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Abstract: The impact of unusual events on the sediment dynamics in rivers is discussed in this paper. The increase in the number of extreme precipitation events and other unusual weather events in Norway strongly suggests that weather conditions are changing. It is difficult to monitor sediment transport during large magnitude floods. It is however well known that they may deliver substantial amounts of sediment. The suspended sediment load in the upper Atna river during the springflood in 1995 was 44 times the mean load measured during the preceding years. The recurrence interval of this flood was estimated to be 100–200 years. The conditions during the occurrence of a particular flood event may also be of considerable importance and measurements during rainfall on frozen ground have indicated unusually high runoff and erosion rates. The seasonal distribution of runoff in several parts of Norway has changed in recent years and higher winter temperatures have produced an increase in the frequency of flood events. A very long lasting flood caused by a prolonged period of rain occurred in the Vikka stream during September to December 2000. The availability of sediment increased with the increasing soil moisture content in the area. As the ground became saturated, more active slope processes caused erosion rates to increase markedly. The combined effects of climate change and human impact on sediment transport in rivers appear to enhance downstream sediment delivery. Flood protection works along river channels prevent sediment from being deposited on the floodplain. River channels that have been lowered in order to reduce groundwater levels in agricultural floodplain areas will experience the same effect. During the last decade extensive ecological changes have taken place in the coastal areas of southern Norway as 90% of the sugar kelp forest has been lost. This change has been attributed to an apparent increase in sediment delivery to the sea along with a rise in sea temperatures. [Copyright &y& Elsevier]

Variations in water and sediment discharges of rivers can affect the human activities and in long-term modify the landscape. The climatic effect such as El Niño-Southern Oscillation (ENSO) is a first-order factor controlling the streamflow and sediment load however, its behaviour and links with water and sediment discharges are not fully known. We evaluate the response of the streamflow and sediment load in relation to ENSO within the largest fluvial system of Mexico: the Usumacinta and Grijalva River basin. The two rivers that compose this basin joined together ~ 50 km off the Gulf of Mexico forming a basin of ~ 112,000 km 2 that has an annual discharge of ~ 2678 m 3 s − 1 . We use data spanning of ~ 56 years from four gauging stations located at the low and middle reaches of the Usumacinta and Grijalva Rivers. The spanning of ~ 56 years of data of water and sediment load allowed us to detect the control exerted by the ENSO on these two processes. Our results indicate that when there is present either El Niño or La Niña, water discharge notably increases. In La Niña, however, river discharge in the Usumacinta and Grijalva is greater compared to that in El Niño. Our results suggest that both ENSO and the cyclonic activity of the Atlantic Ocean are a primary control on water discharge and sediment mobilization of the rivers of Southeast Mexico. [ABSTRACT FROM AUTHOR]

Abstract: Thirteen paleomeanders on the oldest parts of meander belts on floodplains in the Coastal Plain of Georgia and the Carolinas (southeastern USA) were selected for radiocarbon dating to determine the onset of meandering following braiding during the Late Pleistocene during Oxygen Isotope Stage 2. The radiocarbon ages were compared to previously reported Late Pleistocene ages for braid bars and eolian dunes. Results indicate that meandering commenced at circa 15,000 to 16,000 cal years BP and continued throughout the terminal Pleistocene and Holocene. Correlation with other paleoenvironmental records indicates that this shift to meandering was associated with global warming and moister conditions in the southeastern United States that led to a denser vegetation cover and a reduction in sediment yield. The shift to meandering was also associated with some incision and terracing of the Late Pleistocene braided fluvial surfaces. Paleodischarge of the bankfull condition of early Holocene meandering channels was apparently greater than under modern conditions, suggesting wetter conditions at that time than at present. This braided to meandering transition in the southeastern United States provides an example of river response to global climate change in a relatively low latitude region of the world that was not influenced by glacial or periglacial landscape conditions. [Copyright &y& Elsevier]

[Display omitted] • Sediment yield of Italian rivers compared to world datasets. • No significant correlation between catchment area and sediment yield. • Higher variability of annual sediment yield in rivers with lower annual rainfall. • Smaller rivers sediment yield is predicted by the flow exceeded 10 days a year. • Recent sediment yield decrease for rainfall reduction and forestland increase. The knowledge about river sediment yield in Italy is rather scarce and mainly based on small reservoir sedimentation data. This study used the suspended sediment yield field data measured by the national and regional hydrological services. The data of nine rivers and 11 selected flow gauges were used to investigate the control of basic parameters such as catchment area, annual precipitation and a characteristic discharge on sediment yield. The average sediment yield of Italy is close to the world mean but the relationship between catchment area and sediment yield is not significant, though a general decreasing trend with increasing catchment area can be distinguished. The variation of sediment yield with annual precipitation is poorly significant, although a general increasing trend with increasing catchment area can be observed. Sediment yield varies widely. The largest range of variability occurs for annual precipitation between 700 and 800 mm. The data indicate an average suspended sediment yield of 220 t km−2yr−1 and an upper limit of 3000 t km−2yr−1 which is observed in all the study rivers, no matter the catchment size which ranges from 580 to 70091 km2. Such a high value seems to be the maximum sediment yield possible in Italy given the local climatic, tectonic and land use characteristics. The discharge exceeded 10 days a year (2.7% of time) was found to exert a substantial control on sediment yield. Groups of rivers with similar catchment area show significant correlations and almost parallel trendlines. The occurrence of data gaps and multiple years interruptions allowed the investigation on the decadal variation of sediment yield of only very few rivers. The reduction of sediment yield is remarkable. The decrease in annual precipitation and the unprecedented expansion of forests are considered as the main factors causing such marked decrease of sediment yield in Italy. [ABSTRACT FROM AUTHOR]

