The Kluane Lake region in the Canadian Yukon territory is subject to regular drainage-flow dust plumes emanating from the Slims River basin. We have recently employed ground- and satellite-based remote sensing (RS) techniques to analyze the complementarity and redundancy of such RS retrievals relative to springtime Kluane Lake measurements made using a suite of microphysical and meteorological instruments. Our preliminary results include a correlation analysis between ground- and satellite-based CM (coarse or super-μm mode) AOD (aerosol optical depth) retrievals and between ground-based CM AODs and their surface microphysical analogues of particle-volume concentration, supported by 1.5 μm Doppler (HSRL) lidar profiles. The analysis includes an opto-physical interpretation of strongly and weakly correlative illustrations.

Over the last decades, the receiver function technique has been widely used to image sharp discontinuities in elastic properties of the solid Earth at regional scales. To date, very few studies have attempted to use receiver functions for global imaging. One such endeavour has been pursued through the project “Global Lithospheric Imaging using Earthquake Recordings” (GLImER). Building on the advances of GLImER, we have developed PyGLImER - a Python-based software suite capable of creating global images from both P-to-S and S-to-P converted waves via a comprehensive receiver function workflow. This workflow creates a database of receiver functions by downloading seismograms from selected earthquakes and analysing the data via a series of steps that include pre-processing, quality control, deconvolution, and stacking. The stacking can be performed for common conversion points or single stations. All steps leading to the creation of receiver functions are automated. To visualise the generated stacks, the user can choose the desired survey area in a graphical user interface, and then explore the selected region either through 2D cross-sections or a 3D volume. By incorporating results from two independent seismic phases, we can combine the advantages of both phases for imaging different discontinuities. This results in an increased robustness and resolution of the final image. For example, we can use constraints from S receiver function images, which are multiple-free but relatively low resolution, to differentiate between real lithospheric/asthenospheric structures and multiple-induced artefacts in higher-resolution P receiver function images. Our preliminary results agree with those from recent regional and global studies, confirming the workflowís robustness. They also indicate that the new workflow combining P and S receiver functions has the potential to resolve global lithospheric discontinuities such as the lithosphere-asthenosphere boundary (LAB) or the midlithospheric discontinuity (MLD) more reliably than approaches using only one type of incident phase. PyGLImER will be distributed as open-source software, providing an easily accessible tool to rapidly generate high-resolution images of structures in the lithosphere and asthenosphere over large scales.

The Ridgecrest sequence (Mw6.4 and Mw7.1, July 2019, California) is a cross-fault earthquake that has been observed using a wide range of geophysical and geological methods. The sequence ruptured consecutively two orthogonal cross-fault systems within 34 hours (northeast- and northwest-trending). It raised the question of the relation between the two systems of faults both at depth and at the surface, and its impact on the surface displacement pattern. Here we use high-resolution (50 cm) satellite optical image correlation to measure the 3D surface displacement field at 0.5 meters ground resolution for the two earthquakes. Because our images bracket the whole sequence, our displacement and deformation maps include both earthquakes. Our data allow for measuring series of slip profiles in the components parallel and perpendicular to the rupture, and in the vertical direction, to look at the correlation between slip distribution and rupture complexity at the surface. We point out significant differences with previous geodetic and geological-based measurements and show the essential role of distributed faulting and diffuse deformation in the comprehension of surface displacement patterns. We discuss the segmentation of the rupture regarding the fault geometry and along-strike slip variations. We image several surface deformation features with similar orientation to the deeply embedded fabric identified in seismic studies. This northeast-trending fabric influenced the surface deformation both during the foreshock and the mainshock earthquakes. We also derive strain fields from the horizontal displacement maps and show the predominant role of rotational and shear strains in the rupture process. We finally compare our results to kinematic inversions and show that the foreshock did influence the mainshock by clamping the fault and encouraging off-fault diffuse deformation rather than fault slip in some areas.

