Property:CSDMS meeting abstract
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The development of bedrock steps and waterfalls in mountain rivers locally changes flow hydraulics and can thereby alter patterns of sediment transport and erosion. While bedrock steps are thought to erode sometimes faster and sometimes slower than river reaches eroding without steps, it is unclear how differences in step frequency and morphology (e.g., the presence of many small bedrock steps and waterfalls versus the presence of a single large waterfall) alter channel dynamics and erosion rates at the reach scale. Furthermore, we do not know whether some or all step-rich channels are part of a transient knickzone or could be formed at steady state. Here, we use cosmogenic beryllium-10 (Be-10) erosion rates to examine whether bedrock steps alter the reach-averaged erosion rate. We find that all step-rich channels erode faster than or equal to catchment-average rates and preliminary analyses show that reach-scale erosion rates increase with increasing sediment flux, increasing grain size, and increasing step frequency. We compare our field results with a reach-scale erosion model we developed that combines both fluvial erosion at bedrock steps and fluvial erosion in reaches lacking steps. Our new reach-scale erosion model allows us to infer changes in erosion rates as a function of step frequency and step and channel morphology (e.g. dimensions of steps, and width and slope of channel between steps). This model will help interpret the impact of bedrock steps on erosion rates and determine their role in either adjusting or maintaining river profiles. +
The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding. Here, I present a cellular automata model of fault scarp and colluvial wedge evolution built using CelllabCTS and the GrainHill sediment physics from Landlab. The model appears to accurately reflect the development of real fault scarps. When one analyzes the model results, one may note interesting groupings of cells with similar sediment transport histories as the fault scarp evolves. These groupings appear to match real world sedimentological facies, such as 'debris' and 'wash' facies, which brings up an interesting question of how best one can compare model results with geological data. I discuss some approaches and quandaries and how one may go about about translating modeling concepts and language into field concepts and language and vice versa. +
The efficiency of fluvial sediment and particulate organic carbon (POC) burial in river deltas strongly depends on their depositional environment, which can range from protected incised valleys to exposed active margins. Here, we hypothesize that the formation and infilling of incised valleys from Holocene sea-level rise led to increases in fluvial sediment burial efficiency, and, consequently, POC burial. To test this, we developed a new incised valley fill model that estimates incised valley volume and fill rates. We apply this model to all river deltas globally (n~11,000), some of which are filled already but many are still infilling since Holocene sea-level rise slowed ~6ka BP. The rate of incised valley infilling is determined based on global model estimates of fluvial sediment and POC supply. We use our model to explore the magnitude of POC burial during the Holocene, including its potential for global climate regulation. +
The escalating rate of forest mortality, fueled by increasing climate variability and the spread of exotic pests and diseases, is a growing global concern. A significant contributor to this issue in North America is the Emerald Ash Borer (EAB), an invasive pest responsible for the widespread destruction of ash trees (Fraxinus spp.), resulting in a sharp increase in the number of snags. Snags, or dead-standing trees, present significant risks to infrastructure, including buildings and electrical distribution systems. Our study focuses on New Jersey, a highly urbanized state with an extensive electric grid that intersects forested areas, many of which are populated with Fraxinus trees. In this research, an annual risk assessment methodology for evaluating the threat that Fraxinus snags pose to the electrical distribution infrastructure is presented, particularly in the context of New Jersey's ongoing efforts to enhance the resiliency and capacity of its electric distribution network through capacity upgrades. Employing an integrated approach composed of GIS, differential equations, and applied regression modeling, our analysis spans three northern New Jersey counties: Warren, Sussex, and Morris. These counties, which are under the utility management of New Jersey Central Power and Light, harbor a significant portion of the state's Fraxinus population, making them crucial areas for assessing the impact of snags on the electrical distribution infrastructure under different network parameterizations. +
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The evolution of fluvial deltas involves a complex web of processes, many of which are yet poorly understood. In particular, the role of organic matter (peat) accumulation on delta dynamics still remains elusive. Here, we present a simple geometric prism model that couples the evolution of the delta plain with the accumulation of organic-rich sediment. The model is able to explain the observed coupling between the accommodation/peat accumulation ratio and the quality of buried peat/coal deposits in the delta plain. Similarly to multiple modern and ancient organic-rich sedimentary environments, the model preserves the maximum volume fraction of organic sediment in the delta plain when the overall accommodation rate approximately equals the rate of peat accumulation. Further analysis of the model under simple scenarios of base-level rise and pivot subsidence shows that organic matter accumulation can either enhance or alleviate shoreline transgression. +
