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The world’s cryospheric regions, ranging from high mountains to polar regions, have experienced unprecedented atmospheric warming, glacier melting and permafrost thawing since the mid-20th century. This rapid cryosphere degradation has dramatically altered terrestrial/coastal landscapes, characterized by creating debuttressed valleys and thermokarst hillslopes, expanding unstable landscapes, and increasing the access to sub-/pro-glacially stored sediment. Such rapid landscape changes have resulted in increases in erosion and sediment loads, posing threats to riverine and near-shore marine environments and triggering cascading impacts on water-food-energy securities which support the livelihoods of a quarter of the global population.Here, we present a global inventory of cryosphere degradation-driven increases in erosion and sediment yield, including 76 locations from the high Arctic, European mountains, High Mountain Asia and Andes, and 18 Arctic permafrost-coastal sites, collected from over 80 publications. This inventory confirms the widespread increase in sediment transport from cold regions in response to modern deglaciation. Moreover, we identify two to eight-fold increases in sediment fluxes and more than doubled coastal erosion rates in many cold regions between the 1950s and 2010s.Such increases in sediment evacuation from deglaciating/thermokarst regions have been blamed for introducing large amounts of carbon, nitrogen, and pollutants into aquatic ecosystems, impacting primary productivity, river biodiversity, and water quality. In high-mountain areas, increased sediment fluxes have also hampered hydropower exploitation through reservoir sedimentation and turbine abrasion. Meanwhile, accelerated erosion along ice-rich Arctic permafrost coasts has caused an irreversible land loss, costing billions of dollars for relocating or protecting coastal infrastructure.With continuous cryosphere degradation, sediment fluxes are likely to increase in the next decades until reaching a maximum (“Peak Sediment”). Theoretically, the timing of peak sediment can lag decades to hundreds of years behind the peak meltwater due to the remobilization of paraglacial and subglacial sediment legacy. Thereafter, sediment fluxes will decline as glacier/permafrost erosion ceases and active sediment contributing area shrinks. We predict that sediment-transport regimes will shift through three stages, from the ongoing temperature-dominated regime to a temperature-precipitation jointly controlled regime, eventually shifting toward a rainfall-dominated regime roughly between 2100-2200.However, the understanding of sediment dynamics in cold regions is still limited by the lack of long-term observations and the inherent complexity of geomorphic processes, such as episodic events, scale/threshold effects in sediment transport, and positive/negative feedbacks of geomorphic responses. To underpin the forward-looking mitigation strategies for climate-sensitive and fragile cold regions, we call for the enhancement of multi-source sediment monitoring programs, fully distributed physics-based sediment-yield models, and interdisciplinary-international scientific collaborations.

Landslides alter the morphology and sediment dynamics of mountainous terrain. Here, we evaluate how the spatial and temporal variability of landslide triggering events adjust this footprint. We use the HyLands landscape evolution model that explicitly simulates the occurrence of landslide events as well as fluvial incision and sediment dynamics. Both existing landscapes as well as synthetically produced landscapes that evolve over geological timescales are considered. This enables us to identify the required magnitude and frequency of extreme events for them to be recorded in landscape morphology. Moreover, we compare the relative contribution of long-term tectonic processes versus spatially clustered extreme events in shaping mountainous terrain. Finally, we evaluate if and how the temporal occurrence of landslide-triggering events alter morphology. Here we compare two scenarios: a first one evaluates how a landslide-prone landscape responds to events that are uniformly spread through time, a second one tests how such a landscape responds to regionally synchronous events. This contribution aims to clarify the distinctive role of landsliding in shaping mountainous terrain, which will in turn contribute to understanding how landslide prone regions respond to spatial and temporal changes in extreme events.

The Chaos Canyon landslide, which collapsed on the afternoon of June 28th, 2022 in Rocky Mountain National Park presents an opportunity to evaluate instabilities within alpine regions faced with a warming and dynamic climate. Video documentation of the landslide was captured by several eyewitnesses and motivated a rapid field campaign. Initial estimates put the failure area at 66,630 m2, with an average elevation of 3,555 m above sea level. We undertook an investigation of previous movement of this landslide, measured the volume of material involved, evaluated the potential presence of interstitial ice/snow within the failed deposit, and examined potential climatological forcings at work in causing the collapse of the slope. Satellite radar and optical measurements were used to measure deformation of the landslide in the years leading up to collapse. From 2017 to 2019, the landslide moved ∼5 m yr-1, accelerating to 17 m yr-1 in 2019. Movement took place through both internal deformation and basal sliding. Climate analysis reveals the collapse took place during peak snowmelt, and 2022 followed 10 years of higher than average positive degree day sums. We also made use of slope stability modeling to test what factors controlled the stability of the area. Models indicate even a small increase in the water table reduces the Factor of Safety to 3 of material was deposited at the slide toe and ∼1,340,000 ± 133,000 m3 of material was evacuated from the source area. Our holistic approach to the collapse of the Chaos Canyon landslide provided an opportunity to examine a landslide that may be representative of future dynamic alpine topography, wherein failures becomes more common in a warming climate.