Abstract: Alluvial reaches in the source region of the Yangtze and Yellow Rivers, located atop the Qinghai–Tibetan Plateau and mostly at elevations that are typically higher than 3500m, have similar slope and valley setting conditions. However, alluvial reaches in the source region of the Yangtze River exhibit predominantly braided channel planforms, while equivalent reaches in the source region of the Yellow River have more diverse planform morphologies including anastomosing/braided, anabranching/braided, and anabranching/anastomosing reaches. The regional gradient of variation in riparian vegetation and interactions between vegetation development and hydrologic process are shown to be major factors influencing this difference in channel planforms. A short period above freezing, coincident with recurrent yet pulsed flows in the source region of the Yangtze River, suppress riparian vegetation growth, promoting the development of braided channel morphologies. In contrast, a milder climate, coincident with less variable flows in the source region of the Yellow River, permit the establishment of different forms of riparian vegetation, thereby supporting the development of a wider range of channel planform morphologies. [Copyright &y& Elsevier]

Abstract: This paper describes the results of geomorphological, sedimentological and 14C analyses of Late Holocene fluvial sequences in the Moldova River Valley of Romania. This river originates from the Carpathians mountains and is known for the extent of its large floodplain and sediment thickness. Between the Molid and Timişeşti localities (river length: 86km), numerous large fossil trunks of oak, poplar and beech trees are exposed in the riverbanks. Six wood samples were selected for radiocarbon absolute dating (conventional method), and their ages ranged from 410 to 3200calyrs. BP. The thickness of the alluvial sediments above the sampled fossil trunks varied between 2 and 3m, and these sediments predominantly consisted of coarse gravel materials that had similar granulometry to sediments that were present in the modern riverbed. Additionally, in the same investigated areas, successive floodplain cross-sections were constructed based on more than 20 hydrogeological boreholes. For each cross section, all data were used to calculate the local values of bed loads, and these values were compared to the absolute ages of the fossil trunks and were in the range of 300m3/m and 5500m3/m. Based on the calculated values, during the last 780years, the floodplain sedimentation rates were estimated to be in the range of 0.4m3/year at the Molid Section, which was located in the mountainous area of the valley and 44km downstream from the river headwater, and during the last 410years, the sedimentation rate at the Praxia Section, which was located 125km downstream from the river headwater, was 13.3m3/year. In the past 100years, the fluvial processes along the Moldova River were dominated by a narrowing (by an average of 76%) and an incision (up to 2.5m), and a channel metamorphosis from braided to wandering was reported. These results are discussed in the context of Late Holocene regional and local palaeoclimatic reconstructions as well as that of human interventions. [Copyright &y& Elsevier]

Abstract: The suspended sediment deposition (SSD) in the alluvial reach between the Qingtongxia station and the Toudaoguai station of the upper Yellow River has shown a dramatic variation since 1952. However, its spatial and temporal changing pattern and driving factors are still not clear. This paper examines the detailed spatial and temporal variations of the SSD based on the annual suspended sediment load at five gaging stations located in this alluvial reach in 1952–2007. The mean annual SSDs in four sub-reaches (Qingtongxia–Shizuishan, Shizuishan–Bayangaole, Bayangaole–Sanhuhekou, and Sanhuhekou–Toudaoguai) were calculated and analyzed for different periods. The mean annual kilometric SSDs in 1952–2007 were −0.228∗105, 0.97∗105, 0.165∗105 and 0.006∗105 ta−1 km−1 in the four sub-reaches, respectively, with the highest SSD occurred in the Shizuishan–Bayangaole sub-reach. Results also suggested that SSD was mainly accumulated in 1952–1959 before major reservoirs were constructed and in 1986–2007 after three major reservoirs (Qingtongxia, Liujiaxia and Longyangxia) were constructed in the main stream. During 1960–1985, all sub-reaches except the Shizuishan–Bayangaole sub-reach experienced channel erosion. Although climate change may play some roles, the changes in SSD were mainly influenced by human activities. In particular, the water and soil conservation actions, such as the construction of check dams from 1958 in upper stream tributaries, intercepted significant amount of suspended sediment and cause the net erosion of the main channel in the 1960s. The operation of the Qingtongxia reservoir reduced the SSD in this downstream reach in the 1970s and 1980s because upper stream suspended sediment was trapped by the reservoir and reservoir-released relative clear water scoured the downstream channel. Although the Liujiaxia and Longyangxia reservoirs trapped relatively small amount of suspended sediment, they stored a large amount of water during the flood season, reducing the discharge and the erosion capability of the downstream flow. Therefore, this operation mode may increase the SSD in this river reach. In addition, with the gradual loss of the Qingtongxia reservoir''s capacity in sediment storage, more suspended sediment was released to the downstream channel, causing strong SSD in this reach after 1990. [Copyright &y& Elsevier]

