Retreat Rates Research Articles

Research on comprehensive assessment of coastal erosion intensity based on multi index method

The intensity of coastal erosion is a measure of the strength of erosion processes affecting coastal areas. Traditionally, assessments of coastal erosion intensity have relied on singular indices, such as the rate of shoreline retreat or erosion, often prioritizing higher rates over lower ones. This approach, however, lacks comprehensive consideration and scientific rigor. In this study, we adopt a more holistic approach by examining the Qionghai-Wanning coast on the eastern side of Hainan Island. We selected four indices that reflect local conditions and influence coastal erosion strength: Annual rate of shoreline change (T1), Beach annual down-cutting rate (T2), Beach slope (T3), Average particle size of the beach (T4). These indices were used to comprehensively evaluate the erosion intensity of the Qionghai-Wanning coast. The evaluation results categorized the study area into six grades: serious erosion (3.45%), strong erosion (6.90%), erosion (20.69%), micro erosion (44.38%), stabilization (20.69%), and accretion (3.45%). The findings indicate that, under the broader environmental trends of global warming and rising sea levels, most sandy coasts exhibit micro-erosion intensity. Areas experiencing strong and serious erosion are predominantly influenced by human activities, such as those occurring in promenade bays, artificial islands, and harbors. To further understand the relationship between these factors and erosion intensity, we employed the Spearman correlation coefficient method. The analysis revealed that the T1 and the T2 are the primary factors influencing coastal erosion intensity, with the T4 serving as a secondary factor. These factors collectively impact the force and energy absorption of the coast through wave and tidal actions, ultimately determining the intensity of coastal erosion. The multi-index assessment method for coastal erosion intensity demonstrated an accuracy of 82.75%, providing a scientific basis for the management, protection, and restoration of coastal areas.

Diatom assemblages in glacial-fed streams of Italian Western Alps

ABSTRACT The rate of glacier retreat has recently increased, with changes in the glacier discharge, river flow and water characteristics, creating specific environmental conditions for highly specialized organisms. We here investigated diatom communities in glacier-fed rivers of the Valle d’Aosta region (NW-Italy), analyzing data collected between 2010 and 2019 for the WFD monitoring programs. We present a complete checklist of the species inhabiting this region, many of which are classified as endangered in the diatom Red List. We found significant differences between sites with different catchment glacier cover (CGC), in terms of taxonomic composition, ecological guilds and abundance of Red List taxa. In particular, we observed a significant increase in species richness with the decrease in CGC, as well as significant differences in terms of taxonomic composition. We highlighted the role of Achnanthidium lineare as an indicator species for streams with the highest glacial influence, together with Hannaea arcus, Eucocconeis laevis and other oligotrophic low profile species that are well adapted to physical stress induced by glacier runoff. On the other hand, streams with lower glacial influence were characterized by motile species mostly belonging to the genera Navicula and Nitzschia, due to the nutrient increase. Didymosphenia geminata was recorded in streams with marginal glacier cover; recently observed blooms indicate that conditions may become increasingly favorable for the spread of this species in Alpine environments, as glaciers retreat. The abundance of Red List diatoms increased significantly with increasing glacier cover suggesting that glacier-fed rivers are niches for the conservation of diatom biodiversity.

Multitemporal analysis of cliffs evolution along an Atlantic African coast (Safi Region, Morocco)

