A new park is being considered for the confluence of the Los Angeles River and the Arroyo Seco in Los Angeles County, California. Components of the park development may include creation of a temporary lake on the Los Angeles River, removal of channel lining along part of the Arroyo Seco, restoration of native plants, creation of walking paths, and building of facilities such as a boat ramp and a visitor center. This report, prepared in cooperation with the Mountains Recreation and Conservancy Authority, delineates the geological, hydrological, and biological issues that may have an impact on the park development or result from development at the confluence, and identifies a set a tasks to help address these science issues. Geologic issues of concern relate to surface faulting, earthquake ground motions, liquefaction, landsliding, and induced seismicity. Hydrologic issues of concern relate to the hydraulics and water quality of both surface water and ground water. Biological issues of concern include colonization-extinction dynamics, wildlife corridors, wildlife reintroduction, non-native species, ecotoxicology, and restoration of local habitat and ecology. Potential tasks include (1) basic data collection and follow-up monitoring, and (2) statistical and probabilistic analyses and simulation modeling of the seismic, hydraulic, and ecological processes that may have the greatest impact on the park. The science issues and associated tasks delineated for the proposed confluence park will also have transfer value for river restoration in other urban settings.

Edwards Air Force Base (EAFB) is in the Mojave Desert region of southern California. Although the climate in the study area is arid, occasional intense storms result in flooding on the base, damaging roads and buildings. To plan for anticipated development at EAFB, the U.S. Department of the Air Force (USAF) and the U.S. Geological Survey (USGS) began a cooperative study to locate flood-prone areas on the base. This report describes flood hazards and shows flood-prone areas of the base.

A coupled physical‐biogeochemical climate model that includes a dynamic global vegetation model and a representation of a coupled atmosphere‐ocean general circulation model is driven by the nonintervention emission scenarios recently developed by the Intergovernmental Panel on Climate Change (IPCC). Atmospheric CO2, carbon sinks, radiative forcing by greenhouse gases (GHGs) and aerosols, changes in the fields of surface‐air temperature, precipitation, cloud cover, ocean thermal expansion, and vegetation structure are projected. Up to 2100, atmospheric CO2 increases to 540 ppm for the lowest and to 960 ppm for the highest emission scenario analyzed. Sensitivity analyses suggest an uncertainty in these projections of −10 to +30% for a given emission scenario. Radiative forcing is estimated to increase between 3 and 8 W m−2 between now and 2100. Simulated warmer conditions in North America and Eurasia affect ecosystem structure: boreal trees expand poleward in high latitudes and are partly replaced by temperate trees and grasses at lower latitudes. The consequences for terrestrial carbon storage depend on the assumed sensitivity of climate to radiative forcing, the sensitivity of soil respiration to temperature, and the rate of increase in radiative forcing by both CO2 and other GHGs. In the most extreme cases, the terrestrial biosphere becomes a source of carbon during the second half of the century. High GHG emissions and high contributions of non‐CO2 agents to radiative forcing favor a transient terrestrial carbon source by enhancing warming and the associated release of soil carbon.

The atmospheric CO 2 and δ 13 C records for the last millennium have been analyzed to reconstruct the evolution and the temporal variability in the terrestrial and oceanic carbon sinks and to identify natural variations in the marine carbon cycle. Reconstructed natural variations in sinks are usually less than ± 0.2 Gt C yr −1 on time scales of decades to centuries and thus one order of magnitude smaller than the sink fluxes driven by the anthropogenic perturbation. The natural oceanic carbon cycle was generally close to steady state on a multi‐decadal time scale. A large anomalous oceanic carbon sink is found around 1940 that is attributed to a higher than usual El Niño activity. Interannual variations in the oceanic sink as reconstructed for the 1980–1996 period are around ±1 Gt C yr −1 and are significantly correlated with the Southern Oscillation. The relatively low atmospheric CO 2 concentrations between 1600 and 1750 were caused by an additional terrestrial storage of 40 Gt C. The land biota acted as a carbon source between 1750 and 1950 and as a sink afterwards. Terrestrial changes can be explained by land use emission up to 1920. Then, additional mechanisms such as CO 2 fertilization are responsible for an estimated terrestrial sequestration of 100 Gt C between 1920 and 1996.