This code was developed for the purposes of analyzing 1) climate, 2) InSAR data, and 3) smoothing a structure from motion model. These were original functions and scripts in support our our manuscript submitted to Earth Surface Dynamics. This manuscript analyses the Chaos Canyon landslide in Rocky Mountain National Park, Colorado, USA., Code written in R, Matlab, and Python

Rivers originating in the Third Pole (Tibetan Plateau and surrounding high-Asian mountains) are crucial lifelines for one-third of the world’s population. These fragile headwaters are now experiencing amplified climate change, glacier melt, and permafrost thaw. Observational data from 28 headwater basins demonstrate substantial increases in both annual runoff and annual sediment fluxes across the past six decades. The increases have accelerated since the mid-1990s, in response to a warmer and wetter climate. The total riverine sediment load from HMA is projected to more than double by the mid-21st century under an extreme climate change scenario. The substantially increasing riverine sediment loads could negatively impact the hydropower-food-environmental security in the Third Pole region. Such findings also have implications for other cold environments such as the Arctic, Antarctic, and other high mountain areas.

Glaciers erode their beds by abrasion and plucking and entraining sediment on their way downwards driven by gravity. Basal ice becomes a sediment transport agent. To determine glacial transport of sediment, measurements of both the ice flux and its concentration of sediment are needed. Once glaciers reach the ocean, ice and its entrained sediment is released into the ocean by calving. Further transport takes place by icebergs. Quantification of IRD (ice-rafted debris) fluxes, which upon ultimate deposition on the ocean floor is an important climate indicator, becomes even more complicated as icebergs topple and differentially melt while being in transport. While the volume of tidewater glacier ice released by recent calving is quite well constrained by satellite measurements, there is a lack of measurements of the concentration of sediment within the moving ice.Here, we describe a method to collect samples of ice from icebergs systematically for the first time in Greenland together with a strategy to obtain representative samples. Our method is tested in Scoresby Sound, East Greenland in order to describe the transport of sediment into the fjord system related to calving from known glacial source areas. Our data clearly demonstrate that biased and sparse sampling potentially produces unrealistic values of sediment concentrations. Seventy-two samples from 24 icebergs had an average concentration of sediment of 35.5 g/l of ice with a standard deviation of 97%, between the 24 individual icebergs. The origin of the sediment is related to specific source areas. Based on the samples, we present an estimate of the annual transport of sediment out of Scoresby Sound related to calving ~100 (0.3-200) million t yr-1. Finally, we discuss the uncertainties of our estimate.

Computational modelling occupies a unique niche in Earth and environmental sciences. Models serve not just as scientific technology and infrastructure, but also as digital containers of the scientific community's understanding of the natural world. As this understanding improves, so too must the associated software. This dual nature–models as both infrastructure and hypotheses–means that modelling software must be designed to evolve continually as geoscientific knowledge itself evolves. Here we describe design principles, protocols, and tools developed by the Community Surface Dynamics Modeling System (CSDMS) to promote a flexible, interoperable, and ever-improving research software ecosystem. These include a community repository for model sharing and metadata, interface and ontology standards for model interoperability, language bridging tools, a modular programming library for model construction, modular software components for data access, and a Python-based execution and model-coupling framework. Methods of community support and engagement that help create a community-centered software ecosystem are also discussed.