Unstable coastal cliffs represent a major threat to coastal infrastructure, housing, and economic activities, which depend on coastal stability. Understanding recession rates and the factors influencing them is therefore essential for enhancing risk prediction and management. Here, we investigated the evolution of coastal cliffs in a crucial sector of the Atlantic African coast in Morocco, stretching from Cap Beddouza in the north to Jorf Lihoudi in the south, covering an area of around 48 km and including the large city of Safi. The instability of these cliffs constitutes the main coastal geological hazard of the area, which has its geomorphological expression in different types of landslides punctuating the coastal cliff. We employed multidecadal aerial imagery along with GIS technique to calculate the rate of change of the cliff over 66 years. Our results indicate that most of the Safi Region coastal zone has undergone recession with rates of change generally variable from 0.04 to 0.08 m/yr ± 0.01 m. The central part of the study area, conversely, experienced the highest retreat rate, exceeding 0.10 m/yr. The spatial variability of recession rates is explained through geological and morphological factors such as the nature of low-strength clay rock formations, favoring large-scale gravity movements. These data are crucial to better define the current level of coastal hazard in this densely populated portion of the Moroccan coast, given that cliff recession have considerable effects on the economic, social and environmental risk of the area. Moreover, this study represents one of the first applications of the Digital Shoreline Analysis System (DSAS) method to an African coastline segment, specifically from Cape Beddouza to the Lihoudi cliffs. More generally, it is among the few studies focused on cliff recession rates in Africa. While a similar application has been conducted for the cliff base in the northern part of the same study area (Raja et al., 2023), that study primarily addresses coastal cliff failure hazards along the Safi coastline in Morocco. In contrast, the present study is focused on determining long-term cliff recession rates and understanding the distribution of these rates and modes of retreat in relation to the physical processes affecting the study area.

Long-term gully dynamics over cropland in the black soil area of China based on systematic sampling

Understanding the large-scale spatial distribution characteristics of gully development dynamics, particularly over long periods, can help in accurately identifying areas with severe gully erosion and is thus crucial for targeted gully prevention and rehabilitation efforts. This study aimed to investigate the long-term dynamics of permanent gullies on cropland in the Songnen typical black soil region (SBR), which is the most important commercial grain production area in China, covering an area of 212,000 km2. For this purpose, 998 sampling units were selected using the systematic sampling method. Based on Corona KH-4B images from 1970 and Google images from 2018, all gullies within each sampling unit were visually interpreted. In the past 50 years, the number of permanent gullies on cropland in SBR increased by 24.55 %, but the average linear density of gullies in the cropland sampling unit decreased from 0.47 to 0.45 km·km−2 because the average lengths of gullies decreased from 285.90 m to 233.15 m. While 50.50 % of gullies found in 1970 disappeared from the images of 2018, more gullies formed and were widespread in the east part of the study area characterized by a topography of rolling hills. In particular, 66.70 % of gullies were active, including all newly formed gullies and 16.28 % of long-standing gullies (LSGs), and the average gully retreat rate of LSGs was 0.53 m·yr−1, with active LSGs grew at a rate of 3.26 m·yr−1 on average, indicating the severity of gully erosion and limited effectiveness of efforts made to control gully erosion in the black soil region of China. The threat of gully erosion is more serious in the eastern part of SBR, with 44.69 % of cropland suffering gully erosion and 66.14 % of the gullies being active. Moreover, the trend of increased gully erosion in the centre and the west requires further attention. The findings highlight the need for studies on more effective and targeted measures for gully control and their wide application in order to ensure the sustainable utilization of the valuable black soil resources.

Reconciling short- and long-term measurements of coastal cliff erosion rates

Oblique terrestrial laser scanning (TLS) enables topographic change detection at scales (10−1 –100 cm) that are appropriate for coastal cliff erosion monitoring. Despite this, published applications of TLS on cliff are limited to a small number of sites around the world. Here we report new TLS point cloud datasets from 9 years of monitoring (2014–2023) at Rothesay Bay within the Hauraki Gulf, New Zealand, which has relatively low wave energy and a meso-tidal range. The 120 m-length scan area includes cliffs of 10–30 m height, formed of horizontally bedded soft sedimentary flysch rock. The cliffs are fronted by an 140 m wide near-horizontal shore platform that terminates in an abrupt seaward edge. Previous research at this site has estimated long-term cliff erosion rates within a range of 1.4 ± 0.1 to 14.3 ± 0.1 mm/year on the basis of measured shore platform width, assuming that the shore platform has widened over time over 6000 years of stable Holocene sea level, and that the seaward edge of the shore platform has not retreated. Volumetric cliff-face erosion rates were detected through 17 scans over a 9-year window (2014–2023), including intensive monthly TLS scanning between July 2021 and July 2022. Results show that the average cliff recession rate over the past decade has been 41 ± 2 mm/year, and monthly scans show a range in erosion rates of 30 to 288 mm/year. The cliff recession rate detected with TLS is 3 to 30 times higher than erosion rates derived based on the shore platform width. If erosion had been constant at this rate over approximately 6000 years, a total cliff retreat of >245 m would be expected, whereas the contemporary shore platform is only 140 m wide. We discuss two possible hypotheses for the confounding width of the modern shore platform: 1) that modern cliff retreat rates are faster than past erosion rates; 2) that the seaward edge of the shore platform does not reliably demarcate Holocene cliff recession. We present new bathymetric survey mapping seaward of the shore platform edge that reveals multiple rocky features that are distinguished by steep slope breaks and planar surfaces. Understanding the evolution of the intertidal shore platforms during the Holocene era may necessitate new insights on how cliffs formed toward the end of the last marine transgression. This could potentially be investigated through the study of subtidal marine bathymetry.

