Property:CSDMS meeting abstract
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The role of climate change on landscapes is one of the most difficult remaining challenges in geomorphology. It is thought that climate primarily modifies landscapes through sediment production and transport in rivers. However, collecting the data needed to resolve the relationship between climate and sediment transport has remained elusive. This issue stems from a lack of a methodology that can work in a wide variety of river environments. Furthermore, this problem is made pressing by a need to understand the coming effects of human-induced climate change.
To address this problem, I developed a model to capture sediment transport using luminescence, a property of matter normally used to date sediment deposition. Luminescence is generated via exposure to background ionizing radiation and is removed by exposure to sunlight. This behaviour is sensitive to sediment transport and could potentially be used to infer sediment transport parameters. I derive the model by performing a simultaneous conservation of sediment mass and absorbed radiative energy expressed as luminescence. The derivation results in two differential equations that predict the luminescence at any point in a river channel network. The model includes two key sediment transport parameters, the sediment transport velocity and the storage-center exchange rate. From these parameters, other key sediment transport variables such as the characteristic transport length-scale and the sediment virtual velocity can be calculated. These parameters can be constrained by determining the model’s luminescence parameters through field measurement and lab experiments.
I test my model against luminescence measurements made in rivers where these sediment transport parameters are well known. I find that the model can reproduce the observed patterns of luminescence in channel sediment and the parameters from the best-fit model runs reproduce the known sediment transport parameters within uncertainty. The success of the model, and the advent of new technology to measure luminescence using portable devices, suggests that it may now be feasible to collect critical sediment transport data cheaply and rapidly. This method can now be used to test outstanding hypotheses of the influence of climate on sediment transport.
The sand-bed river long-profile evolution model (SRLP) is a complete mechanistic model, describing both transient and steady-state long-profile evolution of a transport-limited sand-bed river with self-forming channel width adjustments by linking sediment transport and river morphodynamics. SRLP allows for planform adjustments as a function of excess shear stress, which is directly related to the critical stress of the bank material (following Parker, 1978, and Dunne and Jerolmack, 2018), thereby linearizing the sediment-transport response to changing river discharge. This one-dimensional, physics-based model captures the internal dynamics of this inherently complicated system, quantifies the changes in the river's bed elevation, cross section, and channel slope, and ultimately provides the critical information about how the river is responding to both natural and anthropogenic disturbances. Our work so far has explored the variability in topographic responses of both steady-state and transient sand-bed channel long-profiles to the changes in sediment and water supply and base level by utilizing SRLP. We also further build on this understanding of how sand-riverbed mobility and the physical factors controlling it couples to the channel form is a key mechanistic link for predicting river response to those external perturbations. Therefore, we now consider how the equilibrium geometry of sand-bed rivers varies as a function of physical controls such as grain size, bed roughness, and bank strength, all of which modify the effective stress available for sediment transport. Then we evaluate the path to steady‐state long-profiles using numerical morphodynamic experiments by SRLP. +
The sediment bed and the water column are tightly coupled in shallow water systems including large portions of the continental shelf. For instance, the continental shelf seafloor receives ~48% of the global flux of organic carbon to the seabed and the shelf benthic flux serves as a key source of nutrients for sustaining marine life. Observational studies of sediment-water exchange require concurrent measurements in both compartments; however, these are difficult to obtain and rarely available. Numerical modelling provides a valuable alternative approach to observational studies, however many previous modeling efforts used simple sediment-water parameterizations that did not capture the nonlinearities of benthic-pelagic coupling. Here, we present a coupled benthic-pelagic model that includes realistic representations of biogeochemical reactions in both compartments, and the fluxes at the interface. The model is built on the modeling algorithms for sediment-water exchange in ROMS and expanded to include carbonate chemistry and anerobic reactions in the seabed. The updated model is tested for three sites where benthic flux and porewater concentration measurements are available in the northern Gulf of Mexico summer hypoxic zone. Model-data comparison demonstrates the robustness of the calibrated model in reproducing the porewater concentration-depth profiles of O2, DIC, TA, NO3 and NH4, as well as the benthic fluxes of the former three. Further sensitivity experiments reveal that labile material input, bio-diffusion intensity and anerobic mineralization pathways are the three major factors regulating the benthic fluxes and porewater concentrations of O2, DIC and TA. To conclude, our model results provide important insights into the variation of sediment-water exchange under different environmental conditions. This model has the potential to be used as a research and management tool to quantify the role of shelf sediment in driving bottom water hypoxia and acidification over continental shelves.