Arising from the non‐uniform dispersal of sediment and water that build deltaic landscapes, morphological change is a fundamental characteristic of river delta behavior. Thus, sustainable deltas require mobility of their channel networks and attendant shifts in landforms. Both behaviors can be misrepresented as degradation, particularly in context of the “stability” that is generally necessitated by human infrastructure and economies. Taking the Ganges‐Brahmaputra‐Meghna Delta as an example, contrary to public perception, this delta system appears to be sustainable at a system scale with high sediment delivery and long‐term net gain in land area. However, many areas of the delta exhibit local dynamics and instability at the scale at which households and communities experience environmental change. Such local landscape “instability” is often cited as evidence that the delta is in decline, whereas much of this change simply reflects the morphodynamics typical of an energetic fluvial‐delta system and do not provide an accurate reflection of overall system health. Here we argue that this disparity between unit‐scale sustainability and local morphodynamic change may be typical of deltaic systems with well‐developed distributary networks and strong spatial gradients in sediment supply and transport energy. Such non‐uniformity and the important connections between network sub‐units (i.e., fluvial, tidal, shelf) suggest that delta risk assessments must integrate local dynamics and sub‐unit connections with unit‐scale behaviors. Structure and dynamics of an integrated deltaic network control the dispersal of water, solids, and solutes to the delta sub‐environment and thus the local to unit‐scale sustainability of the system over time.

Ice flow dynamics of the Greenland ice sheet control the production of sediment. Future acceleration in glacial flow and ice sheet melt will amplify Greenland’s supply of sediment to the coastal zone. Globally, sand and gravel reserves are rapidly depleting while the demand is increasing, largely due to urban expansion, infrastructural improvements and the enhancement of coastal protection in response to climate change. Here, we show that an abundance of sand and gravel provides an opportunity for Greenland to become a global exporter of aggregates and relieve the increasing global demand. The changing Arctic conditions help pave a sustainable way for the country towards economic independence. This way, Greenland could benefit from the challenges brought by climate change. Such exploitation of sand requires careful assessment of the environmental impact and must be implemented in collaboration with the Greenlandic society. Sand and gravel have become important commodities due to infrastructure and coastal protection schemes, leading to shortages on a global level. This Perspective looks at how Greenland could diversify its economy towards export of its sand resources and the potential impacts on the environment and local way of life.

The study of modern hurricane deposits is useful in both identifying ancient hurricane deposits in the rock record and predicting patterns of deposition and erosion produced by future storm events. Hurricane deposits on carbonate platforms have been studied less frequently than have been those along continental coasts. Here we present observations of the characteristics of deposition and scour caused by Hurricane Irma on Little Ambergris Cay, a small uninhabited island located near the southeastern edge of the Caicos platform in the Turks and Caicos Islands. Hurricane Irma passed directly over Little Ambergris Cay on 7 September 2017 as a Category 5 hurricane. We described and sampled multiple types of hurricane deposits and determined that the washover fans were the best sedimentological records for hurricane conditions, as they were subject to very little reworking over time. We compared different model predictions of storm tide and wave height with eyewitness reports and distributions of scour. Examining the washover fans allowed for the construction of a conceptual model for hurricane deposits formed in a high‐energy storm event on a carbonate platform. Characteristics of the washover fans were their small size, the lack of sedimentary structures, and very well sorted sediment. The size and distribution of carbonate boulders eroded and transported by the storm are consistent with depth‐averaged flow velocities in the range of 1.5–5.3 m/s. The strength of the storm and the low‐lying topography, distinct features of a carbonate platform setting, contributed to high levels of sediment bypass and high flow velocities, resulting in small, unstructured deposits.

The morphology of deltas is determined by the spatial extent and variability of the geomorphic processes that shape them. While in some cases resilient, deltas are increasingly threatened by natural and anthropogenic forces, such as sea level rise and land use change, which can drastically alter the rates and patterns of sediment transport. Quantifying process patterns can improve our predictive understanding of how different zones within delta systems will respond to future change. Available remotely sensed imagery can help but appropriate tools are needed for pattern extraction and analysis. We present a method for extracting information about the nature and spatial extent of active geomorphic processes across deltas from ten parameters quantifying the geometry of each of 1239 islands and the channels around them using machine learning. The method consists of a two-step unsupervised machine learning algorithm that clusters islands into spatially continuous zones based on the ten morphological metrics extracted from remotely sensed imagery. By applying this method to the Ganges–Brahmaputra–Meghna Delta, we find that the system can be divided into six major zones. Classification results show that active fluvial island construction and bar migration processes are limited to relatively narrow zones along the main Ganges River and Brahmaputra and Meghna corridors, whereas zones in the mature upper delta plain, with smaller fluvial distributary channels stand out as their own morphometric class. The classification also shows good correspondence with known gradients in the influence of tidal energy with distinct classes for islands in the backwater zone and in the purely tidally-controlled region of the delta. Islands at the delta front, under the mixed influence of tides, fluvial-estuarine construction, and local wave reworking have their own characteristic shape and channel configuration. The method does not distinguish between islands with embankments (polders) and natural islands in the nearby mangrove forest (Sundarbans), suggesting that human modifications have not yet altered the gross geometry of the islands beyond their previous natural morphology. These results demonstrate that machine learning and remotely sensed imagery are useful tools for identifying the spatial patterns of geomorphic processes across delta systems.

