RCP4.5: a pathway for stabilization of radiative forcing by 2100

Representative Concentration Pathway (RCP) 4.5 is a scenario that stabilizes radiative forcing at 4.5?W?m^?2 in the year 2100 without ever exceeding that value. Simulated with the Global Change Assessment Model (GCAM), RCP4.5 includes long-term, global emissions of greenhouse gases, short-lived species, and land-use-land-cover in a global economic framework. RCP4.5 was updated from earlier GCAM scenarios to incorporate historical emissions and land cover information common to the RCP process and follows a cost-minimizing pathway to reach the target radiative forcing. The imperative to limit emissions in order to reach this target drives changes in the energy system, including shifts to electricity, to lower emissions energy technologies and to the deployment of carbon capture and geologic storage technology. In addition, the RCP4.5 emissions price also applies to land use emissions; as a result, forest lands expand from their present day extent. The simulated future emissions and land use were downscaled from the regional simulation to a grid to facilitate transfer to climate models. While there are many alternative pathways to achieve a radiative forcing level of 4.5?W?m^?2, the application of the RCP4.5 provides a common platform for climate models to explore the climate system response to stabilizing the anthropogenic components of radiative forcing.     

Using a historical aerial photograph analysis to inform trout habitat restoration efforts

Restoration of the upper Strawberry River included bank stabilization techniques because it was assumed that excessive bank erosion was degrading spawning habitat for Bonneville cutthroat trout (BCT). Using a long‐term aerial photograph record, the historical range of variability in bank erosion rates and channel geometry was determined, and this information was used to assess present‐day conditions and the rationale for restoration. Relative to historical variability, the channel planform was relatively stable and bank erosion rates were the lowest recorded in the post‐disturbance era. Although a historical loss of riparian vegetation coincided with a shift to a wider and more sinuous channel, lateral migration rates declined and the channel narrowed as riparian cover increased in the decades before restoration, indicating a process of natural recovery. Furthermore, it was found that the percentage of fine sediment in the streambed before restoration was insufficient to affect BCT spawning success. Together these results suggest that bank erosion and fine sediment did not affect the quality of spawning habitat or the abundance of BCT on the upper Strawberry River. The results highlight how a historical analysis can be used to identify the sources of habitat degradation and inform the selection of restoration goals and strategies. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessment of satellite-based rainfall estimates in urban areas in different geographic and climatic regions

This paper presents an assessment of the 3B42 research version rainfall product from NASA’s Tropical Rainfall Measuring Mission Multi-satellite Precipitation Analysis (TMPA). The study provides new results of TMPA data accuracy in urban areas and highlights trends associated with the climatological indicators of temperature and relative humidity in cities. Ten years (1998-2007) of TMPA data were analyzed for three case study cities in the United States (Houston, Atlanta, and Las Vegas) and one in Korea (Cheongju), representing semi-arid to humid climates. At each location, an urbanized river basin and non-urbanized river basin were selected and comparisons between TMPA and rain gage observations were made for recorded storm events in the study period, the largest storm events by total depth, and selected hurricanes and topical storms. The results indicate TMPA data match well with rain gage observations at all locations. TMPA is slightly underestimated for semi-arid regions and overestimated for humid regions. The relative magnitude of TMPA rain event accumulation compared to rain gage accumulation is noted to be smaller for urbanized watersheds and high intensity events. The correlation of TMPA accuracy with temperature and relative humidity and the analysis of accuracy by season indicate TMPA is more accurate for convective rainfall events. This suggests a possible linkage between the observed urban-modified temperatures, hypothesized enhanced convection, and improved TMPA accuracy in urban areas.     

Super-parameterization in ocean modeling: Application to deep convection

We explore the efficacy of “super parameterization” (SP) in ocean modeling in which local 2-d non-hydrostatic plume-resolving fine-grained (FG) models are embedded at each vertical column of a coarse-grained (CG) hydrostatic model. A general multi-scale algorithm is described in which tendencies from the FG models are projected onto the CG model which in turn constrains the average state of the FG models, coupling the two models together. The approach is tested in the context of models of open ocean deep convection and compared with a pure hydrostatic, coarse resolution model using convective adjustment (HYD) and a full 3-d non-hydrostatic plume-resolving simulation (NH). The SP model is found to be greatly superior to HYD at much less computational cost than the fully non-hydrostatic calculation.     