Monitoring of Glacier Area Changes in the Ili River Basin during 1992–2020 Based on Google Earth Engine

The Ili River Basin, a crucial transboundary river in the arid region of Central Asia, plays a significant role in the region’s ecology and water resources. However, current methods for monitoring glacier area changes in this region face challenges in automation and accuracy due to the complex terrain and climatic conditions. This study aims to evaluate the effectiveness of the Google Earth Engine (GEE) platform for monitoring glacier area changes in the Ili River Basin from 1992 to 2020, with a focus on improving data accuracy and processing efficiency. Utilizing the Landsat data series, we employed the random forest (RF) classification algorithm within the GEE platform to extract glacier areas, optimizing a multidimensional feature set using the Jeffries–Matusita (JM) distance method, and applied visual interpretation for data refinement. Our results demonstrated that the GEE platform, combined with the RF algorithm, provided high accuracy in glacier monitoring, achieving an overall accuracy of 89% and a kappa coefficient of 0.85. During the study period, the glacier area in the Ili River Basin decreased by 184.76 km2, with an average annual retreat rate of 6.84 km2, most notably between 3800 and 4400 m in elevation. The analysis revealed that temperature changes had a more pronounced impact on glacier dynamics than precipitation. This approach significantly enhances image utilization efficiency and data processing speed, offering a reliable tool for monitoring glacier dynamics. Future research should focus on integrating additional environmental variables and extending the temporal scope to further refine glacier dynamics modeling and predictions.

Geodynamic Evolution of the Lau Basin

AbstractThe formation of Lau Basin records an extreme event of plate tectonics, with the associated Tonga trench exhibiting the fastest retreat in the world (16 cm/yr). Yet paleogeographic reconstructions suggest that seafloor spreading in the Lau Basin only initiated around 6 Ma. This kinematics is difficult to reconcile with our present understanding of how subduction drives plate motions. Using numerical models, we propose that eastward migration of the Lau Ridge concurrent with trench retreat explains both the narrow width and thickened crust of the Lau Basin. To match the slab geometry and basin width along the Tonga‐Kermadec trench, our models suggest that fast trench retreat rate of 16 cm/yr might start ~15 Ma. Tonga slab rollback induced vigorous mantle flow underneath the South Fiji Basin which is driving the extension and thinning of the basin and contributing to its observed deeper bathymetry compared to neighboring basins.

Regional coastal cliff classification: Application to the cantabrian coast, Spain

The retreat of coastal cliffs is a natural process that occurs due to the interaction of different forcings that can be marine and atmospheric, and conditioned by the lithological properties of the rock material. Several attempts have been done at different scales to quantify and rank the various parameters that influence erosion rates, most of them agreeing that cliff retreat is governed by the lithological properties of the cliffs. Although, due to the large number of parameters involved there is not a clear consensus.The present study aims to characterize the cliffs along the Cantabrian coast by using an unsupervised classification of their physical and lithological characteristics, and by analyzing their retreat behavior. The proposed methodology is scalable to larger coastal areas. The study found that Cantabrian coastal cliffs have a low mean retreat rate of 0.042 m/year, with a maximum retreat rate of up to 0.4 m/year in two locations. Nine distinct groups of cliff behavior have been found, with only two of them presenting high erosional records, which are controlled by lithological features. Cliffs with the highest erosion rates are composed of alternating lithologies and more erodible materials. The results suggest that the factors most influencing erosive retreat in cliffs are the type of lithology and the alternation of different lithologies.

