Showing papers in "Earth Interactions in 2004"

RHESSys: Regional Hydro-Ecologic Simulation System—An Object- Oriented Approach to Spatially Distributed Modeling of Carbon, Water, and Nutrient Cycling

Abstract: Process-based models that can represent multiple and interacting processes provide a framework for combining field-based measure- ments with evolving science-based models of specific hydroecological processes. Use of these models, however, requires that the representation of processes and key assumptions involved be understood by the user community. This paper provides a full description of process implementation in the most recent version of the Regional Hydro-Ecological Simulation System (RHESSys), a model that has been applied in a wide variety of research

Variability in Springtime Thaw in the Terrestrial High Latitudes: Monitoring a Major Control on the Biospheric Assimilation of Atmospheric CO2 with Spaceborne Microwave Remote Sensing

Abstract: Evidence is presented from the satellite microwave remote sensing record that the timing of seasonal thawing and subsequent initiation of the growing season in early spring has advanced by approximately 8 days from 1988 to 2001 for the pan-Arctic basin and Alaska. These trends are highly variable across the region, with North America experiencing a larger advance relative to Eurasia and the entire region. Interannual variability in the timing of spring thaw as detected from the remote sensing record corresponded directly to seasonal anomalies in mean atmospheric CO2 concentrations for the region, including the timing of the seasonal draw down of atmospheric CO2 from terrestrial net primary productivity (NPP) in spring, and seasonal maximum and minimum CO2 concentrations. The timing of the seasonal thaw for a given year was also found to be a significant (P < 0.01) predictor of the seasonal amplitude of atmospheric CO2 for the following year. These results imply that the timing of seasonal thawing...

Including Croplands in a Global Biosphere Model: Methodology and Evaluation at Specific Sites

Abstract: There is a strong international demand for quantitative estimates of both carbon sources/sinks, and water availability at the land surface at various spatial scales (regional to global). These estimates can be derived (and usually are) from global biosphere models, which simulate physiological, biogeochemical, and biophysical processes, using a variety of plant functional types. Now, the representation of the large area covered with managed land (e.g., croplands, grasslands) is still rather basic in these models, which were first designed to simulate natural ecosystems, while more and more land is heavily disturbed by man (crops cover ∼35% and grasslands ∼30%–40% of western Europe's area as a result of massive deforestation mainly in the Middle Ages). In this paper a methodology is presented that combines the use of a dynamic global vegetation model (DGVM) known as Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) and a generic crop model [the Simulateur Multidisciplinaire pour les...

Mapping Surface Broadband Emissivity of the Sahara Desert Using ASTER and MODIS Data

Abstract: Surface broadband emissivity in the thermal infrared region is an important parameter for the studies of the surface energy balance. This paper focuses on estimating a broadband window emissivity from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Moderate Resolution Imaging Spectrometer (MODIS) data. Both sensors are on board the NASA Earth Observing System (EOS) Terra satellite, which was launched in 1999. First, several definitions of the broadband emissivity were investigated, and it was found that the emissivity integrated between 8 and 13.5 μm is the best for estimating the net longwave radiation under clear-sky conditions. Then, a method to estimate broadband emissivity at the continental scale was developed. The method uses two regressions. The first regression is to relate the broadband emissivity to the emissivities for the five ASTER channels using measured emissivities in the laboratory from spectral libraries. The second regression relates the broadban...

Cropland Area and Net Primary Production Computed from 30 Years of USDA Agricultural Harvest Data

Abstract: Croplands cover large areas of the globe and contribute significantly to the global carbon cycle. However, like other ecosystems, limited information exists on spatially explicit, ground-based estimates of carbon fluxes. In this study, county-level cropland area and harvest information reported in the U.S. Department of Agriculture (USDA) National Agricultural Statistics Service (NASS) from 1972 to 2001 was utilized to calculate the temporal behavior of net primary production (NPP) for croplands across the United States. Production data for individual crops were converted to estimates of NPP using crop-specific factors. Because NASS does not include all crops of interest during all years, only a crop type in a county estimate was included if the entire time series was complete. Incomplete reporting occurred primarily with hay. Trends in crop area, NPP, and total production (area times NPP) exhibited significant spatial variation. The largest increases in production occurred in the Midwest, Great ...

