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Climatic change due to land surface alterations
Abstract
A primitive equations global zonally averaged climate model is developed. The model includes biofeedback mechanisms. For the Northern Hemisphere the parameterization of biofeedback mechanisms is similar to that used by Gutman et al. (1984). For the Southern Hemisphere new parameterizations are derived. The model simulates reasonably well the mean annual zonally averaged climate and geobotanic zones.
Deforestation, desertification and irrigation experiments are performed. In the case of deforestation and desertification there is a reduction in the surface net radiation, evaporation and precipitation and an increase in the surface temperature. In the case of irrigation experiment opposite changes occurred. In all the cases considered the changes in evapotranspiration overcome the effect of surface albedo modification. In all the experiments changes are smaller in the Southern Hemisphere.
... The Budyko index is given by Franchito and Rao (1992), Gao and Giorgi (2008), Franchito et al. 2014 and many others: AI B = R/(LP), where R (W m -2 ) is the mean annual net radiation; P (kg s -1 m -2 ) is the annual precipitation, and L (J kg -1 ) is the latent heat of evaporation. The values of AI B for different climate regimes are defined as (Franchito and Rao 1992): 0 \ AI B B 1 = humid (surplus moisture regime; steppe to forest vegetation) 1 \ AI B B 2 = semi-humid (moderately insufficient moisture; savanna) 2 \ AI B B 3 = semi-arid (insufficient moisture; semi-desert) AI B [ 3 = arid (very insufficient moisture; desert) ...
... The Budyko index is given by Franchito and Rao (1992), Gao and Giorgi (2008), Franchito et al. 2014 and many others: AI B = R/(LP), where R (W m -2 ) is the mean annual net radiation; P (kg s -1 m -2 ) is the annual precipitation, and L (J kg -1 ) is the latent heat of evaporation. The values of AI B for different climate regimes are defined as (Franchito and Rao 1992): 0 \ AI B B 1 = humid (surplus moisture regime; steppe to forest vegetation) 1 \ AI B B 2 = semi-humid (moderately insufficient moisture; savanna) 2 \ AI B B 3 = semi-arid (insufficient moisture; semi-desert) AI B [ 3 = arid (very insufficient moisture; desert) ...
... The model gives the P values while PET is calculated through the formula of Thornthwaite (1948). Values of AI U for different climate regimes are (Franchito and Rao 1992): ...
Future changes of the aridity of South America (SA) are investigated. The projected changes of the Budyko and United Nations Environment Programme (UNEP) indices in the mid- and end of the twenty-first century from the ensemble mean RegCM4 simulations using the scenario RCP 8.5 are presented. The RegCM4 model driven by the global models of HadGEM2, MPI, and GFDL for the period 1970–2100 carries out the simulations. For both Budyko and UNEP indices, an aridity increase over SA is projected. Over Brazil, the higher changes were found in the Amazon, North Brazil, and Northeast Brazil (NEB). In the Amazon and North Brazil, an increase of the aridity of 33.8% and 36.9% (for the UNEP index) and 4.6% and 13.9% (for the Budyko index), respectively, are noted at the end of the twenty-first century suggesting an increase of the process of savannization in future climate. In NEB, a rise of 37.3% and 14.1%, respectively, for the UNEP and the Budyko indices, is found, indicating an expansion of areas of the dry land regime.
... Thus, SDMs can be thought of as making a bridge between simpler EBMs and sophisticated GCMs. In a series of papers Franchito and Rao and their collaborators showed the feasibility of using SDMs to study climate change [13]- [22]. In the present work a review of several studies of climate change with SDM is presented. ...
... Although quasi-geostrophic SDMs are adequate for the treatment of the dynamics of the atmosphere in the extratropical region when the interactions between the tropics and higher latitudes are considered the use of the primitive equations is more appropriate. [13] developed a global primitive equation SDM including a biofeedback mechanism based on the parameterizations of [34]. They showed that the global distribution of the geobotanic zones were well simulated by the model (Figure 2). ...
... These results were similar to those obtained by [36]. However, in [13] the changes were obtained in both the hemispheres. ...
The cause-effect relationship is not always possible to trace in GCMs because of the simultaneous inclusion of several highly complex physical processes. Furthermore, the inter-GCM differences are large and there is no simple way to reconcile them. So, simple climate models, like statisticaldynamical models (SDMs), appear to be useful in this context. This kind of models is essentially mechanistic, being directed towards understanding the dependence of a particular mechanism on the other parameters of the problem. In this paper, the utility of SDMs for studies of climate change is discussed in some detail. We show that these models are an indispensable part of hierarchy of climate models.
... In a series of papers, Franchito and Rao and their collaborators showed the feasibility of using SDMs to study the biogeofeedback mechanism which links the state of the surface to the atmosphere (Franchito and Rao 1992; Varejão-Silva et al. 1998: Moraes et al. 2004, 2005, Silva et al. 2006 Franchito et al. 2010). In the present study, the SDM of Franchito et al. (2010) is used. ...
... The model includes a parameterization of the state of the surface that allows a continuous variation of the vegetation with climate. The method to include the interaction between the geobotanic state and climate (biogeophysical feedback) is the same as that proposed by Gutman et al. (1984) for the Northern Hemisphere and Franchito and Rao (1992) for the Southern Hemisphere. It is based on relations empirically determined between geobotanic types and climate conditions described by Budyko (1974). ...
... These changes correspond to an increase in D from 0.67 and 0.7 at 5°S and 5°N, respectively, in the control experiment (forest zone) to 1.2 (savanna zone) in the perturbed experiment. These prescribed values of the land surface albedo and water availability at the surface are obtained from the equations of Franchito and Rao (1992), mentioned in Section " 2 " , for D01.2. In the other latitude belts, the values of the land surface albedo and water availability at the surface vary during model integration. ...
This study investigates the impact of global warming on the savannization of the tropical land region and also examines the relative roles of the impact of the increase of greenhouse gas concentration and future changes in land cover on the tropical climate. For this purpose, a mechanistic–statistical–dynamical climate model with a bidirectional interaction between vegetation and climate is used. The results showed that climate change due to deforestation is more than that due to greenhouse gases in the tropical region. The warming due to deforestation corresponds to around 60% of the warming in the tropical region when the increase of CO2 concentration is included together. However, the global warming due to deforestation is negligible. On the other hand, with the increase of CO2 concentration projected for 2100, there is a lower decrease of evapotranspiration, precipitation and net surface radiation in the tropical region compared with the case with only deforestation. Differently from the case with only deforestation, the effect of the changes in the net surface radiation overcomes that due to the evapotranspiration, so that the warming in the tropical land region is increased. The impact of the increase of CO2 concentration on a deforestation scenario is to increase the reduction of the areas covered by tropical forest (and a corresponding increase in the areas covered by savanna) which may reach 7.5% in future compared with the present climate. Compared with the case with only deforestation, drying may increase by 66.7%. This corroborates with the hypothesis that the process of savannization of the tropical forest can be accelerated in future due to global warming.
... Adicionalmente, os MED são computacionalmente mais econômicos do que MCG, sendo relativamente mais fácil analisar e dignosticar seu comportamento. Numa série de artigos, Franchito e Rao e seus colaboradores têm mostrado a viabilidade do uso de modelos estatístico-dinâmicos em estudos de mudanças climáticas (Franchito e Rao, 1991 Rao, , 1992 Rao, , 1995 Rao e Franchito, 1993; Franchito et al., 1998; Varejão-Silva et al., 1998; Rao et al., 2000). Nesta série de trabalhos, o modelo original desenvolvido por Franchito e Rao (1992) tem sido continuamente melhorado através da inclusão de processos físicos que representem melhor o clima. ...
... m cada faixa latitudinal foi considerada coberta apenas pelo tipo predominante de vegetação. Gutman (1984) usou este modelo para estudar os efeitos climáticos do desmatamento tropical no Hemisfério Norte. Neste experimento, assumiu que a floresta tropical fora substituída por grama em toda a fração de terra do cinturão de latitudes centrado em 5ºN. Franchito and Rao (1992) incorporaram a parametrização de retroalimentação similar à de Gutman et al. (1984) num MED descrito por equações primitivas e estudaram o impacto climático do desmatamento tropical em ambos os hemisférios. A zona perturbada constituiu as regiões situadas entre 10ºS-10ºN. Zhang (1994) desenvolveu um modelo de biosfera para uso em modelo ...
A coupled biosphere-atmosphere statistical-dynamical model (SDM)is used for studying the effects of the Amazonian deforestation on regional climate and testing its ability in reproducing the Amazonian climate. A soil moisture model based on BATS has been incoporated in the SDM in order to study the biogeophysical feedback of change in surface characteristics to regional climate due to the deforestation. Comparison with the observations (LBA data)showed that the model is able to simulate the overall behaviour of climate of tropical land region associated with forest and pasture covered areas. The changes in temperature and energy fluxes are in good agreement with earlier GCMs experiments, showing the usefulness of this kind of simple mechanistic model. Pages: 1411-1420
... Surface energy fluxes and evapotranspiration (ET) are the key drivers of the Earth's climate system at local, regional and global scales (Shukla and Mintz, 1982;Sud and Fennessy, 1982;Sud et al., 1988;Franchito and Rao, 1992;Pielke et al., 1998;Raupach, 1998;Eugster et al., 2000). The Qinghai-Tibet Plateau, China, is a region that is vulnerable and sensitive to global climate change, and despite this, the complex feedbacks that occur in the exchange of energy between the land and atmosphere have not been studied in detail. ...