The shape of gravel-bed rivers controls aquatic habitat, fluvial hazards, landscape evolution, and river response to human impacts. Gravel-bed river shape, on average, obeys the expectations of an equilibrium model in which the width-averaged bankfull shear stress is slightly greater than the critical shear stress required to move the median bed grain size. However, it is important to understand not just average equilibrium form but also responses of river shape to changes in formative conditions, both to elucidate process dynamics and to enable applied prediction. Many natural and human-driven changes to channels, and especially river restoration interventions, involve altering the flow resistance of gravel-bed rivers by changing macro-roughness. Despite rich bodies of literature on 1) macro-roughness effects on flow and sediment transport and 2) controls on gravel-bed river shape, understanding of macro-roughness effects on reach scale channel form evolution remains limited.
We ask how macro-roughness affects gravel-bed river geometry, and how rivers respond to changes in macro-roughness as might occur during river restoration. We develop a simple numerical model for gravel-bed river form in the presence of macro-roughness and use it to investigate trajectories and timescales of channel response to macro-roughnesss changes. Model sensitivity analysis reveals that greater macro-roughness drives channel widening, bed aggradation, and steepening, as the channel remains adjusted to maintain constant shear stresses on the bed and banks regardless of roughness. The presence of a floodplain reduces widening but increases steepening at high roughness values, because high roughness drives flow overbank and increases the width/depth ratio relative to a confined channel. Comparison against topobathymetric data and UAV imagery from the North Fork Snoqualmie River, WA shows that modeled trends in channel adjustment to macro-roughness are generally consistent with data from the field site, but that the field site exhibits significant variability due to processes and feedbacks not captured by our model. We expect our model to be useful for establishing a priori expectations for the effects of process-based restoration projects on river form.
The shoreline is a boundary where survey methods change dramatically, where the time dimension is extremely important, where sediment fluxes are very large, where flotsam is trapped, and where numerical/physical singularities occur as the water depth goes to zero. The shoreline boundary oscillates; and as sea-levels rise what is now shore will become sea. Models of likely response of shorelines require detailed data on the sediment/beach/soil substrates.
We investigated how to obtain the best supporting data using the Louisiana area as example. We investigated to what extent the marine and terrestrial data were already in harmony, and what challenges remain in trying to make one seamless dataset. Of course, technologies like LIDAR carry out highly detailed imaging that achieves this to an extent. But we are focused on direct samplings of the ground-truthing type on which physical properties, fabrics, chemical compositions, grain types, genesis, can be directly determined.
Difficulties: Terrestrial surveys have a different data topology, more focused on soil polygons and boreholes; offshore mappings focus on point-samplings, for instance grabs and cores. Soil descriptions focus on layer-profile identities such as “Mollisol”; offshore datasets focus on bulk textures and compositions. Strong semantic differences exist. Terrestrial areas are greatly modified by agriculture and construction.