Modeling is an important way to assess current and future permafrost spatial distribution and dynamics, especially in data poor areas like the Arctic region. Here, we evaluate a physics-based analytical model, Kudryavtsev's active layer model, which is widely used because it has relatively few data requirements. This model was recently incorporated into a component modeling toolbox, allowing for coupled modeling of permafrost and geomorphic processes over geological timescales. However, systematic quantitative assessment of the influence of its controlling parameters on permafrost temperature and active layer thickness predictions has not been undertaken before. We investigate the sensitivity of the Kudryavtsev's active layer model by Monte Carlo simulations to generate probability distributions for input parameters and compare predictions with a comprehensive benchmark dataset of in-situ permafrost observations over entire Alaska. Predicted permafrost surface temperature is highly dependent on mean annual air temperature (r = 0.78 on average), annual temperature amplitude (−0.41), and winter-averaged snow thickness (0.30). Uncertainty of predicted permafrost temperature is relatively small (RMSE = 1 °C), when air temperature and snow depth are well constrained. Similarly, RMSE between simulated and observed ALT at stations is ~0.08 m. However, under given air temperature and snow conditions, soil water content bias can significantly affect modeled active layer thickness (RMSE = 0.1 m or 40% of the observed active layer thickness). If soil water content has a large bias, improvements in other parameters may not significantly improve the active layer predictions of the Kudryavtsev's model.

Modern deltas are dependent on human-mediated freshwater and sediment fluxes. Changes to these fluxes impact delta biogeophysical functioning and affect the long-term sustainability of these landscapes for human and for natural systems. Here we present contemporary estimates of long-term mean sediment balance and relative sea level rise across 46 global deltas. We model scenarios of contemporary and future water resource management schemes and hydropower infrastructure in upstream river basins to explore how changing sediment fluxes impact relative sea level rise in delta systems. Model results show that contemporary sediment fluxes, anthropogenic drivers of land subsidence, and sea level rise result in delta relative sea level rise rates that average 6.8 mm/y. Assessment of impacts of planned and under-construction dams on relative sea level rise rates suggests increases on the order of 1 mm/y in deltas with new upstream construction. Sediment fluxes are estimated to decrease by up to 60% in the Danube and 21% in the Ganges-Brahmaputra-Meghna if all currently planned dams are constructed. Reduced sediment retention on deltas caused by increased river channelization and management has a larger impact, increasing relative sea level rise on average by nearly 2 mm/y. Long-term delta sustainability requires a more complete understanding of how geophysical and anthropogenic change impact delta geomorphology. Local and regional strategies for sustainable delta management that focus on local and regional drivers of change, especially groundwater and hydrocarbon extraction and upstream dam construction, can be highly impactful even in the context of global climate-induced sea level rise.

Historically, in-situ measurements have been notoriously sparse over the Arctic. As a consequence, the existing gridded data of Surface Air Temperature (SAT) may have large biases in estimating the warming trend in this region. Using data from an expanded monitoring network with 31 stations in the Alaskan Arctic, we demonstrate that the SAT has increased by 2.19 °C in this region, or at a rate of 0.23 °C/decade during 1921-2015. Meanwhile, we found that the SAT warmed at 0.71 °C/decade over 1998-2015, which is two to three times faster than the rate established from the gridded datasets. Focusing on the "hiatus" period 1998-2012 as identified by the Intergovernmental Panel on Climate Change (IPCC) report, the SAT has increased at 0.45 °C/decade, which captures more than 90% of the regional trend for 1951-2012. We suggest that sparse in-situ measurements are responsible for underestimation of the SAT change in the gridded datasets. It is likely that enhanced climate warming may also have happened in the other regions of the Arctic since the late 1990s but left undetected because of incomplete observational coverage.

