Effect of changing vegetation and precipitation on denudation – Part 1: Predicted vegetation composition and cover over the last 21 thousand years along the Coastal Cordillera of Chile

Abstract. Vegetation is crucial for modulating rates of denudation and landscape evolution, as it stabilizes and protects hillslopes and intercepts rainfall. Climate conditions and the atmospheric CO2 concentration, hereafter [CO2], influence the establishment and performance of plants; thus, these factors have a direct influence on vegetation cover. In addition, vegetation dynamics (competition for space, light, nutrients, and water) and stochastic events (mortality and fires) determine the state of vegetation, response times to environmental perturbations and successional development. In spite of this, state-of-the-art reconstructions of past transient vegetation changes have not been accounted for in landscape evolution models. Here, a widely used dynamic vegetation model (LPJ-GUESS) was used to simulate vegetation composition/cover and surface runoff in Chile for the Last Glacial Maximum (LGM), the mid-Holocene (MH) and the present day (PD). In addition, transient vegetation simulations were carried out from the LGM to PD for four sites in the Coastal Cordillera of Chile at a spatial and temporal resolution adequate for coupling with landscape evolution models. A new landform mode was introduced to LPJ-GUESS to enable a better simulation of vegetation dynamics and state at a sub-pixel resolution and to allow for future coupling with landscape evolution models operating at different spatial scales. Using a regionally adapted parameterization, LPJ-GUESS was capable of reproducing PD potential natural vegetation along the strong climatic gradients of Chile, and simulated vegetation cover was also in line with satellite-based observations. Simulated vegetation during the LGM differed markedly from PD conditions. Coastal cold temperate rainforests were displaced northward by about 5∘ and the tree line and vegetation zones were at lower elevations than PD. Transient vegetation simulations indicate a marked shift in vegetation composition starting with the past glacial warming that coincides with a rise in [CO2]. Vegetation cover between the sites ranged from 13 % (LGM: 8 %) to 81 % (LGM: 73 %) for the northern Pan de Azúcar and southern Nahuelbuta sites, respectively, but did not vary by more than 10 % over the 21 000 year simulation. A sensitivity study suggests that [CO2] is an important driver of vegetation changes and, thereby, potentially landscape evolution. Comparisons with other paleoclimate model drivers highlight the importance of model input on simulated vegetation. In the near future, we will directly couple LPJ-GUESS to a landscape evolution model (see companion paper) to build a fully coupled dynamic-vegetation/landscape evolution model that is forced with paleoclimate data from atmospheric general circulation models.

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Effect of changing vegetation on denudation (part 1): Predicted vegetation composition and cover over the last 21 thousand years along the Coastal Cordillera of Chile

10.5194/esurf-2018-14 ◽

2018 ◽

Author(s):

Christian Werner ◽

Manuel Schmid ◽

Todd A. Ehlers ◽

Juan Pablo Fuentes-Espoz ◽

Jörg Steinkamp ◽

...

Keyword(s):

Vegetation Cover ◽

General Circulation ◽

Landscape Evolution ◽

General Circulation Models ◽

Sensitivity Study ◽

Evolution Model ◽

Vegetation Changes ◽

Vegetation Composition ◽

Climate Conditions ◽

Coastal Cordillera

Abstract. Vegetation is crucial for modulating rates of denudation and landscape evolution as it stabilizes and protects hillslopes and intercepts rainfall. Climate conditions and atmospheric CO2 concentration ([CO2]) influence the establishment and performance of plants and thus have a direct influence on vegetation cover. In addition, vegetation dynamics (competition for space, light, nutrients and water) and stochastic events (mortality and fires) determine the state of vegetation, response times to environmental perturbations, and the successional development. In spite of this, state-of-art reconstructions of past transient vegetation changes have not been accounted for in landscape evolution models. Here, a widely used dynamic vegetation model (LPJ-GUESS) was used to simulate vegetation composition/ cover and surface runoff in Chile for the Last Glacial Maximum (LGM), Mid Holocene (MH) and present day (PD). In addition, we conducted transient vegetation simulations from LGM to PD for four sites of the Coastal Cordillera of Chile at a spatial and temporal resolution adequate for coupling with landscape evolution models. Using a regionally-adapted parametrization, LPJ-GUESS was capable of reproducing present day potential natural vegetation along the strong climatic gradients of Chile and simulated vegetation cover was also in line with satellite-based observations. Simulated vegetation during the LGM differed markedly from PD conditions. Coastal cold temperate rainforests where displaced northward by about 5° and the tree line and vegetation zones were at lower elevations than at PD. Transient vegetation simulations indicate a marked shift in vegetation composition starting with the past-glacial warming that coincides with a rise in [CO2]. Vegetation cover between the sites ranged from 13 % (LGM: 8 %) to 81 % (LGM: 73 %) for the northern Pan de Azúcar and southern Nahuelbuta sites, respectively, but did not vary by more than 10 % over the 21,000 yr simulation. A sensitivity study suggests that [CO2] is an important driver of vegetation changes and, thereby, potentially landscape evolution. Comparisons with other paleoclimate model driver highlight the importance of model input on simulated vegetation. In the near future, we will directly couple LPJ-GUESS to a landscape evolution model (see companion paper) to build a fully-coupled dynamic-vegetation/ landscape evolution model that is forced with paleoclimate data from atmospheric general circulation models.