Positives: We discovered several information-integration pathways for merging the data from the two realms. Exhaustive searching uncovered data on the onshore soils and riverbed sediments to match the marine data (e.g. dbSEABED). Named geographical locations are linkable with coordinates through gazetteers. Computational methods exist to merge polygon and point data sets. In semantics, glossaries provide some information to link onshore and offshore descriptions. Seamless mappings are demonstrated, useful in support of cross-shore morphodynamic models. +
The shorelines of atoll reef islands (also called motu, sandy cays, or islets) frequently are the only available landforms in an atoll system, e.g. Kwajalein Atoll encompasses over 2174 km² but only 16 km2 of that area is emergent land, and thus understanding the drivers of coastal landscape evolution is vital. In particular, atolls are highly vulnerable to several threats of climate change from accelerated rates of sea level rise (causing flooding or potential drowning) to ocean acidification (decreasing coral reef resiliency) to ocean warming (causing coral bleaching). However, we lack a thorough understanding of the potential drivers of landscape change in these systems. In addition atolls can be exposed to high energy wave climates, however, the carbonate reef platform that encircles the inner lagoon of an atoll, commonly filters much of the incident wave energy. This reef platform or reef flat is typically shallow (1-2 m below MSL) with a near constant depth across the reef-flat width; the reef-flat widths range from a 100s meters to over a kilometer on different atolls. Both numerical modeling and field observations have found that these shallow reef-flats are key for driving wave breaking at the ocean edge of the reef flat offshore of the atoll reef islands and decreasing wave energy at the shoreline. As demand for construction materials increases, these carbonate reef platforms have been excavated, with large pits ranging from 10-80 m in width and average depths of 4 m. This study seeks to understand how the presence of excavation pits on reef flats change the wave energy at the shoreline. Utilizing 1D XBeach model, we investigate the impact of varying excavation pit geometry on the shoreline wave energy. We found that the presence of an excavation pit increases wave energy at the shoreline. +
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The stratigraphic record is the product of sedimentary processes acting over time. The Regional Ocean Modeling System (ROMS) includes algorithms for the processes of erosion, deposition, and mixing of both non-cohesive (sandy) and cohesive (muddy) sediment, and routines capable of tracking the evolution of event-scale stratigraphy with layers as fine as a few grain diameters thick. Thus ROMS allows users to relate process with product over time scales ranging from a few seconds to years, over vertical space scales of 0.1 mm to meters, and over horizontal space scales of meters to hundreds of kilometers. ROMS requires users to specify the number of bed layers to be tracked at compile time. This improves model efficiency on parallel systems, but complicates the task of tracking stratigraphic evolution. In addition to the number of layers, users can control the minimum and maximum layer thickness and the initial stratigraphy. The effect of these choices and the success of the stratigraphy routines is demonstrated with models of idealized estuaries, deltas, and continental shelves. +
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The surface geology of Late Cretaceous Western Interior Seaway (WIS) has been extensively studied, and many recent studies suggest the presence of dynamic loading due to flat slab subduction. However, it remains unclear how surface processes respond to tectonic forcing originated from either lithospheric flexural isostasy or sub-lithospheric mantle convection. Landscape evolution models represent an ideal tool to test the surface responses under different tectonic histories, each of which is designed to reflect a certain physical mechanism. In this research, we aim to use forward landscape evolution models to investigate the mechanisms accounting for the characteristics in the observed WIS stratigraphy. In our data-oriented landscape evolution models, where we test different scenarios of lithospheric and mantle forcing, the results suggest that only a geographically migratory subsidence can produce tilted strata and shifting depocenter, both of which are key features in the WIS sedimentary record. This implies that the tectonic subsidence of the WIS likely originated from deep mantle downwelling underneath the westward-moving North American plate. Furthermore, this migratory subsidence of mantle origin can also explain the continental drainage reorganization over middle North America after the WIS and the eastward-shifting sediment flux to the Gulf of Mexico during the Cenozoic. +
The tectonic stress fields induced by lateral and vertical variations in the lithosphere induce crustal deformation and lead to the development of fault and topography. Surface deformation and faulting influence channel processes, which may result in changes in drainage patterns. However, there are few studies that systematically compare and examine the connections among the lithospheric stress field, fault development, and observed drainage patterns on global scales. Here, we compare the directions of the lithospheric stress field, the development of fault and topography, and drainage flow patterns. First, we model the lithospheric stress field by computing the gravitational potential energy based on the crustal structure from Crust 1.0 augmented by a thermodynamically derived mantle thickness and density. We obtain the orientations of most and least compressive horizontal stresses and their inferred regimes and compare those with the World Stress Map (2016). We then extract the directions of active faults from the Global Earthquake Model Global Active Faults Database. Lastly, we extract the river flow paths and drainage network patterns from a digital elevation model from the steepest descent direction in the eight-direction flow. Our results show that there is a general correspondence between the predicted and observed patterns of fault orientation and river flow directions with the horizontal most compressive stress direction. The predicted correspondence among stress field, fault, and drainage patterns vary depending on the stress regime and channel order. We find that some locations show river flow patterns consistent with the predicted directions from fault and topographic development based on Anderson’s fault theory, but there are certain locations that show measurable deviations from the predicted patterns. We investigate those areas to better understand the interaction among shallow subsurface stress fields, surface topography, and drainage patterns.