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The evolution of human-flood systems is shaped by complex interactions between hazards, policy decisions, individual risk perception, and the exposure of properties. This complexity is further stressed by the changing climate conditions, making it crucial to understand how these systems will evolve and which regions and populations will be most affected. In this regard, we calibrated socio-environmental models across US coastal communities with historical records of flooding hazards, National Flood Insurance Program (NFIP) economic losses, NFIP policy purchases, housing density, and housing values. Next, we forced future projections of sea level rise, storm surge, and rainfall intensity under Shared Socio-economic Pathways (SSP) SSP245 and SSP585 up to 2100 for each coastal communities, and forecasted the future flooding loss, NFIP active policies, housing density, and housing values. We found significant regional and demographic variations in human-flood dynamics. The Pacific coast, due to high rainfall and storm surge threshold has less exposure, but a more sensitive housing market and NFIP participation rate. In contrast, the Atlantic and Gulf coasts are more exposed to hazards but have a less sensitive housing market and NFIP participation. Relative to historical average, we forecast flood loss to increase by 130% (SSP585) and 25% (SSP245) with a modest policy coverage of 16% (SSP585) and 13% (SSP245). Furthermore, we predict socially vulnerable communities to experience disproportionately more economic loss with a slow policy uptake rate, leading to a growing insurance coverage gap under both climate scenarios. Finally, we tested the effect of heightening levees across the US coast on future flood risk, and found that levee investment can stabilize housing markets, but it won’t eliminate flooding risk entirely due to increased rainfall intensity. Understanding how human-flood systems co-evolve under climate risk helps to recognize population and property at risk and make robust mitigation strategies.
The extent to which chemical and mechanical erosion each contribute to the erosion of cave passages in limestone is an open question. In mixed cave riverbeds that are partially alluviated and partially exposed limestone bedrock, we sometimes see clearly scalloped bedrock. The uniquely soluble properties of limestone imply that these scallops that tessellate to comprise the scalloped bedrock are the result of chemical dissolution. However, because we see silt, sand, and gravel, and because when we visit the same reach of the cave river many times, we see those sediment deposits shift in size and location, we infer that there may also be physical abrasion from sediment impacts on the scalloped bedrock surface. In this paper, we compare the equations that describe dissolution of limestone with those that describe abrasion of bedrock to prove that dissolution and abrasion may be co-occurring processes. Using our numerical model, DKARST (Does karst abrasion result in scalloped tunnels?), in conjunction with previous data from dissolution studies, we quantified parameters that delineate four distinct erosional zones according to the likelihood of contribution to overall erosion from dissolution, abrasion, or both processes combined. We then generalized those erosional zones to a range of scalloped bedrock morphology characteristic wavelengths. Our investigation of the role of mechanical erosion to the scalloping of bedrock in caves provides insight into the settling velocities of particles in turbulent flow over rough beds, as well as the relative roles played by mechanical and chemical processes in broader scale landscape evolution, particularly in karst regions dominated by carbonate bedrock. +
The formation and evolution of channel networks is a critical control on coastal landscapes and fluvial stratigraphy. Analysis of drainage networks often divides them into two regions: a dendritic upstream catchment with behavior governed by erosional processes resulting from the interaction of climate and tectonics, and a transition to a distributary reach governed by depositional processes close to the coast. The landscape built by these larger coastal distributaries is typically dominated by low-relief floodplains and numerous smaller stream networks. Despite the importance of these networks in governing the routing of fluids and sediments that build these landscapes, network geometries and characteristics remain poorly studied and understood. The northern Gulf of Mexico coastal plain is a depositional landscape characterized by the channels and deposits of large fluvial systems that have been prograding into the Gulf of Mexico since the Mesozoic, and hosts smaller stream networks locally known as the Coastal River Basins. Using a compilation of lidar bare earth elevation datasets we systematically identify and map these tributary stream networks across the coastal plain. We calculate for each basin a series of stream metrics that include local relief, slope, and length/contributing area. Additionally, our high-resolution (2m) elevation data allows for detailed analysis of the stream heads and drainage divides between each identified basin. We find that the basin divides for these networks are older distributary channel belts built by the larger fluvial systems. This indicates that the organization and geometry of these coastal networks is initially set and controlled by depositional processes, but the resulting basin morphology is nearly identical to those of drainage networks in predominantly erosional settings. We explore how drainage networks can form in depositional settings as the consequence of sedimentary processes such as river avulsion and ridge formation, with important implications for understanding drivers of drainage network formation, the speed and scale of drainage reorganization in coastal settings, flow routing during floods, and fundamental controls on the creation and preservation of fluvial stratigraphy.