• Channel-bend migration is accelerated by approximately 69%, and cutoffs occur 30% more frequently. • The highest migration rates are observed in cold and upland regions where the normalised curvature radius is between 3.0 and 5.0. • The mobility of upland rivers shows a significant positive and linear correlation with the expansion of glacial lakes. • Climate warming may accelerate the process of frozen bank erosion and consequent river meandering. River meandering and lateral migration, caused by riverbank erosion, is a major global threat to soil, sediment, lands, and habitats. However, compared to the densely populated lowland floodplains, the upland channel morphodynamics of free-flowing rivers in a complex high-elevation alluvial setting have received less attention. In this study, we quantitatively investigated channel morphodynamics and associated frozen bank migration in the upper Yarlung Tsangpo River in the Himalayan headwater basin from the 1980s to the 2010s. By combining remote sensing analysis with field investigations, we found mean migration rates of 244 gravel-bed river bends ranging from 1.63 m/yr in the 1980s to 2.76 m/yr in the 2010s, with a maximum rate of 18.61 m/yr. The highest migration rates were associated with bends that had a width-normalised curvature radius between 3.0 and 5.0 and a sinuosity between 1.2 and 1.5. A ∼69% increase in river-bend migration and 30% more frequent bend cutoffs coincided nicely with the rapid expansion of glacial lakes due to a ∼1 °C increase in mean annual air temperature over the past four decades. Positive correlations were observed between channel migration rate and temperature, mean glacial lake area, and runoff. These results highlight the importance of the unique channel morphodynamics and the intense lateral movements of upland rivers. The close link between these dynamics and climate change suggests that a warmer world may significantly influence bank erosion and associated ecosystem processes of upland alluvial systems, which are essential for comprehending frozen channel dynamics and developing strategies for habitat protection in uplands worldwide. [ABSTRACT FROM AUTHOR]

• Reveal spatial and upstream–downstream patterns of runoff change drivers in eastern Tibetan Plateau for the first time. • Climate change dominant runoff trend and change in eastern Qinghai-Tibetan Plateau. • Quantitatively explained climatic and underlying surface conditions change contributed to runoff change. • Both hydrological model and Budyko framework were employed for robust results. Quantitatively identifying the impact of climatic and underlying surface condition changes on runoff is crucial for the efficient utilization of water resources and understanding hydroclimatic variability processes. This study aims to employ both Grid-RCCC-WBM model and Fu's equation based on Budyko hypothesis to quantitatively analyze the spatial patterns of runoff changes, driving forces, and upstream–downstream relationships in ten typical basins across the eastern Qinghai-Tibet Plateau (QTP) for the first time. Breaks for Additive Season and Trend method was used to detect breakpoints in runoff series and both hydrological model and Budyko equation categorized driving forces of runoff change into change in climatic (including precipitation and potential evaporation) and underlying surface conditions. The results indicated (i) significant abrupt changes in the runoff time series around 1998, with runoff increasing in all basins except for the source region of the Yellow River. (ii) significant upstream–downstream differences in the trend and magnitude of runoff changes between breakpoints in the Yangtze and Lancang Rivers over the past 20 years, and (iii) significant runoff response to climate variability after the breakpoints in the source region of the Yangtze and Yellow river. Our findings revealed that, contrary to the backdrop of decreasing precipitation, the upstream basins maintained increasing runoff relying on permafrost and glacier meltwater, while the downstream basins exhibited decreasing trend. The differences in runoff changes after the detected breakpoints were dominated by changes in underlying surface conditions, with the highest contribution rates observed in the Dajin (494 %), Lanzhou (398%), and Tangnaihai (197%) basins. This study involved both spatial pattern and upstream–downstream relationship of runoff change that can be widely applied to other large-scale regions and especially holds important implications for the scientific and rational utilization of water resources in the QTP. [ABSTRACT FROM AUTHOR]

[Display omitted] • Active hydromorphic podzol in the area store around 63 kgC m−2. • Erosive incision by a river meander resulted in air entry and oxygenation of the Bh. • C content in the Bh of a podzol truncated due to meander diminished by 70%. • Drier climate would induce C emission from Amazonian podzol Bhs. Podzol soils are an important carbon pool in the Amazon, due to the high organic matter (OM) content in their topsoil horizons and deep Bh. To quantify the evolution of the stock and the lability of this carbon pool in the hypothesis of the onset of drier climates, we studied a soil toposequence at the end of which the incision of a river meander lowered the water table, as would result from a drier climate, allowing oxidation the Bh horizons. The soil OM was quantified and characterized (physical fractionation, humification indexes, 14C average age) and its lability under oxic conditions was estimated by measuring respiration during a 660-days experiment. Podzol genesis time was calculated by constraining the carbon fluxes using both C stock and 14C average age. The results confirmed that the studied podzols store large amounts of carbon (62.8 kgC m−2 on average). They resulted from a long genesis time, probably greater than 30–50 ky. Topsoil OM is very labile with a residence time of about 100 y; Bh OM is highly humified with a high C/N (62.7 on average) related to low respiration rates. The measured respiration rates were used to estimate the C emission that would result from drier climates at 55 gC m−2 y−1 on average during the first 100 y, which would correspond, by extrapolation, to 8.5 1012 gC y−1 for all Amazonian podzols. [ABSTRACT FROM AUTHOR]