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The tidal flats of Roberts Bank in British Columbia, Canada contain large areas of the intertidal zone that are vegetated with eelgrass (Zostera Marina and Zostera Japonica). This vegetation has a variable influence on the flow of tidal waters passing over the tidal flats, which we aim to describe in a large-scale 2D hydrodynamic model.
Vegetation on the surface of the tidal flats causes an increase in the roughness that modifies the flow properties. For submerged vegetation, this roughness is most strongly related to the height of the plants in the water; however, for very flexible plants such as eelgrass, the plant height changes with flow velocity since the plants bend with the currents. The roughness is therefore dependent both on flow depth and flow velocity.
Existing studies concerning the effect of flexible vegetation on flow are mostly focused on the small-scale properties of the velocity and turbulence profiles. Such results cannot be directly incorporated into 2D hydrodynamic models. 3D hydrodynamic modeling is computationally demanding and is therefore less appropriate for large-scale studies and engineering applications over large areas. In order to resolve this computational challenge we developed an integrated formulation of the effects of flexible vegetation on the flow, with the following approach: The roughness is represented through an equivalent Manning’s coefficient, which depends on both the water depth and the flow velocity.
Simulations are performed with the Telemac2d model, which has been modified to incorporate the velocity-dependent friction law. Preliminary results show that the proposed law is able to account for qualitative modifications in the tidal flow. In particular, the simulation provides an asymmetric flow pattern that correctly predicts the slower ebb velocities as compared to flood velocities, as observed in the field. +
The understanding of polar regions has advanced tremendously in the past two decades and much of the improved insight into our knowledge of environmental dynamics is due to multidisciplinary and interdisciplinary studies conducted by coordinated and collaborative research programs supported by national funding agencies. Although much remains to be learned with respect to component processes, many of the most urgent scientific, engineering and social questions can only be addressed through the broader perspective of studies on system scales. Questions such as quantifying feedbacks, understanding the implications of sea ice loss to adjacent land areas or society, resolving future predictions of ecosystem evolution or population dynamics all require consideration of complex interactions and interdependent linkages among system components. Research that has identified physical controls on biological processes, or quantified impact/response relationships in physical and biological systems is critically important, and must be continued; however we are approaching a limitation in our ability to accurately project how the Arctic and the Antarctic will respond to a continued warming climate. Complex issues, such as developing accurate model algorithms of feedback processes require higher level synthesis of multiple component interactions. Several examples of important questions that may only be addressed through systems analyses will be addressed. +
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The watershed of the Tapartó and Farallones rivers and the La Arboleda stream in the central zone of Colombia’s western mountain range are known to have experienced important debris flow events historically. In the same manner, there is geomorphological evidence that suggests a complex dynamic associated with the conditions of high slope, heavy rainfall and a soil profile with an important development.<br>The geomorphological analysis carried out in these watersheds enabled recognition of different levels of deposits in addition to their stratigraphic characterization. Likewise, radiocarbon dating allowed the establishment of ages between 100 +/- 30 and 2010 +/- 30 years for the different levels of deposits characterized. The integration of geomorphological and stratigraphic information along with radiocarbon dating allowed for the differentiation of the debris flow dynamics of each of the basins and suggests the existence of three phases. The first is an ancient one (with deposits older than 2000 years), followed by a sub-recent dynamic (represented by levels between 1500 and 2000 years old) and a current dynamic, with low incised deposits systems and ages that do not exceed 500 years. Finally, it was established that even though these basins have great potential for the generation of debris flow events of significant magnitude, the deposits show a tendency of decreasing magnitudes in the last 1000 years.<br>These analyses and their results are input to the construction of knowledge in relation to the understanding of this phenomenon in tropical environments and the generation of elements that would allow to address the problem in other zones with similar characteristics in throughout the country. +