The NASA Earth Science Education Collaborative (NESEC) project has the goal to enable broad participation in authentic NASA Earth Science STEM experiences for lifelong learners. These experiences include citizen science through GLOBE Observer (part of the international GLOBE Program), student investigations and research projects, field campaigns, and internships (including both virtual and in-person participation). NESEC works with strategic partners to develop, deliver, and strengthen these experiences. The 2020 pandemic required shifting our approach to adapt and emphasize ways to participate that did not require going outdoors and could be undertaken from home. These resources included activities, not requiring special equipment and using materials that can be found at home. Activities were that work well with families – including different ages and generations – and encourage exploration, play, and building curiosity together about science and the environment. NESEC leverages partnerships with informal education providers, in particular libraries, which This presentation discusses results of field testing with families and emerging evidence of best practices for partnerships and resources to support science and learning at home.

Forecast-Informed Reservoir Operations (FIRO) enables modern weather forecasting technology to be incorporated into Water Control Plans. FIRO provides water managers with more lead time to selectively retain or release water from reservoirs in anticipation of droughts or floods. Managing reservoirs with improved forecasts can optimize benefits such as water supply and fisheries without impairing flood risk management. FIRO viability at Lake Mendocino was assessed according to five management scenarios and evaluated using 16 metrics. Through detailed hydrologic engineering analysis, the difference in water availability was calculated comparing baseline operations and the FIRO alternatives. Based on the evaluation criteria and implementation considerations, the Modified Hybrid alternative was selected and Ensemble Forecast Operations was designated as a reach goal. The benefits assessment considered the water availability difference between baseline and FIRO operations with respect to recreation, hydropower, municipal and industrial water supply, agricultural water supply, and fisheries. To calculate the recreation benefit, daily use values were applied to estimated recreational activity at Lake Mendocino. Hydropower benefit was calculated by applying regional retail electricity prices to the increased electricity generated under FIRO operations. Municipal and industrial water supply benefit was determined by quantifying changes in consumer surplus due to an increase in water reliability. Changes in consumer surplus were determined by estimating demand curves for water usage and using price elasticity of demand. Agricultural water supply benefits were calculated as annual avoided losses and used the residual imputation method. The least-cost method was used to monetize fisheries benefit of FIRO based on changes in downstream flow and water temperature. Results are being integrated into the Lake Mendocino FIRO Final Viability Assessment, which will be finalized by December 2020. A decision support tool (DST) will allow users to input data from other FIRO projects to predict benefits and inform tradeoff decisions. This presentation will share results of the economic assessment, preview the DST, and describe a transferability test case at Prosser Reservoir in the Truckee River Basin.

Coastal Stratocumulus clouds (Sc) can greatly impact the available solar radiation in areas like southern California. These clouds usually dissipate during the morning, as surface fluxes increase in the day. The dissipation process begins by the thinning of the cloud layer, that then becomes a broken cloud field until the clouds completely dissipate. A better understanding of the process could improve predictions of dissipation time and solar variability for this type of clouds. We investigate the evolution of a broken cloud field using LES simulations of coastal Sc clouds over Southern California (Ghonima et al, JAS 2016). We identify and characterize coherent updrafts, downdrafts, and cloud elements using flow field variables (vertical velocity and liquid water mixing ratio). The cloud layer is observed to become a broken cloud field around hour 8 of the simulation, after which the thinning tendency strongly diminishes and the variability of cloud fraction, cloud thickness, and liquid water path suddenly increases. The few cloud elements remaining at noon are found to be located close to cloud base, unlike at night, when they are distributed throughout the whole cloud layer. The largest updrafts and downdrafts contribute to a large portion of the turbulent fluxes along the day (on average, 40% of vertical velocity variance and 48% of the buoyancy flux), and their relative contribution changes during the day as updrafts become stronger and downdrafts weaken around noon.