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Evaluation of a Unique Approach to High-Resolution Climate Modelling using the Model for Prediction Across Scales (MPAS) version 5.1

10.5194/gmd-2019-34 ◽

2019 ◽

Author(s):

Allison C. Michaelis ◽

Gary M. Lackmann ◽

Walter A. Robinson

Keyword(s):

Climate Change ◽

High Resolution ◽

Sea Ice ◽

Northern Hemisphere ◽

General Circulation ◽

Southern Oscillation ◽

Spatial Scales ◽

General Circulation Models ◽

Climate Modelling ◽

Northern Hemispheric

Abstract. We present multi-seasonal simulations representative of present-day and future thermodynamic environments using the global Model for Prediction Across Scales-Atmosphere (MPAS) version 5.1 with high resolution (15 km) throughout the Northern Hemisphere. We select ten simulation years with varying phases of El Niño-Southern Oscillation (ENSO) and integrate each for 14.5 months. We use analysed sea surface temperature (SST) patterns for present-day simulations. For the future climate simulations, we alter present-day SSTs by applying monthly-averaged temperature changes derived from a 20-member ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5) general circulation models (GCMs) following the Representative Concentration Pathway (RCP) 8.5 emissions scenario. Daily sea ice fields, obtained from the monthly-averaged CMIP5 ensemble mean sea ice, are used for present-day and future simulations. The present-day simulations provide a reasonable reproduction of large-scale atmospheric features in the Northern Hemisphere such as the wintertime midlatitude storm tracks, upper-tropospheric jets, and maritime sea-level pressure features as well as annual precipitation patterns across the tropics. The simulations also adequately represent tropical cyclone (TC) characteristics such as strength, spatial distribution, and seasonal cycles for most of Northern Hemispheric basins. These results demonstrate the applicability of these model simulations for future studies examining climate change effects on various Northern Hemispheric phenomena, and, more generally, the utility of MPAS for studying climate change at spatial scales generally unachievable in GCMs.

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Evaluation of a unique approach to high-resolution climate modeling using the Model for Prediction Across Scales – Atmosphere (MPAS-A) version 5.1

Geoscientific Model Development ◽

10.5194/gmd-12-3725-2019 ◽

2019 ◽

Vol 12 (8) ◽

pp. 3725-3743 ◽

Cited By ~ 5

Author(s):

Allison C. Michaelis ◽

Gary M. Lackmann ◽

Walter A. Robinson

Keyword(s):