The formation of the branching channel network is controlled mainly by water discharge and the boundary shape of receiving basin. The understanding of channel morphology is important because it controls the sediment diversion in a river delta, and determines the sustainability of coastal zones. Numerical models of river deltas have improved remarkably over the past two decades. However, the long-term (millennial scale) simulation of real delta systems remains rare. Here, we attempt to reconstruct the Lafourche Delta channel network, active 1600-600 years before present, with a simple numerical model (Moving Boundary Model for Distributary Channel Networks MB_DCN). Runs with 10 basin boundary shapes and 6 river discharge rate scenarios using the Moving Boundary Model for Distributary Channel Networks (MB_DCN) show that each scenario produced distinguishing channel characteristics including a complex channel network, diverse progradation rates and channel numbers, and number of bifurcations. For the appropriate basin shapes, reasonable water discharges and common sediment transport parameters, MB_DCN produces a channel network that resembles the Lafourche Delta channel network morphology and progradation rates. Our preliminary results suggest that the basin boundary shape and water discharge are the most important control of the distributary channel network in terms of channel geometry and progradation rates. +
The frequency of high temperature events is increasing globally under the current climate change conditions. These extreme events have important consequences for society, affecting public health, the regional habitability and the global economy. We evaluate the changes in frequency and distribution of high temperature events over North America, using three different indices and a set of regional climate simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX). Our results show an increase in the number of high temperature days per summer, in addition to an increase in the frequency of heat wave events for the 21st century. The results reveal large variability among the regional climate models and boundary conditions from the driving models. The increase in the frequency of high temperature simulations examined over North America advocates for strategies to prevent potential effects on food availability, public health and the environment. +
The geologic history of major river canyons is strongly debated, as is the extent to which river canyons record climatic and tectonic signals. Fluvial and hillslope processes work in concert to control canyon evolution; rivers both set the boundary conditions for adjoining hillslopes and respond to delivery of hillslope-derived sediment. But what happens when canyon walls deliver boulders that are too large for a river to carry? River canyons commonly host large blocks of rock derived from resistant hillslope strata. Blocks have recently been shown to control the shapes of hillslopes and channels by inhibiting sediment transport and bedrock erosion. Here we present Blocklab, a 2-D model within the Landlab modeling toolkit that uses a hybrid discrete-continuum framework to track block transport throughout a river canyon landscape. This is the first process-based model for canyon evolution that incorporates the roles of blocks in both hillslope and channel processes. Our model reveals that two-way negative channel-hillslope feedbacks driven by block delivery to the river result in characteristic planview and cross-sectional river canyon forms. Internal negative feedbacks strongly reduce the rate at which erosional signals pass through landscapes, leading to persistent local unsteadiness even under steady tectonic and climatic forcing. Surprisingly, while the presence of blocks in the channel initially slows incision rates, the subsequent removal of blocks from the oversteepened channel substantially increases incision rates. This interplay between channel and hillslope dynamics results in highly variable long-term erosion rates. These autogenic channel-hillslope dynamics can mask external signals, such as changes in rock uplift rate, complicating the interpretation of landscape morphology and erosion histories. +
The growing complexity of landscape evolution models (LEMs) has broadened their use to answer a variety of questions, but approaches for statistically assessing model outputs remain underexplored. Here, we suggest enhancing the study of LEM outputs by utilizing Shannon Entropy, Moran's I, and Geary's C, which provide insights into dynamics and variations within and between simulations, both quantitatively and visually. Three experiments were used as case studies; a constant uplift (Experiment 1), a periodic alternating uplift (Experiment 2), and a spatially variable uplift (Experiment 3). Incorporating the proposed metrics as a comparison module in LEMs offers a methodical way to analyze variations in information content, gauge spatial consistency, and spot simulation divergence. Although our focus is on LEM outputs, similar techniques may be applied to any matrix-based data or digital elevation models (DEMs), allowing for thorough model evaluations and better decision-making in topographic analysis and landscape modeling investigations. This material was developed during the 2024 CSDMS Visiting Scholar Program, being supported by NSF under Grant Nos. EAR-2104102 and EAR-1917695. +
