A document by Dan Sandiford. Click on the document to view its contents.

Natural climate solutions (NCS) have the potential to achieve up to one-third of emission reductions, but uncertainties surrounding their effectiveness hinder their full realization. Here we employ modern portfolio theory to build NCS portfolios (NCSPs) including a variety of pathways listed in Griscom et al. 1. The different pathways are treated as risky assets within a 'carbon mitigation market' with their returns and risks defined by global estimates of mitigation potential. Our aim is to maximize carbon sequestration while minimizing the risk of carbon loss, thus effectively navigating the 'efficient frontier', where the best trade-off between maximum carbon sequestration and risk occurs. Diversifying pathways leads to decreased risk and enhanced resilience, particularly when risks of carbon loss due to environmental stressors are spatially or temporally uncorrelated. The optimal NCSPs provide valuable insights into distributing investments and land within pathway categories (forests, agriculture and wetlands), intervention types (e.g., manage, protect, restore), cost-effectiveness, and geographical contexts. We hope these results help inform policymakers to reduce risk while pursuing ambitious carbon mitigation targets.

In gravel-bed rivers, deterministic approaches to predicting bedload transport use the mean bed shear stress (termed one-dimensional or ‘1D’ equations) or integrate across the frequency distribution of shear stress (2D equations). At low flows, incorporating a range of shear stress values increases prediction accuracy, but at relatively high flows the 1D and 2D approaches are similarly accurate. We contribute to an understanding of the stage-dependent relationship between morphology and bedload transport, and specifically why the mean shear stress characterises transport capacity at formative discharges. We performed physical modelling using a generic Froude-scaled model of a steep laterally-constrained gravel-bed river and captured digital elevation models to perform 2D hydraulic modelling. Both 1D and 2D Meyer-Peter Müller equations were highly accurate across two distinct channel morphologies. In alternate bar channels, transport capacity was controlled by negative feedbacks between flow depth and local bed slope that resulted in a relatively homogeneous distribution of bed shear stress. In plane-bed channels, which lacked the degrees-of-freedom available for large-scale morphologic adjustment, transport capacity was controlled by a spatially variable migrating surface texture. The contrasting spatial patterns of morphology, hydraulics, and surface texture between the two channel morphologies highlight the potential for the same correlation between mean shear stress and transport capacity to emerge through different mechanisms. We suggest that nonlinear feedbacks explain why simple bedload transport equations can be highly effective above a certain flow stage across a range of channel morphologies, and further work should examine whether lateral adjustment confounds this result.

Marine boundary layer clouds tend to organize into closed or open mesoscale cellular convection (MCC). Here, two-dimensional wavelet analysis is applied for the first time to passive microwave retrievals of cloud water path (CWP), water vapor path (WVP), and rain rate from AMSR-E in 2008 over the Northeast and Southeast Pacific, and the Southeast Atlantic subtropical stratocumulus to cumulus transition regions. The (co-)variability between CWP, WVP, and rain rate in 160x160 km2 analysis boxes is partitioned between four mesoscale wavelength octaves (20, 40, 80, and 160 km). The cell scale is identified as the wavelength of the peak CWP variance. Together with a machine-learning classification of cell type, this allows the statistical characteristics of open and closed MCC of various scales, and its relation to WVP, rain rate and potential environmental controlling factors to be analyzed across a very large set of cases. The results show that the cell wavelength is most commonly 40-80 km. Cell-scale CWP perturbations are good predictors of the WVP and rain rate perturbations. A universal cubic dependence of rain rate on CWP is found in closed and open cells of all scales. This suggests that aerosol control on precipitation susceptibility is not as important for open cell formation as are processes that cause increases in cloud water. For cells larger than 20 km, there is no obvious dependence of cell scale on the environmental controlling factors tested, suggesting that the cell scale may depend more on its historical evolution than the current environmental conditions.

This study investigates the response of the semidiurnal tide (SDT) to the 2013 major sudden stratospheric warming (SSW) event using meteor radar wind observations and mechanistic tidal model simulations. In the model, the background atmosphere is constrained to meteorological fields from the Navy Global Environmental Model - High Altitude analysis system. The solar (thermal) and lunar (gravitational) SDT components are forced by incorporating hourly global temperature tendency fields from the ERA5 forecast model, and by specifying the M2 and N2 lunar gravitational potentials, respectively. The simulated SDT response is compared against meteor wind observations from the CMOR (43.3◦N, 80.8◦W), Collm (51.3◦N, 13.0◦E), and Kiruna (67.5◦N, 20.1◦E) radars, showing close agreement with the observed amplitude and phase variability. Numerical experiments investigate the individual roles of the solar and lunar SDT components in shaping the net SDT response. Further experiments isolate the impact of changing propagation conditions through the zonal mean background atmosphere, non-linear wave-wave interactions, and the SSW-induced stratospheric ozone redistribution. Results indicate that between 80-97 km altitude in the northern hemisphere mid-to-high latitudes the net SDT response is driven by the solar SDT component, which itself is shaped by changing propagation conditions through the zonal mean background atmosphere and by non-linear wave-wave interactions. In addition, it is demonstrated that as a result of the rapidly varying solar SDT during the SSW the contribution of the lunar SDT to the total measured tidal field can be significantly overestimated.