Global Population Distribution and Urban Land Use in Geophysical Parameter Space

Abstract: The spatial distribution of human population on the land surface is a fundamental determinant of land-use impacts on Earth's ecosystems. Census enumerations and satellite-detected night lights provide two complementary, but distinct, representations of human population distribution. Census estimates indicate that 37% of Earth's enumerated land area is populated at densities greater than 1 person per square kilometer. Human populations are strongly clustered within this area. Spatial variations in human population density span more than six orders of magnitude with 50% of the 1990 population occupying less than 3% of the inhabited land area. Temporally stable lighted areas detectable from space provide an independent proxy for the spatial distribution of urban settlements and the intensive land-cover changes that accompany them. These ∼60 000 lighted areas account for less than 2% of inhabited land area, and 50% of this lighted area is associated with the largest 5% of cities and conurbations. Urb...

Croplands in West Africa: A Geographically Explicit Dataset for Use in Models

Abstract: West Africa has experienced increases in cultivated lands over the last 50 yr, as well as increasing rates of deforestation. Croplands have expanded to meet the food demands of a rapidly increasing population. Nevertheless, this region remains one of the most food-deprived places on the planet. While the food demands of an increasing population have to be met through cropland expansion or intensification on existing lands, it is important to evaluate the long-term environmental consequences of the ensuing land-use change. Spatially explicit datasets of land use/land cover for the region would be valuable for assessing the environmental consequences of land-cover change, as well as the implications for food security. A review of the currently available moderate-resolution satellite-derived land-cover datasets for the region finds them to be of poor quality. A high-resolution satellite-derived cropland dataset for the Sahel is available; however, extending this to the entire West African region is an expensive proposition and will require a massive undertaking. Therefore, in this study, a new regional dataset of the spatial distribution of croplands for West Africa was created by synthesizing subnational cropland area statistics, a spatial map of population density, and

The Relationship of the Terra MODIS Fire Product and Anthropogenic Features in the Central Siberian Landscape

Abstract: Fires are a common occurrence in the Siberian boreal forest. The thermal anomalies product of the Terra/Moderate Resolution Imaging Spectroradiometer (MODIS) product suite is designed to detect thermal anomalies (i.e., hotspots or fires) on the Earth's surface. Many, but not all, of the hot spots detected by MODIS in Siberia are wild fires. Agricultural burning and industrial activities also contribute. Using MODIS data from the years 2001, 2002, and 2003 along with a geographical information system (GIS), the type, extent, and duration of hot spots were examined. In addition, high correlations were found between the number of fires and proximity to human activities. Different types of land-cover thermal anomalies were found to have a strong, positive correlation with some anthropogenic features, such as roads, human settlements, and mineral industry locations. The agricultural (r2 = 0.95) and the forest (r2 = 0.81) thermal anomalies had the highest positive correlation with proximity to roads. T...

Land-Cover Change Analyses in the Volta Basin of Ghana

Abstract: Multitemporal Landsat Thematic Mapper (TM) images for 1984, 1992, and 1999 were used to map and detect land-cover changes in a 5400-km2 area within the Volta Lake basin of Ghana. The most dominant land-cover change was the conversion of natural vegetation to cropland, which occurred at an annual rate of 5%. While the data suggest an increase in human pressure, reversible change in woodland and grassland occurred in 4% and 2% of the landscape, respectively. A higher proportion of reversible land-cover changes relating to fallow agriculture occurred in about 14% of the landscape, whereas a higher overall increase in woody biomass (10%), compared to an overall decrease of 9%, indicates a certain level of rainfall-induced resilience in the ecosystem. Further research is needed to quantitatively evaluate the mechanisms enhancing vegetation recovery in dryland areas.

