Showing papers in "Earth Interactions in 2009"

Twentieth-Century Droughts and Their Impacts on Terrestrial Carbon Cycling in China

Abstract: Midlatitude regions experienced frequent droughts during the twentieth century, but their impacts on terrestrial carbon balance are unclear. This paper presents a century-scale study of drought effects on the carbon balance of terrestrial ecosystems in China. The authors first characterized the severe extended droughts over the period 1901–2002 using the Palmer drought severity index and then examined how these droughts affected the terrestrial carbon dynamics using tree-ring width chronologies and a process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM). It is found that China suffered from a series of severe extended droughts during the twentieth century. The major drought periods included 1920–30, 1939–47, 1956–58, 1960–63, 1965–68, 1978–80, and 1999–2002. Most droughts generally reduced net primary productivity (NPP) and net ecosystem productivity (NEP) in large parts of drought-affected areas. Moreover, some of the droughts substantially reduced the countrywide annual NPP...

Measuring Woody Encroachment along a Forest–Savanna Boundary in Central Africa

Abstract: Changes in net area of tropical forest are the sum of several processes: deforestation, regeneration of previously deforested areas, and the changing spatial location of the forest–savanna boundary. The authors conducted a long-term (1986–2006) quantification of vegetation change in a 5400 km2 forest–savanna boundary area in central Cameroon. A cross-calibrated normalized difference vegetation index (NDVI) change detection method was used to compare three high-resolution images from 1986, 2000, and 2006. The canopy dimensions and locations of over 1000 trees in the study area were measured, and a very strong relationship between canopy area index (CAI) and NDVI was found. Across 5400 km2 12.6% of the area showed significant positive change in canopy cover from 1986 to 2000 (0.9% yr−1) and 7.8% from 2000 to 2006 (1.29% yr−1), whereas <0.4% of the image showed a significant decrease in either period. The largest changes were in the lower canopy cover classes: the area with <0.2 m2 m−2 CAI decreased...

Recent Declines in Western U.S. Snowpack in the Context of Twentieth-Century Climate Variability

Abstract: A monthly snow accumulation and melt model was used with monthly Precipitation-elevation Regressions on Independent Slopes Model (PRISM) temperature and precipitation data to generate time series of 1 April snow water equivalent (SWE) for 1900 through 2008 in the western United States. Averaged across the western United States, SWE generally was higher than long-term (1900-2008) average conditions during the periods 1900-25, 1944-55, and 1966-82; SWE was lower than long-term average conditions during the periods 1926-43, 1957-65, and 1984-2008. During the period 1900- 2008, the temporal pattern in winter precipitation exhibited wetter-than-average and drier-than-average decadal-scale periods with no long-term increasing or decreasing trend. Winter temperature generally was below average from 1900 to the mid-1950s, close to average from the mid-1950s to the mid-1980s, and above average from the mid-1980s to 2008. In general, periods of higher-than-average SWE have been associated with higher precipitation and lower temperature. Since about 1980, western U.S. winter temperatures have been consistently

Energy Balance Partitioning and Net Radiation Controls on Soil Moisture–Precipitation Feedbacks

Abstract: A series of model runs using the University of Oklahoma's Advanced Regional Prediction System (ARPS) were conducted to investigate the relative impacts of energy balance partitioning and net radiation on soil moisture-precipitation feedbacks in the U.S. central plains and to examine how the dominant physical processes are affected by changes in mean soil moisture and spatial resolution. Soil temperature and Bowen ratio are influenced non- linearly by soil moisture, and by varying the mean soil moisture in the model it was possible to examine the relationship between soil moisture and the scaling characteristics of these fields using the statistical moments. Information theory metrics were used to provide an indication of the uncertainty associated with varying model resolutions. It was determined that energy balance partitioning plays a dominant role in the occurrence of soil moisture-precipitation feedback, while net radiation was not impacted by mean soil moisture. A strong rela- tionship was seen between soil moisture and the scaling properties of Bowen ratio, while soil moisture did not appear to influence the scaling characteristics of soil temperature. Spatial resolution had a large effect on the representation of boundary layer turbulence, with coarser resolutions unable to capture turbulent motions, which are necessary for convective processes. The ability of the model to capture boundary layer turbulence will alter the dynamics of soil moisture-precipitation feedback as the horizontal transport of moisture by turbulent motions will affect the spatial and temporal scales over which feed-