The hazards faced by retreating barrier island systems to the increased rates of sea level rise predicted over the coming century and beyond lacks historic precedent. Consequently, exploration of the sedimentological record can provide key insights into how barrier systems might behave in the future. Continental shelves around the world preserve records of former barriers as relict deposits, providing a window into past behaviors. These relict barrier deposits are usually considered to originate from purely allogenic processes, or external environmental forcing, with barrier abandonment typically attributed to episodes of increased rate of sea level rise. However, using a cross-shore morphodynamic model, we show that the internal dynamics of migrating barriers can also result in autogenic deposition of relict sediments even under a constant rate of sea level rise. Subsequently, we propose that allogenic forcing from sea level rise and autogenic forcing from internal dynamics might interact to produce novel barrier retreat behaviors, with the potential to be recorded on the seabed by relict deposits. We model barriers through a range of scenarios with interacting autogenic and allogenic forcing, showing that the morphology of deposits might be used to infer the relative influence of external and internal processes. Intriguingly, our results demonstrate that the internal dynamics of barriers can both amplify and dampen losses of shoreface sediment to the seabed during increased rates of rise, in some cases with internal processes increasing the risk of barrier destruction. Future classification of relict deposits in the field could help explain if and when these allogenic/autogenic interactions have taken place, revealing long term hazards to modern barrier systems that have not previously been described. +
The high speed winds of a hurricane account for 95% of a hurricane’s storm surge. Thus, parametric wind models are vital components of numerical storm surge modeling. These parametric hurricane wind models are used as inputs for a storm surge computation to hindcast and forecast hurricane surge heights. These wind models are dependent on several input parameters including but not limited to the radius at which the maximum wind speed of the hurricane occurs and the speed of the maximum winds. The impact of these input parameters on the final surge computation is not well known. Our study is a sensitivity analysis of the effect of uncertainty in the input parameters on the uncertainty in the final computation of the storm surge model. This study will help us to understand the robustness of a parametric wind model, the parameters that must be precise in order to reduce model error, and can aid in model simplification. +
The impact of climate on tectonics has been the muse of tectonic geomorphologists for more than 30 years. However, few natural examples exist where connections between climate and tectonics are clear. Here, we present a study of the Sangre de Cristo Mountains (SCM), CO, a normal fault system at the northern tip of the Rio Grande Rift. The SCM represents an ideal natural setting to explore the impact of climate on spatial and temporal slip patterns along the range-bounding fault. Preserved glacial moraines and trimlines are used with the Glacier Reconstruction (GlaRe) toolbox to model glacial extents during the last glacial maximum (LGM). A simple line load model is used to explore the impact of glacial melting on clamping stress along the range front fault, and a flexural isostatic model is applied to estimate the footwall response to deglaciation. Results show that glacial melting reduces fault clamping stress, perhaps enabling accelerated fault slip in the post-glacial period. Flexural isostatic results suggest modest footwall uplift of ~4 m due to ice removal. We compare our results to fault displacement, measured from scarps preserved in Pleistocene and Holocene alluvial fans. The spatial pattern and magnitude of Holocene fault displacement are consistent with our flexural isostatic results. Furthermore, Holocene slip rates are at least a factor of three higher than Pleistocene slip rates. We infer that the flexural isostatic response to footwall deglaciation primarily controls the spatial and temporal fault slip patterns during the Holocene. Our results show that climate-modulated glacial ice loading and unloading can pace the spatial and temporal slip on a range-bounding normal fault system. +
The impact of supraglacial meltwater on the motion of the Greenland Ice Sheet is strongly correlated to spatial and temporal variability of meltwater input. Meltwater infiltrates the bed through moulins and can reduce effective pressure and, consequently, accelerate the ice. However, the subglacial conduit system evacuates the water and can adapt to accommodate different water inputs. The timing of water infiltration impacts the ability of the system to reach equilibrium state. With the progression of the equilibrium line higher up on the ice under warming climate, it is essential to predict how increased meltwater is going to affect ice motion. Understanding these processes will reduce uncertainty in global sea level rise predictions.