Optimizing Patterns of Land Use to Reduce Peak Runoff Flow and Nonpoint Source Pollution with an Integrated Hydrological and Land- Use Model

Abstract: The goal of this study is to develop and apply a methodology for delineating optimal land-use patterns that minimize peak runoff flow at watershed outlets by coupling a hydrological model and a land-use model. Under the assumption supported in prior research that nonpoint source (NPS) pollution is positively correlated with surface runoff volume, the model then yields land-use patterns that minimize nonpoint source pollution. A hydrological simulation model is developed with a modified and spatially explicit Soil Conservation Service (SCS) curve number method to analyze the geographical impacts of land uses. An optimization algorithm is integrated with the simulation model to evaluate different land-use patterns and their response to rainfall runoff events, and to search for optimal land-use patterns. This approach, applied to the southwestern basin of Lake Erie, Old Woman Creek Watershed (Ohio), yields optimal land-use patterns that reduce the peak runoff rate by 15%–20% under 1-, 2-, 5-, and 10...

Mapping Land-Use Change and Monitoring the Impacts of Hardwood- to-Pine Conversion on the Southern Cumberland Plateau in Tennessee

Abstract: Over the past two decades, forests in the southeastern United States have undergone dramatic changes as the result of urban sprawl and conversion to intensively managed pine plantations. The Cumberland Plateau, an important ecoregion in the southeastern United States, contains some of the largest remaining tracts of privately owned, native hardwood forest in North America. These ecologically important forests have been undergoing increasingly rapid rates of hardwood-to-pine conversion, much of which has gone undetected by large-scale statewide inventories. Forest conversion in Tennessee's southern Cumberland Plateau provides a case study highlighting the need for interdisciplinary and spatially explicit assessments of the impact and drivers of land-use change at smaller scales. Aerial and satellite imagery were used to create computer-generated maps of land use and forest cover for a 243 000 ha study area within a seven-county region of the southern Cumberland Plateau in Tennessee to track and do...

Twentieth-Century Sea Surface Temperature Patterns in the Pacific during Decadal Moisture Regimes over the United States

Abstract: Three great moisture anomalies were observed during the twentieth century over the western United States: a pluvial from 1905 to 1917, the Dust Bowl drought (1929–40), and the Southwestern drought of 1946–56. A composite analysis of the concurrent Pacific sea surface temperature (SST) field is used to infer the atmospheric circulation that may have been associated with these objectively defined decadal dry and wet periods. The early-twentieth-century pluvial occurred during a 13-yr SST regime with unusually cold water in the northern and northwestern North Pacific and in the eastern North Pacific. This pattern would favor a “Pineapple Express–like” mean storm track into the west. Warm ENSO-like conditions also observed during the pluvial would have favored an enhanced subtropical jet stream into the southwestern United States. The 11-yr Dust Bowl drought occurred during a poorly defined Pacific SST regime, although unusually cold water was present in the far western North Pacific. Weak warm SST c...

The Impact of Historical Land-Use Changes on the Near-Surface Atmospheric Conditions on the Swiss Plateau

Abstract: The effects of historical land-use changes on the Swiss Plateau on the near-surface atmospheric conditions of typical summer days in July were investigated in a case study. A mesoscale dynamical nonhydrostatic model with a horizontal resolution of 1 km 2 was used. Two simulations of historical (around 1850) and present conditions as well as six sensitivity experiments were conducted in order to assess the importance of changes in the physiological, morphological, and soil properties. The modeled daily average

Impacts of Climate Variation and Catchment Area on Water Balance and Lake Hydrologic Type in Groundwater-Dominated Systems: A Generic Lake Model

Abstract: Lakes are a major geologic feature in humid regions, and multiple lake hydrologic types exist with varying physical and chemical characteristics, connections among lakes, and relationships to the landscape. The authors developed a model of water fluxes through major components of groundwater-dominated lake catchments in a region containing thousands of lakes, the Northern Highland Lake District (NHLD) of northern Wisconsin and the Upper Peninsula of Michigan. The model was calibrated with data from widely differing lakes using the same set of simple equations to represent the hydrologic type, water residence time, and amount and timing of stream and groundwater flows of representative lakes in today's climate. The authors investigated the sensitivity of the water balance of a set of three connected