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The west coast of North America is the setting for one of the world’s largest coastal upwelling regions. Large rivers drain from North America into the northern eastern Pacific Ocean, delivering large loads of sediments, as well as nutrients, organic matter and organisms. The Eel River discharges into the North Pacific just north of Cape Mendocino in Northern California. Its annual discharge (~200 m3/s) is about 1% that of the Mississippi, but its sediment yield (15 million tons/yr) is the highest for its drainage area (9500 km2) in the entire continental US. This strongly seasonal signal, generated largely by winter storm events that flush sediment and detritus into the river and down to the sea, generates dramatic nutrient pulses that may play a role in the timing and magnitude of offshore phytoplankton blooms. Understanding how the interannual variability of weather, moderated by slower trends in climate, affects these pulses, which in turn may alter offshore nutrient availability, is something we hope to explore through a detailed modeling framework. In our coupled modeling framework, the watershed is currently represented by the lumped empirical watershed model HydroTrend for its ability to generate high-frequency water and sediment time series in relatively unstudied basins. The atmosphere is represented by the NCEP North American Regional Reanalysis, a model and data assimilation tool. Eventually, we hope to represent the atmosphere with the Community Earth System Model, a powerful tool for studying climate change projections, which will let us talk about possible future impacts of climate change on coastal productivity. The ocean is represented with the Regional Ocean Modeling System, a powerful and very modular, physically distributed model that can efficiently solve fine-scale resolution grids. The coastal biology will be handled by modification of an iron-limited nutrient-phytoplankton-zooplankton-detritus model. +
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Theories for vertical bedrock river incision are well developed and widely applied; however, understanding how bedrock rivers laterally erode their banks and develop into wide bedrock valleys is a frontier topic in geomorphology. I use a modified version of the Landlab lateral erosion component coupled with the sediment-flux dependent vertical incision component in Landlab to explore the fundamental question of how valley width and widening rates are related to sediment on the channel bed. The lateral erosion component widens valleys through lateral undercutting and eventual collapse of bedrock valley walls. The modified lateral erosion component allows the user to set a characteristic block size of collapsed bedrock material. Collapsed material with smaller blocks sizes is rapidly transported away from the valley wall, allowing continued widening, while collapsed material with larger block sizes protects valley walls from further widening until it has weathered into transportable grain sizes. Model simulations show that valleys are wider in landscapes where collapsed material is closer in size to bedload sediment and narrower in landscapes where collapsed material is much larger than bedload sediment. I also use the newly modified lateral erosion/valley widening component together with additional Landlab components to explore the effects of variable discharge and changes in sediment flux on valley width and valley widening rates. This set of model experiments is a step towards a more nuanced and quantifiable framework for describing and predicting bedrock valley widening through time. Numerical models that include physical processes of valley widening are necessary for further advances of geomorphic applications such as numerical modeling of climate-driven strath terrace formation and hillslope–channel coupling. +
Theories for vertical bedrock river incision are well developed and widely applied; however, understanding how bedrock rivers laterally erode their banks and develop into wide bedrock valleys is a frontier topic in geomorphology. I use a modified version of the Landlab lateral erosion component coupled with the sediment-flux dependent vertical incision component in Landlab to explore the fundamental question of how valley width and widening rates are related to sediment on the channel bed. The lateral erosion component widens valleys through lateral undercutting and eventual collapse of bedrock valley walls. The modified lateral erosion component allows the user to set a characteristic block size of collapsed bedrock material. Collapsed material with smaller blocks sizes is rapidly transported away from the valley wall, allowing continued widening, while collapsed material with larger block sizes protects valley walls from further widening until it has weathered into transportable grain sizes. Model simulations show that valleys are wider in landscapes where collapsed material is closer in size to bedload sediment and narrower in landscapes where collapsed material is much larger than bedload sediment. I also use the newly modified lateral erosion/valley widening component together with additional Landlab components to explore the effects of variable discharge and changes in sediment flux on valley width and valley widening rates. This set of model experiments is a step towards a more nuanced and quantifiable framework for describing and predicting bedrock valley widening through time. Numerical models that include physical processes of valley widening are necessary for further advances of geomorphic applications such as numerical modeling of climate-driven strath terrace formation and hillslope–channel coupling. +
