Author: Weile Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 402
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Book Description
Abstract: Terrestrial vegetation exerts an important influence on climate variability via the exchange of mass, energy, and momentum between the land surface and the atmosphere. This dissertation uses statistical techniques and stochastic models to investigate large scale vegetation/climate interactions in remotely-sensed vegetation datasets and observational climate records. Vegetation feedbacks on climate variability over the North American Grasslands are evaluated by the methodology of Granger causality, which examines statistical causal relationships in a coupled system. Results indicate that positive vegetation anomalies earlier in the growing season significantly "Granger cause" lower rainfall (and higher temperatures) later in summer. Coupled with the positive influence of precipitation on vegetation, these interactions suggest an oscillatory variability of vegetation, which is identified in observations. The observed vegetation-precipitation covariability is then simulated using a coupled stochastic model, which is derived from eco-hydrological principles in a semiarid environment. The model demonstrates that vegetation/precipitation interactions have distinct frequency characteristics, and are oscillatory at intraseasonal time scales, in agreement with observations. The model also indicates that this oscillatory behavior arises because enhanced vegetation depletes soil moisture faster than normal, which induces drier and warmer climate anomalies via the strong soil-moisture/precipitation coupling in this region. Extended analyses also identify intraseasonal oscillatory variability in vegetation anomalies over the boreal forests. This characteristic variability is likely induced by interactions between vegetation and temperature, which maintain a climatological thermal balance within the soil and the lower boundary layer of the atmosphere via the removal of excess heat from the surface through enhanced evapotranspiration. The cooling effect of vegetation on temperature is detected by Granger causality analyses, and is found to be most significant over the boreal forests in lower and central Siberia. Altogether, the findings of this dissertation highlight the role vegetation plays in regulating the water cycle and the energy balance between the surface and the atmosphere. These results present observational evidence for large-scale vegetation feedbacks, and also reveal important characteristics of the vegetation-climate system that deserve further investigation in the future.
Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 846
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Author: Gestal Pose, Marcos
Publisher: IGI Global
ISBN: 1615208941
Category : Computers
Languages : en
Pages : 452
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Book Description
"This publication presents a series of practical applications of different Soft Computing techniques to real-world problems, showing the enormous potential of these techniques in solving problems"--Provided by publisher.
Author: A. Henderson-Sellers
Publisher: Springer Science & Business Media
ISBN: 940113264X
Category : Science
Languages : en
Pages : 237
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Book Description
The chapters in this section place the problems of vegetation and climate interactions in semi-arid regions into the context which recur throughout the book. First, Verstraete and Schwartz review desertification as a process of global change evaluating both the human and climatic factors. The theme of human impact and land management is discussed further by Roberts whose review focuses on semi-arid land-use planning. In the third and final chapter in this section we return to the meteorological theme. Nicholls reviews the effects of El Nino/Southern Oscillation on Australian vegetation stressing, in particular, the interaction between plants and their climatic environment. Vegetatio 91: 3-13, 1991. 3 A. Henderson-Sellers and A. J. Pitman (eds). Vegetation and climate interactions in semi-arid regions. © 1991 Kluwer Academic Publishers. Desertification and global change 2 M. M. Verstraete! & S. A. Schwartz ! Institute for Remote Sensing Applications, CEC Joint Research Centre, Ispra Establishment, TP 440, 1-21020 Ispra (Varese), Italy; 2 Department of Atmospheric, Oceanic and Space Sciences, The University of Michigan, Ann Arbor, MI48109-2143, USA Accepted 24. 8. 1990 Abstract Arid and semiarid regions cover one third of the continental areas on Earth. These regions are very sensitive to a variety of physical, chemical and biological degradation processes collectively called desertification.