Strategies are developed to analyze and represent spatially resolved biosphere models for carbon sequestration in response to changes in atmospheric CO2 and climate by reduced‐form, substitute models. We explore the High‐Resolution Terrestrial Biosphere Model as implemented in the Community Terrestrial Biosphere Model (HRBM/CTBM), the Frankfurt Biosphere Model (FBM), and the box‐type biosphere of the Bern model. Storage by CO2 fertilization is described by combining analytical representations of (1) net primary productivity (NPP) as a function of atmospheric CO2 and (2) a decay impulse response function to characterize the timescales of biospheric carbon turnover. Storage in response to global warming is investigated for the HRBM/CTBM. The relation between the evolution of radiative forcing and climate change is expressed by a combination of impulse response functions and empirical orthogonal functions extracted from results of the European Center/Hamburg (ECHAM3) coupled atmosphere‐ocean general circulation model. A box‐type, differential‐analogue substitute model is developed to represent global carbon storage of the HRBM/CTBM in response to regional changes in Temperature, Precepitation and cloud cover. The substitute models represent the spatially resolved models accurately and cost‐efficiently for carbon sequestration in response to changes in CO2 or in CO2 and climate and for simulations of the global isotopic signals. Deviations in carbon uptake simulated by the spatially resolved models and their substitutes are less than a few percent.

We compared the simulated responses of net primary production, heterotrophic respiration, net ecosystem production and carbon storage in natural terrestrial ecosystems to historical (1765 to 1990) and projected (1990 to 2300) changes of atmospheric CO2 concentration of four terrestrial biosphere models: the Bern model, the Frankfurt Biosphere Model (FBM), the High-Resolution Biosphere Model (HRBM) and the Terrestrial Ecosystem Model (TEM). The results of the model intercomparison suggest that CO2 fertilization of natural terrestrial vegetation has the potential to account for a large fraction of the so-called "missing carbon sink" of 2.0 Pg C in 1990. Estimates of this potential are reduced when the models incorporate the concept that CO2 fertilization can be limited by nutrient availability. Although the model estimates differ on the potential size (126 to 461 Pg C) of the future terrestrial sink caused by CO2 fertilization, the results of the four models suggest that natural terrestrial ecosystems will have a limited capacity to act as a sink of atmospheric CO2 in the future as a result of physiological constraints and nutrient constraints on NPP. All the spatially explicit models estimate a carbon sink in both tropical and northern temperate regions, but the strength of these sinks varies over time. Differences in the simulated response of terrestrial ecosystems to CO2 fertilization among the models in this intercomparison study reflect the fact that the models have highlighted different aspects of the effect of CO2 fertilization on carbon dynamics of natural terrestrial ecosystems including feedback mechanisms. As interactions with nitrogen fertilization, climate change and forest regrowth may play an important role in simulating the response of terrestrial ecosystems to CO2 fertilization, these factors should be included in future analyses. Improvements in spatially explicit data sets, whole-ecosystem experiments and the availability of net carbon exchange measurements across the globe will also help to improve future evaluations of the role of CO2 fertilization on terrestrial carbon storage.

A high-resolution ice-core record of atmospheric CO 2 concentration over the Holocene epoch shows that the global carbon cycle has not been in steady state during the past 11,000 years. Analysis of the CO 2 concentration and carbon stable-isotope records, using a one-dimensional carbon-cycle model,uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial-scale changes of atmospheric CO 2 concentrations.

Preliminary determinations of the magnitude and frequency of peak flows resulting from the storms of December 1996 and January 1997 were made at 292 streamflow gaging stations located in 45 counties in northern and central California. Peak flows were the largest on record at 106 stations, and recurrence intervals were greater than 100 years at 32 stations. Two separate frequencies were determined for the 1997 peak flow at each streamflow station: a frequency based on an analysis that includes annual peak flows through the 1996 water year (ending September 30, 1996) and a frequency based on an analysis that includes the 1997 peak.

Flood-discharge data, current-meter and indirect measurements, and stage-discharge relations, the oldest of which dates to the early 1900's, were used to estimate the uncertainty about annual flood peaks in or near the American River Basin at 20 stream-gaging stations operated by the U.S. Geological Survey. The study estimates that, in the study area, most flood peaks that were determined from current-meter measurements have an uncertainty of about plus or minus 3 percent, whereas the peaks that were determined from indirect measurements have an uncertainty ranging from plus or minus 10 to plus or minus 70 percent. The study also determined that the stage-discharge relations that have been developed for most of the sites in the American River Basin are correct.