Qinghai Lake watershed, located in the northeast of the Qinghai-Tibet Plateau, is a region that is sensitive and vulnerable to global climate change. Both the hydrological cycle and water balance in a watershed are significantly influenced by surface energy fluxes and evapotranspiration (ET); however, there is limited information related to the water and heat fluxes in this area. Using the Bowen ratio energy balance method, we measured surface energy fluxes and ET and then explored their controlling factors in three typical ecosystems from the Qinghai Lake watershed, i.e., Kobresia meadow (KMd.), Potentilla fruticosa shrub (PFSh.) and Achnatherum splendens steppe (ASSt.) between 2012 and 2013 for the first time. It was found that between the different ecosystems, there were large differences in the energy portioning. Annual sensible and latent heats accounted for 56-64% and 35-45% of net radiation, respectively. The Bowen rations were the highest in the ASSt. site and the lowest in the PFSh. site. The Bowen ratios and soil water content (SWC) had negative correlations. Annual ET was 507.9, 493.2 and 413.7 mm for the PFSh., KMd. and ASSt. sites, respectively. The annual ET in the KMd. and PFSh. sites was 16% and 3% less than the annual precipitation, while the ET was 26% higher than precipitation for the ASSt. site. Fluctuations in the daily ET of alpine ecosystems from the Qinghai Lake watershed were primarily controlled by radiation, especially during the growing season; whereas, ET was also controlled by SWC in the ASSt. ecosystem where precipitation was low. This article is protected by copyright. All rights reserved.
... Most of the analyses relating human-caused land degradation to climate change focus on changes in the energy balance of an environment, including the effects of albedo changes in general (Jackson & Idso 1975) and more specifically albedo changes associated with salinization (Williams & Balling 1996), the effects of overgrazing (Bryant et al. 1990), the impacts of vegetation removal due to various causes and the impacts of increased dust concentrations in the atmosphere (for example, see Charney 1975, Mabbutt 1989, Nicholson 1989, Bryant et al. 1990, Williams & Balling 1996. In the last few decades, many models have tried to simulate the impacts of land-use change on local climates, showing that surface changes can have significant impacts on local climate conditions (Charney 1975, Franchito & Rao 1992, Zheng & Eltahir 1997. These models support the idea that local albedo changes will have impacts on local energy balances and can affect mesoscale circulation events. ...
This study uses a well-established water balance methodology, the Thornthwaite-Mather approach, to evaluate the effects of soil water holding capacity assumptions on estimates of African evapotranspiration rates, moisture deficit, and moisture surplus conditions. Under constant climate conditions, the model tests the impact of using a constant 150 mm soil water holding capacity compared to using a newly derived soil water holding capacity data set (the Dunne-Willmott data set). The study also uses a worldwide survey of soil degradation between 1950 and 1980 (GLASOD: Global Assessment of Soil Degradation) to evaluate the impacts of human-induced soil degradation on local water balances. The GLASOD data are used to alter local soil water holding capacities based on the Dunne-Willmott data to simulate human soil degradation patterns in Africa. Results indicate that the use of simplified soil water holding capacities can lead to significant errors in estimated evapotranspiration rates and water surplus and deficit conditions in Africa. Regions most affected are those with seasonal wet and dry climates, which are also those locations with the greatest climate variability. Because these are often the climates most studied to detect and model environmental change, it is important that accurate soil moisture estimates be used to simulate climate conditions in these regions. Results also indicate that soil degradation occurring over a 30 yr period (1950 to 1980) has had a significant impact on local water resources. The greatest impacts of these changes are in some of the more productive agricultural areas in the wetter sub-humid climates. Changes include increased runoff during wet seasons and an extended drought period during the dry seasons. Given that these agricultural systems have less flexibility to respond to long-term desiccation as compared to pastoral systems, this could lead to significant changes in local growing seasons and perhaps overall productivity in the future.
... No entanto, essas modificações foram pequenas e não comprometeram os resultados finais da simulação. O valor do albedo da superfície foi calculado a partir da distribuição dos diferentes tipos de cobertura e de estimativas do valor do albedo para cada tipo de superfície, como em Franchito e Rao (1992) Tabela 3.2 -Frações dos tipos de cobertura para o UMG e para o presente (entre parênteses) ...
... et al ., 2004;Twine et al ., 2004;Scanlon et al ., 2005, 2007, Zhang and Schilling, 2006Cotton and Pielke, 2007;Pereira et al ., 2010). Despite some uncertainties in the magnitude of the impacts, it is increasingly recognized as an important forcing of local (Landsberg, 1970;Balling, 1988;Segal et al ., 1989b, Rabin et al ., 1990Balling et al ., 1998;Arnfield, 2003;Campra et al ., 2008;NRC, 2012), regional (Barnston and Schickedanz, 1984;Zheng et al ., 2002;Foley et al ., 2003a;Mohr et al ., 2003;Oleson et al ., 2004;Voldoire and Royer, R. MAHMOOD et al. 2004;Gero et al ., 2006;Ray et al ., 2006;Betts et al ., 2007;Costa et al ., 2007;Abiodun et al ., 2008;Klingman et al ., 2008;Lee et al ., 2008;Nuñez et al ., 2008;Kvalevåg et al , 2010;Hu et al ., 2010), and global climate (Franchito and Rao, 1992;Wu and Raman, 1997;DeFries et al ., 2002;Kabat et al ., 2004;Avissar and Werth, 2005;Feddema et al ., 2005;NRC , 2005;Gordon et al ., 2005;Cui et al ., 2006;Ramankutty et al ., 2006;Takata et al ., 2009;Sacks et al ., 2009;Puma and Cook, 2010;Davin and Noblet-Ducoudré, 2010;Strengers et al ., 2010;Lee et al ., 2011;Lawrence et al ., 2012). As with carbon dioxide (CO 2 ), LCC affects the climate system on multi-decadal time scales and longer. ...
Land cover changes (LCCs) play an important role in the climate system. Research over recent decades highlights the impacts of these changes on atmospheric temperature, humidity, cloud cover, circulation, and precipitation. These impacts range from the local- and regional-scale to sub-continental and global-scale. It has been found that the impacts of regional-scale LCC in one area may also be manifested in other parts of the world as a climatic teleconnection. In light of these findings, this article provides an overview and synthesis of some of the most notable types of LCC and their impacts on climate. These LCC types include agriculture, deforestation and afforestation, desertification, and urbanization. In addition, this article provides a discussion on challenges to, and future research directions in, assessing the climatic impacts of LCC.
... The changes in the forest areas in the C4 experiment are fundamentally the same as those found in the re-sults of the deforestation experiments of Franchito and Rao (1992) and Defries et al. (2002). ...
Several numerical simulations were performed, using a global climate model that includes a realistic land surface model, to investigate the impact of Asian tropical vegetation changes on the climate. The control simulation, under conditions of the actual vegetation, and three vegetation-change impact experiments were performed. The results of the impact experiments were compared with those of the control simulation. The horizontal resolution of the model used in these simulations was 1.875°, being finer than that of the models used in previous vegetation-change impact studies. As a result, it was determined that the effects of vegetation changes in the Asian tropical region had spatially different features.
The morphological, physiological, and physical changes of the land surface vegetation in the Asian tropical region certainly induce statistically significant climate changes in these and the surrounding areas. That is, from the results of the bare soil and C4 grass experiments, the decrease in the roughness length, and from the results of the green-less experiment, the decrease of the latent heat flux, exert strong influences on the horizontal and convective circulations of the atmosphere. Consequently, the distribution of precipitation will undergo a change. Other energy and water balances at the land surface are also influenced by the vegetation changes, and the induced changes are generally statistically significant.
The influences of vegetation changes in the Asian tropical region were more complicated than those in the Amazon. One reason for this was that the Asian tropical region is strongly influenced by the Asian monsoon circulation; another reason is that the land–sea distribution and the distribution of vegetation in the Asian tropical region are not as simple as in a tropical rain forest like the Amazon.
... Human interventions leading to changes in natural surface characteristics are believed to directly induce serious climatic changes. Employing climate models, Rotter et al. (1975), Shukla and Mintz (1982), Shukla et al. (1990), Franchito and Rao (1992), Bras (1993, 1994), Eltahir (1996) and Hoffman and Jackson (2000) have examined this hypothesis and indicated the sensitivity of local and regional climates to extensive deforestation and conversion of natural land cover. When Zheng and Eltahir (1997) used a simulation model to study the response of West African monsoon to desertification and deforestation, they found that the impact of deforestation is far more serious than desertification. ...
There exists an impressive amount of work for Sudan showing the anthropogenic degradation of natural vegetation cover. However,
there are few examples of consequent climatic changes in literature. This work, thus, seeks to assess such effects of environmental
forcing on various climatic patterns over the past few decades. Within the frame of the present analysis, the results are
quite striking and are in concordance with scientific contentions that such land degradation could result in climatic modification.