Author: Gregory R. Quetin
Publisher:
ISBN:
Category :
Languages : en
Pages : 141
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Book Description
The natural composition of terrestrial ecosystems can be shaped by climate to take advantage of local environmental conditions. Ecosystem functioning, e.g. interaction between photosynthesis and temperature, can also acclimate to different climatological states. The combination of these two factors thus determines ecological-climate interactions. The ecosystem functioning also plays a key role in predicting the carbon cycle, hydrological cycle, terrestrial surface energy balance, and the feedbacks in the climate system. Predicting the response of the Earth's biosphere to global warming requires the ability to mechanistically represent the processes controlling ecosystem functioning through photosynthesis, respiration, and water use. The physical environment in a place shapes the vegetation there, but vegetation also has the potential to shape the environment, e.g. increased photosynthesis and transpiration moisten the atmosphere. These two-way ecoclimate interactions create the potential for feedbacks between vegetation at the physical environment that depend on the vegetation and the climate of a place, and can change throughout the year. In Chapter 1, we derive a global empirical map of the sensitivity of vegetation to climate using the response of satellite-observed greenness to interannual variations in temperature and precipitation. We infer mechanisms constraining ecosystem functioning by analyzing how the sensitivity of vegetation to climate varies across climate space. Our analysis yields empirical evidence for multiple physical and biological mediators of the sensitivity of vegetation to climate at large spatial scales. In hot and wet locations, vegetation is greener in warmer years despite temperatures likely exceeding thermally optimum conditions. However, sunlight generally increases during warmer years, suggesting that the increased stress from higher atmospheric water demand is offset by higher rates of photosynthesis. The sensitivity of vegetation transitions in sign (greener when warmer or drier to greener when cooler or wetter) along an emergent line in climate space with a slope of about 59 mm/yr/C, twice as steep as contours of aridity. The mismatch between these slopes is evidence at a global scale of the limitation of both water supply due to inefficiencies in plant access to rainfall, and plant physiological responses to atmospheric water demand. This empirical pattern can provide a functional constraint for process-based models, helping to improve predictions of the global-scale response of vegetation to a changing climate. In Chapter 2, we use observations of vegetation interaction with the physical environment to identify where ecosystem functioning is well simulated in an ensemble of Earth system models. We leverage this data-model comparison to hypothesize which physiological mechanisms - photosynthetic efficiency, respiration, water supply, atmospheric water demand, and sunlight availability - dominate the ecosystem response in places with different climates. The models are generally successful in reproducing the broad sign and shape of ecosystem function across climate space except for simulating generally lower leaf area during warmer years in places with hot wet climates. In addition, simulated ecosystem interaction with temperature is generally larger and changes more rapidly across a gradient of temperature than is observed. We hypothesize that the amplified interaction and change are both due to a lack of adaptation and acclimation in simulations. This discrepancy with observations suggests that simulated responses of vegetation to global warming, and feedbacks between vegetation and climate, are too strong in the models. Finally, models and observations share an abrupt threshold between dry regions and wet regions where strong positive vegetation response to precipitation falls to nearly zero in places receiving around 1000 mm/year. In Chapter 3, we investigate how ecoclimate interactions change across seasons in the Amazon basin. We use observations of solar induced fluorescence from the Orbiting Carbon Observatory 2 (OCO2) to statistically analyze the sensitivity of fluorescence to synoptic variations in temperature and precipitation. In addition to studying the sensitivity of vegetation to climate across seasons, we use OCO2 measurements of total column water vapor (TCWV) and CO2 concentration (XCO2) to investigate the influence of the Amazon basin vegetation on the CO2 concentration and water vapor of the atmosphere leaving the basin. Our analysis determines the seasonal importance of vegetation activity on the outflow of CO2 from the Amazon basin, while providing evidence that transpiration is primarily driven by variations in temperature during the dry season, rather than photosynthesis. We establish a statistical relationship between fluorescence (as a proxy for vegetation photosynthesis), temperature, and precipitation, as well as the difference between the outflow of atmospheric water vapor from the inflow water vapor, basin fluorescence, temperature, and precipitation.