Over the last decade, the opportunistic use of broadband Ocean Bottom Seismometer (OBS) recordings has been extremely beneficial for baleen whales studies as they regularly record their stereotyped calls ([10-40] Hz). Often deployed in remote areas, OBSs offer additional and often unprecedented locations for acoustic data collection. The long-term, widespread networks are then ideal for passive acoustic monitoring. Therefore OBS-recorded data are crucial to conservation purposes from monitoring their post-exploitation recovery to improving our understanding of these endangered species and threats. As an example of the potential of OBSs for baleen whale studies, this work exploits data collected by the RHUM-RUM (Réunion Hotspot and Upper Mantle - Réunions Unterer Mantel) seismic network. It aimed initially at imaging the mantle structure beneath the Western Indian Ocean and the dynamics of La Réunion volcanic hotspot. To that extent, 57 OBSs were deployed on the ocean floor, covering an area of 2000x2000 km2 (Lat. 16-34°S, Long. 048-070°E), from October 2012 to November 2013. The RHUM-RUM data provides the second opportunity to record species-specific or regionally-distinct signals of Blue Whales (BWs; Antarctic and Madagascar Pygmy BW) within the Western Indian Ocean Sanctuary. BW calls can propagate from tens to hundreds of kilometers. Consequently, results show that recordings from a single OBS are sufficient to determine the acoustic presence of a species and estimate the range of a calling individual. However, the data analysis benefits from the use of automatic and reliable detection processes. Additional information arises from increasing the number of sensors: a small array of the RHUM-RUM network (20km inter-sensor distance) is used for localization and tracking, essential for animal counting. Besides, the broader configuration showed repartition and migration patterns of the studied species. These recordings from the bottom of the ocean shed new light on the study of BWs and, more generally, low-frequency sounds in this area.

Meter-scale AUV mapping of 85-km of the summit and rift zones of Axial Seamount shows systematic variation in morphology of the lava flows with depth and distance from the caldera. ROV sampling reveals flow age and chemistry variations. Each rift zone has a steady downward slope of ~2° outside the caldera. In the caldera and first few km down the rift zones, flows are predominantly channelized sheet flows with collapses along the channels. Mid-rift, drained inflated hummocky flows consisting of complex mounds with tumuli and lava lakes, and narrow ridges of hummocky mounds become common. On the axis of the south rift, the first cones with craters occur 3.2 km from the caldera at 1600 m depth, and broad inflated hummocky flows emplaced through complex lava tubes first appear 6 km down-rift at 1715 m. On the north rift, similar cones and complex flows appear at 10.5 km down-rift at 1725 m depth. The historical flows exemplify this variation: on the upper south rift as channelized sheet flows in 1998 and 2011 erupted from fissures that extended 6.5 km down-rift; on the middle north rift, inflated hummocky flows up to 126 m thick erupted in 2015 from fissures 17.5 km from the caldera; and on the distal south rift, a narrow ridge of coalesced hummocks 160 m tall formed during the 2011 eruption. Older and older lavas remain exposed at greater distances from the more active summit and upper rift zones. Deep on the rift zones, stellate and steep cones with smooth talus slopes occur that did not feed expansive flows, despite being constructed of hotter, less viscous, near-primary magmas. These cones are first observed on both rift zones at 1800 m depth and 18 km from the caldera. Deeper still, emanating from both distal rift axes beginning ~30 km from the caldera, lie voluminous inflated sheet and inflated hummocky flows 30 to 135 m thick with combined area of over 150 km2. The plagioclase-phyric voluminous flows on the south rift erupted ~1250 years ago, and the aphyric ones on the north rift ~13,000 years ago. Eruption rate is the most likely cause of the flow morphology changes since estimated magma viscosity does not correlate with flow morphology. Lateral transport through long dikes would slow magma delivery unless dike widths are large. The near-primary magmas may have risen through narrow conduits from the mantle to the distal rifts.