Temporal variability of meltwater input is difficult to measure on the ice sheet due to the difficulties in instrumenting constantly melting stream beds. Therefore, glacier dynamic models rely on surface mass balance models to simulate the discharge. Those models usually neglect spatial properties of the drainage basin and are not able to reproduce the peak meltwater discharge in supraglacial streams. Lags between peak melt and peak discharge vary from one stream to another, and factors influencing the delay between peak melt and peak discharge have not been thoroughly explored. For this reason, we propose to build a distributed and physically based model using Landlab to reproduce flow routing on the Greenland Ice Sheet. This model will produce discharge values on a grid using three grid layers that calculate: 1) meltwater production, 2) flow direction, and 3) water displacement velocity. Model inputs will be weather, elevation, and snow coverage data. This model will enable us to explore and extract the main parameters influencing lags and predict the spatial pattern of infiltration lags at an ice sheet scale. +
The impacts of climate change on extent of permafrost degradation in the Himalayas are not well understood due to lack of historical ground-based observations. The area of permafrost exceeds that of glaciers in almost all Hindu Kush Himalayan (HKH) countries. However, very little is known about permafrost in the region as only a few local measurements have been conducted which is not sufficient to produce the fundamental level of knowledge of the spatial existence of permafrost. We intend to simulate permafrost conditions in Western Himalayas in India using Hyperspectral and Microwave remote sensing methods and computational models for the quantitative assessment of the current state of permafrost and the predictions of the extent and impacts of future changes. We also aim to identify the strength and limitations of remotely sensed data sets when they are applied together with data from other sources for permafrost modelling. We look forward to modelling ground temperatures using remote sensing data and reanalysis products as input data on a regional scale and support our analysis with measured in situ data of ground temperatures. Overall, we approach to model the current state and predictable future changes in the state of permafrost in Western Himalayas and also couple our results with similar research outcomes in atmospheric sciences, glaciology, and hydrology in the region. +
The increasing demand for sediments as source material for beach nourishment projects highlights the need to understand inner-shelf transport dynamics. At cape-related shoals, from where sedimentary materials are customarily extracted, the variability in particulate transport and related bedform evolution are not well understood.
To analyze bed elevation variability at a shoal adjacent to Cape Canaveral, Florida, an acoustic Doppler current profiler (ADCP) was deployed in spring 2014 at the outer swale of Shoal E, ~20 km south east of the cape tip at a depth of ~13 m. ADCP-derived velocity profiles and suspended particle concentrations were used to quantify instantaneous temporal changes in bed elevation (dζ/dt) using a simplified version of the Exner equation. Using mass conservation, temporal (deposition and entrainment) and spatial gradients in suspended sediment concentrations were calculated, although neither bed-load fluxes nor spatial gradients in velocities were considered.
Calculated values for instantaneous dζ/dt ranged from erosion at ~1e-3 m/s to accretion at 0.5e-3 m/s. Most of the variability was found at subtidal (<1 cycle/day) and tidal (~2 cycles/day) periodicities. Bed changes were small (<0.005 m/s) when tidal motions were important, e.g. from May 6 to 16, whereas subtidal motions at periods of 1 and 8 days dominated erosion/accretion events between May 16 and 31. Values suggest a bed erosion of 3.1e-3 m during ~30 days of the experiment, which was 2 orders of magnitude less, and had a contrary tendency to the average accretion of ~150e-3 m in 37 days measured between July 28 and September 3 at the edge of Southeast Shoal, i.e. ~5 km to the northwest.
In addition to the fact that measurements were not performed simultaneously at the same location, the discrepancy in dζ/dt could be attributed to the underestimation of bed changes due to the exclusion of bed-load fluxes. Despite several uncertainties, these findings provide preliminary evidence regarding the role of seasonal and storm-driven subtidal flows in particulate transport at cape-associated shoals. Our methodology can be used to inform numerical models of sediment transport and morphological evolution along inner continental shelves.