Seasonality of Retreat Rate of a Wave‐Exposed Marsh Edge

AbstractWave‐driven erosion of marsh boundaries is a major cause of marsh loss, but little research has captured the effect of seasonal differences on marsh‐edge retreat rates to illuminate temporal patterns of when the majority of this erosion is occurring. Using five surface models captured over a study year of a marsh with a steep escarped boundary in South San Francisco Bay, we find a pronounced seasonal signal, where rapid marsh retreat in the spring and summer is driven by a strong sea breeze but little change is found in the marsh‐edge position in the fall and winter. We found accretion in the mudflat transition region close to the marsh boundary in the calmer seasons however, suggesting intertwined morphodynamics of mudflats and the eroding marsh‐scarp. We observed large spatial heterogeneity in retreat rates within seasons, but less on longer (annual and decadal) timescales. The relationship between marsh‐edge retreat rates and properties of the wave field nearby is explored and contextualized against extant relationships, but our results speak to the difficulty in addressing spatial erosion/accretion variability on short (seasonal) timescales with simple models.

GIS-BASED ESTIMATION OF SHORELINE CHANGE AT THE OLIE PIER HARBOR HERITAGE SITE, MANGGAR, EAST BELITUNG, INDONESIA

The coastal area is a dynamic region influenced by continuous interactions between land and the sea. Changes in coastal compositions are closely related to shoreline instability. This study analyzes coastline changes at the Olie Pier Heritage Site, Manggar, East Belitung, Indonesia, using statistical-based techniques EPR (End Point Rate) and NSM (Net Shoreline Movement) 2015 to 2023. The DSAS (Digital Shoreline Analysis System) was employed to calculate the shoreline alterations in every transect with a distance of about 100 m. The study area is generally predominated by a moderate abrasion. The EPR and NSM values indicate a potential for future shoreline changes, considering the present status and future estimations of oceanographic parameters (currents, wind, waves, tides). The highest erosion is identified in the Lalang Village with a shoreline retreat (NSM) of -65.38 m and a retreat rate (EPR) of 8.78 m/year. On the other hand, the highest accretion is observed in the Baru Village with a NSM of -56.68 m and EPR of 7.61 m/year. The implications of these shoreline changes on the heritage site and the coastal environment contribute to the management of coastal areas amidst global environmental challenges. This study provides valuable insights into conservation and sustainable development efforts in the coastal region of East Belitung.

The deglacial history of 79N glacier and the Northeast Greenland Ice Stream

The Northeast Greenland Ice Stream (NEGIS) is the main artery for ice discharge from the northeast sector of the Greenland Ice Sheet (GrIS) to the North Atlantic. Understanding the past, present and future stability of the NEGIS with respect to atmospheric and oceanic forcing is of global importance as it drains around 17% of the GrIS and has a sea-level equivalent of 1.6 m. This paper reconstructs the deglacial and Holocene history of Nioghalvfjerdsbræ (or 79N Glacier); a major outlet of the NEGIS.At high elevation (>900 m asl) autochthonous blockfield, a lack of glacially moulded bedrock and pre LGM exposure ages point to a complex exposure/burial history extending back over half a million years. However, post Marine Isotope Stage 12, enhanced glacial erosion led to fjord incision and plateaux abandonment. Between 900 and 600 m asl the terrain is largely unmodified by glacial scour but post LGM erratics indicate the advection of cold-based ice through the fjord. In contrast, below ∼600 m asl Nioghalvfjerdsfjorden exhibits a geomorphological signal indicative of a warm-based ice stream operating during the last glacial cycle. Dated ice marginal landforms and terrain along the fjord walls show initial thinning rates were slow between ∼23 and 10 ka, but post-10 ka it is evident that Nioghalvfjerdsfjorden deglaciated extremely quickly with complete fjord deglaciation below ∼500 m asl between 10.0 and 8.5 ka.Both increasing air and ocean temperatures were pivotal in driving surface lowering and submarine melt during deglaciation, but the final withdrawal of ice through Nioghalvfjerdsfjorden was facilitated by the action of marine ice sheet instability. Our estimates show that thinning and retreat rates reached a maximum of 5.29 ma−1 and 613 ma−1, respectively, as the ice margin withdrew westwards. This would place the Early Holocene disintegration of this outlet of the NEGIS at the upper bounds of contemporary thinning and retreat rates seen both in Greenland and Antarctica. Combined with recent evidence of ice stream shutdown during the Holocene, as well as predictions of changing ice flow dynamics within downstream sections of the NEGIS catchment, this suggests that significant re-organisation of the terminal zone of the ice stream is imminent over the next century.