Author: Lucy Gelb
Publisher:
ISBN:
Category : Biogeography
Languages : en
Pages : 93
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Book Description
"The distribution of vegetation in water-limited ecosystems is a product of complex and nonlinear interactions between climatic forcings (e.g., precipitation, temperature, solar radiation) and the underlying geomorphic template, which includes topography, geology, and soils. Changes in climate, particularly in precipitation and temperature, can dramatically alter the organization of vegetation. This is especially true in ecotones such as our area of study: the semi-arid transition between Great Basin shrub-steppe ecosystems and the coniferous forests of the Northern Rockies. Understanding and predicting how the spatial composition of terrestrial vegetation communities will change in these ecosystems is critical to predicting important future landscape changes such as landslides, erosion, fires, and water storage capacity. This study promotes understanding of the relative sensitivity of vegetation types to changes in weather and climate in water-limited environments using a land modeling framework. Specifically, we use the Landlab framework to develop and conduct a suite of numerical experiments that use ensemble methods to diagnose how changes in precipitation and temperature regimes affect the organization of plant functional types across varying hillslope aspects. This methodology yielded a broader perspective than previous studies that rely on analysis of deterministic runs, including detailed information about the variation within the results of each climate scenario we modeled. The impact of topographic variation such as changes in elevation or aspect are not not the same for temperature and precipitation, and understanding the relative importance of each is useful when extending the implications of results from this study to varying real-world locations. We synthesized a watershed using Landlab́09s landscape evolution capabilities to produce a topographic setting with contrasting hillslope aspects and randomly seeded vegetation (trees, shrubs, grasses, and bare soil). We then allowed that initial vegetation distribution to equilibrate to climatic conditions broadly consistent with contemporary climate. We then subjected the output distribution of vegetation to a perturbed climate, created by interpolating a group of Coupled Model Inter-Comparison Project 5 (CMIP5) climate projections that were downscaled using the Multivariate Adaptive Constructed Analogs (MACA) method to the approximate elevation of the site. We designed a suite of numerical experiments that investigated the sensitivity of the distribution of vegetation to changes in precipitation and temperature independently, as well as the combined effects of changes in both. To examine the sensitivity of vegetation composition to individual realizations of precipitation and temperature time series, and therefore the robustness of any conclusions about changes in vegetation composition to climate, we took an ensemble approach with all simulations in which five-hundred realizations of precipitation and temperature forcings consistent with the altered climate were used to drive the climate change scenarios. We then investigated the probability density functions of the distribution of tree, shrub, grass, and bare soil coverage across aspects and simulations. Regardless of scenario, we find that vegetation patterns on north-facing slopes were constant regardless of changes to precipitation or temperature alone. By contrast, vegetation patterns on south-facing slopes were sensitive to changes in both precipitation and temperature. In climate scenarios with reduced precipitation, the percentage of area covered by trees declined on south-facing slopes, while shrub coverage increased to fill areas vacated by trees. Temperature exacerbated this trend. A climate scenario with low precipitation and high temperatures had the lowest recorded tree cover on south-facing slopes, though high precipitation negated the effects of temperature. Using the Landlab framework allowed us to rapidly develop an effective model of the relative sensitives of vegetation types and conclude that precipitation is the most important variable with regard to forest replacement by grasses and shrubs in response to climate change. It is important to underscore, however, that the modeling framework used does not currently include key biogeochemical processes known to influence semi-arid ecosystems. As such, this study cannot examine nutrient limitations in these semi-arid ecosystems. This suggests a potential avenue for future study that leverages the modeling framework and approach taken here."--Boise State University ScholarWorks.
Author: Jake F. Weltzin
Publisher: University of Arizona Press
ISBN: 9780816522477
Category : Science
Languages : en
Pages : 264
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Book Description
By the beginning of the twenty-first century, few people could deny the reality of global change. But while most alarm has been over increasing temperatures, other changes are occurring in precipitation patternsÑvariations that may be due in part to global warming but also to factors such as changes in atmospheric circulation and land surfaces. This volume provides a central source of information about this newly emerging area of global change research. It presents ongoing investigations into the responses of plant communities and ecosystems to the experimental manipulation of precipitation in a variety of field settingsÑparticularly in the western and central United States, where precipitation is already scarce or variable. By exploring methods that can be used to predict responses of ecosystems to changes in precipitation regimes, it demonstrates new approaches to global change research and highlights the importance of precipitation regimes in structuring ecosystems. The contributors first document the importance of precipitation, soil characteristics, and soil moisture to plant life. They then focus on the roles of precipitation amount, seasonality, and frequency in shaping varied terrestrial ecosystems: desert, sagebrush steppe, oak savanna, tall- and mixed-grass prairie, and eastern deciduous forest. These case studies illustrate many complex, tightly woven, interactive relationships among precipitation, soils, and plantsÑrelationships that will dictate the responses of ecosystems to changes in precipitation regimes. The approaches utilized in these chapters include spatial comparisons of vegetation structure and function across different ecosytems; analyses of changes in plant architecture and physiology in response to temporal variation in precipitation; experiments to manipulate water availability; and modeling approaches that characterize the relationships between climate variables and vegetation types. All seek to assess vegetation responses to major shifts in climate that appear to be occurring at present and may become the norm in the future. As the first volume to discuss and document current and cutting-edge concepts and approaches to research into changing precipitation regimes and terrestrial ecosystems, this book shows the importance of developing reliable predictions of the precipitation changes that may occur with global warming. These studies clearly demonstrate that patterns of environmental variation and the nature of vegetation responses are complex phenomena that are only beginning to be understood, and that these experimental approaches are critical for our understanding of future change.