There is no quantifiable definition of what comprises a peer reviewer, leading to a lack of trust in the outcomes of peer review by the public and some government officials. Using contextual content analysis, this study uncovered concepts from federal science policy and agency peer review guidance documents to begin the creation of such a definition. The first stage determined which term is most often used for a peer reviewer as seen in the U.S. Office of Management and Budget’s (OMB) Final Information Quality Bulletin for Peer Review 2005. The second stage analyzed the U.S. Department of Energy, Energy Efficiency & Renewable Energy, the U.S. Department of Interior, Bureau of Safety and Environmental Enforcement and the U.S. Department of Justice, Office on Violence Against Women peer review guidelines to determine the number of mentions of each concept (knowledge, skills, experience), if a definition of a merit peer reviewer is provided, and descriptors associated with qualities, or sub-concepts pertaining to peer reviews including discipline, teaching, education, postdoctoral positions, certifications, grant funding, publications, presentations, awards and consulting work. Stage one results found that the term reviewer is the most used in describing a peer reviewer for all three federal agencies and the OMB bulletin. Results of stage two show that both knowledge (M=9) and experience (M=14.33) categories were the largest reported with few mentions of skills (M=3.33). Each agency provided a definition of reviewer and qualifications they must meet. This analysis of three federal peer review guidance documents shows that the federal guidance on expertise, if measured by both experience as well as knowledge, is being followed. It would be a worthy effort to do an analysis of the publications, experience and knowledge of those selected for peer review and compare it to each agencies criteria to build a profile of reviewer characteristics. In addition to contributing to the scant literature on peer review, these findings will help narrow the qualities merit peer reviewers need and will assist with future research exploring all U.S. Federal Agency peer review manuals in which qualities in both knowledge and experience could be quantified, helping to defining an accurate measurement of goodness of fit for reviewers.

The position of the grounding line of marine terminating glaciers, the boundary where glacier ice is no longer supported by the ground and starts floating, is a key parameter for a better understanding of glacier dynamics and better quantification of glacier mass balance. Grounding lines have so far been delineated by human interpreters from Differential Interferometric Synthetic Aperture Radar (D-InSAR) products. This is an arduous and time-consuming process that is not scalable for large-scale delineation from the ever-larger amount of remote-sensing data becoming available, which is necessary for a better understanding of glaciological processes. In order to solve this issue, we present a deep learning approach using a convolutional neural network with parallel atrous convolutions and an asymmetric encoding/decoding structure to successfully delineate thousands of grounding lines rapidly and accurately. Furthermore, the neural network outputs uncertainty estimates, which have so far been missing from grounding line delineations. Over the Getz Ice Shelf in West Antarctica, we find a mean difference of 232 meters, or 2.3 pixels, between automatic delineations and manual delineations on test data not used during training. The spread of differences is given by a median absolute deviation of 101 meters. The performance of the neural network is comparable to that of human interpreters, with manual delineations falling within the uncertainty range of automatic delineations. Similar differences exist between multiple manual delineations, with a slightly higher mean difference (268 meters) and a lower spread (median absolute deviation of 52 meters). We show our deep learning pipeline is easily generalizable and scalable to the entire ice sheet, revolutionizing the availability of grounding line delineations for glaciological studies.