Recent climate change is characterised by rapid global warming, but the goal of the Paris Agreement is to achieve a stable climate where global temperatures remain well below 2°C above pre-industrial levels. Inferences about conditions at or below 2°C are usually made based on transient climate projections. To better understand climate change impacts on natural and human systems under the Paris Agreement, we must understand how a stable climate may differ from transient conditions at the same warming level. Here we examine differences between transient and quasi-equilibrium climates based on greenhouse gas-only model simulations at 1.5°C and 2°C global warming. We find substantial local differences between seasonal-average temperatures, with mid-latitude land regions in boreal summer considerably warmer in a transient climate than a quasi-equilibrium state at both 1.5°C and 2°C global warming. Our research demonstrates that the rate of global warming must be considered in regional projections.

Estimating parameters for distributed hydrological models is a challenging and long studied task. Parameter transfer functions, which define model parameters as functions of geo-physical properties of a catchment, might improve the calibration procedure, increase process realism and can enable prediction in ungauged areas. We present the Function Space Optimization (FSO), a symbolic regression method for estimating parameter transfer functions for distributed hydrological models. FSO is based on the idea of transferring the search for mathematical expressions into a continuous vector space that can be used for optimization. This is accomplished by using a text generating neural network with a variational autoencoder architecture, that can learn to compress the information of mathematical functions. To evaluate the performance of FSO, we conducted a case study using a parsimonious hydrological model and synthetic discharge data. The case study consisted of two FSO applications: Single-criteria FSO, where only discharge was used for optimization and multi-criteria FSO, where additional spatiotemporal observations of model states were used for transfer function estimation. The results show that FSO is able to estimate transfer functions correctly or approximate them sufficiently. We observed a reduced fit of the parameter density functions resulting from the inferred transfer functions for less sensitive model parameters. For those it was sufficient to estimate functions resulting in parameter distributions with approximately the same mean parameter values as the real transfer functions. The results of the multi-criteria FSO showed that using multiple spatiotemporal observations for optimization increased the quality of estimation considerably.

Arctic Amplification is robustly seen in climate model simulations of future warming and in the paleoclimate record. Here, we show that in the instrumental record Arctic Amplification is only a recent phenomenon, and that for much of the 20th century the Arctic cooled while the global-mean temperature rose. To investigate why this occurred, we analyze large ensembles of comprehensive climate model simulations under different forcing scenarios. Our results suggest that the global warming from greenhouse gases was largely offset in the Arctic by regional cooling due to aerosols, with internal climate variability also contributing to Arctic cooling and global warming trends during this period. This suggests that the disruption of Arctic Amplification was due to a combination of factors unique to the 20th century, and that enhanced Arctic warming should be expected to be a consistent feature of climate change over the coming century.

 Bayesian calibration based estimation of proglacial lake volume  Method applied to sixty-six lakes located in the High Mountain Asia  Reduction of maximum error in modelled lake volume by >5 times as compared to existing scaling models  Requires minimal calibration with observations as compared to scaling models

In prior work we found that precise approximation of the continuity constraint is crucial for accurate propagation of tracer data when advected through a background incompressible velocity field (Sime et al., 2021). Here we extend this investigation to compressible flows using the anelastic liquid approximation (ALA) and address four related issues: 1. exact conservation of tracer discretized fields through a background compressible velocity; 2. exact mass conservation; 3. addition and removal of tracers without affecting (exact) conservation to preserve a consistent number of tracers per cell; and 4. the diffusion of tracer data, for example, as induced by thermal or chemical effects. In this process we also present an abstract formulation of the interior penalty hybrid discontinuous Galerkin (HDG) finite element formulation for diffusion problems, and apply it to the advection-diffusion and compressible Stokes systems. Finally we present numerical experiments exhibiting the HDG compressible Stokes momentum formulation’s superconvergent compressibility approximation and reproduce community numerical benchmarks from the literature for the ALA.