Higher temperature and less rainfall, sunshine duration and global radiation have been noticed. Evapotranspiration has responded
more to the warming and drying conditions, thus showed signs of increasing rates, especially during the wet season. However,
the extent of increase seems to have been suppressed by the decrease in sunshine duration and solar radiation as well as the
inconsistent behaviour of wind speed. Changes in the variability of the within-year monthly observations have also occurred,
thus suggesting an increase in the occurrence of extremes. The observed climatic modification in the country has exaggerated
the insidious drought conditions. The present findings are hoped to contribute to our understanding of the effects of environmental
problem and assist in considering policy responses.
... il moisture changes and the importance of soil moisture could override the changes to the albedo. Combining the local energy balance model with a global climate model, Lanicci et al. (1987) found that soil moisture changes in the drylands of the American Great Plains could have an important impact on the location and intensity of convective storms. Franchito & Rao (1992) developed a global model that includes detailed biogeophysical feedbacks to simulate the effects of desertification and found that desertification causes a reduction in local net radiation, soil moisture, evaporation and precipitation which consequently results in an increase in local surface and near-surface temperature. In our region, ...
A thermal anomaly was observed on the remote sensing images in the sand dunes across the Israel–Egypt border. The Israeli side with more vegetation cover has higher (>2°C) land surface temperature (LST) during the day than the Egyptian side where bare sand prevails. This anomaly is very obvious at about noon in the hot dry summer season. A micrometeorological model has been established in terms of surface energy balance for simulating the surface temperature change and heat flux variation of the region. The purpose of this modeling is to understand the mechanism leading to the occurrence of the thermal anomaly and to reveal the key factors controlling the surface temperature change. The characteristic of the model lies in its coupling soil temperature changing simultaneously with soil moisture movement, described as two differential equations. The methodology for the numerical solution of the model has been developed. The required meteorological data and soil parameters were measured at the study region in the hot summer season for the simulation. Two typical and the most important surface patterns of the region are considered: biogenic crust representing the Israeli side and the bare sand representing the Egyptian side. Results from simulation indicate that surface albedo contributes most to the surface temperature difference between the two typical surfaces, which is followed by sub-soil properties (mainly soil moisture) difference. Biogenic crust has lower surface albedo than bare sand. Consequently, it absorbs much more incident sky radiation. During the hot summer season, the region is very dry and vegetation is in dormancy. The canopy of most shrubs reduces to minimum. Even though the Israeli side has more vegetation, the evapo-transpiration contributed by the vegetation is still very small (<7%) in comparison with the net radiation. This small latent heat flux has little effect on the surface energy balance process in the arid environment. LST change in the desert region is mainly controlled by the amount of incident solar energy absorbed by the ground as soil heat. Therefore, the anomalous LST change and thermal variation on both sides of the region can still be explained as the direct result of the obvious albedo difference on both sides. This albedo difference is mainly caused by the sharp contrast of surface composition especially different biogenic crust and bare sand cover rates on both sides. The overgrazing and other anthropogenic stresses are the direct reasons leading to the bare sand (high albedo) prevalent on the Egyptian side while the conservation policy helps the development of biogenic crust and vegetation (low albedo) on the Israeli side.
... Landscape discontinuities, resulting from spatial heterogeneity of these characteristics, can induce atmospheric mesoscale circulations, which have strong impact on the structure of planetary boundary layer, clouds and precipitation [34]. Consequently, large-scale changes in land use can result in changed regional patterns of temperature and precipitation [39]. For example, the reduction of transpiration resulting from overgrazing in northern Mexico increased sensible heat flux, causing regional warming by 2.0-4.0 ...
Surface energy balance and 24-h evapotranspiration were mapped on an agricultural landscape with SRF willows using a remote sensing-based model to provide information on the water use by different land cover types. The results demonstrate the influence of land cover and vegetation type on surface energy balance and water losses. The evapotranspiration from forests was much higher than for other land cover types, corresponding to the significant cooling of the land surface. The SRF willow plantings were on average 3.6 °C cooler than the surrounding grassy areas; the 24-hour evapotranspiration from willows was 1.6 times higher than the evapotranspiration from surrounding grass, but lower than evapotranspiration from the forests. The possibility of changes in evapotranspiration patterns, local climate, and regional water balance with increasing acreage in SRF crop are discussed.
... Agriculture activities leaded to a vast change in the global land use, thus altering the vegetation distribution and therefore the climate. For example, deforestation reduces net radiation and precipitation and increases surface temperatures while irrigation has opposite effects (Franchito and Rao, 1992). Expansion of cultivated land is currently limited to some tropical humid regions, but in the past three centuries the area of cultivated land increased on average by 600% and currently the best estimate obtained from census data and satellite images states that croplands and pasturelands cover 12% and 22% of the Earth's land surface, respectively (Raddatz, 2007). ...
The main issues related to the atmospheric pollution are the stratospheric ozone depletion, the transboundary air pollution, the troposphere air quality and the climate change. The three last decades have seen the birth of several measures for the atmosphere safeguard. Agricultural activities play a key role in determining, preventing and mitigating atmospheric pollution. The emission to atmosphere of different ozone-depleting substances is regulated by the Montreal Protocol. The role of agriculture activity in ozone depletion is linked to the utilization of methyl bromide as soil sterilant and to the emission of nitrogen oxides and nitrous oxide, from agricultural soils. The Convention on long-range transboundary air pollution regulates the emission of several pollutants, i.e. sulphur dioxide, nitrogen oxides, ammonia, non methane volatile organic compounds, carbon monoxide, heavy metals, persistent organic pollutants, and tropospheric ozone. The agriculture sector is responsible for a large part of the emissions of ammonia and nitrogen oxides, mainly through manure management and nitrogen fertilization, and of most persistent organic pollutants, largely used in the past as insecticides and fungicides. The increase of the greenhouse gases (GHGs) concentration in the atmosphere is under the control of the Kyoto Protocol. Agriculture accounts for 59-63% of global non-CO2 GHGs emissions but at the same time it contributes to the atmospheric CO2 concentration stabilisation through the substitution of fossil fuels by biofuels and the sequestration of C in soil and vegetal biomass. In this paper we provide an outline of the numerous scientific and legislative initiatives aimed at protecting the atmosphere, and we analyse in detail the agriculture sector in order to highlight both its contribution to atmospheric pollution and the actions aimed at preventing and mitigating it.
... see fig. 1 in Sellers et al. 1995). Ecosystems influence weather and climate over period of seconds to years through exchanges of energy, moisture, and momentum between the land surface and the atmosphere (Waggoner & Reifsnyder 1968;Shukla & Mintz 1982;Dickinson 1984;Dickinson et al. 1986;Sellers et al. 1986;Pan & Mahrt 1987;Dickinson et al. 1992;Bonan 1994;Sellers et al. 1996a) and the changes in global-scale atmospheric circulation that can result from changes in these fluxes (Charney 1975;Chervin 1979;Sud & Fennessy 1982;Sud & Smith 1985;Sud et al. 1988;Dickinson & Henderson-Sellers 1988;Delworth & Manabe 1989;Nobre et al. 1991;Bonan et al. 1992;Franchito & Rao 1992;McGuffie et al. 1995;Chase et al. 1996;Randall et al. 1996;Sellers et al. 1996c;Zhang et al. 1996). Ecosystem structure and function is strongly determined on timescales of decades to centuries by climate influences, primarily through temperature ranges and water availability (Woodward 1987;Woodward & McKee 1991;Prentice et al. 1992;Neilson & Marks 1994;Neilson 1995;HendersonSellers & McGuffie 1995;Bugmann 1997;Chapin & Starfield 1997). ...
This paper overviews the short-term (biophysical) and long-term tout to around 100 year timescales; biogeochemical and biogeographical) influences of the land surface on weather and climate. From our review of the literature, the evidence is convincing that terrestrial ecosystem dynamics on these timescales significantly influence atmospheric processes. In studies of past and possible future climate change, terrestrial ecosystem dynamics are as important as changes in atmospheric dynamics and composition, ocean circulation, ice sheet extent, and orbit perturbations.
... O modelo climático utilizado é o desenvolvido por Franchito e Rao (1992). O modelo é estatísticodinâmico, global, de equações primitivas, com duas camadas atmosféricas efetivas. ...
A parameterization of shortwave and longwave radiative fluxes derived from detailed radiative transfer models is included in a global zonally averaged climate model (ZACM) with two bulk atmospheric layers. The model is validated comparing the model simulations with the observed mean annual and seasonal zonally averaged climate. The results show that the simulation of the radiative fluxes matches well with the observations. Also, the ZACM variables are in good agreement with the observations. The model is used to investigate its reponse to the greenhouse effect regarding the doubling of CO2 and the changing of cloud amount and height. An enhancement of the greenhouse effect is noted in the case 2 x CO2 and when the cloud layer is higher. However, an increase of the cloud amount in all the latitude belts provokes an increase of the surface temperature near poles and a decrease in all the other regions.
... É um modelo estatistico-dinâmico média zonal, de duas camadas, global, de equações primitivas, em coordenada sigma. Este modelo tem sido usado em vários estudos de mudança climáticas (Franchito e Rao, 1992 Rao, , 1995 Rao e Franchito, 1993; Varejão-Silva et al., 1998). Assim, uma descrição detalhada pode ser encontrada nestes trabalhos anteriores. ...