Validation and Use of a Semidistributed Hydrological Modeling System to Predict Short-Term Effects of Clear-Cutting on a Watershed Hydrological Regime

Abstract: The Gestion Integree des Bassins versants a l'aide d'un Systeme Informatise (GIBSI), a semidistributed hydrological modeling system, was evaluated for its ability to simulate the impact of deforestation on the hydrological regime of the Famine River watershed (728 km2), a subwatershed of the Chaudiere River, Quebec, Canada. Annual, spring and summer, and low-water runoff, as well as peak flows, were estimated for both a base-case scenario and a deforestation scenario using 31 annual meteorological series. GIBSI simulated an average increase of annual runoff after clear-cutting of 57% (268 mm) and the proportion of runoff to precipitation increased from 40% to 63%. The average increase in spring runoff was 25%, while in summer it was 138%. For summer low-flow periods, GIBSI simulated an average increase in runoff of 102%. For spring and summer peak-flow rates, hydrographs generated by GIBSI showed that average spring peak flows were increased after deforestation by 26% while summer peak flows were...

Land-Cover Dynamics in an Urban Area of Ghana

Abstract: The objectives of this study were to quantify land-cover changes. A short-term projection of land-cover distribution in a 2400-ha (1 ha = 10 000 m2 ) area of northern Ghana was generated. Landsat Thematic Mapper images acquired in 1984, 1992, and 1999 were used for land-cover mapping, whereas land-cover projections were carried out using transition probability techniques. Remote sensing analyses showed that in the first period (1984–92), the dominant land-cover change process was the expansion of the built-up area (26 ha yr−1) as a result of an increase in demand for housing by the increasing population. Expansion of the built-up area continued at the rate of 35 ha yr−1 in the second period (1992–99), as well as development of peri-urban agriculture (24 ha yr−1) to meet the food demand of the rapidly growing population. Projection of land-cover distribution showed that the built-up area would further increase at the expense of cropland and natural vegetation, covering about 39% of the landscape b...

Land Use—Iron Pollution in Mangrove Habitat of Karachi, Indus Delta

Abstract: The coastal area of Karachi, Pakistan, which lies at the northwestern part of the Indus delta, is heavily polluted particularly in the mangrove habitat. The present study traces the pathway of trace metal iron from the source to the different mangrove parts via seawater and sediment. The concentration in the sediment was as high as 34 436 ppm and as low as 0.01 ppm in seawater, while vegetative mangrove parts like pneumatophores, bark, twigs, and leaves possessed generally less than 1000 ppm. The concentration factor (CF) of mangroves was very low, indicating minimum bioavailability of iron from the sediment. The concentration of the metal decreases progressively through different sections of the mangrove habitat in the following sequence: from sediment to pneumatophores to bark to leaves to twigs to seawater.

Understanding Controls on Historical River Discharge in the World’s Largest Drainage Basins

Abstract: Long-term (20 yr) river discharge records from 30 of the world’s largest river basins have been used to characterize surface hydrologic flows in relation to net precipitation inputs, ocean climate teleconnections, and human land/water use patterns. This groundwork study is presented as a precedent to distributed simulation modeling of surface hydrologic flows in large river basins. Correlation analysis is used as a screening method to classify river basins into categories based on major controls on discharge, for example, climate, land use, and dams. Comparisons of paired station records at upstream and downstream discharge locations within each major river basin suggest that the discharge signals represented in upstream discharge records are sustained in the downstream station records for nearly two-thirds of the drainage basins selected. River basins that showed the strongest localized climate control over historical discharge records, in terms of correlations with net basinwide precipitation r...

