentum inside a vegetation canopy using the “sandwich” approach for its representation is derived. Second, it is examined analytically to determine whether its solution is always positive. Third, the equation for the turbulent transfer coefficient is solved numerically, using an iterative procedure for calculating the attenuation factor in the expression for the wind speed inside a vegetation canopy that is assumed to be a linear combination of an exponential function and a logarithmic function. The proposed method is tested using 1) the observations for the wind profiles in a Japanese larch plantation and a pine forest and 2) the outputs for surface fluxes and total soil water content obtained by the Land–Air Parameterization Scheme (LAPS)...

The main features of the hydrological module in the Land Air Parameterization Scheme (LAPS)

Abstract This paper describes the hydrological module of the biophysical scheme named LAPS (Land-Air Parameterization Scheme) which is designed as a software package which can be included as part of an atmospheric model or as a stand-alone model. It includes: hydrological processes, bare soil transfer processes and canopy transfer processes. In the hydrological module the direct loss of liquid water across the scheme domain boundaries is considered as separate processes which can be summarised as follows: overland flow (when a precipitation excess is over infiltration capacity or when the surface becomes saturated), subsurface runoff (horizontal drainage from unsaturated flow) and vertical drainage through the lower scheme boundary. Moving from the top to the bottom of the soil, the water column has the three layers where the vertical water flow is considered according to Darcys law. The performance of this module through long term integration, using HAPEX-MOBILHY data set are examined.

Impact of climate change and carbon dioxide fertilization effect on irrigation water demand and yield of soybean in Serbia

The Decision Support System for Agrotechnology Transfer (DSSAT) v. 4·2 crop model was used to estimate climate change impacts on soybean yield in Serbia in simulations for 2030 and 2050 integration periods using three global climate change models (GCMs): the European Centre Hamburg Model (ECHAM), The Hadley Centre Coupled Model (HadCM) and the National Center for Atmospheric Research Parallel Climate Model (NCAR-PCM) under two scenarios from the IPCC Special Report on Emissions Scenarios (IPCC 2001): A1B SRES and A2 SRES. Input data included weather data from a 1971–2000 baseline period from ten weather stations assimilated from the Republic Hydrometeorological Service of Serbia. Output results from the three GCMs under the two scenarios for 2030 and 2050 were statistically downscaled with the ‘Met & Roll’ weather generator for predicted climate conditions. Mechanical and chemical soil properties were collected in the vicinity of weather stations and analysed by the Agency for Environmental Safety in Belgrade. Genetic coefficients, for the soybean maturity group II variety, were slightly modified using the DSSAT-SOYGRO model ones. The results showed a considerable benefit of carbon dioxide fertilization on soybean yield and yield increases at all locations. The greatest estimated yield increases obtained using outputs the HadCM model for 2030 both scenarios; in 2050, however, the A2 scenario resulted in smaller increase in yield at some locations. The highest increase in yield was in the central and eastern parts of Serbia. Analyses of the climate change impacts on irrigation demand showed a great increase in the irrigation demand amount per growing season. The average irrigation demand reached the highest values in the southern and eastern parts of Serbia. Water productivity reached highest values in eastern and central locations, while the minimum is expected in the most southern and northern location. According to all results it can be concluded that soybean will benefit greatly under climate change conditions and that soybean cropping, currently most concentrated in the Vojvodina region in northern Serbia, expanding in the central part and one location in eastern Serbia.

Vulnerabilities and Adaptation Options of European Agriculture

Through a change in climatic conditions and variability, for example, certain extreme weather events (heat waves, droughts, etc.) are likely to occur more frequently in different spatial and time scales in future. Since agriculture is one the man’ activities more dependant on weather behaviour, the impact on risks of agricultural production is indeed one of the most important issues in climate change assessments. Therefore an early recognition of risks and implementation of adaptation strategies is crucial as anticipatory; precautionary adaptation is more effective and less costly than forced, last minute, emergency adaptation or retrofitting. Results of climate change impact and adaptation studies often show considerable different results, depending on the spatial scale of regionalisation. However, for a decision maker, only a high spatial resolution of related study results is useful as it can represent local conditions and its spatial variability much better. This paper is based on the findings of the ADAGIO project (adagio-eu.org), which was focused on regional studies in order to uncover regional specific problems. In this context a bottom-up approach was used beside the top-down one of using scientific studies, involving regional experts and farmers in the evaluation of potential regional vulnerabilities and adaptation options. Results show, for example, that production risks, such as increasing drought and heat, are reported for most European regions. However, the vulnerabilities in the different regions are very much influenced by characteristics of the dominating agroecosystems and prevailing socio-economic conditions.