Regional Earth System Research Articles

Baltic Sea Operational Oceanography—A Stimulant for Regional Earth System Research

Two important communities related to oceanography in the Baltic Sea are those working on operational oceanography and Earth system science, with focusing on the same water body but different temporal scales. They have been coordinated through two organizations/programs: the Baltic Sea Operational Oceanographic System (BOOS) and the Baltic Sea Experiment (BALTEX) and its successor, the Baltic Earth Program (Earth system science for the Baltic Sea region), respectively. Although the two communities have archived significant progresses in their own fields since early 1990s, there were few interactions between the communities. Rapid advancements of operational oceanography on ocean monitoring, data sharing, modelling and historical ocean state reconstruction in the last decade have provided a wide range of data, products and modelling tools which may be used in Earth system and climate change research. This is especially true when operational oceanography in the Baltic Sea is in a transition to a seamless service, i.e., from basin to local scales, from synoptic to climate scales and from physical to biogeochemical and biological systems. On the other hand, the Baltic Sea Earth system research can help to improve operational oceanography by contributing research observations and transferring their research achievements to the operational system. Based on a review of state-of-the-art of BOOS monitoring and modelling capabilities and on-going BOOS research, this paper will highlight topics and areas which are related to the Baltic Earth Grand Challenges, i.e., salinity dynamics, land-sea biogeochemical linkages, natural hazards and extreme events, sea level dynamics, coastal morphology and erosion, regional variability of water and energy exchanges, and multi-drivers of regional Earth system changes. Potential win-win cooperation and interaction between the BOOS and the Baltic Earth communities are also proposed and discussed.

Thirty Years of Regional Climate Modeling: Where Are We and Where Are We Going next?

AbstractThe year 2019 marks the thirtieth anniversary of the development of the first regional climate model (RCM), and here an overview is provided of the progress in regional modeling research and of the main challenges lying ahead. RCMs were primarily developed to provide fine‐scale climate information for impact studies, but they have evolved into general and multipurpose modeling tools. Among the main achievements in RCM research the focus is on: the development of community RCMs applicable to a wide variety of studies and regional contexts; the increase of model simulation length up to centennial scales and spatial resolutions up to convection‐permitting scales (few kilometers), leading to a better understanding of regional to local climate change signals; the development of fully coupled Regional Earth System Models; the inception of intercomparison projects culminating in the international Coordinated Regional Climate Downscaling Experiment; the extensive use of RCM simulations for impact assessments; and the involvement of the scientific community from developing countries in climate modeling research. Among the outstanding issues in need of more attention are the Added Value of using this downscaling technique; various technical aspects concerning RCM simulations; and uncertainties in RCM‐based climate projections. Future directions in RCM research are discussed, with highlight on: transition to convection‐permitting modeling systems; further development of Regional Earth System Models including the human component; next phase of the Coordinated Regional Climate Downscaling Experiment project; and use of RCMs in the distillation of actionable information for contribution to climate service activities. A brief historical overview of regional climate modeling is also presented.

Indian Summer Monsoon as simulated by the regional earth system model RegCM-ES: the role of local air–sea interaction

In this study the regional earth system model RegCM-ES is applied over the South Asia CORDEX domain to improve the simulation of the variability of the Indian Summer Monsoon. RegCM-ES has been integrated for 30 years, from 1979 to 2008, with a spatial resolution of 50 km in the atmospheric component, 18 km in the ocean and 50 or 12 km in the two hydrological models used for this study. A new hydrological component, the Cetemps Hydrological Model (CHyM), is included in the coupled system composed by the regional climate model RegCM4 and the ocean model MITgcm. In our analysis we show how the two way air–sea feedback simulated by the coupled system largely improves the representation of intraseasonal (ISV) and interannual (IAV) modes of variability of the Indian Summer Monsoon Rainfall (ISMR). The comparison with the Hydrological Discharge (HD) model shows large improvements in simulating the correct amount of freshwater river discharge over the Bay of Bengal (BoB), one of the fundamental factor responsible for the formation of the shallow barrier layer (BL) over the BoB. However, the improvements in river discharge do not have a clear effect on the BL due to excessive mixing in the ocean model. The improvements in the simulation of IAV are primarily due to the ability of RegCM-ES to reproduce the Intraseasonal Oscillation modes and to the complex mechanism related to the delayed response of the ISMR to the ENSO forcing. Our results highlight the very important role of fine scale air–sea feedbacks in modulating the ISMR and the internal dynamics of this phenomenon.