Sangamon watershed is recognized as one of the most worth noting regions for water and environmental supply planning and management purposes according to its intensively management for soybean and corn production. It is also a representative area with limited geological and hydraulic measurement data, in which sustainable ground water and environmental management is essential. To better understand the hydraulic properties of the entire watershed, a multi-fidelity Gaussian Processes (Kriging) model was applied to predict the hydraulic conductivity of the upper Sangamon watershed, using previous multi-sources of field observation data (Electrical Earth Resistivity and pumping test data). The model also provided a quantification of uncertainty of the predicted values, which helps us to make reliable suggestions for the future design of hydraulic observations. The data fidelity effect to the model was discussed by comparing multi-fidelity and single-high-fidelity Kriging results. The model predicted values suggest that the accuracy of multi-fidelity Kriging depends on the locations and the distribution of both the high- and low-fidelity data. When high-fidelity data points are sparse and far away from the low-fidelity data points, the information provided from the low-fidelity data becomes extremely important, which can greatly enhance the model performance and accuracy. This study has paved the way to a more efficient parameter estimation in under-sampled sites by effectively estimating large-scale parameter maps using small-scale measurements and by applying uncertainty quantification method to a real watershed observation case. It will also draw upon and contribute to advances in Bayesian experimental design, and will optimally result in financial savings.

To manage potential risks due to H2 leaks into the near-surface geosphere from H2 underground storages (e.g. salt caverns, aquifer), reliable monitoring methods along with a precise knowledge of the geochemical environmental impacts are necessary. Thus, the evolution of some prominent parameters in soil and aquifers can be determined: gas concentrations, redox potential, ionic balance and trace elements. As part of the ROSTOCK’H project, Ineris simulated H2 leakage by injection of dissolved H2 into a shallow aquifer (~20 m deep) in an experimental site within the Paris basin. This experiment aimed to testing advanced monitoring techniques and studying hydrogeochemical impacts at shallow depths. The aquifer water has calcium-bicarbonate facies and a neutral pH. Eight piezometers were aligned over 80 m according to the aquifer main flow (west-east). Hydrogeochemical monitoring devices were set up. One of the piezometers was equipped with a completion connected to a Raman probe and a specific Mid-IR cell for continuous measurement of aqueous gases. At the experiment outset, 5 m3 of water were extracted from the aquifer to be saturated with H2 under atmospheric conditions, before being reinjected through the injection well. About 100 LSTP of dissolved H2 (concentration of 1,8 mg/L) was injected in the aquifer. The H2 injection was preceded by the injection of underground water containing tracers (He(aq), uranine and LiCl) in order to warn the H2 plume arrival in the piezometers located downstream of the injection well. The concentrations of aqueous gases (He, H2, N2, O2, CO2, H2S and CH4) were measured in a control piezometer (20 m upstream) and in six piezometers up to 60 m downstream. Thus, the maximum H2 contents were detected up to 20 m downstream of the injection well: 0.6 mg/L at 5 m, 0.17 mg/L at 7 m then 1.8 µg/L of H2 at 10 and 20 m during the first week. Following the H2(aq) addition, the aquifer physico-chemistry has been modified: low increase in pH, high decrease in redox potential and O2(aq). These results confirm the feasibility of detecting and monitoring H2 in shallow aquifers in very low concentration conditions and highlight the potential impacts. This is of first importance for establishing the surveillance and security aspects related to with H2 storage.

Habitable regions of Europa may include a subsurface ocean and transient liquid environments within its icy shell. Ocean-surface communication may occur on 1–2 million-year (My) timescales or even more rapidly in chaos regions. Any ice-entombed organisms could remain viable at near-surface depths (10–100 cm) over 1–10 ky. The proposed Europa Lander will target samples at depths >10 cm, potentially enabling recovery of viable organisms if sampling conditions are ideal. Any life there would likely represent a separate genesis event from Earth life. Life detection approaches should therefore not only target life as we know it (contamination, common physicochemistry), but also as we don’t know it, to lower the risk of false negatives. We propose to target prebiotic, ancient, or extant life using a novel fully-electronic single-molecule detection strategy. Now in early development (PICASSO), the Electronic Life-detection Instrument for Enceladus/Europa (ELIE) instrument will utilize quantum electron tunneling between nanogap electrodes to interrogate the electronic structure of single molecules. Nanogaps are formed by breaking a gold nanowire embedded on a silicon chip. Bending is then used to control the gap size in the sub-nanometer regime. A molecule can be identified by its characteristic conductance and interaction time as a function of gap size. This technology can detect and distinguish among amino acids, and detect RNA and DNA bases and short base sequences. The extrapolated limit of detection for single amino acids is ~200 ppt after 5 min of sampling (~1 pMol/g). Integrating upfront separation methods will enhance specificity and sensitivity. Our lab-bench prototype integrates a nanogap chip, low-noise amplifier, and a laptop for data processing. We target a ~1 kg flight instrument mass. ELIE will be able to measure two key biosignatures: the amino acid complexity distribution, and charged informational polymers, through to be universal for aqueous based life.