• Detailed source-to-sink analysis between the Qilian Shan and the Jiudong Basin. • Provenance analysis reveals two changes of drainage pattern since 7.0 Ma. • Drainage evolution was closely linked to both tectonic uplift and climate change. • Climatic cooling at ∼2.75 Ma promoted river capture. In tectonically active regions, surface uplift is generally considered to be an important cause of drainage evolution, but the effect of climate change on this process has not been fully evaluated. In this study, we conducted a provenance analysis of Minghai (MH) drill-core sediments from the foreland basin (i.e., the Jiudong Basin) of the Zoulang Nan Shan (the central part of the northern Qilian Shan). We aimed to reconstruct the fluvial evolution of the basin and to determine the role of tectonic activity and climate change in the evolutionary process. Provenance analyses indicate the existence of two changes in drainage pattern since 7.0 Ma that are closely linked to the thrusting process of the North Qilian Shan fault system. During the first (∼4.5 Ma) change, the in-sequence thrusting induced rapid uplift of the Yumu Shan in the frontal area of the Zoulang Nan Shan, which caused diversion of the rivers flowing through the Yumu Shan. During the second change (∼2.75 Ma), the thrusting of the North Qilian Shan fault caused intense uplift of the Zoulang Nan Shan, resulting in the capture by transverse rivers in its northern slope of rivers within the mountain range. Additionally, aridification at ∼4.5 Ma and climatic cooling at ∼2.75 Ma affected the evolution of the rivers. The aridification at ∼4.5 Ma resulted in reduced runoff, erosion, and fluvial incision rate, and facilitated the first change in the drainage pattern. The climatic cooling at ∼2.75 Ma induced rapid erosion in the upper reaches of the rivers and enlarged the erosion rate contrast between the south and north side of the Zoulang Nan Shan, both of which facilitated the second change in the drainage pattern. Overall, our study reflects the combined effects of tectonic uplift and climate change on the drainage evolution process. [ABSTRACT FROM AUTHOR]

• A series of river terraces are developed in the upper Jinsha River. • The short-term incision rate of the upper Jinsha River is 0.18–5.47 mm/yr. • The two depth intervals of the incision are 1200 ± 220 m and 340 ± 250 m respectively. • The main driving force of river incision is tectonic uplift. • Climate change is the switch button of river incision and accumulation behavior. The region occupied by three parallel rivers on the southeastern edge of the Tibetan Plateau is a zone with dramatically fluctuating topography and a complex tectonic setting. Deeply incised river valleys have become an ideal place for scholars to study the coupling relationships among river erosion, climate change and regional uplift. The fluvial terraces preserved in the upper Jinsha River provide the basis for exploring the history of river erosion. Through field investigation and dating results of terraces, the short-term incision rates of the upper Jinsha River are determined to be 0.18–5.47 mm/yr. In addition, the palaeo-profiles, which were reconstructed using two analytical methods, show that there are two depth intervals for the incision in the Jinsha River, namely, 1200 ± 220 m and 340 ± 250 m. They correspond to two early planation surfaces of the river, and the long-term average incision rates of the upper Jinsha River are estimated to be 0.23–0.34 mm/yr. By analysing the relationship between fluvial terrace formation and climate change, combined with the formation history of the early planation surface, it is recognized that the main force driving incision in the upper reaches of the Jinsha River comes from regional uplift. Climate change causes a continuous alteration between river incision and sediment accumulation, and this transition is also perturbed by mass flow events. [ABSTRACT FROM AUTHOR]

Abstract The El Niño/Southern Oscillation (ENSO) is the dominant mode of inter-annual climate variability, strongly affecting summer precipitation and streamflow of large rivers. So far, no effort has been made to relate ENSO events with alluvial river stability. Based on the historical document of the lower Yellow River (LYR) and the data of previously reconstructed ENSO variability, the present study aims to establish the relation between the LYR's artificial levee breaching events (LBEs) and the ENSO events from 924 CE to 1938, and thereby reveal how river instability responds to climate change in millennial scale, for a better understanding of the coupling relation between the climate, hydrology and river channel changes. From 924 CE to 1938, there are 303 La Niña influenced years (ENSO variability < −0.5), of which 172 (56.8%) are related to the occurrence of LBE. We divided the reconstructed ENSO variability into 9 classes and calculated the LBE frequency for each class. We found that the LBE frequency is negatively correlated with class average value of ENSO variability, significant at p < 0.05. By relating the 21 major course shifting events (CSEs) of the LYR (924 CE to 1938) to the occurrence of La Niña influenced years, we found that 13 (61.9%) were influenced by La Niña. The decadal LBE frequency (F b) and decadal average of ENSO amplitude show anti-phase variations since 1100 CE, with r = −0.356 (n = 82, p = 0.0010) after a linear detrending treatment. Through the control on summer rainfall and therefore on floods in the Yellow River, La Niña events influence the occurrence of the LBEs and CSEs in the LYR. Highlights • We first relate the ENSO with river channel instability from 924 CE to 1938. • The lower Yellow River LBE (bank breaching event) years account for 56.8% of the La Niña influenced years. • Of the 21 major course shifting events (CSE) of the lower Yellow River, 61.9% were influenced by La Niña. • Through control on rainfall and floods, La Niña influences LBEs and CSEs. [ABSTRACT FROM AUTHOR]