River stresses in anthropogenic times: Large-scale global patterns and extended environmental timelines

Global perspectives on the complexities of environmental change impacts associated with past and present human activity are needed for the food and water security challenges of the twenty-first century. This is especially true for rivers, for which the onset and persistence of a range in human activities, altering their function and form, have been temporally and spatially variable. Ancient civilisations, states and empires extended geographically to cover sub-continental areas where their river modifying activities became linked to regional Earth system stresses arising from climate and land use change. We present a new interpretative framework for characterising and classifying human impact on river systems, emphasising that this has taken place over decadal to millennial time periods on a sub-continental scale. This 16-element classification and documentation of different human transformations, including land management, urbanisation, industry and engineering activities, is used to explore anthropogenic channel and floodplain disruptions that have followed each other in different sequences in different places. It is significant that these inadvertent and deliberate human interventions have also taken place in parallel with contrasting climatic fluctuations that have been sub-continental in scale and varied in time. We assess the influence of the dominant modes of regional climate variability (monsoons, El Niño Southern Oscillation, Indian Ocean Dipole, North Atlantic Oscillation, Pacific Decadal Oscillation and Siberian High) on the speed and pattern of river system adjustment to anthropogenic perturbations. Some river civilisations have proved resilient to change given their adaptive management, while others have been overwhelmed by climate-related changes in river morphodynamics. We conclude that integrated socioeconomic, climatic and hydromorphological histories provide usefully instructive antecedents for sensibly managing, as they evolve, the even more serious coupled environmental stresses likely in the future.

Self‐Amplifying Feedbacks Accelerate Greening and Warming of the Arctic

AbstractIncreased greening, higher vegetation productivity, and shrubification have been observed in Arctic tundra in response to recent warming. Such changes have affected the near‐surface climate through opposing biogeophysical feedbacks (BF) associated with changes to albedo and evapotranspiration. However, the likely spatiotemporal variations of BF to future climate change and the consequences for Arctic vegetation and ecology have not been robustly quantified. We apply a regional Earth system model (RCA‐GUESS) interactively coupling atmospheric dynamics to land vegetation response in three potential 21st‐century radiative forcing simulations for the Arctic. We find that BF, dominated by albedo‐mediated warming in early spring and evapotranspiration‐mediated cooling in summer, have the potential to amplify or modulate local warming and enhance summer precipitation over land. The magnitude of these effects depends on radiative forcing and subsequent ecosystem responses. Thus, it is important to account for BF when assessing future Arctic climate change and its ecosystem impacts.

Regional earth system modeling: review and future directions

The authors review recent advances in the development of coupled Regional Earth System Models (RESMs), a field that is still in its early stages. To date, coupled regional atmosphere-ocean-sea ice,...

Spatial and temporal patterns of plantation forests in the United States since the 1930s: an annual and gridded data set for regional Earth system modeling

Abstract. Plantation forest area in the conterminous United States (CONUS) ranked second among the world's nations in the land area apportioned to forest plantation. As compared to the naturally regenerated forests, plantation forests demonstrate significant differences in biophysical characteristics, and biogeochemical and hydrological cycles as a result of more intensive management practices. Inventory data have been reported for multiple time periods on plot, state, and regional scales across the CONUS, but the requisite annual and spatially explicit plantation data set over a long-term period for analysis of the role of plantation management on regional or national scales is lacking. Through synthesis of multiple inventory data sources, this study developed methods to spatialize the time series plantation forest and tree species distribution data for the CONUS over the 1928–2012 time period. According to this new data set, plantation forest area increased from near zero in the 1930s to 268.27 thousand km2 in 2012, accounting for 8.65 % of the total forestland area in the CONUS. Regionally, the South contained the highest proportion of plantation forests, accounting for about 19.34 % of total forestland area in 2012. This time series and gridded data set developed here can be readily applied in regional Earth system modeling frameworks for assessing the impacts of plantation management practices on forest productivity, carbon and nitrogen stocks, and greenhouse gases (e.g., CO2, CH4, and N2O) and water fluxes on regional or national scales. The gridded plantation distribution and tree species maps, and the interpolated state-level annual tree planting area and plantation area during 1928–2012, are available from https://doi.org/10.1594/PANGAEA.873558.