Glacial acceleration is the largest source of uncertainty in sea-level-rise assessment, according to the Intergovernmental Panel on Climate Change. Of the different types of glacial acceleration, surging is the least understood. In this paper, we demonstrate how a combination of automated algorithms dedicated to analysis of two entirely different observation types - satellite altimetry from NASA’s ICESat-2 and satellite imagery from Planet SkySat - can aid in advancing glaciology, utilizing state-of-the art remote sensing /Earth observation technology. NASA’s Ice, Cloud and land Elevation Satellite ICESat-2, launched 15~September~2018, carries the first space-borne multi-beam micro-pulse photon counting laser altimeter system, the Advanced Topographic Laser Altimeter System (ATLAS). ATLAS observations are collected in three pairs of weak and strong beams with 0.7m nominal along-track spacing (under clear-sky conditions). The recording of the observations as a photon-point cloud requires a dedicated algorithm for identification of signal photons and determination of surface heights. As a solution, we developed the density-dimension algorithm for ice surfaces, the DDA-ice. ATLAS data analyzed with the DDA-ice allow determination of heights over heavily crevassed ice surfaces, which are characteristics of accelerating glaciers. The study presented here builds on a special multi-component data set, obtained through synoptic observations of an Arctic glacier system during surge (Negribreen, Svalbard): Airborne altimeter and image data collected during our ICESat-2 validation campaign, and SkySat image data from a special acquisition collected as part of NASA’s Commercial Smallsat Data Acquisitions Pilot program. These are complemented by WorldView (Maxar) and ESA Sentinel-1 data. With a spatial resolution of 0.7-0.86m, SkySat data and WorldView lend themselves to automated classification of crevasse types. Altogether, we obtain a characterization in 3 dimensions that allows discrimination of ice-surface types from surging glaciers (Negribreen) and continuously fast-moving and accelerating glaciers (Jakobshavn Isbrae) based on morphological characteristics.

How dire are the security implications of climate change? Research findings on the relationship between climate and conflict are diverse and contested, leaving policymakers of various types uncertain about productive ways to integrate climate into risk assessments and action plans. This talk reflects on the benefits of inclusive, rather than confrontational, approaches to reconciling scholarly and scientific disagreements. Using a recent expert elicitation-based, consensus-building exercise as a positive case study (Mach et al. 2019), this talk demonstrates how academic communities can make their work both more legible and representative when engaging with policy practitioners.

Absorption of sunlight forms a diurnal warm layer (DWL) in the afternoon at the surface and upper meters of the ocean when wind is weak. Analyses using models and remote sensing data disagree on the frequency of DWLs stronger than 1 °C. In situ time series in the central Indian Ocean showed the DWL exceeded 1 °C for 24% of days in October-December 2011 during the Dynamics of the Madden Julian Oscillation (DYNAMO) experiment. For 4 days with mean wind of 1.4 m/s, the DWL was 1.5-2.5 °C. We observed atmospheric turbulence over the DWL using Doppler lidar. Mixed layer turbulence is convective, generated mostly by surface buoyancy flux. The turbulent kinetic energy dissipation of the convective marine atmospheric mixed layer scales with surface buoyancy flux like diurnal convective boundary layers over land and convective mixed layers in the ocean and lakes. This convection in the afternoon is out of phase with buoyancy flux from nocturnal atmospheric net radiative cooling. The afternoon atmospheric convective turbulence over the tropical ocean mixes heat and humidity from the ocean to the lifted condensation level of clouds.