• Hydrology and sediment supply in regulated Godavari R., India simulated using SWAT. • Simulations illustrate importance of reservoirs in distributed hydrologic modelling. • Geomorphic stability index computed from pre/post- dam flow and sediment transport. • Observed incision is related to the simulated geomorphic stability index. • Climate change could move rivers below existing dams toward states of net erosion. Long-term geomorphic evolution of rivers depends both on the amount of sediment supply and on the river's ability to transport that sediment. Climate change is anticipated to change flow frequency distributions and sediment yield and could thus alter the geomorphic trajectory of many regulated rivers. We aim to examine the possible geomorphic response of the upper Godavari River, India, to climate change using two well-accepted metrics: the frequency of the sediment-transporting flows (T*) and the ratio of the sediment flux below and above a dam (S*). Soil and Water Assessment Tool (SWAT) was used to simulate streamflow and sediment yield in the basin. We calibrated and validated the model using SWAT-CUP for pre- (1971–75) and post-dam (1976–81) conditions downstream of Jayakwadi dam. The model performance was good (NS value > 0.6 for discharge and PBIAS < ± 10 for sediment) with low uncertainty (p-factor > 0.6 and r-factor <1) and it improved significantly by factoring the operation of the reservoirs into the simulation. We ran the model for 10 years consecutively in the pre and post-dam states for baseline (1971–81) and future (2090–99) climate conditions derived from NEX-GDDP climate projections (Emission scenario RCP 8.5 & 4.5). A linear relationship between T*/S* and observed erosion (m) below the dam provided the basis for estimating the amount of erosion associated with future climate states. Our simulations show substantially larger T* below the dam site in 40% of the 2090s scenarios relative to the baseline conditions. These could be associated with 4–6 times the erosion compared to the baseline. Severe erosion is indicated only under RCP 8.5. Simulations suggest that amplified peak releases from dams in the future could lead to greater downstream erosion potential. [ABSTRACT FROM AUTHOR]

The interaction of wind and water may well be the key influence on the modern geomorphology of the arid regions of the world, and has had a strong influence on long-term landscape evolution in these areas. This is the case for the landforms of the northern United Arab Emirates, where aeolian landforms in the west lie on alluvial deposits, and are adjacent to fluvial landforms in the east. Even within the aeolian forms there is evidence of modern and past water activity. Modern river flow is rare and largely confined to the mountains. However, rivers and alluvial activity were more important during certain periods in the past. This study describes the landforms of the Northern Emirates (NE) and relates their form and evolution to alternating periods of arid and humid climates. The study was initially carried out to provide a background for the soil survey of the NE. Details of landform character and materials were explored during the survey, which involved detailed site and soil descriptions at 10,020 auger and Geoprobe sites (2 m depth), 200 backhoe pits (2 m depth), and 150 drill observations (10 m depth). The main landforms identified in the study area are the Hajar Mountains, alluvial plains (fans, plains and wadis), dunes (ridges, sand veneer, rising dunes) and coastal forms. The influence of uplift and tilting of the Hajar Mountains during the Miocene and more recently is considered. Sea level changes in the Arabian Gulf are also important. The impacts of past climate change on the evolution of landforms is discussed and related to alternating periods of arid and wet climates. The north-westerly Shamal wind is primarily responsible for the formation and continued evolution of the dune fields seen in the NE today. [ABSTRACT FROM AUTHOR]

The Venetian–Friulian Plain is the northernmost alluvial environment facing the Adriatic Sea and it represents the transition from the Mediterranean domain to the Alps and the temperate regions of central and eastern Europe. The investigated area consists of the alluvial systems of Brenta, Piave and Tagliamento rivers, forming distinct alluvial megafans fed by mountain basins of 1567, 3899 and 2580 km 2 , respectively. The database of radiocarbon dates related to the Holocene alluvial evolution of the Venetian–Friulian Plain consists of 136 samples, 65 of them classified as change-after dates. We analyzed statistically the database with the aim of detecting periods of enhanced flooding activity. The individual calibration probability intervals of each radiocarbon age were summed, producing a cumulative probability density function (CPDF) plot for each alluvial system and for the whole database. Each change-after CPDF plot has been subtracted to its correspondent CPDF plot of the entire sub-dataset, obtaining a relative cumulative probability function (RCPF) curve. The analysis of these curves evidences that statistically significant information are available between about 8.5 and 0.8 ka cal BP. In particular, nine periods of enhanced flooding activity have been identified: 8.4–8.3, 7.5–7.2, 6.9–6.2, 5.5–5.3, 4.7–4.5, 2.3–2.1, 1.9–1.7, 1.6–1.4 and 1.3–0.8 ka cal BP. In the interval 8.5–0.8 ka cal BP, some sub-periods are not statistically significant because of the relatively few change-after dates available. Notably, between 4.5 and 2.3 ka cal BP no interval has been recognized, even if some important flooding deposits are documented in the stratigraphic and geomorphological record. Meta-analyses revealed quite a good correlation of several flooding periods occurred in the study area with the flooding record of the Lake Iseo (northern Italy), as well as with positive peaks in the Ice Rafted Debris (IRD) curve for the North Atlantic, namely Bond events 1, 3, 4 and 5. Comparison with other flood sequences obtained in Great Britain, Spain, Poland and Germany with the same statistical approach used in this work confirms the presence of some common intervals. In particular, synchronous periods of hydrological crisis are recorded in NE Italy and Great Britain at 7.5–7.3, 6.9–6.5, 6.3–6.2, 4.7–4.5, 2.3–2.1, 1.5–1.4, 1.3–1.1, 0.9–0.8 ka cal BP. Two of them, 4.7–4.5 and 0.9–0.8 ka cal BP, occurred also in the Iberian Peninsula. These results suggest that during the middle and late Holocene enhanced flooding activity in NE Italy is recurrently connected to events or phases of climatic deterioration at regional and continental scale, with minor influence of local forcings. [ABSTRACT FROM AUTHOR]

