On behalf of the authors and readers of Reviews of Geophysics (RoG), the American Geophysical Union, and the broader scientific community, the editors wish to wholeheartedly thank those who reviewed manuscripts for RoG in 2024.
On behalf of the authors and readers of Reviews of Geophysics (RoG), the American Geophysical Union, and the broader scientific community, the editors wish to wholeheartedly thank those who reviewed manuscripts for RoG in 2024.
Climate change drives disturbance in hydrology and geomorphology in terrestrial polar landscapes underlain by permafrost, yet measurements of, and theories to understand, these changes are limited. Water flowing from permafrost hillslopes to channels is often modulated by water tracks, zones of enhanced soil moisture in unchannelized depressions that concentrate water flow downslope. Water tracks, which dominate hillslope hydrology in some permafrost landscapes, lack a consistent definition and identification method, and their global occurrence, morphology, climate relationships, and geomorphic roles remain understudied despite their role in the permafrost carbon cycle. Combining a literature review with a synthesis of prior work, we identify uniting and distinguishing characteristics between water tracks from disparate polar sites with a toolkit for future field and remotely sensed identification of water tracks. We place previous studies within a quantitative framework of “top-down” climate and “bottom-up” geology controls on track morphology and hydrogeomorphic function. We find the term “water track” is applied to a broad category of concentrated suprapermafrost flowpaths exhibiting varying morphology, degrees of self-organization, hydraulic characteristics, subsurface composition, vegetation, relationships to thaw tables, and stream order/hillslope position. We propose that the widespread occurrence of water tracks on both poles across varying geologic, ecologic, and climatic factors implies that water tracks are in dynamic equilibrium with the permafrost environment but that they may experience change as the climate continues to warm. Current knowledge gaps include these features' trajectories in the face of ongoing climate change and their role as an analog landform for an active Martian hydrosphere.
Assessing landslide risk is a fundamental requirement to plan suitable prevention actions. To date, most risk studies focus on individual slopes or catchments. Whereas regional, national or continental scale assessments are hardly available because of methodological and/or data limitations. In this contribution, we present an overview of all requirements and limitations in landslide risk studies across all spatial scales, by means of a hybrid form that combines elements of original research with the comprehensive characteristics of a review study. The review critically analyses each component in the landslide risk analysis providing a detailed explanation of their state-of-the-art, with dedicated sections on susceptibility, hazard, exposure, and vulnerability. To put the theoretical framework to test, we also dive into a case study, expressed at the continental scale. Specifically, we take the main European mountain ranges and provide the reader with a textbook example of risk assessment for such a large territory. In doing so, we take into account issues associated with cross-national differences in landslide mapping. As a result, we identify landslide-prone European landscape and explore the associated possible economic consequences (human settlements and agricultural areas). We also analyze the population at risk during daytime and nighttime. Moreover, a modern view of the problem is explored in the form of how risk outcomes should be delivered to master planners and geoscientific personnel alike. Specifically, we convert our output into an interactive Web Application (https://pan-european-landslide-risk.github.io/) to include notions of scientific communication both to a large public as well as to a technical audience.
Karst water resources are valuable freshwater sources for around 10% of the world's population. Nonetheless, anthropogenic impacts and global changes have seriously deteriorated karst water quality and dependent ecosystems. Multiscale karstic heterogeneity—referring to the spatial variations of the karst aquifer's physical and chemical characteristics at varying scales—is the main challenge in describing karst flow and contaminant transport dynamics. Solute transport models are powerful tools to represent and predict the spatiotemporal behaviors of contaminant migration in karst water resources. By enhancing our understanding of the transport processes, the solute transport models enable us to explore contamination risks and potential outcomes of the contamination-related issues in karst systems. Because of that, they are often used for monitoring, controlling, and managing karst water quality and dependent ecosystem functioning. This paper reviews the current state of knowledge on the modeling of karst transport processes with a focus on single-phase solute transport. By unveiling the fundamental challenges underlying a successful real-world application of karst transport models, we discuss to what extent and how we can handle these challenges. By further deriving the key challenges afront the successful modeling applications in karst systems, we, therefore, provide directions to ensure the reliable modeling of karst transport dynamics in the present context of global changes.