Effects of spatially distributed sectoral water management on the redistribution of water resources in an integrated water model

AbstractRealistic representations of sectoral water withdrawals and consumptive demands and their allocation to surface and groundwater sources are important for improving modeling of the integrated water cycle. To inform future model development, we enhance the representation of water management in a regional Earth system (ES) model with a spatially distributed allocation of sectoral water demands simulated by a regional integrated assessment (IA) model to surface and groundwater systems. The integrated modeling framework (IA‐ES) is evaluated by analyzing the simulated regulated flow and sectoral supply deficit in major hydrologic regions of the conterminous U.S, which differ from ES studies looking at water storage variations. Decreases in historical supply deficit are used as metrics to evaluate IA‐ES model improvement in representating the complex sectoral human activities for assessing future adaptation and mitigation strategies. We also assess the spatial changes in both regulated flow and unmet demands, for irrigation and nonirrigation sectors, resulting from the individual and combined additions of groundwater and return flow modules. Results show that groundwater use has a pronounced regional and sectoral effect by reducing water supply deficit. The effects of sectoral return flow exhibit a clear east‐west contrast in the hydrologic patterns, so the return flow component combined with the IA sectoral demands is a major driver for spatial redistribution of water resources and water deficits in the US. Our analysis highlights the need for spatially distributed sectoral representation of water management to capture the regional differences in interbasin redistribution of water resources and deficits.

Impacts of land use on climate and ecosystem productivity over the Amazon and the South American continent

The Amazon basin is characterized by a strong interplay between the atmosphere and vegetation. Anthropogenic land use and land cover change (LULCC) affects vegetation and the exchange of energy and water with the atmosphere. Here we have assessed potential LULCC impacts on climate and natural vegetation dynamics over South America with a regional Earth system model that also accounts for vegetation dynamics. The biophysical and biogeochemical impacts from LULCC were addressed with two simulations over the CORDEX-South America domain. The results show that LULCC imposes local and remote influences on South American climate. These include significant local warming over the LULCC-affected area, changes in circulation patterns over the Amazon basin during the dry season, and an intensified hydrological cycle over much of the LULCC-affected area during the wet season. These changes affect the natural vegetation productivity which shows contrasting and significant changes between northwestern (around 10% increase) and southeastern (up to 10% decrease) parts of the Amazon basin caused by mesoscale circulation changes during the dry season, and increased productivity in parts of the LULCC-affected areas. We conclude that ongoing deforestation around the fringes of the Amazon could impact pristine forest by changing mesoscale circulation patterns, amplifying the degradation of natural vegetation caused by direct, local impacts of land use activities.

The coastal streamflow flux in the Regional Arctic System Model

AbstractThe coastal streamflow flux from the Arctic drainage basin is an important driver of dynamics in the coupled ice‐ocean system. Comprising more than one third of the total freshwater flux into the Arctic Ocean, streamflow is a key component of the regional and global freshwater cycle. To better represent the coupling of the streamflow flux to the ocean, we have developed and applied the RVIC streamflow routing model within the Regional Arctic System Model (RASM). The RASM is a high‐resolution regional Earth System Model whose domain includes all of the Arctic drainage basin. In this paper, we introduce the RVIC streamflow routing model, detailing its application within RASM and its advancements in terms of representing high‐resolution streamflow processes. We evaluate model simulated streamflow relative to in situ observations and demonstrate a method for improving model performance using a simple optimization procedure. We also present a new, spatially and temporally consistent, high‐resolution data set of coastal freshwater fluxes for the Arctic drainage basin and surrounding areas that is based on a fully coupled RASM simulation and intended for use in Arctic Ocean modeling applications. This data set is evaluated relative to other coastal streamflow data sets commonly used by the ocean modeling community. We demonstrate that the RASM‐simulated streamflow flux better represents the annual cycle than existing data sets, especially in ungauged areas. Finally, we assess the impact that streamflow has on the coupled ice‐ocean system, finding that the presence of streamflow leads to reduced sea surface salinity, increased sea surface temperatures, and decreased sea ice thickness.