A zonally-averaged climate model is used to study the effects of the Tibetean plateau on the monsoonal circulation. A smothed zonally-averaged topography which has a form similar to that observed is used. The results show that the model is able to reproduce the principal characteristics of the monsoonal circulation such as the seasonal wind reversal and the easterly jet in the boreal summer. Even in the absence of the Tibetean plateau the model is able to reproduce the monsoon features. However, the circulation is weak and the position of the monsoon components is altered. This suggests that the main role of the plateau barrier is to modify the intensity and the position of the monsoonal circulation.
... O modelo utilizado é um modelo global, de equações primitivas, de duas camadas, e em coordenada sigma, similar ao desenvolvido por Franchito e Rao (1992). Possui parametrizações do aquecimento diabático (radiação solar e de onda longa, convecção de pequena escala, fluxo de calor latente e condução para a subsuperfície), dos turbilhões de grande escala e do atrito. ...
A two-layer, global, primitive equation zonally averaged model with diurnal cycle of radiation is used for studying the seasonal variations of the Inter-Tropical Convergence Zone (ITCZ). In order to investigate the mechanism that affects the displacement of the ITCZ over different types of surfaces three numerical experiments were made, considering: a)the earth's surface covered by the actual fractions of land, ocean, ice and snow; b)the earth's surface covered only by ocean ("aqua-planet"); and c)the earth's surface covered only by land ("continental planet"). The results showed that in the case of the "aqua-planet"the seasonal variation of the ITCZ was around 15°, like in the case considering the earth's surface covered by the fractions of the different types of surface; in the case of the "continental planet", the seasonal variationof the ITCZ was larger than in the other cases (around 25°). It was also that in the case of the earth's surface covered by land there was a strong seasonal inversion of the wind from the winter to the summer hemisphere. In the case of the erath's surface covered by ocean the seasonal inversion of the wind was moderate. RESUMO: Um modelo estatistico-dinamico de media zonal, de duas camadas, global, de equacoes primitivas, incluindo uma representacao do ciclo diurno da radiacao solar e utilizado para o estudo das variacoes sazonais da Zona de Convergencia Intertropical (ZCIT). Para investigar os mecanismos que afetam seu deslocamento sobre diferentes tipos de superficie foram realizados tres experimentos, que consideraram a superficie do globo coberta: a)pelas fracoes reais de terra, oceano, gelo e neve; b?somente por oceano ("planeta aquatico"); e c)somente por terra ("planeta continental"). Os resultados mostraram que, no caso do "planeta aquatico", a ZCIT teve um deslocamento sazonal de 15° de latitude, como no caso de se considerar as fracoes reais dos diferentes tipos de superficie dentro dos cinturoes de latitude; no caso do "planeta continental", a ZCIT teve um deslocamento sazonal maior, cerca de 25° de latitude. Foi notado, no caso do experimento com a superficie coberta por continente, uma forte inversao sazonal do vento, do hemisferio de inverno para o verao. No caso do experimento com a superficie coberta por oceano, a inversao sazonal do vento foi moderada Pages: 75-84
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
A zonally-averaged climate model is used to study the effects of the Tibetean plateau on the monsoonal circulation. A smothed zonally-averaged topography which has a form similar to that observed is used. The results show that the model is able to reproduce the principal characteristics of the monsoonal circulation such as the seasonal wind reversal and the easterly jet in the boreal summer. Even in the absence of the Tibetean plateau the model is able to reproduce the monsoon features. However, the circulation is weak and the position of the monsoon components is altered. This suggests that the main role of the plateau barrier is to modify the intensity and the position of the monsoonal circulation.
This paper reviews the biophysical and social linkages between climate change and desertification or dryland degradation. It argues that while the physical linkages are fairly well identified, it is within the emerging linkages between social processes related to climate change and desertification that some of the most effective measures can be put into place. It suggests that the underlying causes of vulnerability to both climate change and desertification include the political ecology of resource control, urbanization, and economic globalization affecting domestic markets and agricultural specialization. Particular attention is paid to using local livelihoods and vulnerability as a point of departure for measures designed to ameliorate the impacts of climate change and desertification.
The study of land surface-atmosphere interactions is vital to understanding climatic variations in the Earth's planetary boundary layer, particularly given continual land cover modifications by humans on local to regional scales. An agriculturally important region ideal for the study of land surface-atmosphere interactions is the Midwest United States "Corn Belt." To evaluate the mesoscale relationships between Corn Belt land surface properties and a key indicator of the surface-atmosphere feedback in humid climates—warm-season convective cloud development—conventional meteorological data, digital maps of land surface properties, and satellite data were examined in a GIS framework for the May-September periods of 1991 through 1999. The results indicate associations between the surface and atmospheric moisture content and the formation of convective clouds: cumulus clouds initiate first and persist longer over a dry (moist) surface with an initially dry (moist) atmosphere. These relationships are evident when forcing from the free atmosphere is either extremely weak (i.e., when fronts and other disturbances are absent and 500 mb winds are <7 ms-1), weak (same as extremely weak, except 500 mb winds are 7-13 ms-1), or strong (same as extremely weak, except 500 mb winds >18 ms-1). However, the association between convective cloud development and other land surface properties (e.g., land use-land cover [LULC], soil order, elevation, and slope) is not consistent spatially. We find that a surface moisture-convective cloud relationship dominates Corn Belt land surface-atmosphere interactions across a range of barotropic synoptic conditions under different atmospheric moisture contents. The study results can help lead to improved prediction of convective cloud formation, and more realistic modeling of land surface-atmospheric interactions for weather and climate forecasting.
Human Impacts on Weather and Climate is a nonmathematical presentation
of the basic physical concepts of how human activity may affect weather
and climate. This book assesses the current hypotheses and examines
whether the impacts are measurable. It critically evaluates the
scientific status of weather modification by cloud seeding, human
impacts on regional weather and climate, and human impacts on global
climate, including the greenhouse gas hypothesis. Human Impacts on
Weather and Climate will be valuable for upper-division undergraduate
courses or graduate courses in meteorology, geophysics, earth and
atmospheric science, as well as for policy makers and readers with an
interest in how humans are affecting the atmosphere.
A coupled biosphere-atmosphere statistical-dynamical model is used to study the relative roles of the impact of the land change caused by tropical deforestation and global warming on energy balance and climate. Three experiments were made: 1) deforestation, 2) deforestation + 2 x CO2, and 3) deforestation + CO2, CH4, N2O, and O-3 for 2100. In experiment 1, the climatic impact of the Amazonian deforestation is studied. In experiment 2, the effect of doubling CO2 is included. In experiment 3, the concentrations of the greenhouse gases (GHGs) correspond to the A1FI scenario from the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios. The results showed that the percentage of the warming caused by deforestation relative to the warming when the increase in GHG concentrations is included is higher than 60% in the tropical region. On the other hand, with the increase in GHG concentrations, a reduction in the decrease of evapotranspiration and precipitation in the tropical region occurs when compared with the deforestation case. Because of an increase in the net longwave flux at the surface, there is a reduction in the decrease of the surface net radiation flux when compared with the case of only deforestation. This leads to an increase in the surface temperature. Although the changes are higher at 5 degrees S, the percentage of them when the increase in GHG concentrations is included together with deforestation relative to the case of only deforestation is higher at 5 degrees N (higher than 50% for the surface temperature and higher than 90% for the foliage and air foliage temperatures) in both experiments 2 and 3.
The intense interest in desertification and climate change has stimulated detailed studies of temperature records in many areas of the world. In this investigation, the temperature records from the Middle East region are analyzed over the period 1950-1990. Results reveal a linear, statistically significant temperature increase of 0.07 °C/decade over the 41-year period. An analysis of spatial controls on these temperature changes reveals a warming effect associated with both overgrazing and the degree of human-induced desertification. The results of this study are consistent with theoretical and empirical studies predicting and demonstrating a warming signal associated with these land surface changes in the world's dryland areas.
Visionary 19th and 20th century macroengineers have dreamt about transformations of North Africa's large contiguous arid landscape. Their most vital macroprojects plans are reviewed here, with the intent of promoting the early 21st century construction of the Sahara Tent Greenbelt + “insol” building. Pneumatic tenting of ∼ 3.5 million square kilometres of desert prototypes a late 21st century distended building for Mars' terraformation, which is ∼ 35 times greater in area than the proposed STG. Covering 50% of the Sahara leaves other people to dream, while calculations for the whole of the region indicate the potential impact of a first try.
Twentieth century temperature records for a latitudinal band extending from 10°N to 50°N are stratified using a recent UNEP map showing areas affected by overgrazing. Linear trend analysis shows that the overgrazed areas have warmed at a rate of 0.0057 K year−1 while land areas in the latitudinal band not impacted by overgrazing have warmed at a rate of 0.0035 K year−1. The difference in temperature between the two groups has increased at a statistically significant rate over the 1901–1990 time period. While this temperature increase apparently associated with overgrazing may be important locally and regionally, the impact of overgrazing probably accounts for less than 1% of global warming over the same time period.
Close examination of the global temperature record, together with other factors, does not support the global warming models’ predictions – the thermal response to a doubling of CO2 is likely to be ‘remarkably small’.