The existing National Aeronautics and Space Administration NASA Moderate Resolution Imaging Spectroradiometer MODIS MOD35_L2 cloud mask performance was assessed using imagery of Kangerlussuaq Fjord, Greenland. It was found to perform suboptimally, especially near glacially fed river mouths, due to sediment-laden water being highly reflective in near-infrared wavelengths. In situ observations of suspended sediment concentration SSC were compared against MODIS band 1 and 2 reflectance and show a reflectance saturation effect past which increasing SSC values fail to increase the reflectance of water. A new mask optimized for turbid waters uses the reflectance saturation effect observed in high-SSC water. This new mask and a custom adaption of individual tests within the existing MOD35_L2 cloud mask were tested. The new mask outperforms the standard MOD35_L2 mask and the combination of new and custom masks was shown to screen out clouds very well in Greenland fjords. It is thought that with local measurements of MODIS band 1 and 2 reflectance values of turbid water to serve as training data, this mask should perform equally well in other turbid coastal waters.

A new resource makes it easier for researchers to explore predictions of how melting permafrost might affect carbon release, wetlands, and river deltas as they evolve and other interacting effects.

Geoprocesses, Geohazards—CSDMS 2018: A CSDMS hosted Workshop; Boulder, Colorado, 22–24 May 2018

To expand agricultural production and address water scarcity, India is moving forward with the National River Linking Project (NRLP), which will connect 44 rivers via 9,600 km of canals. Here, we compile the first complete database of proposed NRLP dams, reservoirs and canals, including operating schedules for Himalayan infrastructure. We evaluate potential NRLP-derived changes to mean annual water discharge for 29 rivers and mean monthly water and sediment discharge for six rivers flowing to five major deltas. Sediment rating curves are used to quantify the impacts of changing water discharge within the rivers, and basin-wide trapping efficiency is established for new reservoirs. Given full implementation of the NRLP, we forecast reductions in annual suspended sediment transport to deltas of 40–85% (Mahanadi), 71–99% (Godavari) and 60–97% (Krishna) due to profound reservoir trapping and peak streamflow reductions. The Ganga before its confluence with the Brahmaputra is projected to experience a 39–75% reduction in annual suspended load. The Brahmaputra before its confluence with the Ganga is projected to experience a 9–25% reduction in suspended load, despite losing only 6% of its annual water flow. We calculate a projected corresponding aggradation decrease for the Ganga-Brahmaputra delta from 3.6 to 2.5 mm y–1, which is a large enough change to drive relative sea-level rise at the delta front. At the remaining four deltas, the NRLP will exacerbate current sediment starvation. We reconstruct the annual water transfer volume proposed for the NRLP to be 245 km3 y–1, higher than previous estimates due to the inclusion of along-canal usage. If completed, the NRLP will transform watershed boundaries, with more than half of the land in India contributing a portion of its runoff to a new mouth. These impacts may have profound environmental and public health implications, particularly in the context of future climate change.

This study uses model projections of the open water season (for 1920–2100) to investigate Arctic sea-ice decline. Nearshore regions began shifting from pre-industrial conditions in 1990, and human influence is projected to emerge in 2040. Sea ice impacts most of the Arctic environment, from ocean circulation and marine ecosystems to animal migration and marine transportation. Sea ice has thinned and decreased in age over the observational record1,2. Ice extent has decreased3. Reduced ice cover has warmed the surface ocean4, accelerated coastal erosion5,6 and impacted biological productivity7. Declines in Arctic sea-ice extent cannot be explained by internal climate variability alone and can be attributed to anthropogenic effects8,9. However, extent is a poor measure of ice decline at specific locations as it integrates over the entire Arctic basin and thus contains no spatial information. The open water season, in contrast, is a metric that represents the duration of open water over a year at an individual location10,11. Here we present maps of the open water season over the period 1920–2100 using daily output from a 30-member initial-condition ensemble of business-as-usual climate simulations12 that characterize the expansion of Arctic open water, determine when the open water season will move away from pre-industrial conditions (‘shift’ time) and identify when human forcing will take the Arctic sea-ice system outside its normal bounds (‘emergence’ time). The majority of the Arctic nearshore regions began shifting in 1990 and will begin leaving the range of internal variability in 2040. Models suggest that ice will cover coastal regions for only half of the year by 2070.