Land Surface Climate in the Regional Arctic System Model

AbstractThe Regional Arctic System Model (RASM) is a fully coupled, regional Earth system model applied over the pan-Arctic domain. This paper discusses the implementation of the Variable Infiltration Capacity land surface model (VIC) in RASM and evaluates the ability of RASM, version 1.0, to capture key features of the land surface climate and hydrologic cycle for the period 1979–2014 in comparison with uncoupled VIC simulations, reanalysis datasets, satellite measurements, and in situ observations. RASM reproduces the dominant features of the land surface climatology in the Arctic, such as the amount and regional distribution of precipitation, the partitioning of precipitation between runoff and evapotranspiration, the effects of snow on the water and energy balance, and the differences in turbulent fluxes between the tundra and taiga biomes. Surface air temperature biases in RASM, compared to reanalysis datasets ERA-Interim and MERRA, are generally less than 2°C; however, in the cold seasons there are local biases that exceed 6°C. Compared to satellite observations, RASM captures the annual cycle of snow-covered area well, although melt progresses about two weeks faster than observations in the late spring at high latitudes. With respect to derived fluxes, such as latent heat or runoff, RASM is shown to have similar performance statistics as ERA-Interim while differing substantially from MERRA, which consistently overestimates the evaporative flux across the Arctic region.

Vegetation–climate feedbacks modulate rainfall patterns in Africa under future climate change

Abstract. Africa has been undergoing significant changes in climate and vegetation in recent decades, and continued changes may be expected over this century. Vegetation cover and composition impose important influences on the regional climate in Africa. Climate-driven changes in vegetation structure and the distribution of forests versus savannah and grassland may feed back to climate via shifts in the surface energy balance, hydrological cycle and resultant effects on surface pressure and larger-scale atmospheric circulation. We used a regional Earth system model incorporating interactive vegetation–atmosphere coupling to investigate the potential role of vegetation-mediated biophysical feedbacks on climate dynamics in Africa in an RCP8.5-based future climate scenario. The model was applied at high resolution (0.44 × 0.44°) for the CORDEX-Africa domain with boundary conditions from the CanESM2 general circulation model. We found that increased tree cover and leaf-area index (LAI) associated with a CO2 and climate-driven increase in net primary productivity, particularly over subtropical savannah areas, not only imposed important local effect on the regional climate by altering surface energy fluxes but also resulted in remote effects over central Africa by modulating the land–ocean temperature contrast, Atlantic Walker circulation and moisture inflow feeding the central African tropical rainforest region with precipitation. The vegetation-mediated feedbacks were in general negative with respect to temperature, dampening the warming trend simulated in the absence of feedbacks, and positive with respect to precipitation, enhancing rainfall reduction over the rainforest areas. Our results highlight the importance of accounting for vegetation–atmosphere interactions in climate projections for tropical and subtropical Africa.

Med-CORDEX Initiative for Mediterranean Climate Studies

Abstract The Mediterranean is expected to be one of the most prominent and vulnerable climate change “hotspots” of the twenty-first century, and the physical mechanisms underlying this finding are still not clear. Furthermore, complex interactions and feedbacks involving ocean–atmosphere–land–biogeochemical processes play a prominent role in modulating the climate and environment of the Mediterranean region on a range of spatial and temporal scales. Therefore, it is critical to provide robust climate change information for use in vulnerability–impact–adaptation assessment studies considering the Mediterranean as a fully coupled environmental system. The Mediterranean Coordinated Regional Downscaling Experiment (Med-CORDEX) initiative aims at coordinating the Mediterranean climate modeling community toward the development of fully coupled regional climate simulations, improving all relevant components of the system from atmosphere and ocean dynamics to land surface, hydrology, and biogeochemical processes. The primary goals of Med-CORDEX are to improve understanding of past climate variability and trends and to provide more accurate and reliable future projections, assessing in a quantitative and robust way the added value of using high-resolution and coupled regional climate models. The coordination activities and the scientific outcomes of Med-CORDEX can produce an important framework to foster the development of regional Earth system models in several key regions worldwide.