The Effect of Including Biospheric Responses to CO2 on the Impact of Land-Cover Change over Australia

Abstract: Increasing atmospheric carbon dioxide concentration and the resulting change in temperature affect vegetation physiologically and structurally. These physiological and structural changes are biospheric feedbacks that may enhance or moderate the impacts due to human-induced land-cover change. It is therefore potentially important to include these biospheric feedbacks in experiments that explore the impact of land-cover change on climate. In this paper, it is shown that the vegetation response to higher carbon dioxide concentrations and warmer temperatures moderates the impacts of historical human-induced land-cover change in Australia. The magnitude of these biospheric feedbacks is explored, and it is shown that including them in climate simulations results in smaller land-cover change impacts on latent heat flux (by about 10–20 W m−2) and temperature (by about 0.3°C), irrespective of the direction of change caused initially by land-cover change. Further, the magnitude of the feedback on temperatu...

Scale-Dependent Relationships between Land-Use Change and Its Determinants in the Volta Basin of Ghana

Abstract: Relationships between cropland change and presumed determinants were analyzed at scales ranging from 30 to 5100 m using logistic regression. The plot of the odds ratio across the spatial scales indicated that both biophysical and social variables were important in explaining cropland change. In the first period (1984–92), biophysical factors were the dominant factors, while market-related variables were more dominant between 1992 and 1999. Response to changing economic opportunities was the underlying cause of this trend. Policies that would make commercialization of agriculture viable are required in the Volta basin of Ghana.

Water Flux in a Cashew Orchard during a Wet-to-Dry Transition Period: Analysis of Sap Flow and Eddy Correlation Measurements

Abstract: Information regarding biosphere–atmosphere interactions is important in the study of a hydrological cycle. To this purpose, xylem sap flow (SF) using the Granier system and evapotranspiration (ET) using the eddy correlation method were measured during a “wet-to-dry” transition period in a young cashew (Anacardium occidentale L.) plantation. Estimates of half-hourly tree transpiration made from stem sap flow measurements and above-canopy eddy correlation measurements of water vapor flux were compared for a period of 22 days of complete records. Cross-correlation analysis was used to estimate the time lags (τ) between the time courses of SF and ET, and between SF and ET with solar radiation (RS) and vapor pressure deficit (D). Applying a simple functional technique, values of τ = 43 min (November), τ = 46 min (December), and τ = 75 min (January) with an overall τ = 53 min (using all data) between the time courses of ET and SF were estimated. A positive lag indicates that SF lags behind ET. However,...

Ecodynamic and Eddy-Admitting Dimethyl Sulfide Simulations in a Global Ocean Biogeochemistry/Circulation Model

Abstract: The authors describe planetary-scale modeling of mixed-layer dimethyl sulfide (DMS) processing and distributions, conducted at a resolution of 0.28° using the Parallel Ocean Program (POP). Ecodynamic routines embedded within POP track the interactions of bacteria, multiple phytoplankton species, zooplankton, and both dissolved and detrital organics. Biogeochemistry linked to the ecosystem includes full elemental cycling for iron, nitrogen, silicon, carbon, and the portion of the sulfur cycle leading through the formation of intracellular dimethyl sulfoniopropionate (DMSP) to dissolved DMS. The two reduced sulfur compounds are emitted from the numerical plant bins at average rates proportional to the taxonomically dependent DMSP content. Within the water column they are subjected to photolysis, interconversion, consumption by the bacterial pool, and loss into the troposphere. Biogeochemical species distributions were calculated synchronously with the POP ocean circulation for the period 1995–2000....

Soil C Accumulation in a White Oak CO2-Enrichment Experiment via Enhanced Root Production

Abstract: After four growing seasons, soil below white oak trees exposed to elevated atmospheric carbon dioxide levels (ambient + 300 ppm) had an average of 14% more soil carbon than soil below trees exposed to ambient levels of carbon dioxide. The soil carbon inventories in five soil cores collected from ambient chambers and six soil cores collected from elevated chambers at the Global Change Field Research Site, Oak Ridge, Tennessee, were measured. The authors conclude that the increase in soil carbon was due to an increase in belowground soil carbon input, because aboveground litter inputs were excluded by experimental design. These findings are consistent with the hypothesis that elevated carbon dioxide levels are increasing the amount of carbon stored in soil.