Cliff dynamics in western Crimea

The paper considers the long-term dynamics of clayey cliffs of the Western Crimea in view of the problem of further recreational development of the Crimean Peninsula. Open-source satellite imagery and long-term (over 40 years) cliff section measurements were analyzed. The paper provides data on the geomorphology of individual coastal sites. It is shown that landslides are the main mechanism causing the cliff retreat on the larger part of the coastline. Slumps are typical for the southern part of the region and their movement episodes are relatively rare. Landslides become more active during the winter — spring period, when the moisture content of clayey cliff rocks increases substantially and the abrasion intensifies. Landslides can also be triggered by short-term heavy precipitation, which is usually observed in the summer. There is no definite relationship between the amount of annual precipitation, storm activity and landslide activity, either synchronous or with a time lag. No regularity in landslide dynamics was identified. It was found that the average long-term rates of cliff edge retreat are 0.1–1.2 m/year. In the northern part of the coast, the rates are the highest, decreasing towards the southern part of the region. The obtained average annual rates of cliff edge retreat are significantly less than those previously reported in the literature. There is a decrease in the beach-forming sediment supply due to a reduction in the stretch of the cliffs. Out of 50 km coastline with cliffs, only 39 km are left in the study area due to being covered by various structures and terracing. The paper also discusses anthropogenic activity, which leads to the formation and movement of man-made landslides and an increase in natural landslide activity. It is shown that the construction of transverse beach-retaining structures leads to blocking of littoral sediment transport, and to increase in the cliff retreat rate outside the protected reach.

Cliff Retreat Rates Associated with a Low-Level Radioactive Waste Disposal Facility in Los Alamos, New Mexico, USA

We present an analysis and interpretation of potential cliff stability at a low-level waste disposal facility at Los Alamos National Laboratory, New Mexico, using cliff morphologic and fracture characteristics coupled with carbon-14 surface exposure dating. Our study is important as it directly bears on the licensing criteria for low-level radioactive waste sites. We find that future characteristic cliff failures will likely not breach disposal pits and shafts over the 1000-year minimum regulatory period. Further, we find, using a multivariate regression model, that slope angle and cliff face aspect are sub-equal in importance to predict regions of high risk of failure when combined with surface exposure ages and assuming that old exposure ages are most indicative of stability (instability) and therefore can aid decision making in final design implementation.

Changing rates of escarpment retreat linked to environmental change in a sedimentary tableland, Stołowe Mountains, SW Poland

Long-term rates of escarpment retreat in sedimentary tablelands have been rarely determined and their possible variability in relation to major environmental changes has often been speculative, especially in older contributions. Moreover, rates reported so far were almost exclusively from arid regions. In this paper we present a dataset of 20 cosmogenic exposure ages, obtained for cliffs and boulders produced by rock-slope disintegration, left in front of a retreating 150-m-high escarpment of a sandstone mesa in SW Poland. The most distant boulders are >400 m away from the cliffs. Following previous research in the region, boulders are mainly products of in situ disintegration and hence, their present-day position on the slope approximates the past position of the cliffs, allowing for the calculations of cliff retreat. Exposure ages systematically increase with the distance from the present-day cliff line and cover the last 100 kyr, implying an average retreat rate of 4.18 mm/yr. However, the dataset splits into several sub-populations, each with its own trend, meaning that the rates of retreat varied with time. A maximum was reached during the Late Pleistocene and transition to the Holocene, when the rates exceeded 10 mm/yr and may have reached 100 mm/yr. The rates seemed distinctly lower between MIS5 and LGM and during the Holocene. We propose that the transition towards a warmer climate at the Pleistocene/Holocene boundary, with an increased frequency of freezing-thawing cycles, the degradation of permafrost and unblocking of groundwater drainage enhanced caprock disintegration and accelerated the break-off rates of caprock. During periods of most efficient cliff disintegration and boulder production the rates of escarpment retreat at the field site could have been two orders of magnitude higher than in the hyperarid areas. However, despite changing rates of retreat major processes involved in escarpment evolution seem to have remained the same.