Areas of Chalone Creek and Bear Valley drainage basins in Pinnacles National Monument, California, are subject to frontal storms that can cause major flooding from November to April in areas designated for public use. To enhance visitor safety and to protect cultural and natural resources, the U.S. Geological Survey in cooperation with the National Park Service studied flood-hazard potentials within the boundaries of the Pinnacles National Monument. This study area extends from about a quarter of a mile north of Chalone Creek Campground to the mouth of Bear Valley and from the east monument entrance to Chalone Creek. Historical data of precipitation and floodflow within the monument area are sparse to nonexistent, therefore, U.S. Soil Conservation Service unit-hydrograph procedures were used to determine the magnitude of a 100-year flood. Because of a lack of specific storm-rainfall data, a simulated storm was applied to the basins using a digital-computer model developed by the Soil Conservation Service. A graphical relation was used to define the regionally based maximum flood for Chalone Creek and Bear Valley. Water-surface elevations and inundation areas were determined using a conventional step-backwater program. Flood-zone boundaries were derived from the computed water-surface elevations. The 100-year flood plain for both streams would be inundated at all points by the regional maximum flood. Most of the buildings and proposed building sites in the monument area are above the elevation of the 100-year flood, except the proposed building sites near the horse corral and the east monument entrance. The 100-year flood may cause reverse flow through a 12-inch culvert embedded in the embankment of Old Pinnacles Campground Road in the center of Chalone Creek Campground. The likelihood of this occurring is dependant upon the amount of aggradation that occurs upstream; therefore, the campground area also is considered to be within the 100-year flood zone.

The results of a study conducted to develop a model of waterway user charge impacts and test the model on a case study region are summarized. The model developed is a Markov decision theory model with an implied transition period of five years. The transition probabilities were estimated subjectively based on a state space defined by change in freight traffic movement. Reward estimates were based on multiple criteria such as change in shipping costs and change in equity. The rewards were developed from a variation on the rank-based expected-value method of evaluation. These were also produced subjectively based on the results of previous studies. The input on the upper Mississippi River case study site was processed by a Markov decision theory computer program. Considerable sensitivity analysis on rewards and transition probabilities was done. In the majority of cases, the alternative of no user charge was favored. In certain periods of high growth in freight traffic, a low-level fuel tax was favored. The case study results themselves are not as significant as the problem structuring that was accomplished and the introduction of time and nonmonetary criteria into the evaluation process. /Author/

The objective of this paper is to describe the development of the line source sorting model NETSEN II and its use in conjunction with the EPA's automobile exhaust emissions model analysis model. Speed-profile analogies from the Regional Air Pollution Study of the St. Louis air quality control region (AQCR), developed for use in the model emissions model, are used. The model emissions model was designed to calculate the amounts of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOX) emitted by individual automobiles or groups of automobiles stratified by age and geographic location. The NETSEN II is an updated version of NETSEN with additional variables and subroutines and the ability to test for the following roadway characteristics in defining a line source at any level of data refinement (a line source being the smallest segment of inventoried roadway depictable with a given specific set of attriputes): average daily traffic, five types of special typography, four types of capacity alternations, eight types of sensitive land uses, five types of activity centers, five types of progressive movement, channelization, functional classification, link distance, peak speed differences, truck and bus volumes, and volume-capacity (V/C) ratio. In this research, the inputs to NETSEN II are the appropriate uses control cards for selection of line sources and the network roadway inventory; and the output is a set of line sources that meet specified characteristics which is used as the project's first output, the second being the emission rates computed by the modal emissions model, the third the emission factors for trucks, and the fourth a control card to determine the total percentage of all trucks, the hours of the day for which emissions data are desired, and whether or not emissions are to be added to the grid totals of stored separately as hourly totals. With these inputs, line source emissions were computed. Besides NETSEN II itself, the data analysis and modeling efforts of the project yielded: development of a truly microscale emissions estimation modals which allows emissions to be analyzed as a function of highly localized traffic operating conditions and roadway descriptions through integration of NETSEN II and the modal emissions model; the ability to develop accurate analogies of speed-profile and emission characteristics for links that do not possess speed-profiled data; and thus an accurate and exhaustive statement of emissions obtained for line sources in the St. Louis AQCR.