Precipitation is an essential climate and forcing variable for modeling the global water cycle. Particularly, the Integrated Multi-satellitE Retrievals for GPM (IMERG) product retrospectively provides unprecedented two-decades of high-resolution satellite precipitation estimates (0.1-deg, 30-min) globally. The primary goal of this study is to examine the similarities and differences between the two latest and also arguably most popular GPM IMERG Early and Final Run (ER and FR) products systematically over the globe. The results reveal that: (1) ER systematically estimates 13.0% higher annual rainfall than FR, particularly over land (13.8%); (2) ER and FR show less difference with instantaneous rates (Root Mean Squared Difference: RMSD=2.38 mm/h and normalized RMSD: RMSD_norm=1.10), especially in Europe (RMSD=2.16 mm/h) and cold areas (RMSD_norm=0.87); and (3) with similar detectability of extreme events and timely data delivery, ER is favored for use in hydrometeorological applications, especially in early warning of flooding. Throughout this study, large discrepancies between ER and FR are found in inland water bodies, (semi) arid regions, and complex terrains, possibly owing to morphing differences and gauge corrections while magnified by surface emissivity and precipitation dynamics. The exploration of their similarities and differences provides a first-order global assessment of various hydrological utilities: FR is designed to be more suitable for retrospective hydroclimatology and water resource management, while the earliest available ER product, though not bias-corrected by ground gauges, shows suitable applicability in operational modeling setting for early rainfall-triggered hazard alerts.

Land cover changes (LCC) show biophysical effect on regional climate because they modify the land surface albedo, evapotranspiration, and surface roughness. Many previous studies focused on the effects of individual land cover transitions, such as idealized large-scale scenarios of deforestation/afforestation or historical forest clearance, but the combined effects from the detected recent historical land cover changes in Europe have not been explored. In this study, we use a combination of a regional climate model (the Weather Research and Forecasting model, WRF, v3.9.1) with a high resolution land cover data to explore the effects on surface temperature of land cover changes between 1992 and 2015. Previous studies use one unrealistic large-scale simulation for each LCC to estimate its climate effects which present large variations especially in mid-latitudes. Our analysis introduces a new method simultaneously considering the effects of the mix of historical land cover changes in Europe and the individual one contribution. This approach, based on a ridge statistical regression, does not require an explicit consideration of the different components of the surface energy budget, and directly shows the temperature changes from each land transition. Around 70 Mha of land transitions occurred in Europe from 1992 to 2015. Approximately 25 Mha of agricultural land was left abandoned, which was only partially compensated by cropland expansion (about 20 Mha). Declines in agricultural land mostly occurred in favor of forests (15 Mha) and urban settlements (8 Mha). Compared to 1992, we find that the land covers of 2015 are associated with an average temperature cooling of -0.12±0.20 °C, with seasonal and spatial variations. At a continental level, the mean cooling is mainly driven by agriculture abandonment (cropland-to-forest transitions). Idealized simulations where cropland transitions to other land classes are excluded result in a mean warming of +0.10±0.19 °C, especially during summer. Conversions to urban land always resulted in warming effects, whereas the local temperature response to forest gains and losses shows opposite signs from the western and central part of the domain (where forests have cooling effects) to the eastern part (where forests are associated to warming). Gradients in soil moisture and local climate conditions are the main drivers of these differences. Our findings are a first attempt to quantify the regional climate response to historical LCC in Europe, and our method allows to unmix the temperature signal of a grid cell to the underlying LCCs (i.e., temperature impact per land transition). Further developing biophysical implications from LCCs for their ultimate consideration in land use planning can improve synergies for climate change adaptation and mitigation. Key words: land use/cover change; regional climate mode; biophysical climate; EURO-CORDEX