Author: Marc Pace Marcella
Publisher:
ISBN:
Category :
Languages : en
Pages : 282
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Book Description
This dissertation describes the role of land surface processes in shaping semi-arid climates, namely those of Southwest Asia and Northwest Africa. The interactions between dust emissions, irrigation, and climate processes are studied and quantified using a regional climate model to perform a series of carefully designed numerical experiments. The performance of the numerical model is tested by comparing simulation results against observations from satellites and other standard platforms. Modeling results indicate significant improvements in simulating mineral aerosols over Southwest Asia. Results suggest that including representations for sub-grid scale wind gustiness as well as mineral aerosols at the boundaries, improve the model skill in simulating the spatial distribution and magnitude of suspended dust. Over Southwest Asia, a large bias in original simulations of surface temperature is eliminated by improving surface albedo, and including mineral aerosols and irrigation. These modifications reduced other biases associated with simulated surface shortwave incident radiation, surface absorbed radiation, and surface vapor pressure. As a result of these improvements, the model now successfully reproduces the climate of Southwest Asia. Another set of numerical experiments is performed over West Africa focusing on the same processes of dust emissions and irrigation. Over the Sahel region, it is found that both mineral aerosols and irrigation have similar effects on the surrounding climate: cooling of surface temperature, increased surface humidity, but no change in rainfall. With dust, a shallower boundary layer redistributes moisture closer to the surface thus offsetting negative temperature effects on the boundary layer moist static energy. With irrigation, a large reduction of the boundary layer height results in less triggering of convective activity and hence mitigates any increase in convective rainfall efficiency due to irrigation. Lastly, a numerical simulation over West Africa that includes simultaneous representations of dust emissions and irrigation is analyzed. Increased soil moisture, vegetation coverage, and dry deposition due to irrigation result in decreased emissions and suspension of dust. This experiment revealed an additional feedback due to irrigation: warming of the surface temperature due to a reduction in mineral aerosols concentration.
Author: Ashish Sharma
Publisher:
ISBN:
Category : Arid regions climate
Languages : en
Pages : 130
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Book Description
This study performs numerical modeling for the climate of semi-arid regions by running a high-resolution atmospheric model constrained by large-scale climatic boundary conditions, a practice commonly called climate downscaling. These investigations focus especially on precipitation and temperature, quantities that are critical to life in semi-arid regions. Using the Weather Research and Forecast (WRF) model, a non-hydrostatic geophysical fluid dynamical model with a full suite of physical parameterization, a series of numerical sensitivity experiments are conducted to test how the intensity and spatial/temporal distribution of precipitation change with grid resolution, time step size, the resolution of lower boundary topography and surface characteristics. Two regions, Arizona in U.S. and Aral Sea region in central Asia, are chosen as the test-beds for the numerical experiments: The former for its complex terrain and the latter for the dramatic man-made changes in its lower boundary conditions (the shrinkage of Aral Sea). Sensitivity tests show that the parameterization schemes for rainfall are not resolution-independent, thus a refinement of resolution is no guarantee of a better result. But, simulations (at all resolutions) do capture the inter-annual variability of rainfall over Arizona. Nevertheless, temperature is simulated more accurately with refinement in resolution. Results show that both seasonal mean rainfall and frequency of extreme rainfall events increase with resolution. For Aral Sea, sensitivity tests indicate that while the shrinkage of Aral Sea has a dramatic impact on the precipitation over the confine of (former) Aral Sea itself, its effect on the precipitation over greater central Asia is not necessarily greater than the inter-annual variability induced by the lateral boundary conditions in the model and large scale warming in the region. The numerical simulations in the study are cross validated with observations to address the realism of the regional climate model. The findings of this sensitivity study are useful for water resource management in semi-arid regions. Such high spatio-temporal resolution gridded-data can be used as an input for hydrological models for regions such as Arizona with complex terrain and sparse observations. Results from simulations of Aral Sea region are expected to contribute to ecosystems management for Central Asia.
Author: Sietse Oene Los
Publisher:
ISBN:
Category : Climatic changes
Languages : en
Pages : 214
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Book Description
This dissertation deals with temporal and spatial variations in the biosphere observed by satellite and the linkages of these variations with variations in the global climate. The study is part of a larger Earth Observing System (EOS) Interdisciplinary Science (IDS) Biosphere-Atmosphere Interactions project that deals with the implications of these interactions of biosphere-atmosphere interactions for the global carbon cycle. For this dissertation, both model results and observations were used.