Quantifying Aperiodic Cliff Top and Cliff Face Retreat Rates for an Eroding Drumlin on Ireland’s Atlantic Coast Using Structure-from-Motion

Quantifying Aperiodic Cliff Top and Cliff Face Retreat Rates for an Eroding Drumlin on Ireland’s Atlantic Coast Using Structure-from-Motion

Recent rapid initiation and growth of retrogressive thaw slumps in the Hoh Xil region of the Qinghai-Tibetan Plateau

With persistent climate warming, a rapid increase in retrogressive thaw slump (RTS) activity has been observed in the permafrost region of the Qinghai-Tibetan Plateau (QTP). However, the initiation and growth dynamics of these RTSs have not yet been fully investigated. In this study, annual RTS observations from 2013 to 2021 within the Hoh Xil region (HXR), based on field investigations and satellite imagery interpretations, are presented. The total number and affected areas of RTSs in the HXR significantly increased during the last 8 years, and such an increase mainly occurred in 2016 when an anomalously high air temperature appeared during the thawing season, which induced the massive occurrence of active layer detachment slides. The mean headwall retreat rate of RTSs in the HXR ranged from 2.4–3.2 m/y from 2013, or their initialization, to 2021, and the highest headwall retreat occurred in the first 2–3 years after RTS initiation. In addition, the headwall retreat rate of RTSs in the study region was significantly affected by the climatic factors, including average daily air temperature, thawing degree days, and cumulative precipitation and also controlled by the ratio of slump floor slope to undisturbed terrain slope, the headwall height, and permafrost conditions. The study’s findings can serve as a reference for hazard mitigation and regional carbon cycle assessment of the QTP.

Shoreline retreat and beach nourishment are projected to increase in Southern California

Sandy beaches in Southern California are experiencing rising coastal erosion due to changes in precipitation patterns and urban growth. As a result, beach nourishment is necessary for mitigation. In our study, we forecast the rates of shoreline retreat and the required volumes of sand nourishment to mitigate it for the coming decades. We employ photogrammetric multi-decadal shoreline positioning and Digital Shoreline Analysis System methods to measure and predict the coastal evolution of the Gulf of Santa Catalina in Southern California. This region is hypothesized to be globally representative of other semi-arid sandy coasts facing similar hydroclimatic and anthropogenic challenges. Our findings indicate that Southern California’s shoreline retreat rates for sandy beaches will increase from the present average value of ~−1.45 to −2.12 meters per year in 2050 and to −3.18 meters per year in 2100. Consequently, the annual volume of sand required for beach nourishment could triple by 2050, increasing from the present-day amount of ~1223 to ~3669 cubic meters per year per kilometer. However, the associated cost for this nourishment will grow five times, exacerbating several coastal communities’ economic and logistical pressures. Similar trends are emerging globally, with semi-arid developing nations already grappling with coastal hazards and may struggle to manage the escalating costs of curbing beach nourishment.

Glacier Changes from 1990 to 2022 in the Aksu River Basin, Western Tien Shan

Mountain glaciers are considered natural indicators of warming and a device for climatic change. In addition, it is also a solid reservoir of freshwater resources. Along with climate change, clarifying the dynamic changes of glacier in the Aksu River Basin (ARB) are important for hydrological processes. The study examined the variations in glacier area, elevation, and their reaction to climate change in the ARB between 1990 and 2022. The glacier melt on the runoff is explored from 2003 to 2020. This investigation utilized Landsat and Sentinal-2 images, ICESat, CryoSat, meteorological and hydrological data. The findings suggest that: (1) The glacier area in the ARB retreated by 309.40 km2 (9.37%, 0.29%·a−1) from 1990 to 2022. From 2003 to 2021, the ARB glacier surface elevation retreat rate of 0.38 ± 0.12 m·a−1 (0.32 ± 0.10 m w.e.a−1). Comparison with 2003–2009, the retreat rate is faster from 2010 to 2021. (2) From 1990 to 2022, the Toxkan and the Kumalak River Basin’s glacier area decreases between 61.28 km2 (0.28%·a−1) and 248.13 km2 (0.30%·a−1). Additionally, the rate of glacier surface elevation declined by −0.34 ± 0.11 m·a−1, −0.42 ± 0.14 m·a−1 from 2003 to 2021. (3) The mass balance sensitivities to cold season precipitation and ablation-phase accumulated temperatures are +0.27 ± 0.08 m w.e.a−1(10%)−1 and −0.33 ± 0.10 m w.e.a−1 °C−1, respectively. The mass loss is (962.55 ± 0.57) × 106 m3 w.e.a−1, (1087.50 ± 0.68) × 106 m3 w.e.a−1 during 2003–2009, 2010–2021 respectively. Warmer ablation-phase accumulated temperatures dominate glacier retreat in the ARB. (4) Glacier meltwater accounted for 34.57% and 41.56% of the Aksu River’s runoff during the ablation-phase of 2003–2009 and 2010–2020, respectively. The research has important implications for maintaining the stability of water resource systems based on glacier meltwater.