Climate Change ◽

High Resolution ◽

Sea Ice ◽

Northern Hemisphere ◽

General Circulation ◽

Large Scale ◽

Southern Oscillation ◽

Spatial Scales ◽

Coupled Model ◽

General Circulation Models

Abstract. We present multi-seasonal simulations representative of present-day and future environments using the global Model for Prediction Across Scales – Atmosphere (MPAS-A) version 5.1 with high resolution (15 km) throughout the Northern Hemisphere. We select 10 simulation years with varying phases of El Niño–Southern Oscillation (ENSO) and integrate each for 14.5 months. We use analyzed sea surface temperature (SST) patterns for present-day simulations. For the future climate simulations, we alter present-day SSTs by applying monthly-averaged temperature changes derived from a 20-member ensemble of Coupled Model Intercomparison Project phase 5 (CMIP5) general circulation models (GCMs) following the Representative Concentration Pathway (RCP) 8.5 emissions scenario. Daily sea ice fields, obtained from the monthly-averaged CMIP5 ensemble mean sea ice, are used for present-day and future simulations. The present-day simulations provide a reasonable reproduction of large-scale atmospheric features in the Northern Hemisphere such as the wintertime midlatitude storm tracks, upper-tropospheric jets, and maritime sea-level pressure features as well as annual precipitation patterns across the tropics. The simulations also adequately represent tropical cyclone (TC) characteristics such as strength, spatial distribution, and seasonal cycles for most Northern Hemisphere basins. These results demonstrate the applicability of these model simulations for future studies examining climate change effects on various Northern Hemisphere phenomena, and, more generally, the utility of MPAS-A for studying climate change at spatial scales generally unachievable in GCMs.

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Local Regimes of Atmospheric Variability: A Case Study of Southern California

Journal of Climate ◽

10.1175/jcli3837.1 ◽

2006 ◽

Vol 19 (17) ◽

pp. 4308-4325 ◽

Cited By ~ 75

Author(s):

Sebastien Conil ◽

Alex Hall

Keyword(s):

Spatial Structure ◽

Land Surface ◽

General Circulation ◽

Large Scale ◽

Spatial Scales ◽

Surface Wind ◽

General Circulation Models ◽

Climate Impacts ◽

Atmospheric Variability ◽

Composite Surface

Abstract The primary regimes of local atmospheric variability are examined in a 6-km regional atmospheric model of the southern third of California, an area of significant land surface heterogeneity, intense topography, and climate diversity. The model was forced by reanalysis boundary conditions over the period 1995–2003. The region is approximately the same size as a typical grid box of the current generation of general circulation models used for global climate prediction and reanalysis product generation, and so can be thought of as a laboratory for the study of climate at spatial scales smaller than those resolved by global simulations and reanalysis products. It is found that the simulated circulation during the October–March wet season, when variability is most significant, can be understood through an objective classification technique in terms of three wind regimes. The composite surface wind patterns associated with these regimes exhibit significant spatial structure within the model domain, consistent with the complex topography of the region. These regimes also correspond nearly perfectly with the simulation’s highly structured patterns of variability in hydrology and temperature, and therefore are the main contributors to the local climate variability. The regimes are approximately equally likely to occur regardless of the phase of the classical large-scale modes of atmospheric variability prevailing in the Pacific–North American sector. The high degree of spatial structure of the local regimes and their tightly associated climate impacts, as well as their ambiguous relationship with the primary modes of large-scale variability, demonstrate that the local perspective offered by the high-resolution model is necessary to understand and predict the climate variations of the region.

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Volcanic hazard exacerbated by future global warming–driven increase in heavy rainfall.

10.31223/x5z906 ◽

2021 ◽

Author(s):

Jamie Farquharson ◽

Falk Amelung

Keyword(s):

Global Warming ◽

General Circulation ◽

Heavy Rainfall ◽

Spatial Scales ◽

General Circulation Models ◽

Volcanic Hazards ◽

Volcanic Arcs ◽

Increased Risk ◽

Future Global Warming ◽

Wide Range

Heavy rainfall drives a range of eruptive and noneruptive volcanic hazards; over the Holocene, the incidence of many such hazards has increased due to rapid climate change. Here we show that extreme heavy rainfall is projected to increase with continued global warming throughout the 21st century in most subaerial volcanic regions, dramatically increasing the potential for rainfall-induced volcanic hazards. This result is based on a comparative analysis of nine general circulation models, and is prevalent across a wide range of spatial scales, from countries and volcanic arcs down to individual volcanic systems. Our results suggest that if global warming continues unchecked, the incidence of primary and secondary rainfall-related volcanic activity—such as dome explosions or flank collapse—will increase at more than 700 volcanoes around the globe. Improved coupling between scientific observations—in particular, of local and regional precipitation—and policy decisions, may go some way towards mitigating the increased risk throughout the next 80 years.