This article illustrates the large-scale connectivity of the atmosphere–ocean coupled system and generalizes the concept to regional scales and to other components of the earth system. Connections at a distance, or teleconnections, can occur by the direct transfer of mass by changes in regular circulations or by propagating waves initiated by a variety of mechanisms. Questions as to what extent recognized teleconnection patterns can be associated with identifiable forcing mechanisms, to what extent these patterns are interrelated and how they might cause, react to, or interact with changing forcing such as changes in atmospheric composition, land cover, or the distribution of sea ice to produce climate changes are examined.
Physical and health risks are very high among aged persons. The precise implications of population ageing for future levels of health and healthcare utilization depend on whether the increases in life expectancy experienced in general are accompanied by an increase or a decrease in health problems in later life. The health risks of the presence of an aged person in a household can result in a catastrophic shock for the family and render such households more exposed to poverty. The increased cost of medical bills means that large numbers of the elderly in the developing world are deprived of access to health and to better health treatment. This article examines this question empirically, using the largest national survey in the Indian state of Kerala, comparing elderly with non-elderly households. We also attempt to find the impact of unhealthy lifestyles on the financial status of these households, due to hospitalization as a result of an aged person's illness.
The interannual variability of deep convection over the South American sector and regional hydrometeorological anomalies are studied using International Satellite Cloud Climatology Project (ISCCP) data for 1984–1988. Satellite‐derived convection anomalies are compared with regional rainfall and river runoff anomalies.
At the height of the austral summer, the deep convective clouds (DCC) and ISCCP depict the centres of intense convection over central Amazonia and the mouth of the River Amazon, as well as the enhanced convection over north‐east Brazil, which is related to the Atlantic Intertropical Convergence Zone (ITCZ). Positive/negative regional hydrometeorological anomalies are consistent with positive/negative anomalies in the deep convection over northern Amazonia, the mouth of the River Amazon and north north‐east Brazil, whereas this is not always true over southern Amazonia and southern Brazil. Over north‐east Brazil and the mouth of the River Amazon, abundant rainfall and large DCC are both in agreement with variations in the latitudinal position and intensity of the Atlantic ITCZ, which extends between 4°N and 5°S along the Atlantic coast, where the precipitation maximum is found. The related rainfall anomalies over Amazonia and north‐east Brazil during years with anomalously warm or cool surface waters in the central equatorial Pacific (e.g. the El Niño event in 1987), are consistent with the convection anomalies as depicted by the ISCCP deep convective clouds. For the Amazon Basin and north‐east Brazil, DCC based on 2.5°×2.5° horizontal resolution explained about 50 per cent of the variance of rainfall at individual surface stations.
A new finding is the enhanced convective activity located at the east side of the central Andes and over central Amazonia around 5°S, with a region of reduced convection in between. These two subcentres are oriented west‐east and are part of the summertime semi‐permanent centre of convection over the Amazon Basin, and have not been identified previously from the analysis of outgoing longwave radiation (OLR) or highly reflective clouds. These subcentres of large DCC exhibit interannual variations in intensity and location, where the centre located near the east flank of the Andes shows a wider range of latitudinal variations than that located over central Amazonia. South of this area convection and rainfall decreases rapidly.
Since at least 1964 macro-engineering has proposed solutions for Earth-biosphere problems affecting mankind and its infrastructures. From 1929–1948 Herman Sorgel put forth his ‘Atlantropa Macroproject, which was designed to lower the Mediterranean Sea by 1 m every year by natural evaporation and to irrigate the Sahara with diverted Zaire River freshwater. The present author has slightly modernized Sorgel's gift to Homo sapiens. Construction of ‘Atlantropa’ would provide Macro-engineering and Terraforming with a much-needed practice run for the remaking of our Solar System's planets.
This study uses a well-established water balance methodology to evaluate the relative impact of global warming and soil degradation due to desertification on future African water resources. Using a baseline climatology, a GCM global warming scenario, a newly derived soil water-holding capacity data set, and a worldwide survey of soil degradation between 1950 and 1980, four climate and soil degradation scenarios are created to simulate the potential impact of global warming and soil degradation on African water resources for the 2010–2039 time period. Results indicate that, on a continental scale, the impact of global warming will be significantly greater than the impact of soil degradation. However, when only considering the locations where desertification is an issue (wet and dry climate regions), the potential effects of these two different human impacts on local water resources can be expected to be on the same order of magnitude. Drying associated with global warming is primarily the result of increased water demand (potential evapotranspiration) across the entire continent. While there are small increases in precipitation under global warming conditions, they are inadequate to meet the increased water demand. Soil degradation is most severe in highly populated, wet and dry climate regions and results in decreased water-holding capacities in these locations. This results in increased water surplus conditions during wet seasons when the soil's ability to absorb precipitation is reduced. At the same time, water deficits in these locations increase because of reduced soil water availability in the dry seasons. The net result of the combined scenarios is an intensification and extension of drought conditions during dry seasons.
The intense interest in the greenhouse effect has stimulated detailed studies of temperature records in North America, Europe, and Australia. In this investigation, the temperature records from the Middle East region (defined here as the land area extending from Morocco to Afghanistan) are investigated over the period 1950–1990. Results reveal a linear, statistically significant, temperature increase of 0.07C per decade over the study area that may or may not be associated with the concurrent rise in equivalent carbon dioxide from approximately 350 ppm to 430 ppm. Seasonal analyses reveal that most of this increase has occurred in the spring season, moderate amounts of warming occurred in the summer and fall seasons, and virtually no warming has occurred in the winter months. An analysis of spatial controls on these temperature changes reveals a general cooling effect associated with the atmospheric sulfate levels and a warming effect associated with the degree of human-induced desertification. The results of this study may prove useful to policymakers in the Middle East who are confronted with many difficult decisions regarding highly interrelated global warming and energy issues.
In this study, a zonally-averaged statistical climate model (SDM) is used to investigate the impact of global warming on the
distribution of the geobotanic zones over the globe. The model includes a parameterization of the biogeophysical feedback
mechanism that links the state of surface to the atmosphere (a bidirectional interaction between vegetation and climate).
In the control experiment (simulation of the present-day climate) the geobotanic state is well simulated by the model, so
that the distribution of the geobotanic zones over the globe shows a very good agreement with the observed ones. The impact
of global warming on the distribution of the geobotanic zones is investigated considering the increase of CO2 concentration for the B1, A2 and A1FI scenarios. The results showed that the geobotanic zones over the entire earth can be
modified in future due to global warming. Expansion of subtropical desert and semi-desert zones in the Northern and Southern
Hemispheres, retreat of glaciers and sea-ice, with the Arctic region being particularly affected and a reduction of the tropical
rainforest and boreal forest can occur due to the increase of the greenhouse gases concentration. The effects were more pronounced
in the A1FI and A2 scenarios compared with the B1 scenario. The SDM results confirm IPCC AR4 projections of future climate
and are consistent with simulations of more complex GCMs, reinforcing the necessity of the mitigation of climate change associated
to global warming.
KeywordsGlobal warming–Geobotanic zones distribution–Statistical-dynamical model–Interaction between the atmosphere and vegetation
A parameterization of shortwave and longwave radiation fluxes derived from detailed radiative transfer models is included in a global primitive equation statistical-dynamical model (SDM) with two bulk atmospheric layers. The model is validated comparing the model simulations with the observed mean annual and seasonal zonally averaged climate. The results show that the simulation of the shortwave and longwave radiation fluxes matches well with the observations. The SDM variables such as surface and 500 hPa temperatures, zonal winds at 250 hPa and 750 hPa, vertical velocity at 500 hPa and precipitation are also in good agreement with the observations. A comparison between the results obtained with the present SDM and those with the previous version of the model indicates that the model results improved when the parameterization of the radiative fluxes based on detailed radiative transfer models are included into the SDM.
The SDM is used to investigate its response to the greenhouse effect. Sensitivity experiments regarding the doubling of CO2 and the changing of the cloud amount and height are performed. In the case 2×CO2 the model results are consistent with those obtained from GCMs, showing a warming of the climate system. An enhancement of the greenhouse effect is also noted when the cloud layer is higher. However, an increase of the cloud amount in all the latitude belts provokes an increase of the surface temperature near poles and a decrease in all the other regions. This suggests that the greenhouse effect overcomes the albedo effect in the polar latitudes and the opposite occurs in other regions. In all the experiments the changes in the surface temperature are larger near poles, mainly in the Southern Hemisphere.
A coupled biosphere-atmosphere statistical-dynamical model (SDM) is used to study the climatic effects of Amazonian deforestation.
A soil moisture model based on BATS has been incorporated into the SDM in order to study the biogeophysical feedback of change
in surface characteristics to regional climate due to the deforestation. In the control experiment, the mean annual and mean
seasonal climate is well simulated by the model when compared with NCEP/NCAR reanalysis data. In the deforestation experiment,
the evergreen broadleaf trees in the Amazonian region are substituted by short grass. The effects of Amazonian deforestation
on regional climate are analysed taking into account the model simulations for the land portion of the latitude belts comprising
the tropical region. Amazonian deforestation results in regional climate changes such as a decrease in evaporation, precipitation,
available surface net radiation and soil moisture content, and an increase in temperatures and sensible heat flux. The reduction
in transpiration was responsible for the most part of the decrease in total evapotranspiration. The reduction in precipitation
was larger than the decrease in evapotranspiration so that runoff was reduced. The simulation of the diurnal cycle of the
surface temperature shows an increase in temperature during the day and a decrease at night, which is in agreement with observations,
whereas earlier GCM experiments showed an increase both during the day and night. In general, the changes in temperature and
energy fluxes are in good agreement with GCM experiments, showing that the SDM is able to simulate the characteristics of
the tropical climate that are associated with the substitution of forest by pasture areas.