An integrated assessment of erosion drivers facilitating gully expansion rates—A near century multi‐temporal analysis from South Africa

AbstractRural areas in the Eastern Cape Province of South Africa are severely affected by gully erosion, yet little is known about the rates at which these features are expanding. This study explores the areal extent, physical mechanisms, rates, and drivers of gully expansion with the aim of investigating how erosion rates fluctuate in response to temporal variations of drivers over the last century. Investigations involved the creation of an erosion inventory geo‐database, the identification of area‐specific physical expansion mechanisms, an assessment of static and dynamic drivers, and a multi‐temporal study of 25 gullies in the Mthatha area. Results show gully erosion affects 2.3% of the study area, with gullies exhibiting an average annual areal increase of 2.08%, a sidewall retreat rate of 0.2 m/y, and a headcut retreat of 1.03 m/y over an 82‐year period between 1938 and 2020. A multi‐temporal case study of the Ngwevana Gully showed average annual areal growth rates ranging from 3.9% between 1938 and 1948 to 0.7% between 2017 and 2020. Findings indicate that although gullies consistently expand their areal footprint, they do so at fluctuating rates. An assessment of erosion drivers reveals that temporal promotion or suppression of these erosion rates occurs in response to the complex and dynamic interactions of both natural mechanisms and anthropogenic activities. In Mthatha, the periods of increased rates of erosion are linked to large‐scale flooding events during drier climate cycles, which were further exacerbated by invasive dryland agricultural practices, inappropriate land use, haphazard infrastructure development, and rapid population increases facilitated by past Apartheid settlement laws.

A warming-induced glacier reduction causes lower streamflow in the upper Tarim River Basin

Study areaThree headwater basins of the Tarim River Study focusThis study built upon existing knowledge by incorporating threshold melting temperatures into the Spatial Processes in Hydrology (SPHY) model and decomposing the streamflow changes into individual runoff components. Additional glacier retreat rate data were used to calibrate the improved SPHY, which provides better constrained estimates of glacier response to climate change. We employed bias-corrected simulations from Coupled Model Intercomparison Project Phase 6 (CMIP6) models to drive the improved SPHY under four future scenarios (SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5). New hydrological insights for the regionModeling results show accelerated glacier melt in the future, with glacier volume at the end of this century projected to be less than 20% of the current level under SSP5–8.5. Furthermore, future streamflow is expected to decrease, most notably in the Karakash River basin under the SSP1–2.6 scenario. The reduction in streamflow, mainly during the summer months, results from decreased glacier melt runoff, which cannot be offset by increased rainfall runoff. Additionally, the implementation of climate change mitigation measures could delay glacier loss, but the dominant component of runoff would still shift from current glacier melt to future rainfall. Plain language summaryGlobal warming accelerates the hydrological cycle, altering the temporal and spatial patterns of streamflow, especially in cold regions, such as the Tarim River Basin. Understanding future streamflow changes is important for the economic development and ecological protection of this region, which will help to manage the risk of water shortages and to plan engineering works to mitigate water shortage crises. We therefore used state-of-the-art climate simulation to project future streamflow changes over three basins of the Upper Tarim River. We found that under all future scenarios, runoff will decrease in these basins. This decrease is mainly due to glacier retreat and cannot be mitigated by anticipated increases in rainfall in the future.