Mediterranean fluvial hydrology is characterised by decadal-to-multi-centennial length wet and dry episodes with abrupt transitions related to changes in atmospheric circulation. Since the mid-1990s site-based flood chronologies from slackwater deposits in bedrock rivers and regionally aggregated flood histories from alluvial deposits have developed increasingly higher resolution chronological frameworks, although regional coverage is still uneven. This paper analyses the spatial and temporal distribution of extreme Holocene hydrological events recorded in fluvial stratigraphy in the Iberian Peninsula (Spain and Portugal), southern France, southern Italy, Northern Africa (Morocco and Tunisia) and eastern Mediterranean (Greece, Crete, Turkey, Cyprus and Israel). This study constitutes the most comprehensive investigation of Holocene river flooding ever undertaken in the Mediterranean and is based on the analysis of 515 14 C and 53 OSL dates. It reveals that flood periods in different regions cluster into distinct time intervals, although region-wide flooding episodes can be identified at 7400–7150, 4800–4600, 4100–3700, 3300–3200, 2850–2750, 2300–2100, 1700–1600, 1500–1400, 950–800, ca. 300, 200–100 cal. BP. Periods with more frequent floods in the western Iberian region coincide with transitions to cool and wetter conditions and persistent negative NAO mode. In Northern Africa increased flood frequency coincides with periods of generally drier climate, while in the eastern Mediterranean there is a higher incidence of extreme flood events under wetter conditions. Our meta-data analysis identifies an out-of-phase pattern of extreme events across the Mediterranean over multi-centennial timescales, which is particularly evident between the western Iberian and eastern Mediterranean regions. This centennial-to-multi-centennial see-saw pattern in flooding indicates that bipolar hydroclimatic conditions existed in the Mediterranean during the Holocene. [ABSTRACT FROM AUTHOR]

Abstract: Forests in the Southern Rockies Ecoregion surround the headwaters of several major rivers in the western and central US. Future climatic changes will increase the incidence of wildfire in those forests, and will likely lead to changes in downstream water quality, including sediment loads. We estimated soil loss under the historic climate and two IPCC climate change emissions scenarios (A2 and B1); each scenario was modeled using statistically downscaled climate data from global circulation models (GCMs; ECHAM5 and HadCM3) for each of thirteen land cover types. We used the Revised Universal Soil Loss Equation (RUSLE) and developed a way to calculate rainfall erosivity, a key factor in RUSLE, to account for climate change. We also incorporated the effects of climate change on wildfire to create stochastic spatial distributions of wildfires and to inform changes in land cover. Based on 100 simulations of future wildfire applied to RUSLE for each GCM-scenario combination, we found that soil loss will likely increase above historic levels but that considerable uncertainty remains about the amount of increase. Across the GCM-scenario combinations, mean soil loss increased above historic levels by from 3% (HadCM3-A2) to 65% (ECHAM5-B1) for climate change only and the effects of wildfire increased soil loss an additional 3 to 5%. [Copyright &y& Elsevier]

A large number of studies have focused on water erosion in the southern Alps because of its intensity and the high erodability affecting numerous outcrops in this region.The aim of this paper is to determine the relations between natural and human factors on the one hand, geomorphologic behaviour of hillslopes and fluvio-torrential dynamics at two time scales (geological and historical) on the other hand. This paper specially focuses on the recent weakening of torrential activity and its linkage with reforestation and rural desertion on the watersheds. Another objective is to compare these results with a rich mainly French scientific production on this theme.Experimental data on:–current erosion measurements and the analysis of its processes on the one hand,–and geomorphologic background of river beds and slopes,are compared and analysed using archives and the present knowledge on historical climate.It has been shown that the overexploitation of watersheds leads to an increase in soil loss, in the number and intensity of floods in alpine valleys, as well as to an enhancement of sediment transport. However, climatic changes during the Holocene and during the past millennium have resulted in changes in morphological behaviour of the hillslopes upstream and of river beds downstream.Moreover, a strong sedimentary deficit can be observed over the last three or four decades in all the Alpine massifs. The consequences of this sediment deficit are firstly an entrenchment of river beds, which threatens bridges and embankments. This recent trend is probably due to the excessive extraction of material in gravel pits and the sedimentation in the numerous dams built between 1920 and 1980 in the entire alpine range. However, the entrenchment appeared recently on non-exploited rivers; therefore, the deficit is also due to the success of the natural and artificial reforestation and torrent correction since the end of 19th century. [Copyright &y& Elsevier]

