Biogeosciences 

This special issue arises from work conducted by the AMAP Expert Group on short-lived climate forcers for an assessment that will be finalized in 2021. It will include only invited papers.

Remote sensing observations in the microwave frequencies have been intensively used to map and investigate water dynamics at the land surface. Microwave observations are also increasingly used to observe changes in vegetation structure and function and to study interactions between water and vegetation. For example, microwave observables such as brightness temperature, radar backscatter, polarization, SAR interferometry, GNSS reflectometry, and variables retrieved from them such as vegetation optical depth and soil moisture allow one to map ecosystem states. All these variables can be used to study processes, states, and temporal changes in vegetation–water interactions such as in vegetation phenology, canopy structure, biomass, photosynthesis, evapotranspiration, interception, dew formation, vegetation water content, water stress, surface and root-zone soil moisture, and irrigation.

The special issue aims to advance our understanding on existing and new techniques, methods, and applications of microwave remote sensing for vegetation–water interactions. We welcome studies that use active or passive microwave satellite, airborne, tower, and field observations to monitor processes, states, and temporal dynamics of vegetation–water interactions by

1. developing and evaluating microwave radiative transfer models for vegetation and water;
2. retrieving land surface variables through radiative transfer model inversion, machine learning, or hybrid approaches;
3. evaluating and constraining land surface, ecosystem, crop, forest, and hydrological models with microwave observations; and
4. assessing field experiments on the impacts of plant water dynamics on microwave observations.

This special issue is an outcome of sessions BG3.20 (Global Earth observation for improved understanding of terrestrial ecosystem dynamics) and HS6.4 (Remote sensing of interactions between vegetation and hydrology) held at the General Assembly 2020 of the European Geoscience Union and of the related precursor sessions in previous years. However, the special issue is open for all submissions within its scope.

Fire is an essential feature of terrestrial ecosystems and plays an important role in the Earth system. Fires are regulated by climate, vegetation characteristics, and human activity and also feedback to them in multiple ways. For example, fires can shape vegetation composition and structure; adjust land carbon, nutrient, water, and energy cycles; change atmospheric composition, chemistry, and physics; and affect air quality and human health. Elevated fire activity in 2019 across the arctic, Amazon, and other regions underscores the urgency of a quantitative understanding of fire as an Earth system process that interacts with vegetation, climate, and humans. The EGU2020 B3.17 session on the role of fire in the Earth system received the most abstracts in the Biogeosciences division this year and was highly attended during the live chat. The abstracts cover several aspects of interactions between fire and the biosphere, atmosphere, and humans across various temporal and spatial scales using modelling, field and laboratory observations, and remote sensing. Given that the topic is highly interdisciplinary and overarching, we propose an inter-journal (ESD/BG/ACP/GMD/NHESS) special issue for this session with ESD as the lead journal, and we also encourage the submission of topic-related studies outside the EGU fire session. The special issue will bring together new advances in understanding the feedbacks and interactions between fire and other components of the Earth system at all temporal and spatial scales using various methods, including (1) impacts of fire on weather, climate, and atmospheric chemistry; (2) interactions between fire, the biogeochemical cycle, vegetation composition and structure, and land water and energy budgets; (3) influence of humans on fire and vice versa; (4) fire characteristics (e.g., fire duration, emission factor, emission height, smoke transport); (5) spatial and temporal changes of fires in the past, present, and future; (6) fire products and models, their validation, and error/bias assessment; and (7) analytical tools designed to enhance situational awareness among fire practitioners and early warning systems, addressing specific needs of operational fire behaviour modelling.

Fostering the establishment of a global ocean observing system, Walter Munk defined the 20th century as the “century of undersampling”, and this is especially true for marine biogeochemical observations. Biogeochemical Argo is bringing us into a new era that is characterized by an unprecedented availability of high-resolution biogeochemical profiles, delivered throughout the year and globally distributed. Thanks to these observations, the dynamics of ocean carbon, oxygen, nutrients, primary producers, pH, and bio-optical properties can be examined in all three spatial dimensions. The increased availability of these observations allows us to unravel biogeochemical processes and to develop and validate hypotheses across a range of spatial and temporal scales. These new observations will also substantially improve the quality of biogeochemical models by allowing vigorous validation, improved parameterizations, and formal data assimilation.

In this special issue, we welcome contributions leveraging the high data availability provided by BGC-Argo floats combined with theoretical or numerical models, data assimilation, machine learning, multi-platform sensors, or other novel interpretative methodologies that expand the surface view of ocean ecosystem dynamics into the vertical dimension.

The purpose of the special issue is to collect the high-quality contributions presented at the oral and poster sessions entitled “Biogeochemistry in the BGC-Argo Era: From Process Studies to Ecosystem Forecasts” held at Ocean Sciences Meeting 2020 in San Diego. Moreover, the special issue is open to other relevant contributions.

Compound weather and climate events refer to combinations of multiple weather and climate drivers and/or hazards that lead to potentially large impacts. Compound events encompass a highly diverse set of events including concurrent climate extremes but also an array of nonstandard high-impact events. Consequently, research on compound events requires expertise from a variety of disciplines such as climate science, hydrology, impact modelling, engineering, and statistics, among others. The European COST Action DAMOCLES (http://damocles.compoundevents.org) provides a platform for compound event research and for generating synergies between the different research domains. This inter-journal special issue will serve as an outlet for the work within DAMOCLES and aims to advance our understanding of different aspects of compound events, including present-day and future risk assessments of such events, modelling of individual compound events, bottom-up approaches to identify new types of compound events, and novel model evaluation techniques. It is open for all submissions within its scope.