This paper lists selected observational and modeling studies which provide evidence that agriculture, through the transformation and management of vegetation, has had, and continues to have, an impact upon the weather and climate on the local, regional and global scales. The influence of agriculture on weather and climate, through the alteration of the physiological properties of the land cover, is illustrated by examples from the cropped grassland of the Canadian Prairies.The physiological and physical properties of the vegetation, along with the land cover's impact upon the level of available soil moisture, affect the weather and climate by influencing the transfer of heat, moisture and momentum from the land surface to the overlying air. The principle physiological properties are leaf area, stomatal resistance, and rooting depth; the main physical properties are albedo and surface roughness. By land clearing, cultivation and the grazing of domesticated animals, man has transformed and now manages the vegetation over vast areas of the globe. Agriculture influences the availability of energy and water vapour mass for moist deep convection on the local and regional scales. By creating latent heat flux discontinuities, it may induce mesoscale circulations that initiate moist deep convection. Agriculture, by affecting the level of stored soil moisture, moisture that is available to the vegetation during a later period, may influence the level of convective activity within a region during a subsequent season. Thus agriculture, through the physiological and physical properties of the land cover, has had, and continues to have, an impact upon near surface weather elements and, more significantly, upon the regional hydrologic cycle.Spatially coherent and persistent patterns of thunderstorms play a role in the export of heat and moisture from lower to higher latitudes—this may effect the general circulation. Thus agriculture, by influencing the occurrence, location and intensity of moist deep convection, particularly in the tropics, may also influence global weather and climate.
Three models are applied to estimating evapotranspiration in central Australia, using limited routine meteorological data and the NOAA-14 AVHRR overpass. By minimizing the difference between model predicted surface temperature and satellite derived temperature to adjust the estimated soil moisture, both an instantaneous physically based model and a one dimensional boundary layer simulation yielded consistent results. This highlights the sensitivity of surface temperature to soil moisture and suggests that radiometric surface temperature can be used to adjust simple water balance estimates of soil moisture providing a simple and effective means of estimating large scale evapotranspiration in remote arid regions.
Over the past few years, ecologists have increasingly recognized the existence of strong self-reinforcing (or self-organizing) interactions within systems at a variety of scales. Positive feedback within food chains has been reported from terrestrial and aquatic ecosystems. Accumulating evidence supports the existence within communities of cooperative guilds - tit-for-tat relationships based on diffuse mutualisms and favored by environmental unpredictability. At the landscape level, both real world experience and models indicate that processes such as hydrology and the propagation of disturbance can be strongly self-reinforcing (i.e. the landscape structure supports the process, and vice versa). Hence the picture emerges of a hierarchy of self-organizing systems that span food chains, communities and landscapes/regions.
Given the well-documented fact that human body proportions covary with climate (presumably due to the action of selection), one would expect that the Ipiutak and Tigara Inuit samples from Point Hope, Alaska, would be characterized by an extremely cold-adapted body shape. Comparison of the Point Hope Inuit samples to a large (n > 900) sample of European and European-derived, African and African-derived, and Native American skeletons (including Koniag Inuit from Kodiak Island, Alaska) confirms that the Point Hope Inuit evince a cold-adapted body form, but analyses also reveal some unexpected results. For example, one might suspect that the Point Hope samples would show a more cold-adapted body form than the Koniag, given their more extreme environment, but this is not the case. Additionally, univariate analyses seldom show the Inuit samples to be more cold-adapted in body shape than Europeans, and multivariate cluster analyses that include a myriad of body shape variables such as femoral head diameter, bi-iliac breadth, and limb segment lengths fail to effectively separate the Inuit samples from Europeans. In fact, in terms of body shape, the European and the Inuit samples tend to be cold-adapted and tend to be separated in multivariate space from the more tropically adapted Africans, especially those groups from south of the Sahara.
Modelos de transferência radiativa foram implementados num modelo atmosférico estatístico-dinâmico (MED) com vegetação acoplada, para simular o clima médio zonal anual e os impactos climáticos antropogênicos devido à queima da biomassa da floresta Amazônica. Em geral, este modelo foi capaz de simular o clima médio zonal anual atual, quando comparado com os dados de reanalise do National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). Os impactos observados do clima médio zonal anual continental devido à queima da biomassa da floresta Amazônica foram: redução no saldo de radiação e na radiação solar absorvida na superfície, aumento na temperatura da superfície e no saldo de radiação infravermelho termal na superfície; e o decréscimo na evapotranspiração e na precipitação. Os efeitos dos gases estufas CO2 e CH4 foram pequenos quando comparados com as alterações das características da superfície terrestre e da alteração de aerossóis de fumaça liberados para a atmosfera. ABSTRACT: Radiative transfer models were implemented in a coupled vegetation statistical dynamical atmospheric model (MED), for simulating the annual zonal mean climate and anthropogenic climate impacts due to biomass burning in Amazonian forest. In general, this model was able to simulate the present annual zonal mean climate, when compared with National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data. The observed impacts on the annual zonal mean continental climate due to biomass burning in Amazonian forest were: reduction in the net radiation and in the absorbed solar radiation at the surface, increased in the surface temperature and in the net thermal infrared radiation at the surface, increased of evapotranspiration and precipitation. The greenhouse effects CO2 and CH4 were smal when compared with the effects simulated of the changes in the land surface characteristics and in the smoke aerosols released in the atmosphere.
A zonally-averaged climate model is used for studying the seasonal variations of the Inter-Tropical Convergence Zone (ITCZ). In order to investigate the mechanisms that affects the displacement of ITCZ over different types of surface three numerical experiments were made, considering: a) the earths surface covered by the actual portions of land, ocean and snow/ice; b) the earths ocean covered only by ocean; and c) the earths surface covered only by land. The results showed that in the cases a) and b) the seasonal variation of ITCZ was around 15° latitude, and in the case c) the seasonal variation of ITCZ was larger than the other cases (around 25° latitude). It was noted that in the case of earths surface covered by ocean (land) there was a moderate (strong) seasonal inversion of the wind from wonter to summer hemisphere.
A biosphere model based on BATS (Biosphere-Atmosphere Transfer Scheme) is coupled to a primitive equation global statistical-dynamical model in order to study the climatic impact due to land surface alterations. The fraction of the earth's surface covered by each vegetation type according to HATS is obtained for each latitude belt. In the control experiment, the mean annual zonally averaged climate is well simulated when compared with observations. Deforestation and desertification experiments are performed. In the deforestation experiment, the evergreen broadleaf tree in the Amazonian region is substituted by short grass; in the desertification experiment the semidesert, and the tall grass and deciduous shrubs are substituted by desert and semidesert in the African continent, respectively. The results show that in both the experiments there is a reduction in evapotranspiration and precipitation in the perturbed region and an increase in the soil surface temperature, the temperature of the foliage air layer, and the foliage temperature. Also, the latent heat flux decreased in the perturbed cases relative to the control case. To partially compensate for the decrease in latent hearing, sensible heat flux increased in the perturbed cases compared with the control case. The changes in the deforestation case are greater in the latitude belt centered at 5 degrees S, where in most part the Amazonian forest is situated. Otherwise, the changes in the desertification are greater in the latitude belt centered at 15 degrees N. When there ic; also degradation of the African tropical forest (substitution of evergreen broadleaf trees by short grass), the greatest changes occur southward from that region tin the latitude belt centered at 5 degrees N), and the magnitude of the changes are also increased. This shows the important role of the modification of tropical forest when there is degradation of the vegetation in the African region from 20 degrees N to 0 degrees degrees. The results regarding the changes in the temperature and in the energy fluxes are in agreement with those of earlier experiments carried our with sophisticated general circulation models, which shows the usefulness of this kind of simple model. Pages: 1749-1767
A biosphere model based on the Biosphere Atmosphere Transfer Scheme (BATS) suitable for coupling with a simple climate model is described. In this model the equations of BATS are adapted to the energy flux formulations of the statistical-dynamical model developed by Franchito & Rao (Climatic Change, 22:1-34; 1992). In this work the land surface model was run to perfom sensitivity tests regarding the behaviour of the model variables with respect to prescribed model parameters and contrasting vegetation types, such as evergreen broadleaf forest and short grass. The results show that the soil surface temperature increases with the decrease of the fractional area of vegetation cover due to the lower surface solar radiation flux absorption in both types of vegetation. As the water interception increases the wet foliage air layer prevents the evaporation of the soil water, so that there is an increase of the ground surface temperature. The surface temperature is lower in the forest than in the case of short grass due to the surface roughness effect. In the case of dry soil the available energy increases with the increase of the fractional area of vegetation cover because the latent heat flux increases quickly and the sensible heat flux decreases slowly. In the situation of fully wet soil the available energy dependence on the interception is reduced due to the effect of water evaporation at the ground surface that increases the latent heat flux, even if the interception is small or nil. A factor z is inserted in the expression that gives the fractional area of the leaf canopy cover by water in order to take into account the effect of the part of vegetation predominantly porous. The lower values of z give better results regarding the component terms of the evapotranspiration. However, the total flux of water vapor to atmosphere does not