• Suspended sediment fluxes of a small glacierized catchment in the Caucasus were evaluated. • An exceptional erosion event changed the sediment dynamics. • The proglacial area with buried ice is the main sediment source during non-rainy days. • About half of the annual sediment fluxes moved during high runoff events. Suspended sediment yields from glacierized catchments are often among the highest in the world, and their sediment dynamics can be highly variable. This study was undertaken in the 9.1 km2 glacierized catchment of the Djankuat River located in the Russian part of the Northern Caucasus. The outlet of the study catchment is a hydrological gauging station located at an altitude of 2635 m a.m.s.l. ('N43°12′31.71″, E42°44′05.93″). The catchment includes a temperate valley glacier (area = 2.42 km2) and three smaller hanging glaciers, several moraine deposits, rock walls, and a large and expanding proglacial area. The main goal of our study was to assess the impact of an exceptional erosion event on 1st July 2015 (with an annual exceedance probability of less than 0.1%) on suspended sediment yields and the relative contributions of various sediment sources The work combined direct suspended sediment discharge measurements at the gauging station during five ablation seasons (2015–2019) with geomorphic mapping techniques based on detailed field observations and sediment source fingerprinting. Results show that mean annual suspended sediment yields reached 1118 t km−2 year−1 which is one of the highest measured estimates for any of the glacierized mountain rivers globally. About half of the annual suspended sediment flux was exported during a limited number (1–12% of the annual events) of extreme hydrological events. The sediments mobilized by bank and riverbed erosion within the new lower reach of a tributary channel which appeared after the breakthrough of a lateral moraine became the primary sediment source. It contributed over 50% of the suspended sediment on days with extreme rainfall. Contributions to the suspended sediment load from the glacier source were event-dependent and were only dominant (c. 60–70%) in the upper reaches of the proglacial area (first 800 m). The proglacial part of the study catchment with buried ice was the main sediment source (79%) during non-rain days. [ABSTRACT FROM AUTHOR]

• Natural and anthropogenic geomorphological processes modeled the Chico River basin. • Four major change stages occurred in the basin hydrography during the Cenozoic. • Until the mid-20th century, Chico River drained water from Senguer River Basin. • Arid climate and anthropogenic impact favored the split of both river basins. • Nowadays, the Chico River is intermittent, and the Senguer River basin is endorheic. We aimed to assess how geomorphological processes during the Cenozoic, including those triggered by human intervention, modeled the landscape and affected the hydrography of the Chico River basin (Argentinean Patagonia). We analyzed the hydrography, mapped the geomorphology, and propose a landscape model of the study area. We found the Chico River basin geomorphology, drainage surface, and hydrological regime were affected by Paleogene and Neogene tectonic uplift, Pleistocene glaciations, Holocene climatic change and also, the human impact. We described four different stages (Early to Late Pliocene; Early to Late Pleistocene; Early to Middle Holocene; Middle Holocene to present) of the basin hydrography and drainage surface. The main conclusion is that the current boundaries of the Chico River basin were established after the mid-20th century. Formerly, the Chico River was the downstream extension of the Senguer River basin (located northwest of the study area), with both rivers forming a single system. However, prevailing arid climatic conditions since the Middle Holocene together with the climatic variability and anthropogenic activities during the last century produced the current disconnection between the Chico and Senguer river basins. Consequently, the Senguer River basin has changed from exorheic to endorheic, and the Chico has turned into an intermittent river. [ABSTRACT FROM AUTHOR]

• Damming dominated reduced sediment fluxes, followed by climate change. • The Wenchuan Earthquake had little effect on long-term downstream sediment flux. • The drastically decreased sediment fluxes benefit the Three Gorges Reservoir. Riverine sediment flux is a crucial proxy influencing channel morphology, biogeochemical processes, and riverine ecosystems. However, recent climate change and multiple anthropogenic activities have substantially altered the sediment regimes of the world's rivers. On a basis of the "multiple double mass curves" method, this study selected the Jialing River (JR) basin as a case study to distinguish the relative impacts of climate change, land-use change, and damming on changes in the runoff and sediment flux over the past 60 years. The results showed that the sediment fluxes in the JR basin drastically decreased by 57–77% from the baseline period (1950s–1984) to the post-change period (1985–2017) mainly due to damming (60–75%), climate change (5–30%), and revegetation (10–20%). The runoff in the JR basin also exhibited a reduction (12–22%) likely because of the joint impacts of a reduction in precipitation and the restoration of vegetation. Although the 2008 Wenchuan Earthquake (M = 7.9) increased the short-term sediment fluxes, its impact on the long-term sediment fluxes in the downstream areas of the JR basin was limited as a result of the buffering effect of the thousands of constructed reservoirs. The decreased sediment fluxes in the JR basin benefit the life expectancy of the Three Gorges Reservoir (the world's largest hydropower plant), but the reduced runoff can exacerbate water stress. The findings of our study have important implications for better management of water resources, sediment fluxes, and reservoir sedimentation not only for the JR basin, but also for the Three Gorges Reservoir. [ABSTRACT FROM AUTHOR]

• Mountainous basins are and will further be affected by climate change and extremes. • Climatic and hydrological changes differ in different basins. • Snow/glacier melt changes the amount and seasonal dynamics of streamflow. • Uncertainties about data and methods should be considered in further research. Water resources are critical in semiarid Xinjiang, northwestern China, a mountainous region that heavily relies on meltwater, making it sensitive to climate change. A better understanding of climatic and hydrological changes is therefore highly required for water resources management. In this review, spatio-temporal climate change, climate extremes, snow and glacier fluctuations and variability in semiarid Xinjiang are summarized. In general terms, the available historical data demonstrate a rising mean temperature, likely increased precipitation (subject to greater uncertainty), declining snow cover and glacier extent, and increased streamflow in most rivers. Although the changes of projected future climate differ with different climate resembles, average temperature is expected to increase and seasonal precipitation will experience a slightly increase tendency. Additionally, climate extremes are predicted to become more frequent. Projected future streamflow is expected to increase although initial increase may be followed by a long-term decrease. Water demand is predicted to increase due to irrigation, population growth and economic development. We thereby conclude that water variability in semiarid Xinjiang is and will further be affected by future climate change and their hydrological impacts. However, climatic and hydrological changes differ in different basins, and the impacts of climate change on hydrological changes cannot be generalized. Historical and future climatic and hydrological changes have possible implications for vegetation and can intensify regional hydrological cycle and enhance pressure on seasonal water availability. Future research on climatic and hydrological changes in this region should reveal the mechanisms behind the change phenomenon, quantify the implications on water resources management and expand observational networks, in particular focus on snow and glacier melt processes, as meltwater is a crucial water source in this region. This research may provide suggestions for water resources management in semiarid Xinjiang and endorheic basins where totally depending on water from the surrounding mountains in central Asia or elsewhere. [ABSTRACT FROM AUTHOR]