The Yellow River, China, experienced >1000 levee breaches during the last 3000 years. A reduced-complexity model is developed in this study to explore the effects of climate change and human activity on flood levels, levee breaches, and river avulsions. The model integrates yearly morphological change along a channel belt with daily river fluxes and hourly evolution of levee breaches. Model sensitivity analysis reveals that under natural conditions, superelevation of the channel belt dominates flood frequency. When there is significant human-accelerated basin erosion and breach repair, the dominant factors shift to a combination of mean annual precipitation, superelevation, critical shear stress of weak channel banks, and the time interval between breach initiation and its repair. The effect of precipitation on flood frequency is amplified by land use changes in the hinterland, particularly in the erodible Loess Plateau. Uncertainty analysis estimates the most likely values of the dominant factors for six historical periods between 850 B.C. and A.D. 1839, which are used to quantitatively reconstruct flood dynamics. During 850 B.C. to A.D. 1839, when the sediment load increased fourfold, the breach recurrence interval was shortened from more than 500 years to less than 6 years, and the breach outflow rate increased ~27 times. River management practices during A.D. 1579 to A.D. 1839 focused on levees and triggered a severe positive feedback of increased levee heights and flood hazard exacerbation. Raising the levee heights proved to be ineffective for sustainable flood management.

The Greenland ice sheet is experiencing dramatic melt that is likely to continue with rapid Arctic warming. However, the proportion of meltwater stored before reaching the global ocean remains difficult to quantify. We use NASA MODIS surface reflectance data to estimate river discharge from two West Greenland rivers – the Watson River near Kangerlussuaq and the Naujat Kuat River near Nuuk – over the summers of 2000–12. By comparison with in situ river discharge observations, ‘inundation–discharge’ relations were constructed for both rivers. MODIS-based total annual discharges agree well with total discharge estimated from in situ observations (86% of summer discharge in 2009 to 96% in 2011 at the Watson River, and 106% of total discharge in 2011 to 104% in 2012 at the Naujat Kuat River). We find, however, that a time-lapse camera, deployed at the Watson River in summer 2012, better captures the variations in observed discharge, benefiting from fewer data gaps due to clouds. The MODIS-derived estimates indicate that summer discharge has not significantly increased over the last decade, despite a strong warming trend. Also, meltwater runoff estimates derived from the regional climate model RACMO2/GR for the drainage basins are higher than our reconstructions of river discharge. These results provide indirect evidence for a considerable component of water storage within the glacio-hydrological system.

Climate change has the potential to erode coastlines, but a rediscovered archive of aerial photographs from the Second World War shows that in southern Greenland, deltas have recently extended seaward. Climate change has the potential to erode coastlines, for example as a result of increased wave activity, but the net effect depends on the balance between creative and destructive forces. Mette Bendixen and colleagues show that deltas in southwestern Greenland have grown over the past few decades, following a period of stability in the mid-twentieth century. The delta expansions occurred during periods of reduced sea ice and increased melt from the Greenland Ice Sheet. Although many coastlines remain under threat, these findings reveal the intimate interactions that arise in a warming climate. A loss of ice seems to lead to increased sediment delivery, which has resulted in the expansion, rather than degradation, of Greenland's deltas. Climate changes are pronounced in Arctic regions and increase the vulnerability of the Arctic coastal zone1. For example, increases in melting of the Greenland Ice Sheet and reductions in sea ice and permafrost distribution are likely to alter coastal morphodynamics. The deltas of Greenland are largely unaffected by human activity, but increased freshwater runoff and sediment fluxes may increase the size of the deltas, whereas increased wave activity in ice-free periods could reduce their size, with the net impact being unclear until now. Here we show that southwestern Greenland deltas were largely stable from the 1940s to 1980s, but prograded (that is, sediment deposition extended the delta into the sea) in a warming Arctic from the 1980s to 2010s. Our results are based on the areal changes of 121 deltas since the 1940s, assessed using newly discovered aerial photographs and remotely sensed imagery. We find that delta progradation was driven by high freshwater runoff from the Greenland Ice Sheet coinciding with periods of open water. Progradation was controlled by the local initial environmental conditions (that is, accumulated air temperatures above 0 °C per year, freshwater runoff and sea ice in the 1980s) rather than by local changes in these conditions from the 1980s to 2010s at each delta. This is in contrast to a dominantly eroding trend of Arctic sedimentary coasts along the coastal plains of Alaska2, Siberia3 and western Canada4, and to the spatially variable patterns of erosion and accretion along the large deltas of the main rivers in the Arctic5,6,7. Our results improve the understanding of Arctic coastal evolution in a changing climate, and reveal the impacts on coastal areas of increasing ice mass loss and the associated freshwater runoff and lengthening of open-water periods.