The past 2 decades of research has demonstrated the value of co-production as a process that creates information that is usable to decision makers. However, research has also shown that those organizations that are already larger, more technically-capable, and located closer to the sources of new information are more likely to engage in co-production with boundary organizations. The question then arises of how smaller entities, who may actually have greater need for capacity, can benefit from investments in new science aimed at improving decision making for water management. In this project we conducted 5 case studies of the information use preferences and practices among small-scale water systems (small municipalities and Water Conservancy Districts) in the Upper Colorado River Basin to understand the opportunities and constraints for the uptake of new sources of information. Like previous work, results indicated that scale, skill, understandability, and lack of capacity limited the use of available information. Furthermore, entities did not engage in co-production with knowledge-related boundary organizations to any extent. However, small water providers did consistently mention the value of contact with other water systems in the area, and the value of being able to reach out to certain key individuals who were looked to as trusted sources of opinion on current information products and trends. Managers emphasized the importance of experience in operating a water system and involvement in operations as critical factors that engendered trust in these key individuals. Finally, certain water systems were seen as leaders in the local area, and constantly mentioned as sources of information and innovative ideas. These findings suggest the importance of both key individual practitioners in pioneering and disseminating new information, as well as more broadly the role of a community of practice in reaching small water providers. Implications for boundary organizations and emerging networks are discussed.

A document by Hugo Carrillo. Click on the document to view its contents.

Meteorological droughts will become the principal factor driving compound hot-dry events and analysis thereof is therefore fundamental with regard to understanding future climate patterns. The average citizen knows little of geometry, but it plays an essential role in the characteristics of the droughts, by means of “fractional lengths”. We analysed the fractality of the meteorological droughts under the most recent climate change scenarios. A temporal fractality measure based upon the Cantor set reveals consensual changes in the behavior of droughts worldwide. Most regions will undergo a slight increase in fractality (up to +10% on average), particularly associated with an acceleration of the hydrological cycle and the Hadley cell expansion, with a shift towards the higher latitudes of the tropical edge in both hemispheres. Geometrical measures were applied to the dry spells (<1mm) simulated by Earth System Models of the Coupled Model Intercomparison Project Phase 6 (CMIP6), showing more concentrated or unequal distribution of droughts in mid latitudes. Simultaneously, the polar regions might benefit from more regular precipitation patterns. Other inequality measures, such as the indices of Gini and Monjo, showed similar results. In general terms, the earth’s climate will be more fractal in the rainfall-related patterns, which likely means that the consequences will be more catastrophic for the human population.

A new, simple parameterisation scheme for scalar (heat and moisture) exchange over sea ice and the marginal ice zone is tested in a numerical weather and climate prediction model. This new “Blended A87” scheme accounts for the influence of aerodynamic roughness on the relationship between momentum and scalar exchange over consolidated sea ice, in line with long-standing theory and recent field observations, and in contrast to the crude schemes currently operational in most models. Using aircraft observations and Met Office Unified Model simulations of cold-air outbreak (CAO) conditions over aerodynamically rough sea ice, we demonstrate striking improvements in model performance when the Blended A87 scheme replaces the model’s operational treatment for surface scalar exchange, provided that the aerodynamic roughness over consolidated ice is appropriately prescribed. The mean biases in surface sensible heat flux, surface latent heat flux, near-surface air temperature and surface temperature reduce from 25 to 11 W m-2, 22 to 12 W m-2, 0.8 to 0.0 K, and 1.4 to 0.8 K, respectively. We demonstrate that such impacts on surface exchange over sea ice can have a marked impact on the evolution of the atmospheric boundary layer across hundreds of kilometres downwind of the sea ice during CAO conditions in the model. Our results highlight the importance of spatiotemporal variability in the topography of consolidated sea ice for both momentum and scalar exchange over sea ice; accounting for which remains a challenge for modelling polar weather and climate.

The horizontal records of ocean-bottom seismometers (OBS) are usually highly noisy, generally due to ocean-bottom currents tilting the instrument, which greatly limits their practical usage in ocean-bottom seismology. In shallow water, water waves with energy concentration around 0.07~Hz induce additional noise on OBSs. Such noise is not well understood. In this article, we propose a noise model to explain the horizontal noise around 0.07 Hz. The noise model consists of three types of noise, that is, water-wave-induced noise, other noise with a relatively constant orientation, and background random noise. The wave-induced horizontal acceleration is theoretically shown to be proportional to the time derivative of ocean-bottom pressure. We validate the noise model and related theories using realistic observations. Results are potentially applicable to determine the propagation direction of water waves nearshore, and also provide constraints on the underlying Earth structure. The results can also be applied to the removal of wave-induced noise, achieving a typical maximum improvement in the signal-to-noise ratio of 10-20 dB for time periods with strong wave noise.