Rock glaciers are distinctive debris landforms found worldwide in cold mountainous regions. They express the long-term movement of perennially frozen ground. Rock Glacier Velocity (RGV), defined as the time series of the annualized surface velocity of a rock glacier unit or a part of it, has been accepted as an Essential Climate Variable Permafrost Quantity in 2022. This review aims to highlight the relationship between rock glacier velocity and climatic factors, emphasizing the scientific relevance of interannual rock glacier velocity in generating RGV products within the context of observed rock glacier kinematics. Under global warming, rock glacier velocity exhibits widespread (multi-)decennial acceleration. This acceleration varies regionally in onset timing (from the 1950s to the 2010s) and magnitude (up to a factor of 10), and has been observed in regions such as the European Alps, High Mountain Asia, and the Andes. Despite different local conditions, a synchronous interannual velocity pattern prevails in the European Alps since the 2000s, highlighting the primary influence of climate. A common pattern is the seasonal velocity rhythm, which peaks in late summer to autumn and declines in spring. RGV assesses permafrost evolution via (multi-)decennial and interannual changes in rock glacier velocity, influenced by air temperature shifts with varying time lags and snow cover effects. Although not integrated into the RGV products, seasonal variations should be examined. This rhythmic behavior is attributed to alterations in pore water pressure influenced by air temperature, snow cover, and ground water conditions.
The soil health assessment has evolved from focusing primarily on agricultural productivity to an integrated evaluation of soil biota and biotic processes that impact soil properties. Consequently, soil health assessment has shifted from a predominantly physicochemical approach to incorporating ecological, biological and molecular microbiology indicators. This shift enables a comprehensive exploration of soil microbial community properties and their responses to environmental changes arising from climate change and anthropogenic disturbances. Despite the increasing availability of soil health indicators (physical, chemical, and biological) and data, a holistic mechanistic linkage has not yet been fully established between indicators and soil functions across multiple spatiotemporal scales. This article reviews the state-of-the-art of soil health monitoring, focusing on understanding how soil-microbiome-plant processes contribute to feedback mechanisms and causes of changes in soil properties, as well as the impact these changes have on soil functions. Furthermore, we survey the opportunities afforded by the soil-plant digital twin approach, an integrative framework that amalgamates process-based models, Earth Observation data, data assimilation, and physics-informed machine learning, to achieve a nuanced comprehension of soil health. This review delineates the prospective trajectory for monitoring soil health by embracing a digital twin approach to systematically observe and model the soil-plant system. We further identify gaps and opportunities, and provide perspectives for future research for an enhanced understanding of the intricate interplay between soil properties, soil hydrological processes, soil-plant hydraulics, soil microbiome, and landscape genomics.
Topography affects the distribution and movement of water on Earth, yet new insights about topographic controls continue to surprise us and exciting puzzles remain. Here we combine literature review and data synthesis to explore the influence of topography on the global terrestrial water cycle, from the atmosphere down to the groundwater. Above the land surface, topography induces gradients and contrasts in water and energy availability. Long-term precipitation usually increases with elevation in the mid-latitudes, while it peaks at low- to mid-elevations in the tropics. Potential evaporation tends to decrease with elevation in all climate zones. At the land surface, topography is expressed in snow distribution, vegetation zonation, geomorphic landforms, the critical zone, and drainage networks. Evaporation and vegetation activity are often highest at low- to mid-elevations where neither temperature, nor energy availability, nor water availability—often modulated by lateral moisture redistribution—impose strong limitations. Below the land surface, topography drives the movement of groundwater from local to continental scales. In many steep upland regions, groundwater systems are well connected to streams and provide ample baseflow, and streams often start losing water in foothills where bedrock transitions into highly permeable sediment. We conclude by presenting organizing principles, discussing the implications of climate change and human activity, and identifying data needs and knowledge gaps. A defining feature resulting from topography is the presence of gradients and contrasts, whose interactions explain many of the patterns we observe in nature and how they might change in the future.