The Ganges-Brahmaputra-Meghna (Bengal) Delta in Bangladesh has been described as a delta in peril of catastrophic coastal flooding because sediment deposition on delta plain surfaces is insufficient to offset rates of subsidence and sea level rise. Widespread armoring of the delta by coastal embankments meant to protect crops from flooding has limited natural floodplain deposition, and in the tidally dominated delta, dikes lead to rapid compaction and lowered land surface levels. This renders the deltaic floodplains susceptible to flooding by sea level rise and storm surges capable of breaching poorly maintained embankments. However, natural physical processes are spatially variable across the delta front and therefore the impact of dikes on sediment dispersal and morphology should reflect these variations. We present the first ever reported sedimentation rates from the densely populated and human-controlled floodplains of the central lower Bengal Delta. We combine direct sedimentation measurements and short-lived radionuclides to show that transport processes and lateral sedimentation are highly variable across the delta. Overall aggradation rates average 2.3 ± 9 cm y–1, which is more than double the estimated average rate of local sea level rise; 83% of sampled sites contained sediment tagged with detectable 7Be, indicating flood-pulse sourced sediments are widely delivered to the delta plain, including embanked areas. A numerical model is then used to demonstrate lateral accretion patterns arising from 50 years of sedimentation delivered through smaller order channels. Dominant modes of transport are reflected in the sediment routing and aggradation across the lower delta plain, though embankments are major controls on sediment dynamics throughout the delta. This challenges the assumption that the Bengal Delta is doomed to drown; rather it signifies that effective preparation for climate change requires consideration of how infrastructure and spatially variable physical dynamics influence sediment dispersal on seasonal and decadal time scales.

Sea ice limits the interaction of the land and ocean water in the Arctic winter and influences this interaction in the summer by governing the fetch. In many parts of the Arctic, the open-water season is increasing in duration and summertime sea-ice extents are decreasing. Sea ice provides a first-order control on the physical vulnerability of Arctic coasts to erosion, inundation, and damage to settlements and infrastructures by ocean water. We ask how the changing sea-ice cover has influenced coastal erosion over the satellite record. First, we present a pan-Arctic analysis of satellite-based sea-ice concentration specifically along the Arctic coasts. The median length of the 2012 open-water season, in comparison to 1979, expanded by between 1.5 and 3-fold by Arctic Sea sector, which allows for open water during the stormy Arctic fall. Second, we present a case study of Drew Point, Alaska, a site on the Beaufort Sea, characterized by ice-rich permafrost and rapid coastal-erosion rates, where both the duration of the open-water season and distance to the sea-ice edge, particularly towards the northwest, have increased. At Drew Point, winds from the northwest result in increased water levels at the coast and control the process of submarine notch incision, the rate-limiting step of coastal retreat. When open-water conditions exist, the distance to the sea ice edge exerts control on the water level and wave field through its control on fetch. We find that the extreme values of water-level setup have increased consistently with increasing fetch.

Many of the world′s largest river deltas are sinking due to sediment loading, compaction, and tectonics but also recently because of groundwater extraction, hydrocarbon extraction, and reduced aggradation. Little is known, however, about the full spatial variability of subsidence rates in complex delta systems. This study reconstructs subsidence rates in the eastern portion of the Ganges-Brahmaputra Delta (GBD), Bangladesh, covering more than 10,000 km2 at a high spatial resolution of 100 m. The map was produced using Interferometric Synthetic Aperture Radar (InSAR) covering the period 2007 to 2011. Eighteen Advanced Land Observing Satellite Phased-Array L-band SAR scenes were used to generate 30 interferograms calibrated with GPS. Interferograms were stacked to yield average subsidence rates over the study period. Small Baseline Subset-InSAR was then applied to validate the results against an additional GPS record from Dhaka, Bangladesh. Land subsidence of 0 to > 10 mm/yr is seen in Dhaka, with variability likely related to local variations in shallow subsurface sediment properties. Outside of the city, rates vary from 0 to > 18 mm/yr, with the lowest rates appearing primarily in Pleistocene Madhupur Clay and the highest rates in Holocene organic-rich muds. Results demonstrate that subsidence in this delta is primarily controlled by local stratigraphy, with rates varying by more than an order of magnitude depending on lithology. The ability of L-band InSAR to differentiate between stratigraphic units in this humid, vegetated subtropical river delta demonstrates the power of interferometry as a tool for studying the subsurface in deltaic environments.