Visualizing the Large-Scale Patterns of ENSO-Related Climate Anomalies in North America

Abstract: The variations of large-scale climatic controls and surface responses through the annual cycle during strong positive (El Nino) and negative (La Nina) phase ENSO events are analyzed to assess the within-year and among-year variations of climate anomalies. Data from the NCEP–NCAR reanalysis project are presented as small-multiple maps to illustrate the spatial and temporal variability in North American climate associated with extreme phases of ENSO. Temperature, mean sea level pressure, 500-mb geopotential heights, and 850-mb specific humidity have composite-anomaly patterns that exhibit the greatest degree of spatial and temporal coherence. In general, the composite-anomaly patterns for El Nino and La Nina events are of opposite sign, with stronger, more spatially coherent anomalies occurring during El Nino events than during La Nina events. However, the strength and coherency of the precipitation anomaly patterns are reduced in the interior intermountain west during both positive and negative ph...

Vegetation Control in the Long-Term Self-Stabilization of the Liangzhou Oasis of the Upper Shiyang River Watershed of West-Central Gansu, Northwest China

Abstract: This paper explores the relationship between vegetation in the Liangzhou Oasis in the Upper Shiyang River watershed (USRW) of west-central Gansu, China, and within-watershed precipitation, soil water storage, and oasis self-support. Oases along the base of the Qilian Mountains receive a significant portion of their water supply (over 90%) from surface and subsurface flow originating from the Qilian Mountains. Investigation of vegetation control on oasis water conditions in the USRW is based on an application of a process model of soil water hydrology. The model is used to simulate long-term soil water content (SWC) in the Liangzhou Oasis as a function of (i) monthly composites of Moderate Resolution Imaging Spectroradiometer (MODIS) images of land surface and mean air temperature, (ii) spatiotemporal calculations of monthly precipitation and relative humidity generated with the assistance of genetic algorithms (GAs), and (iii) a 80-m-resolution digital elevation model (DEM) of the area. Modeled r...

Challenges to Reproduce Vegetation Structure and Dynamics in Amazonia Using a Coupled Climate–Biosphere Model

Abstract: The Amazon rain forest constitutes one of the major global stocks of carbon. Recent studies, including the last Intergovernmental Panel on Climate Change report and the Coupled Climate Carbon Cycle Model Intercomparison Project, have suggested that it may reduce in size and lose biomass during the twenty-first century through a savannization process. A better understanding of how this ecosystem structure, dynamics, and carbon balance may respond to future climate changes is needed. This article investigates how well a fully coupled atmosphere–biosphere model can reproduce vegetation structure and dynamics in Amazonia to the extent permitted by available data. The accurate representation of the coupled climate–biosphere dynamics requires the accurate representation of climate, net primary production (NPP), and its partition among the several carbon pool components. The simulated climate is validated against precipitation (within 5% of four datasets) and incident solar radiation (within 7% of obser...