change with z. Sensitivity tests are made with respect to the factor Y introduced in the expression of the water vapor flux to the atmosphere in order to adjust the partitioning of the available energy into latent and sensible heat. The results show that the latent (sensible) heat increases (decreases) with the increase in Y. Although the variation of Y modifies the Bowens ratio there is no change of the evapotranspiration partitioning into its components. RESUMO: Um modelo de biosfera baseado no esquema BATS (Biosphere Atmosphere Transfer Scheme) útil para ser acoplado a um modelo climático simples é descrito. Neste modelo as equações do esquema BATS são adaptadas às formulações dos fluxos de energia do modelo estatístico-dinâmico desenvolvido por Franchito & Rao (Climatic Change, 22: 1-34; 1992). Neste trabalho, o modelo de processos de superfície foi rodado para realizar testes de sensibilidade referentes ao comportamento das variáveis do modelo com respeito a parâmetros prescritos e tipos de vegetação contrastantes, tais como floresta perenifólia e gramíneas. Os resultados mostraram que a temperatura da superfície do solo aumenta com o decréscimo da fração da cobertura vegetal devido à menor absorção do fluxo de radiação solar na superfície em ambos os tipos de vegetação. À medida que a interceptação aumenta a camada de ar na folhagem úmida impede a evaporação de água no solo, de forma que há um aumento da temperatura da superfície do solo. A temperatura da superficie é menor sob a floresta perenifólia do que sob gramíneas baixas devido ao efeito da rugosidade da superfície. No caso de solo seco a energia disponível aumenta quanto maior for a fração de cobertura vegetal pois o fluxo de calor latente aumenta rapidamente enquanto que o fluxo de calor sensível reduz-se mais lentamente. Na situação de solo plenamente abastecido de água, a dependência da energia disponível em relação à interceptação diminui devido ao efeito da evaporação de água à superfície do solo, a qual aumenta o fluxo de calor latente mesmo que a interceptação é pequena ou nula. Um fator z foi inserido na expressão referente à fração da folhagem coberta pela água interceptada para levar em conta o efeito da parte da vegetação predominantemente porosa. Melhores resultados dos cálculos dos termos componentes da evapotranspiração foram obtidos com menores valores de z. Contudo, o fluxo total de vapor dágua para a atmosfera não se altera com z. Foram realizados testes de sensibilidade com respeito ao fator Y, introduzido na expressão do fluxo de vapor dágua para a atmosfera para ajustar a partição da energia disponível em calor sensível e latente. Os resultados mostraram que o fluxo de calor latente (sensível) aumenta (decresce) quanto maior for Y. Embora a variação de Y modifica a razão de Bowen, não há alteração na partição da evapotranspiração em seus termos componentes. Pages: 191-208
A primitive equation global zonally averaged general circulation model is used to study the effects of the topography on the atmospheric annual cycle. A smoothed zonally averaged topography that has a form similar to that observed was used. The control experiment showed that the model was capable of capturing the zonally averaged behavior of the annual cycle. The model is able to capture some characteristics of the monsoonlike circulation such as the seasonal wind reversal and the easterly jet in the boreal summer. Even in the absence of topography the model was able to reproduce the monsoonlike features. However, the circulation was weak and the position of its components was altered. This suggests that the topography has an important role in modifying the intensity and position of the monsoon circulation. Sensitivity tests were made in order to investigate the effects of high elevation and its steep southern slope. Two experiments were performed: 1) increasing the elevation of orography without changing the steepness of the slope, and 2) increasing both the elevation and the steepness of the slope. The results indicated that the steepness of the southern slope seems to control the monsoonlike flow in the model. The model was also capable of reproducing a monsoonlike response to changed external conditions. When the values of the earths orbital parameters (precession, obliquity, and eccentricity) were changed to those of 9000 yr BP, the precipitation and circulation intensified, which seems to agree with paleoclimatic evidence Pages: 779-794
A method is suggested for introducing long-term interaction between the
geobotanic state and climate (a biogeophysical feedback mechanism) into
climate models. It is based upon making the geobotanic state,
characterized by the snow-free surface albedo and the water availability
parameter, dependent upon the ratio of annual radiation balance to
annual precipitation (the so-called radiative index of dryness).This
approach is illustrated using a zonally averaged annual steady-state
climate model which is based on the hemispheric climate model of Ohring
and Adler. Zonal data statistics are employed to obtain simple
relationships consistent with the zonality of the system. The heating
parameterization of the original model is modified so that precipitation
and cloud amount are computed using vertical velocity at 500 mb, which
is calculated from the thermodynamic equation.Experiments with the model
indicate that the simulated climate and geobotanic zones are in good
agreement with observations. Sensitivity studies suggest that
biogeophysical feedback has a negligible effect on the model's response
to solar constant variations but may be important in the evaluation of
the long-term impact of surface albedo changes.
OF the various mechanisms suggested by which man might change the planetary climate, the removal of tropical rain forests to increase arable acreage seems to be one of the more imminent. For this reason we selected this as one of the first problems to be tested in our recently updated climate model. Bearing in mind the fallibility of computer simulations, we find overall global cooling and a reduction in precipitation: a larger tropical reduction being almost balanced by a subtropical increase.
Improving the realism and accuracy of the GLAS general circulation model (by adding an interactive biosphere that will simulate the transfers of latent and sensible heat from land surface to atmosphere as functions of the atmospheric conditions and the morphology and physiology of the vegetation) is proposed.
A zonally-averaged steady-state hemispheric mean-annual climate model is used for conducting a series of experiments on land surface alterations: desertification, deforestation and irrigation. In each experiment a fixed perturbation of surface albedo and water availability is imposed in a single latitude belt. The desertification and deforestation experiments simulate modifications to the geobotanic state due to destruction of vegetation by overgrazing and excessive cultivation of the land in the semiarid and tropical zones, respectively. The irrigation experiment simulates the climatic impact of massive irrigation of the desert belt. -from Author
The observation program of the International Geophysical Year has provided new meteorological data that have made possible more precise computations of the heat balance of the earth. Greater accuracy has also been achieved through improvement or computation methods. Using data for 2,000 stations, including 300 points in ocean areas, the authors have constructed world maps for major components of the heat balance. From these maps they have derived mean latitudinal values of the components (radiation balance, loss of heat in evaporation, turbulent heat exchange, redistribution of heat through ocean currents). The findings have been generalized for continents, oceans and the earth as a whole.
The article discusses the present state of knowledge of the basic components of the heat balance of the earth's surface (radiation balance, loss of heat to evaporation, turbulent heat exchange) and the distribution of these components in time and space. Soviet research is concerned with applying heat-balance data to the study of physical-geographical processes (hydrologic regime, plant and soil cover), to the study of integrated geographic problems (geographic zonality) and practical problems (weather and hydrologic forecasting, the use of solar energy for productive purposes, and the use of heat-balance data for planning reclamation projects and other nature-transforming measures.)
A simple method for integrating the primitive equations is presented which allows for a timestep increment up to twice that of the conventional leapfrog scheme. It consists of a time-averaging operator, which incorporates three consecutive time levels, on the pressure gradient terms in the equations of motion. An attractive feature of the method is its case in programming, since the resulting finite-difference equations can he solved explicitly. Presented here are linear analyses of the method applied to the barotropic and two-layer baroclinic gravity waves. Also presented is an analysis of the method with a time-damping device incorporated, which is an alternative in controlling linearly amplifying computational modes.
Inclusion of a land-surface scheme with a vegetation canopy into a version of the NCAR Community Climate Model (CCM) with a diurnal as well as a seasonal cycle permits an exploratory study of the possible effects of tropical deforestation. In a 13-month integration that assumes that all of the Amazon tropical forest in South American is replaced by impoverished grassland, surface hydrological and temperature effects dominate the response. Reduced mixing and less interception and evaporation from the canopy cause runoff to increase and surface temperatures to rise by 3-5 K. The period of driest soil is increased in the model from one month to several, but the possibility that this change is random cannot be excluded. Increased temperatures and drier soil could have a detrimental impact on survival of the remaining forest and on attempts at cultivation in deforested areas. -from Authors
Solutions previously obtained for the zonally averaged climate of the
northern hemisphere are extended to cover the southern hemisphere. In
addition to the specification of the new surface state parameters for
the southern hemisphere, some new parameterizations and improved data
for parameters are introduced. The new solutions contain the main
features of the southern hemisphere zonal climatic distribution,
including the double maximum in the mean zonal current, but the fact
that some details are still in conflict with observation indicates a
continued need for improvement of the model.
A zonally-averaged steady-state hemispheric mean-annual climate model is
used for conducting a series of experiments on land surface alterations:
desertification, deforestation and irrigation. In each experiment a
fixed perturbation of surface albedo and water availability is imposed
in a single latitude belt (but a different perturbation is specified in
each experiment). The desertification and deforestation experiments
simulate modifications to the geobotanic state due to destruction of
vegetation by overgrazing and excessive cultivation of the land in the
semiarid and tropical zones, respectively. The irrigation experiment
simulates the climatic impact of massive irrigation of the desert
belt.Results indicate that the effect of changes in evapotranspiration
rather than in surface albedo is predominant in regulating the surface
temperature. It is shown that the impact of biofeedback is strongest in
the area adjacent to the perturbation zone. It is also concluded that
the prescribed perturbations of the geobotanic state are not sufficient
to modify climate to an extent that these perturbations would persist.