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Gravity Waves in Planetary Atmospheres: Their Effects and Parameterization in Global Circulation Models

Atmosphere ◽

10.3390/atmos10090531 ◽

2019 ◽

Vol 10 (9) ◽

pp. 531 ◽

Cited By ~ 6

Author(s):

Alexander S. Medvedev ◽

Erdal Yiğit

Keyword(s):

Gravity Waves ◽

General Circulation ◽

Numerical Models ◽

Spatial Scales ◽

General Circulation Models ◽

Planetary Atmospheres ◽

Vertical Coupling ◽

Global Circulation Models ◽

Wave Effects ◽

Forcing Mechanisms

The dynamical and thermodynamical importance of gravity waves was initially recognized in the atmosphere of Earth. Extensive studies over recent decades demonstrated that gravity waves exist in atmospheres of other planets, similarly play a significant role in the vertical coupling of atmospheric layers and, thus, must be included in numerical general circulation models. Since the spatial scales of gravity waves are smaller than the typical spatial resolution of most models, atmospheric forcing produced by them must be parameterized. This paper presents a review of gravity waves in planetary atmospheres, outlines their main characteristics and forcing mechanisms, and summarizes approaches to capturing gravity wave effects in numerical models. The main goal of this review is to bridge research communities studying atmospheres of Earth and other planets.

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Dune vegetation dynamics from 1937 to 1976 in the Mlalazi-Richards Bay area of Natal, South Africa

Bothalia ◽

10.4102/abc.v14i3/4.1225 ◽

1983 ◽

Vol 14 (3/4) ◽

pp. 661-667 ◽

Cited By ~ 10

Author(s):

P. J. Weisser ◽

R. Müller

Keyword(s):

South Africa ◽

Vegetation Cover ◽

Vegetation Dynamics ◽

Forest Plantations ◽

Vegetation Changes ◽

Dune Vegetation ◽

Forest Habitat ◽

Acacia Karroo ◽

Bay Area ◽

Richards Bay

Dune vegetation changes were studied qualitatively with the aid of air photos taken in 1937, 1957 and 1976.Results were transferred to 1:10 000 scale maps. In 1937 roughly 80% of the dune forest habitat was occupied by planted fields and post cultivation serai stages such as Secondary Grasslands and Dwarf Shrubland, Secondary Scrub and Acacia karroo Woodland. In three areas, the vegetation cover had been completely destroyed and drift sands had formed. In the 1950’s the trend of vegetation degradation was changed by the implementation of an afforestation programme by the Department of Forestry. The 1976 air photos indicate that the post cultivation serai stages of 1937 had been largely replaced by forest plantations. In secondary, unafforested areas the vegetation is evolving rapidly towards a Secondary Dune Forest.

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HyLands 1.0: a hybrid landscape evolution model to simulate the impact of landslides and landslide-derived sediment on landscape evolution

Geoscientific Model Development ◽

10.5194/gmd-13-3863-2020 ◽

2020 ◽

Vol 13 (9) ◽

pp. 3863-3886

Author(s):

Benjamin Campforts ◽

Charles M. Shobe ◽

Philippe Steer ◽

Matthias Vanmaercke ◽

Dimitri Lague ◽

...

Keyword(s):

Sediment Transport ◽

Landscape Evolution ◽

Flow Direction ◽

Spatial Scales ◽

Sediment Dynamics ◽

Evolution Model ◽

Sediment Delivery ◽

River Dynamics ◽

River Incision ◽

The Impact

Abstract. Landslides are the main source of sediment in most mountain ranges. Rivers then act as conveyor belts, evacuating landslide-derived sediment. Sediment dynamics are known to influence landscape evolution through interactions among landslide sediment delivery, fluvial transport and river incision into bedrock. Sediment delivery and its interaction with river incision therefore control the pace of landscape evolution and mediate relationships among tectonics, climate and erosion. Numerical landscape evolution models (LEMs) are well suited to study the interactions among these surface processes. They enable evaluation of a range of hypotheses at varying temporal and spatial scales. While many models have been used to study the dynamic interplay between tectonics, erosion and climate, the role of interactions between landslide-derived sediment and river incision has received much less attention. Here, we present HyLands, a hybrid landscape evolution model integrated within the TopoToolbox Landscape Evolution Model (TTLEM) framework. The hybrid nature of the model lies in its capacity to simulate both erosion and deposition at any place in the landscape due to fluvial bedrock incision, sediment transport, and rapid, stochastic mass wasting through landsliding. Fluvial sediment transport and bedrock incision are calculated using the recently developed Stream Power with Alluvium Conservation and Entrainment (SPACE) model. Therefore, rivers can dynamically transition from detachment-limited to transport-limited and from bedrock to bedrock–alluvial to fully alluviated states. Erosion and sediment production by landsliding are calculated using a Mohr–Coulomb stability analysis, while landslide-derived sediment is routed and deposited using a multiple-flow-direction, nonlinear deposition method. We describe and evaluate the HyLands 1.0 model using analytical solutions and observations. We first illustrate the functionality of HyLands to capture river dynamics ranging from detachment-limited to transport-limited conditions. Second, we apply the model to a portion of the Namche Barwa massif in eastern Tibet and compare simulated and observed landslide magnitude–frequency and area–volume scaling relationships. Finally, we illustrate the relevance of explicitly simulating landsliding and sediment dynamics over longer timescales for landscape evolution in general and river dynamics in particular. With HyLands we provide a new tool to understand both the long- and short-term coupling between stochastic hillslope processes, river incision and source-to-sink sediment dynamics.