The Bioavailability of Effluent-derived Organic Nitrogen along an Estuarine Salinity Gradient

Total maximum daily loads for nitrogen (N) are currently being established for the Chesapeake Bay watershed. While we know inorganic N is bioavailable in the environment and therefore its input contributes to cultural eutrophication, the bioavailability of organic N is unclear. Using bioassay experiments, we examined the impact of effluent-derived organic nitrogen (EON) from wastewater treatment plants on natural water samples collected along an estuarine/salinity gradient within the lower Chesapeake Bay watershed. All of the inorganic N and between 31% and 96% of the EON was removed during biotic bioassays within the first 2 days. Further, there was substantial abiotic reactivity of effluent N when it was added to natural water samples. Results demonstrate that organic and inorganic N in effluent is removed to support the growth of microbial communities. These are the first results aimed at assessing the reactivity of EON in natural waters along an estuarine/salinity gradient.     

Organic matter in ria sediments: Relevance of terrestial sources and temporal variations in rates of accumulation

The Ria of Vigo, one of the classical rias of SW Europe, is an environment of high production of organic matter naturally induced by the Galician upwelling. The organic matter is partly supplied by small rivers but mainly by sewage plants along the ria shoreline; jointly they contribute 725 t y⁻¹ of POC, of which 72% is of anthropogenic origin. The freshwater flux is equivalent to a supply of 5 g m⁻² yr⁻¹ of allochtonous POC to the ria floor. However the rate of accumulation of POC is dominated by the order of magnitude higher supply of autochthonous material from the net primary production. The present accumulation rate of organic matter (49-58 g_POC m⁻² yr⁻¹) is lower than the average supply, estimated from the sedimentary record, to the ria since the middle of the nineteen Century (>60 g_POC m⁻² yr⁻¹). This difference may be due to anthropogenic activity or changes in the upwelling pattern. The composition of the organic matter in the sediment reflects the relative importance of the various sources (terrestrial-marine). While terrestrial woody materials dominate the inner ria, phytoplankton remains dominate the remainder of the ria. Rock-Evaluation analysis indicates the inner ria is the site of deposition of gas-prone material and it is inferred that the outer ria of oil-prone organic matter. The controls on the accumulation of POC in the rias show many differences to those found in estuaries affected by anthropogenic activities e.g. agriculture and increasing human population.     

Increased Variability of Microbial Communities in Restored Salt Marshes nearly 30?Years After Tidal Flow Restoration

We analyzed microbial diversity and community composition from four salt marsh sites that were impounded for 40?C50?years and subsequently restored and four unimpounded sites in southeastern Connecticut over one growing season. Community composition and diversity were assessed by terminal restriction fragment length polymorphism (TRFLP) and sequence analysis of 16S ribosomal RNA (rRNA) genes. Our results indicated diverse communities, with sequences representing 14 different bacterial divisions. Proteobacteria, Bacteroidetes, and Planctomycetes dominated clone libraries from both restored and unimpounded sites. Multivariate analysis of the TRFLP data suggest significant site, sample date, and restoration status effects, but the exact causes of these effects are not clear. Composition of clone libraries and abundance of bacterial 16S rRNA genes were not significantly different between restored sites and unimpounded sites, but restored sites showed greater temporal and spatial variability of bacterial communities based on TRFLP profiles compared with unimpounded sites, and variability was greatest at sites more recently restored. In summary, our study suggests there may be long-lasting effects on stability of bacterial communities in restored salt marshes and raises questions about the resilience and ultimate recovery of the communities after chronic disturbance.     

TAOS: The Taiwanese–American Occultation Survey

The Taiwanese–American Occultation Survey (TAOS) seeks to determinethe number and size spectrum for small (～3 km) bodies in the KuiperBelt. This will be accomplished by searching for the brief occultations of brightstars (R～14) by these objects. We have designed and built a specialpurpose photometric monitoring system for this purpose. TAOS comprisesfour 50 cm telescopes, each equipped with a 2048×2048 pixel CCDcamera, in a compact array located in the central highlands of Taiwan. TAOSwill monitor up to 3,000 stars at 5 Hz. The system will go into scientificoperation at the end of 003.