Enhanced Classifications of Engineered Paved Surfaces for Urban Systems Modeling

Abstract: There is a greater need than ever for the ability to accurately model urban system impacts resulting around the planet Rapid urbanization is transforming landscapes from vegetation to an engineered infrastructure and thus altering land cover and land use These alterations impact urban and global climate change, energy demand, human health, and ecological service functions This article presents an overview of a refined land-cover classification protocol that seeks to refine current land-cover classifications of engineered paved surfaces This new approach provides those who model urban systems and engineer the environment as well as other scientists and policy makers an expanded understanding of how intervention to the system can most effectively be accomplished through enhanced modeling An object-oriented analysis regime is presented for an industrial park utilizing commercial software in conjunction with multispectral and panchromatic Quickbird satellite imagery A detailed examination of ho

Biophysical Evaluation of Land-Cover Products for Land–Climate Modeling

Abstract: The need for accurate characterization of the land surface as boundary conditions in climate models has been recognized widely in the climate modeling community. A large number of land-cover datasets are currently used in climate models either to better represent surface conditions or to study the impacts of surface changes. Deciding upon land-cover datasets can be challenging because the datasets are made with different sensors, ranging methodologies, and varying classification objectives. A new statistical measure Q was developed to evaluate land-cover datasets in land–climate interaction research. This measure calculates biophysical precision of land-cover datasets using 1-km monthly Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) product. This method aggregates within-class biophysical consistency, calculated as LAI variation, across a study domain and over multiple years into a single statistic. A smaller mean Q value for a land-cover product indicates more precis...

The Influence of El Nino on the Spring Fallout of Asian Bird Species at Attu Island

Abstract: Several studies have documented the effect of the recent secular climate warming on the distributions and geographical ranges of birds. Here the authors report the strong impact of a recurring climatic pattern in the equatorial Pacific, the El Nino–Southern Oscillation (ENSO) cycle of warm (El Nino) and cold (La Nina) events, on spring migrants along the Far Eastern flyway in northeast Asia. In El Nino years, an unusually large number of birds that use the flyway are observed at Attu Island, westernmost of the Aleutian Islands, nearly 960 km away from the Asian coast. This study is based on a 20-yr dataset documenting the year-to-year variation of Asian birds arriving on Attu in the spring season and uses a three-phased analytical methodology to examine climate impacts on bird movements and populations. The authors offer evidence that birds are displaced toward the Attu area in strong eastward-moving storms. They also present results from a reverse trajectory model that was used to simulate traje...

Effects of Recent Environmental Changes on Global Seismicity and Volcanism

Abstract: A covariation of recent global environmental changes and seismicity on Earth is demonstrated. Presently, rising concern about anthropogenic activities and their consequences on the cryosphere and environment have always overlooked changes related to future tectonic activity. Possible factors affecting an increase in the number of earthquakes and volcanic eruptions are reviewed and discussed.

Consistency in Global Climate Change Model Predictions of Regional Precipitation Trends

Abstract: Projections of human-induced climate change impacts arising from the emission of atmospheric chemical constituents such as carbon dioxide typically utilize multiple integrations (or ensembles) of numerous numerical climate change models to arrive at multimodel ensembles from which mean and median values and probabilities can be inferred about the response of various components of the observed climate system. Some responses are considered reliable in as much as the simulated responses show consistency within ensembles and across models. Other responses—particularly at regional levels and for certain parameters such as precipitation—show little intermodel consistency even in the sign of the projected climate changes. The authors’ results show that in these regions the consistency in the sign of projected precipitation variations is greater for intramodel runs (e.g., runs from the same model) than intermodel runs (e.g., runs from different models), indicating that knowledge of the internal “dynamics...

Identification of Nonlinear Behavior in Transient Climate Change Projections of Soil Moisture over the United States

Abstract: While most projections of climate change and its regional impacts focus on overall changes in the state of the climate system, useful information can also be found in the evolution of the climate system from one state to another Here the authors introduce one method for identifying regions in which significant and systematic long-term nonlinear evolutions may be present, even given quasi-linear anthropogenic forcing Using climate change projections taken from simulations of NCAR’s Community Climate System Model, version 3 (CCSM3), the authors then employ the technique to isolate systematic nonlinear behavior of soil moisture variations over the United States While the projections presented here only represent the results from one model system, it is argued that such nonlinear behavior is an important characteristic of future climate change that should be considered when discussing both short-term and long-term impacts of anthropogenic climate forcing