Physical and chemical erosion associated with water both affect land–atmosphere carbon exchanges. However, previous studies have often addressed these processes separately or used oversimplified mechanisms, leading to ongoing debates and uncertainties about erosion-induced carbon fluxes. We provide an overview of the on-site carbon uptake fluxes induced by physical erosion (0.05–0.29 Pg C yr−1, globally) and chemical erosion (0.26–0.48 Pg C yr−1). Then, we discuss off-site carbon dynamics (during transport, deposition, and burial). Soil organic carbon mineralization during transport is nearly 0.37–1.20 Pg C yr−1 on the globe. We also summarize the overall carbon fluxes into estuaries (0.71–1.06 Pg C yr−1) and identify the sources of different types of carbon within them, most of which are associated with land erosion. Current approaches for quantifying physical-erosion-induced vertical carbon fluxes focus on two distinct temporal scales: short-term dynamics (ranging from minutes to decades), emphasizing net vertical carbon flux, and long-term dynamics (spanning millennial to geological timescales), examining the fate of eroded carbon over extended periods. In addition to direct chemical measurement and modeling approaches, estimation using indicators of riverine material is popular for constraining chemical-erosion-driven carbon fluxes. Lastly, we highlight the key challenges for quantifying related fluxes. To overcome potential biases in future studies, we strongly recommend integrated research that addresses both physical and chemical erosion over a well-defined timescale. A comprehensive understanding of the mechanisms driving erosion-induced lateral and vertical carbon fluxes is crucial for closing the global carbon budget.
The significance of crop evapotranspiration (ETa) to climate science, agronomic research, and water resources is not in dispute. What continues to draw attention is how variability in ETa is driven by changing environments, abiotic stresses, and management practices. Here, the impacts of elevated CO2 concentration (e[CO2]), elevated ozone concentration (e[O3]), warming, abiotic stresses (water, salinity, heat stresses), and management practices (planting density, irrigation methods, mulching, nitrogen application) on cropland ETa were reviewed, along with their possible causes and estimation. Water and salinity stresses, e[O3], and drip irrigation adoption generally led to lower total growing–season ETa. However, total growing–season ETa responses to e[CO2], warming, heat stress, mulching, planting density, and nitrogen supplement appear inconsistent across empirical studies. The effects of e[CO2], e[O3], water and salinity stresses on total growing–season ETa are attributed to their influence on stomatal conductance, root water uptake, root and leaf area development, microclimate, and potentially phenology. Total growing–season ETa in response to warming is affected by variations in ambient growing–season mean air temperature and phenology. The differences in crop ETa under varying planting densities are due to their differences in leaf area. The responses of ETa to heat stress, mulching, and nitrogen application represent trade–off between their opposite effects on transpiration and evaporation, along with possibly phenology. Modified ETa models currently in use can estimate the response of ETa to the many aforementioned factors except for e[O3], heat stress, and nitrogen application. These factors offer a blueprint for future research inquiries.
Asian megadeltas, specifically the Ganges-Brahmaputra-Meghna, Irrawaddy, Chao Phraya, Mekong, and Red River deltas host half of the world's deltaic population and are vital for Asian countries' ecosystems and food production. These deltas are extremely vulnerable to global change. Accelerating relative sea-level rise, combined with rapid socio-economic development intensifies these vulnerabilities and calls for a comprehensive understanding of current and future coastal flood dynamics. Here we provide a state-of-the-art on the current knowledge and recent advances in quantifying and understanding the drivers of coastal flood-related hazards in these deltas. We discuss the environmental and physical drivers, including climate influence, hydrology, oceanography, geomorphology, and geophysical processes and how they interact from short to long-term changes, including during extreme events. We also jointly examine how human disturbances, with catchment interventions, land use changes and resource exploitations, contribute to coastal flooding in the deltas. Through a systems perspective, we characterize the current state of the deltaic systems and provide essential insights for shaping their sustainable future trajectories regarding the multifaceted challenges of coastal flooding.
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