Validation of newly designed regional earth system model (RegESM) for Mediterranean Basin

We present a validation analysis of a regional earth system model system (RegESM) for the Mediterranean Basin. The used configuration of the modeling system includes two active components: a regional climate model (RegCM4) and an ocean modeling system (ROMS). To assess the performance of the coupled modeling system in representing the climate of the basin, the results of the coupled simulation (C50E) are compared to the results obtained by a standalone atmospheric simulation (R50E) as well as several observation datasets. Although there is persistent cold bias in fall and winter, which is also seen in previous studies, the model reproduces the inter-annual variability and the seasonal cycles of sea surface temperature (SST) in a general good agreement with the available observations. The analysis of the near-surface wind distribution and the main circulation of the sea indicates that the coupled model can reproduce the main characteristics of the Mediterranean Sea surface and intermediate layer circulation as well as the seasonal variability of wind speed and direction when it is compared with the available observational datasets. The results also reveal that the simulated near-surface wind speed and direction have poor performance in the Gulf of Lion and surrounding regions that also affects the large positive SST bias in the region due to the insufficient horizontal resolution of the atmospheric component of the coupled modeling system. The simulated seasonal climatologies of the surface heat flux components are also consistent with the CORE.2 and NOCS datasets along with the overestimation in net long-wave radiation and latent heat flux (or evaporation, E), although a large observational uncertainty is found in these variables. Also, the coupled model tends to improve the latent heat flux by providing a better representation of the air–sea interaction as well as total heat flux budget over the sea. Both models are also able to reproduce the temporal evolution of the inter-annual anomaly of surface air temperature and precipitation (P) over defined sub-regions. The Mediterranean water budget (E, P and E–P) estimates also show that the coupled model has high skill in the representation of water budget of the Mediterranean Sea. To conclude, the coupled model reproduces climatological land surface fields and the sea surface variables in the range of observation uncertainty and allow studying air–sea interaction and main regional climate characteristics of the basin.

Multispherical interactions and their effects on the Tibetan Plateau's earth system: a review of the recent researches

Abstract The Tibetan Plateau (TP) is a regional Earth system showing very strong interactions among its lithosphere, hydrosphere, cryosphere, biosphere, atmosphere, and anthrosphere. These interactions manifest TP's impact on surrounding regions and reflect TP's response to the global change. Quantifying the multispherical interactions is critically important to understand the TP environment. Our recent years researches including the ongoing program entitled ‘Tibetan Multi-Spheres Interactions and Their Resource-Environment Significance (TIMI)’, the completed program entitled. ‘Paleo-Altitudes of Tibetan Plateau and Environment (PATE)’, as well as the other relating projects have focused on multidisciplinary research approaches and emphasized on three major pathways: Eurasia-Indian plates collision on deep-Earth dynamics, uplift impact on Earth's mantle–crust dynamics, and contemporary interface on land surface and atmospheric dynamics. Our researches have taken in situ measurement as priority and developed several platforms of data acquisition and analysis, including the platforms of water-phase transformations, and ecosystem observations. Our field investigations have been conducted to obtain data about stratum, paleontology, paleoenvironment, genetic differentiation of animals and plants. We have developed conceptual and mathematical models for crust uplift formation, paleoclimate, glacial melt, water–air interface flux, vegetation climate, and soil erosion. We have also assessed the anthropogenic impacts on environment. Our researches have achieved new and reliable redating of the mantle–crust interaction and initial formation of the TP, found the interaction between tectonics and uplift of the TP and resultant paleoaltitude acting as a spreading source; discovered the interaction between the westerlies and Indian monsoon acting as a control chain that dominates the TP's contemporary environment. The scientific results can play fundamental roles in supporting the TP's resource exploration and societal sustainable development.