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Theories have been proposed using idealized tracer age modeling for ocean ventilation, atmospheric circulation, soil, stream and groundwater flow. In this research we developing new models for the dynamic age of water in hydroecological systems. Approaches generally assume a steady flow regime and stationarity in the concentration (tracer) distribution function for age, although recent work shows that this is not a necessary assumption. In this paper a dynamic model for flow, concentration, and age for soil water is presented including the effect of macropore behavior on the relative age of recharge and transpired water. Several theoretical and practical issues are presented. +
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There exists a rich understanding of channel forms and processes for rivers with unidirectional flows, and for their estuarine components with bidirectional flows. On the other hand, complementary insight on the transitional reach linking these flows has not been well developed. This study highlights the analyses of high resolution, high accuracy bathymetric surveys along a coastal plain river at 30 - 94 km upstream of the estuary mouth. The goal of this work is to identify geomorphic indicators of the fluvial-tidal transition channel. Trends with sharp breaks were detected in along-channel variations of depth, hydraulic radius, channel shape, bed elevation and sinuosity, but cross-section area of flow provided the greatest insight. The transition channel is characterized as a reach with greater than 50% decline in area of flow relative to the background values at the upstream and downstream ends. Further downstream the river is a mixed bedrock-alluvium system, and a 22 km reach of discontinuous bedrock outcrops has a marked influence on local channel metrics, and corresponding backwater effects on upstream metrics. Despite the confounding effects of bedrock on channel form the transition channel linking estuarine and fluvial channel segments is apparent as a 13 km geomorphic discontinuity in flow area along a channel reach of relatively uniform width. Finally, it is proposed that bedrock outcrops enhance tidal energy dissipation and influence the position of the fluvial-tidal transition reach, and associated geomorphic and hydrodynamic features. +
There is growing recognition that outwash events are potent agents of morphological change in some coastal regions. Outwash associated with inundation from the back side (bay, lagoon, sound, or marsh) occurred during Hurricane Harvey in Texas (2017) and Hurricane Dorian in North Carolina (2019). In both cases, floodwaters crossed the barrier islands and drained to the ocean through gaps in the primary dune lines, incising deep (~2-m) channels 30- 100-m wide in the islands and depositing the sand in the ocean. In both cases, partial recovery occurred within days and months as nearshore and beach processes generated spits, bars, berms, and overwash fans that rebuilt the beach and closed the channels, creating a series of ponds. Normally, washover deposits are quickly (1 – 2 years) revegetated with beach grasses that trap wind-driven sand and initiate dune building. However, in Texas, North Carolina, and several other locations where outwash channels were observed, the channels have remained largely unvegetated and no dunes have appeared. We have adapted a simple conceptual model to account for these observations. The model argues that the rate of vegetation growth depends, at least partially, on the amount of vegetation already present. In the case of overwash, material is deposited on older washover fans or platforms that contain live plants, seeds, rhizomes, and other organic material, and (following others) we suggest that the amount of vegetative material is a function of washover-deposit thickness. In contrast, when washout channels are filled, none of that material is present, and our model assigns these deposits very low initial amounts of vegetative material. Thus, vegetation growth on the two landscapes occurs at different rates, and the former outwash channels are unable to build elevation as quickly, leaving them continuously exposed to overwash events. A quantitative implementation of this model provides results that match well with observations at several sites.
