Ferenc Ács

A Coupled Soil-Vegetation Scheme: Description, Parameters, Validation, and, Sensitivity Studies

Abstract A coupled soil-vegetation scheme is presented. A one-layer canopy and a three-layer soil representation is used. The impact of canopy morphological properties on radiation and momentum transfer in the vegetation is modeled as simply as possible. The impact of the plant physiology on water transport through the vegetation layer is elaborated on in detail. The canopy resistance is calculated as the product of the fractional relative stomatal conductances of different governing factors. The scheme is tested using point micrometerological and biophysical data. It is shown that the agreement between simulated and measured turbulent fluxes is fairly good. Some sensitivity analyses are also made. The sensitivity of latent and sensible heal flux distribution is investigated with respect to the variations in the leaf drag coefficient Cd, the root density in the soil surface layer Rdes, and various formulations of the relative stomatal conductance for expressing the effect of vegetation moisture availabili...

A coupled soil moisture and surface temperature prediction model

Abstract A model for soil moisture and soil surface temperature prediction for bare soil is considered in this paper. In describing evaporation rate. soil structure and moisture were taken into account as much as possible. Soil moisture prediction was carried out using Sellers’ method. Hydraullic properties were determined both known values for the given type of soil and the empirical equations of Clapp and Hornberger. Soil surface temperature prediction were made using the “force-restore” method. Sensible and latent heat fluxes were determined using a resistance representation taking into consideration atmospheric stability. The model results were compared with some field data of soil temperature and latent and sensible heat fluxes. The agreement between the model-calculated and the observed heat fluxes was fairly good. Soil moisture and temperature prediction were satisfactory, although an excessive drying occurred at the beginning of a five-day simulation period. Some sensitivity analyses were also mad...

A COMPARATIVE ANALYSIS OF TRANSPIRATION AND BARE SOIL EVAPORATION

Transpiration Ev and bare soil evaporation Eb processes are comparatively analysed assuming homogeneous and inhomogeneous areal distributions of volumetric soil moisture content ϑ. For a homogeneous areal distribution of ϑ we use a deterministic model, while for inhomogeneous distributions a statistical-deterministic diagnostic surface energy balance model is applied. The areal variations of ϑ are simulated by Monte-Carlo runs assuming normal distributions of ϑ.The numerical experiments are performed for loam. In the experiments we used different parameterizations for vegetation and bare soil surface resistances and strong atmospheric forcing. According to the results theEv(ϑ)-Eb(ϑ) differences are great, especially in dry conditions. In spite of this, the available energy flux curves of vegetation Av(ϑ) and bare soil Ab(ϑ) surfaces differ much less than the Ev(ϑ) and Eb(ϑ) curves. The results suggest that Ev is much more non-linearly related to environmental conditions than Eb. Both Ev and Eb depend on the distribution of ϑ, the wetness regime and the parameterization used. With the parameterizations, Eb showed greater variations than Ev. These results are valid when there are no advective effects or mesoscale circulation patterns and the stratification is unstable.

Climate change in Hungary during the twentieth century according to Feddema

Climate change in Hungary during the twentieth century is analyzed using Feddema’s original scheme suitable for global scale applications (F-GS) and Feddema’s fine-tuned scheme designed for Hungarian applications (F-HU). Input data of precipitation (P) and air temperature (T) are taken from the Climatic Research Unit (CRU) TS 1.2 database constructing P-T data referring to three 30-year periods (1901–1930, 1941–1970, 1971–2000) and two 50-year periods (1901–1950, 1951–2000). The method and data organizational effects are compared using these schemes and data sets. The results show that the evaluation of the climate change process depends much more on the methodological rather than on data organizational effects. Methodical fine-tuning effects considerably improved the spatial distribution, while the organization of data improved the insight into the dynamic of the processes. According to F-GS, there is no climate change on 76.7 % of Hungarian territory. According to F-HU, such areas amount to only 38.5 %. The main climate change process for F-GS is drying, while for F-HU drying and warming beside either drying or warming. For both models, the most climate change affected areas are characterized by higher altitudes, such as in the Mecsek and Villány Mountains (geographical region Transdanubia), in the Bükk Mountains (geographical region North Hungarian Mountains), and in the region of the so-called Danube Bend. The spatially most realistic climate description is obtained by using F-HU and the 30-year data sets. It is to be noted that Köppen’s, Holdridge’s, and Thornthwaite’s methods are less suitable than F-HU for representing the process of climate change in Hungary in the twentieth century.

Climate of Hungary in the twentieth century according to Feddema

Feddema’s (Physical Geography 26:442–466, 2005) bioclimatic classification scheme is applied to Hungary for the twentieth century using the Climatic Research Unit (CRU) data series. The method is tested in two modes. In the first, its original form is used which is suitable for global scale analysis. In the second, the criteria used in the method are slightly modified for mesoscale classification purposes. In both versions, potential evapotranspiration (PET) is calculated using McKenney and Rosenberg’s (Meteorol 64:81–110, 1993) formula. We showed that McKenney and Rosenberg’s formula could be applied to Hungary. According to Feddema’s global scale application, local climates of the three main geographical regions, the Great Hungarian Plain, the North Hungarian Mountains, and Transdanubia, can be distinguished. However, the spatial distribution pattern within the regions is poorly reproduced, if at all. According to Feddema’s mesoscale application, a picture of climatic subregions could be observed.

Sensitivity of WRF-simulated planetary boundary layer height to land cover and soil changes

Planetary boundary layer (PBL) height sensitivity to both so-called single and accumulated land cover and soil changes is investigated in shallow convection under cloud-free conditions to compare the effects. Single land cover type and soil changes are carried out to be able to unequivocally separate the cause and effect relationships. The Yonsei University scheme in the framework of the Weather Research Forecasting (WRF) mesoscale modeling system is used as a research tool. The area investigated lies in the Carpathian Basin, where anticyclonic weather type influence dominated on the five summer days chosen for simulations. Observation-based methods applied for validating diurnal PBL height courses manifest great deviations reaching 500–1300 m. The obtained deviations are somewhat smaller around midday and greater at night. They can originate either from the differences in the measuring principles or from the differences in the atmospheric profiles used. Concerning sensitivity analyses, we showed that PBL height differences caused by soil change are comparable with the PBL height differences caused by land cover change. The differences are much greater in the single than in the accumulated tests. Space averaged diurnal course difference around midday reaching a few tens of meters can be presumably treated as strongly significant. PBL height differences obtained in the sensitivity analyses are, at least in our case, smaller than those obtained by applying different observation based methods. The results may be utilized in PBL height diurnal course analyses.

Soil-atmosphere relationships: The Hungarian perspective

Abstract This study discusses scientific contributions analyzing soil-atmosphere relationships. These studies deal with both the biogeophysical and biogeochemical aspects of this relationship, with biogeophysical aspects being in the majority. All of the studies refer either directly or indirectly to the fundamental importance of soil moisture content. Moisture has a basic influence on the spatiotemporal pattern of evapotranspiration, and so 1) on cloud formation and precipitation events by regulating the intensity of convection, and 2) on the trace-gas exchanges in the near-surface atmosphere. Hungarian modeling efforts have highlighted that soils in the Pannonian Basin have region-specific features. Consequently, shallow and deep convection processes are also, to some extent, region-specific, at least in terms of the diurnal change of the planetary boundary layer height and the spatial distribution of convective precipitation. The soil-dependent region-distinctiveness of these two phenomena has been recognized; at the same time the strength of the relationships has not yet been quantified.