The study of the relationship between the upper and lower layers in the Gulf of Mexico (GoM) has experienced a lot of progress in recent years. Nevertheless, an examination of this coupling for the entire GoM in a statistically consistent manner is still needed. Layer thickness data from a GoM 21-year free-running simulation is used to examine the coupling between the upper (<250 m) and lower (>1000 m) layers with focus on the dominant modes of variability through a Hilbert Empirical Orthogonal Functions (HEOFs) analysis. The three leading modes of the upper layer are associated with the Loop Current’s (LC) lifecycle and LC eddy (LCE) shedding, with lower-layer variability vertically corresponding and intensified along certain bathymetric features. These modes are periodic, indicating recurrence of circulation patterns in agreement with observations. The fourth mode of the upper layer is associated with the translation of LCEs and their dissipation in the northwestern GoM, which significantly contributes to a richer lower-layer variability in a vast area of the western GoM. The lower mode describes the deep anticyclone-cyclone accompanying the LCEs, the strengthening of the circulation along the Sigsbee Gyre western branch, and the variability over the Sigsbee plain. It does not show cyclicity, suggesting persistence of the associated circulation patterns with a dominant timescale of 14 months. Evidence and corroboration of recently observed lower-layer circulation features are provided. The application of the HEOFs technique used here can complement the three-dimensional oceanic assimilation methods by projecting surface information to depth in a physically consistent manner.

We have used Mars Exploration Rover Opportunity data to investigate the origin and alteration of lithic types along the western rim of Noachian-aged Endeavour crater on Meridiani Planum. Two geologic units are identified along the rim. The Shoemaker formation consists of two types of polymict impact breccia: clast-rich with coarser clasts in upper units; clast-poor with smaller clasts in lower units. Comparison with observations at terrestrial craters show that the lower units represent more distal ejecta from one or more earlier impacts, and the upper units are ejecta from Endeavour crater. Both are mixtures of target rocks of basaltic composition. Subtle compositional differences are caused by differences in post-impact alteration along the crater rim. The lower Shoemaker units and the Matijevic formation represent pre-Endeavour geology, which we equate with the regionally mapped Noachian subdued cratered unit. An alteration style unique to these rocks is formation of Si- and Al-rich vein-like structures crosscutting outcrops, and formation of smectite. Post-Endeavour alteration is dominated by sulfate formation. Rim-crossing fracture zones include regions of alteration that produced Mg-sulfates as a dominant phase, plausibly closely associated in time with the Endeavour impact. Calcium-sulfate vein formation occurred over an extended time period, including pre-Endeavour impact and after the Endeavour rim had been substantially degraded, likely after deposition of the Burns formation that surrounds and embays the rim. Differences in Mg, Ca and Cl concentrations on rock surfaces and interiors indicate mobilization of salts by transient water that has occurred recently and may be ongoing.

We present the first continental-scale seismic model of the lithosphere and underlying mantle beneath Southeast Asia obtained from adjoint waveform tomography (often referred to as full-waveform inversion or FWI), using seismic data filtered at periods from 20 - 150s. Based on >3,000h of analyzed waveform data gathered from ~13,000 unique source-receiver pairs, we image isotropic P-wave velocity, radially anisotropic S-wave velocity and density via an iterative non-linear inversion that begins from a 1-D reference model. At each iteration, the full 3-D wavefield is determined through an anelastic Earth, accommodating effects of topography, bathymetry and ocean load. Our data selection aims to maximize sensitivity to deep structure by accounting for body-wave arrivals separately. SASSY21, our final model after 87 iterations, is able to explain true-amplitude data from events and receivers not included in the inversion. The trade-off between inversion parameters is estimated through an analysis of the Hessian-vector product. SASSY21 reveals detailed anomalies down to the mantle transition zone, including multiple subduction zones. The most prominent feature is the (Indo-)Australian plate descending beneath Indonesia, which is imaged as one continuous slab along the 180-degree curvature of the Banda Arc. The tomography confirms the existence of a hole in the slab beneath Mount Tambora and locates a high S-wave velocity zone beneath northern Borneo that may be associated with subduction termination in the mid-late Miocene. A previously undiscovered feature beneath the east coast of Borneo is also revealed, which may be a signature of post-subduction processes, delamination or underthrusting from the formation of Sulawesi.