Regional Dynamical Downscaling and the CORDEX Initiative

We review the challenges and future perspectives of regional climate model (RCM), or dynamical downscaling, activities. Among the main technical issues in need of better understanding are those of selection and sensitivity to the model domain and resolution, techniques for providing lateral boundary conditions, and RCM internal variability. The added value (AV) obtained with the use of RCMs remains a central issue, which needs more rigorous and comprehensive analysis strategies. Within the context of regional climate projections, large ensembles of simulations are needed to better understand the models and characterize uncertainties. This has provided an impetus for the development of the Coordinated Regional Downscaling Experiment (CORDEX), the first international program offering a common protocol for downscaling experiments, and we discuss how CORDEX can address the key scientific challenges in downscaling research. Among the main future developments in RCM research, we highlight the development of coupled regional Earth system models and the transition to very high-resolution, cloud-resolving models.

21st century United States emissions mitigation could increase water stress more than the climate change it is mitigating

There is evidence that warming leads to greater evapotranspiration and surface drying, thus contributing to increasing intensity and duration of drought and implying that mitigation would reduce water stresses. However, understanding the overall impact of climate change mitigation on water resources requires accounting for the second part of the equation, i.e., the impact of mitigation-induced changes in water demands from human activities. By using integrated, high-resolution models of human and natural system processes to understand potential synergies and/or constraints within the climate-energy-water nexus, we show that in the United States, over the course of the 21st century and under one set of consistent socioeconomics, the reductions in water stress from slower rates of climate change resulting from emission mitigation are overwhelmed by the increased water stress from the emissions mitigation itself. The finding that the human dimension outpaces the benefits from mitigating climate change is contradictory to the general perception that climate change mitigation improves water conditions. This research shows the potential for unintended and negative consequences of climate change mitigation.

Foreword to the special issue: regional earth system modeling

Foreword to the special issue: regional earth system modeling

The Regional Downscaling Approach: a Brief History and Recent Advances

In recent years, two major topics have emerged in regional climate modeling. One topic is the extension of regional climate models of the atmosphere to regional Earth system models. Specifically, the coupling of regional atmosphere-ocean models is an important step toward reducing the dependency of regional climate simulations on global models. The second topic is the decrease of the horizontal grid spacing such that convection can be explicitly computed. These topics present new challenges for the observational data used to evaluate the models. To date, gridded observation data on the kilometer scale have been only available over a few specific regions. The size of regional climate model ensembles has considerably increased in recent years. Thus, how to manage large datasets and how to select representative subsets are challenges that must be addressed. Comparatively, little progress has been achieved in the fields of boundary conditions and physical parameterizations.

Assessing the O2 budget under sea ice: An experimental and modelling approach

Abstract The objective of this study was to assess the O2 budget in the water under sea ice combining observations and modelling. Modelling was used to discriminate between physical processes, gas-specific transport (i.e., ice-atmosphere gas fluxes and gas bubble buoyancy) and bacterial respiration (BR) and to constrain bacterial growth efficiency (BGE). A module describing the changes of the under-ice water properties, due to brine rejection and temperature-dependent BR, was implemented in the one-dimensional halo-thermodynamic sea ice model LIM1D. Our results show that BR was the dominant biogeochemical driver of O2 concentration in the water under ice (in a system without primary producers), followed by gas specific transport. The model suggests that the actual contribution of BR and gas specific transport to the change in seawater O2 concentration was 37% during ice growth and 48% during melt. BGE in the water under sea ice, as retrieved from the simulated O2 budget, was found to be between 0.4 and 0.5, which is in line with published BGE values for cold marine waters. Given the importance of BR to seawater O2 in the present study, it can be assumed that bacteria contribute substantially to organic matter consumption and gas fluxes in ice-covered polar oceans. In addition, we propose a parameterization of polar marine bacterial respiration, based on the strong temperature dependence of bacterial respiration and the high growth efficiency observed here, for further biogeochemical ocean modelling applications, such as regional or large-scale Earth System models.