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Assessing z-level modelling of the ice shelf - ocean boundary layer

10.5194/egusphere-egu2020-10388 ◽

2020 ◽

Author(s):

Ryan Patmore ◽

Paul Holland ◽

Catherine Vreugdenhil

Keyword(s):

Boundary Layer ◽

General Circulation ◽

Spatial Scales ◽

General Circulation Models ◽

Small Scale ◽

Ice Shelf ◽

Shelf Dynamics ◽

Boundary Layer Dynamics ◽

Global Sea Level ◽

Ocean Boundary

<p>Ice shelf dynamics play a key role in the climate. Melt-rates along the ice shelf-ocean interface are an important aspect in determining the character of global sea level rise. A representation of ice shelf melt is currently implemented in various z-level General Circulation Models (GCMs) by employing parameterisations of the small scale boundary layer dynamics. However, these parameterisations are strongly dependent on the near boundary flow and at the spatial scales for which GCMs are intended the boundary layer is not well resolved. We investigate the ability of a GCM in representing these small scale boundary effects. This is done using MITgcm in an idealised setting with a sloping ice-ocean interface.</p>

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Emulation of long-term changes in global climate: Application to the late Pliocene and future

10.5194/cp-2017-57 ◽

2017 ◽

Author(s):

Natalie S. Lord ◽

Michel Crucifix ◽

Dan J. Lunt ◽

Mike C. Thorne ◽

Nabila Bounceur ◽

...

Keyword(s):

Spatial Resolution ◽

General Circulation ◽

Spatial Scales ◽

Computational Cost ◽

General Circulation Models ◽

Atmospheric Co2 ◽

Proxy Data ◽

Late Pliocene ◽

Climate Evolution

Abstract. Multi-millennial transient simulations of climate changes have a range of important applications, such as for investigating key geologic events and transitions for which high resolution palaeoenvironmental proxy data are available, or for projecting the long-term impacts of future climate evolution on the performance of geological repositories for the disposal of radioactive wastes. However, due to the high computational requirements of current fully coupled General Circulation Models (GCMs), long-term simulations can generally only be performed with less complex models and/or at lower spatial resolution. In this study, we present novel long-term “continuous” projections of climate evolution based on the output from GCMs, via the use of a statistical emulator. The emulator is calibrated using ensembles of GCM simulations which have varying orbital configurations and atmospheric CO2 concentrations and enables a variety of investigations of long-term climate change to be conducted which would not be possible with other modelling techniques at the same temporal and spatial scales. To illustrate the potential applications, we apply the emulator to the late Pliocene (by modelling SAT), comparing its results with palaeo-proxy data for a number of global sites, and to the next 200 thousand years (kyr) (by modelling SAT and precipitation). A range of CO2 scenarios are modelled for each period. During the late Pliocene, we find that emulated SAT varies on an approximately precessional timescale, with evidence of increased obliquity response at times. A comparison of atmospheric CO2 concentration for this period, estimated using the proxy data and emulator results and using proxy CO2 records, finds that relatively similar concentrations are produced at lower latitudes, although higher latitude sites show larger discrepancies. In our second illustrative application, spanning the next 200 kyr into the future, we find that SAT oscillations appear to be primarily influenced by obliquity for the first ~ 120 kyr, whilst eccentricity is relatively low, after which precession plays a more dominant role. Conversely, variations in precipitation over the entire period demonstrate a strong precessional signal. Overall, we find that the emulator provides a useful and powerful tool for rapidly simulating the long-term evolution of climate, both past and future, due to its relatively high spatial resolution and relatively low computational cost.

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