The Arctic climate is changing, inducing accelerating retreat of ice-rich permafrost coastal bluffs. Along Alaska's Beaufort Sea coast, erosion rates have increased roughly threefold from 6.8 to 19 m yr−1 since 1955 while the sea ice-free season has increased roughly twofold from 45 to 100 days since 1979. We develop a numerical model of bluff retreat to assess the relative roles of the length of sea ice-free season, sea level, water temperature, nearshore wavefield, and permafrost temperature in controlling erosion rates in this setting. The model captures the processes of erosion observed in short-term monitoring experiments along the Beaufort Sea coast, including evolution of melt notches, topple of ice wedge-bounded blocks, and degradation of these blocks. Model results agree with time-lapse imagery of bluff evolution and time series of ocean-based instrumentation. Erosion is highly episodic with 40% of erosion is accomplished during less than 5% of the sea ice-free season. Among the formulations of the submarine erosion rate we assessed, we advocate those that employ both water temperature and nearshore wavefield. As high water levels are a prerequisite for erosion, any future changes that increase the frequency with which water levels exceed the base of the bluffs will increase rates of coastal erosion. The certain increases in sea level and potential changes in storminess will both contribute to this effect. As water temperature also influences erosion rates, any further expansion of the sea ice-free season into the midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates.

The Indus River/Delta system is highly dynamic, reflecting the impacts of monsoonal-driven floods and cyclone-induced storm surges, earthquakes ranging up to Mw = 7.8, and inundations from tsunamis. 19th century Indus discharge was likely larger than today, but upstream seasonal spillways limited the maximum flood discharge. Upstream avulsions during the 2010 flood similarly reduced the downstream discharge, so that only 43% of the floodwaters reached the river mouth. The present-day Indus River is wider with larger meander wavelengths (∼13 km) compared to the 4–8 km meander wavelengths for the super-elevated historical channel deposits. The Indus River is presently affected by: (1) artificial flood levees, (2) barrages and their irrigation canals, (3) sediment impoundment behind upstream reservoirs, and (4) inter-basin diversion. This silt-dominated river formerly transported 270+ Mt/y of sediment to its delta; the now-transformed river carries little water or sediment (currently ∼13 Mt/y) to its delta, and the river often runs dry. Modern-day reduction in fluvial fluxes is expressed as fewer distributary channels, from 17 channels in 1861 to just 1 significant channel in 2000. Abandoned delta channels are being tidally reworked. Since 1944, the delta has lost 12.7 km2/y of land altering a stunning 25% of the delta; 21% of the 1944 delta area was eroded, and 7% of new delta area formed. The erosion rate averaged ∼69 Mt/y, deposition averaged ∼22 Mt/y, providing a net loss of ∼47 Mt/y particularly in the Rann of Kachchh area that is undergoing tectonic subsidence.

[1] Differential Interferometric Synthetic Aperture Radar is applied to the coast of the Yellow River delta (YRD) in China. Like many deltas, the coastline of the YRD is dominated by aquaculture. Advanced Land Observation Satellite Phased Array L-Band Synthetic Aperture Radar (SAR) and Envisat Advanced SAR data acquired between 2007 and 2011 show that subsidence rates are as high as 250 mm/y at aquaculture facilities, likely due to groundwater pumping. These rates exceed local and global average sea level rise by nearly 2 orders of magnitude and suggest that subsidence and associated relative sea level rise may present a significant hazard for Asian megadeltas.

The United States faces a crisis in education: a dire shortage of students sufficiently prepared in the STEM (Science, Technology, Engineering and Mathematics) disciplines to competitively enter the workforce (National Education Technology Plan, 2010). At the same time, there is increasing demand for well-trained geoscientists in a variety of careers related to the environment and natural resources. Many efforts, including the recently released Earth Science and Climate Literacy Principles, seek to promote better Earth science education, as well as to strengthen the Earth science literacy of the entire US population. Yet even those undergraduate students who choose to major in geology or related geoscience disciplines rarely acquire sufficient quantitative skills to be truly competitive graduate students or professionals. Experience with modeling, during their undergraduate careers, could greatly increase the quantitative literacy of geoscience majors and help them appreciate the real world applicability of mathematics and computational methods in their future careers in the geosciences.