This poster shows a top-down modeling work using a simple climate and economy model to examine pathways to achieve the climate stabilization targets stipulated in the Paris Agreement. A motivation for this presentation is to seek a possibility to complement this type of work with a bottom-up approach such as agent-based modeling so that climate mitigation pathways can be investigated from different angles.
In this work, we raise two issues: 1) Negative emission technologies such as Bioenergy with Carbon dioxide Capture and Storage (BioCCS) play an ever more crucial role in meeting the 2°C stabilization target. However, such technologies are currently at their infancy and their future penetrations may fall short of the scale required to stabilize the warming. 2) The overshoot in the mid-century prior to a full realization of negative emissions would give rise to a risk because such a temporal but excessive warming above 2°C might amplify itself by strengthening climate-carbon cycle feedbacks. It has not been extensively assessed yet how carbon cycle feedbacks might play out during the overshoot in the context of negative emissions.
This study explores how 2°C stabilization pathways, in particular those which undergo overshoot, can be influenced by carbon cycle feedbacks and asks their climatic and economic consequences. We compute 2°C stabilization emissions scenarios under a cost-effectiveness principle, in which the total abatement costs are minimized such that the global warming is capped at 2°C. We employ a reduced-complexity model, the Aggregated Carbon Cycle, Atmospheric Chemistry, and Climate model (ACC2), which comprises a box model of the global carbon cycle, simple parameterizations of the atmospheric chemistry, and a land-ocean energy balance model. The total abatement costs are estimated from the marginal abatement cost functions for CO2, CH4, N2O, and BC.
Our results show that, if carbon cycle feedbacks turn out to be stronger than what is known today, it would incur substantial abatement costs to keep up with the 2°C stabilization goal. Our results also suggest that it would be less expensive in the long run to plan for a 2°C stabilization pathway by considering strong carbon cycle feedbacks because it would cost more if we correct the emission pathway in the mid-century to adjust for unexpectedly large carbon cycle feedbacks during overshoot. Furthermore, our tentative results point to a key policy message: do not rely on negative emissions to achieve the 2°C target. It would make more sense to gear climate mitigation actions toward the stabilization target without betting on negative emissions because negative emissions might create large overshoot in case of strong feedbacks.
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This presentation addresses an important limitation to scientific productivity in fields that rely on computational modeling of landscape processes. Landscape models compute flows of mass, such as water, sediment, glacial ice, volcanic material, or landslide debris, across a gridded terrain surface. Science and engineering applications of these models range from short-term flood forecasting to long-term landform evolution. At present, software development behind these models is highly compartmentalized and idiosyncratic, despite the strong similarity in core algorithms and data structures between otherwise diverse models.
We report progress on a proof-of-concept study in which an existing landscape model code is adapted and enhanced to provide a set of independent, interoperable components (written initially in C++). These include: (1) a gridding engine to handle both regular and unstructured meshes, (2) an interface for space-time rainfall input, (3) a surface hydrology component, (4) an erosion-deposition component, (5) a vegetation component and (6) a simulation driver. The components can communicate with each other in one of two ways: using a simple C++ driver script, or using the Community Surface Dynamics Modeling System (CSDMS) Model Coupling Framework.
A central element is the gridding engine, which provides the ability to rapidly instantiate and configure a 2D simulation grid. Initially, the grid is an unstructured Delaunay/Voronoi mesh. Because the internal representation of geometry and topology is quite generic—consisting of nodes (cells), directed edges, polygon faces, etc.—the software can be enhanced to provide other grid formats, such as a simple raster or a quad-tree representation. The gridding engine also provides basic capabilities for finite-volume numerics, such as calculation of scalar gradients between pairs of neighboring cells, and calculation of flux divergence within cells.
Our hope is that these interoperable and interchangeable components with simple, standardized interfaces, will transform the nature and speed of progress in the landscape sciences by allowing scientist-programmers to focus on the processes of interest rather than on the underlying software infrastructure.