A hierarchy of zonally averaged atmospheric models is used to study the
role of mean meridional motions and large-scale eddies in determining
the zonal climate. Five models are developed: a radiative-convective
equilibrium model (no large-scale motion), a zonally uniform model (no
longitudinal asymmetries), an energy balance model (parameterized energy
transport), a model that combines the physics of the two previous
models, and a full statistical-dynamic model (with parameterizations of
eddy momentum transport as well as eddy sensible heat transport).In the
most complete model, the zonally averaged primitive equations are solved
after parameterizing the eddies, friction and the diabatic heating
rates. All the models have two layers in the vertical and a latitudinal
grid resolution of 5°. For simplicity, we treat a `dry earth' case
and calculate annual-average equilibrium states with each of the five
models.We find that in the tropics a parameterized energy transport
commonly used in energy balance models does not accurately simulate the
energy transport as determined by an explicit calculation of the Hadley
cell. The explicitly calculated Hadley transport is generally greater
than the parameterized transport and leads to very small horizontal
temperature gradients in the tropics. The strength of the Hadley cell is
determined by both the local heating distribution and extratropical heat
and momentum transport by the eddies. The extratropical mean meridional
motions are primarily driven by the requirements of the momentum budget.
An indirect (Ferrel) cell appears only when eddy momentum transport is
included in the model.
A global climatic model, allowing for seasonal coupling and interaction
between continents and oceans, is developed, utilizing an idealized
land-water distribution similar to that observed. The basic equation
used is the thermodynamic energy equation averaged over time and space.
It is written and solved for the mean surface temperature separately for
continents and oceans. A time step of one month is used. The vertical
variations of temperature, specific humidity, and the zonal and
meridional components of the wind velocity are parameterized. The
surface velocity components are obtained from modified forms of the
first two equations of motion. The model includes variable snow and ice
cover, meridional transport of heat and water vapor by mean and eddy
atmospheric circulations, storage and transport of heat by the oceans,
the effect of aerosols on atmospheric turbidity, and the contribution of
H2O, CO2, O3, and clouds to the
infrared balance. Cloud cover, the surface relative humidity, and the
surface albedo of snow- and ice-free areas are specified.Using present
values for the input parameters, the model reproduces quite well several
of the major thermal and dynamic characteristics of the earth-atmosphere
system. It is very sensitive to variations of the optical thickness of
the atmosphere and of the solar constant. Slight changes in these
variables greatly modify the surface temperature field, especially at
high latitudes of the Northern Hemisphere. There is some indication of
the existence of at least two possible steady-state climates with the
same set of input parameters.
A simple, zonally averaged numerical model is developed for simulating
certain features of the annual mean climate of the Northern Hemisphere.
The model is based on the two-level quasi-geostrophic potential
vorticity system of equations and a surface beat balance equation. Ale
main output consists of the latitudinal variations of temperature at the
surface and 500 mb and of zonal wind at 250 and 750 mb. Meridional
transport of quasi-geostrophic potential vorticity is simulated by an
eddy ~ process using exchange coefficients based on observational data.
Solar radiative processes included are absorption by water vapor, ozone
and cloud particles, scattering by air molecules and clouds, and
reflection by the surface. Longwave radiative processes include
absorption and emission by water vapor, carbon dioxide and clouds. Other
beat transfer processes-convection, evaporation, condensation and ocean
currents-are pammeterized.Using present boundary conditions, the model
is used to compute the present climate. Comparison of the computed
climate with the observed climate shows good agreement. A special
attempt is made to compare some of the radiation quantities computed by
the model with satellite observations and radiation budget
calculations.The sensitivity of the computed climate to changes in some
of the boundary conditions is investigated. These sensitivity
experiments are performed with and without an ice feedback mechanism.
The ice feedback mechanism is based on empirical relations between the
fractions of a latitude belt covered by snow and ice in winter and
slimmer and the mean annual surface temperature. When the atmospheric
carbon dioxide content is doubled, the hemispheric mean surface
temperature increases by 0.5°C in the absence of ice feedback, the
largest increases taking place at high latitudes. Ice albedo feedback
amplifies the hemispheric average temperature change by about 50%;
amplifications as large as several hundred percent are obtained in polar
regions. A change in mean surface temperature of ±1°C for a
±1% change in solar constant is obtained in the absence of ice
feedback, but this is amplified to 1.5°C (decreased solar constant)
and 1.4°C (increased solar constant) when ice feedback is included.
As In the 2×CO2 case, polar amplification factors due
to ice albedo feedback are several hundred percent. When hemispheric
cloud amount is increased, the surface temperature decreases but in the
absence of ice feedback the magnitude of the change approaches zero near
the poles. A hemispheric increase in the altitude of the cloud layer
causes an increase in surface temperatures. These results are compared
with those obtained with other climate models.
The heat budget of the Walker circulation near 10°S is studied. The
primary drive for the circulation is the heating due to zonal variations
in condensation. The relative heating and cooling at different
longitudes is balanced approximately by adiabatic cooling and heating
due to rising and sinking motions. In the region where the condensation
heating is a maximum two different analyses indicate that the
evaporation is a minimum, even though the sea surface temperature is a
maximum. This is because the surface heating is dominated by the
insolation, which is a minimum in the region of enhanced condensation
where the cloud cover is a maximum. This implies that the region of
enhanced condensation is associated with a region of moisture
convergence rather than with a region of enhanced evaporation, and that
the sea surface temperature gradients only play a secondary role in
forcing the Walker circulation.
Charney's (1975) suggestion that high desert albedo initiates a biogeophysical positive feedback response by the atmosphere has been tested in the 2-D zonal atmospheric model, ZAM2. The results agree with the earlier test in the NASA GISS 3-D GCM model (Charney et al. 1975) in confirming a positive feedback through precipitation but indicate a negative feedback in terms of temperature. The latter suggests that tropical deserts may play a role in air conditioning or placing an upper-bound on the temperature of our planet.
Equations governing the axially-symmetric time-average state of the atmosphere and the transient departures from this mean state are set down. As a first step toward a solution of this system for seasonal average conditions, a model is formulated based on the thermodynamical energy equation for the vertical average of the mean state, and on the perturbation solutions of the linearized equations governing the baroclinic growth of transient eddies. All forms of non-adiabatic heating within the atmosphere and at the earth's surface are parameterized. The resulting differential equation governing the axially-symmetric mean potential temperature distribution takes the form of a steadystate diffusion equation in surface spherical coordinates, with a variable Austausch coefficient which is to be determined iteratively as a dependent variable.
Global solutions, for winter and summer equilibrium conditions, are obtained for the thermal structure, the heat balance components, the transient eddy variances of temperature and meridional wind speed, and the covariance representing the meridional eddy heat transport. These solutions are for different types of surface conditions (ocean, land), and for a successively more complete variety of modes of heat transfer ranging from pure radiation to a combination of radiation, latent heat processes, and conduction and convection within the atmosphere and the subsurface layers. The results for this latter complete case seem to be a reasonable first order approximation to the observed distributions. Suggestions are made for improving and generalizing the study.
General Circulation Models (GCMs) by definition calculate large-scale dynamical and thermodynamical processes and their associated feedbacks from first principles. This aspect of GCMs is widely believed to give them an advantage in simulating global scale climate changes as compared to simpler models which do not calculate the large-scale processes from first principles. However, it is pointed out that the meridional transports of heat simulated GCMs used in climate change experiments differ from observational analyses and from other GCMs by as much as a factor of two. It is also demonstrated that GCM simulations of the large scale transports of heat are sensitive to the (uncertain) subgrid scale parameterizations. This leads to the question whether current GCMs are in fact superior to simpler models for simulating temperature changes associated with global scale climate change.
Earth macroclimate mean zonally averaged state equilibrium solution, using thermohydrodynamic equations
A simple realistic biosphere model for calculating the transfer of energy, mass and momentum between the atmosphere and the vegetated surface of the earth has been developed for use in atmospheric general circulation models. The vegetation in each terrestrial model grid is represented by an upper level, representing the perennial canopy of trees and shrubs, and a lower level, representing the annual cover of grasses and other heraceous species. The vegetation morphology and the physical and physiological properties of the vegetation layers determine such properties as: the reflection, transmission, absorption and emission of direct and diffuse radiation; the infiltration, drainage, and storage of the residual rainfall in the soil; and the control over the stomatal functioning. The model, with prescribed vegetation parameters and soil interactive soil moisture, can be used for prediction of the atmospheric circulation and precipitaion fields for short periods of up to a few weeks.
Physical Climatology: 1973, ~k New Climate Model
- H Sergio
- V Franchito
- W D Brahmananda Rao Sellers
Sergio H. Franchito and V. Brahmananda Rao Sellers, W. D.: 1965, Physical Climatology, University of Chicago Press, 272 pp. Sellers, W. D.: 1973, ~k New Climate Model', J. AppL Meteor. 12, 241-254.
Vegetation of the Earth and Ecological Systems of the Geo-Biosphere
- H Walter
Atmospheric Analysis and Prediction Division
- R E Dickinson
- A Henderson-Sellers
- P J Kennedy
- M F Wilson
Balancing the Global Heat Budget?
- M I Budyko