The influence of hydrodynamics on delta morphology is well-understood: fluvial, tidal and wave processes sculpt deltas into characteristic shapes that serve as geomorphic signatures of the underlying dynamics. This work examines how complex interactions between major rivers and tides influence the dendritic, island-dense morphology of the Ganges-Brahmaputra-Meghna Delta (GBMD). In the uppermost delta plain, fluvial processes dominate. Moving downstream, tides begin to interact with fluvial dynamics in a “mixed” process zone. Near the terminus of the GBMD in the Bay of Bengal, tidal processes take over, particularly in the western, abandoned lobes of the delta. This work focuses on how sediment transport and floodplain deposition patterns and rates change along that process transition. Using geomorphic metrics such as island area, aspect and channel sinuosity within new machine learning techniques, we resolved areas of the delta that display similar process signatures. Ideal island cases were selected from several zones across the fluvial-tidal transition. Using Delft3D, we modeled the patterns of geomorphic change that result from multiple flood ranges (low, medium and extreme) and sediment cases (-50%, average +50% suspended sediment concentration of 4 cohesive grain classes). Preliminary results indicate floods can deposit 2 – 3 cm of sediment per year across the delta, albeit in distinct patterns due to local differences in hydrodynamic processes. By using this highly-resolved nested model approach, deposition rates can be upscaled to estimate the amount of sediment being reworked within the individual process zones. The results obtained can then be used to illustrate how the different hydrodynamic zones contribute to the large-scale evolution of the delta, and explore how the system will respond to predicted global sea level rise over the next century. +
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The interaction of the subsiding, subtropical limb of the Hadley circulation and the easterly North Pacific trade winds establishes a persistent thermal inversion about halfway up the eastern flank of the Big Island of Hawaii. This restricts convective rainfall to the lower elevations, resulting in stream channels that cross an order-of-magnitude rainfall gradient, active ephemerally above the inversion and perennially below it. Above the inversion–capped cloud layer, precipitation is on the order of 400 mm/yr, and the landscape features thin, weakly-developed soils, gentle hillslopes, and ephemeral, shallowly incised bedrock streams and grassland gullies. Below the inversion, where rainfall is >3000 mm/yr, the perennial streams run through 50- to 100-m-deep gulches, with steep forested walls covered by thick tropical soils that are prone to landsliding. Meter- to 50-meter waterfalls are common downstream of the inversion layer, and incision of the deep gulches may proceed by upstream migration of these knickpoints from the coast. The positions of these knickpoints likely reflect the history of lava flows in these catchments, base level changes due to landsliding at the coast, and the statistics of water and sediment discharge above and below the trade inversion and through time.
This landscape has evolved entirely in the last 0.3 Ma, and thus under conditions of glacial-interglacial climate oscillations. During glacial periods, the inversion’s average elevation was likely depressed, although the magnitude of this depression is not well-constrained. An ice cap that was present on Mauna Kea altered the hydrology of the upper slopes of the mountain, providing a continuous source of meltwater to channels that, in the modern setting, are active only during winter storms and rare hurricane strikes. The frequency and intensity of such storms during glaciations are also not well-known.
To quantify these effects, we would like to use climate models to inform landscape evolution models. A key difficulty in coupling these types of models is the separation of time and spatial scales involved. Global climate models typically run on grids of 1 degree or more, at temporal resolution of seconds and run lengths of years to decades. Landscape evolution models (LEMs) reside at the other end of both dimensions, with typical spatial resolutions of meters to km and temporal resolutions of years or decades. The entire duration of a climate model run may be shorter than the timestep of a typical LEM.
We report initial results from our efforts to bridge the relevant scales by downscaling large-scale climate model output for last-glacial and modern times with NCAR’s regional-scale Weather Research and Forecasting (WRF) model. The predicted precipitation fields are input to a hydrologic model to generate realistic discharge statistics useful for landscape modeling. This modeling chain may be validated for the modern climate using atmospheric observations, including the modern distribution of inversion height, and USGS stream gauge data. For glacial periods, the ability of the weather model to correctly predict snowlines on Mauna Kea provides a first-order point of calibration.