[Display omitted] • 322 closed lake catchments are grouped by topography and land surface descriptors. • Similar physical geography and climatology may cause different lake area responses. • Precipitation controlled the inconsistent growth of lakes within the same cluster. • During strong evaporation periods, it is common to observe a decrease in lake area. • Precipitation, temperature, and glaciers change more dramatically after 2000. Naturally closed lakes located on the Tibetan Plateau provide a more authentic depiction of climate change and have undergone significant but dissimilar changes over the past four decades. Although previous research has concentrated on closed lake changes at regional and continental scales, the dominant factors related to closed lakes at the catchment scale remain elusive. This study employed the hierarchical minimum variance clustering method, six representative topographies and land surface descriptors to classify the catchments of 322 closed lakes (>1 km2) across the Tibetan Plateau from 1981 to 2020. To better understand the factors driving the changes in catchment-scale lake areas, we assigned two distinct attribute classes to the resulting classifications: hydro-meteorological characteristics and geographical environmental aspects. Our analysis revealed that five clusters are geographically coherent and exhibit distinct hydro-meteorological characteristics. By assessing decadal-scale changes in catchment characteristics over time for lakes in five clusters with area change of greater than ± 50 %, we found that the most significant driver of catchment changes from 1981 to 2000 was a continuous decline in snowmelt, followed by a substantial increase in precipitation, temperature, and glacial meltwater from 2000 to 2020. Regarding trends and magnitude, different lake area responses may occur in areas with similar physical geography and climatology (i.e., the same cluster). During the past four decades, only 3 % of lakes (19) shrank in area and decreased in change rate. Also, intense evaporation corresponds to a period of decrease in lake area. Despite the variation in lake area change among clusters, precipitation dominates the inconsistent increase in lake area under similar physical geography and climatology, with some exceptions strongly related to groundwater and melted permafrost recharge. Our findings have laid the groundwork for understanding this region's catchment characteristics and the resulting complex hydrological behavior. [ABSTRACT FROM AUTHOR]

The applicability of the uncalibrated CLIGEN (CLImate GENerator) model was assessed using long-term precipitation data at 1-min interval from 18 sites in eastern and central China. The model performance was evaluated in terms of daily precipitation depth, storm duration and peak intensities of 1-min (I 1 ), 5-min (I 5 ) and 30-min (I 30 ) for all storms and four categories grouped by daily precipitation depth: light (<10 mm), moderate (10–25 mm), heavy (25–50 mm), and intense (≥50 mm) storms. Additionally, the applicability of CLIGEN in generating climate inputs for the Revised Universal Soil Loss Equation (RUSLE) in China and calculating the intensity-duration-frequency (IDF) values for a series of storm duration (5-min to 24-h) and return periods (2 to 100-years) were assessed. Results showed that CLIGEN was able to accurately reproduce the statistics and probability distributions of daily precipitation depth for all storms and the four categories. The mean storm duration was underestimated for 3 of the 4 storm categories but was overestimated for light storms. CLIGEN underestimated I 1 and overestimated I 30 in general, whereas no obvious bias was observed in I 5 for these 18 sites. In addition, the relative error in the generated duration and peak intensity increased as the magnitude of precipitation increased from moderate to intense storms, which implies that the model does not perform as well for intense storms as other storms. Rainfall erosivity generated with CLIGEN outputs was systematically larger than, but well correlated with, the measured erosivity values (slope = 0.547, R 2  = 0.96 for the R-factor; slope = 0.576, R 2  = 0.81 for the 10-year storm erosivity). Extreme intensities for given duration and return periods were systematically over-predicted using the output from CLIGEN, and the bias between measured and CLIGEN generated intensity-duration-frequency (IDF) values varied with duration intervals. The average of the regression slopes for the six return periods (2-year to 100-year) between measured (X) and generated (Y) intensities (Y =  b X) increased from 1.19 (5-min) to 1.43 (1-h), then decreased to 1.01 (12-h) and 0.96 (24-h). As a stochastic weather generator, CLIGEN is able to reproduce daily precipitation very well, but its capacity to simulate storm duration and the peak intensity for a given time interval needs to be improved, especially for heavy and intense storms, based on this study. [ABSTRACT FROM AUTHOR]

• The parameters of the empirical models for rainfall erosivity estimation vary with month. • The new reconstructed rainfall erosivity estimates closely correlated with the observed values. • The rainfall erosivity over the TP presents a significant increasing trend over the past 40 years. As a typical fragile ecological plateau area, the risk of water erosion on the Tibetan Plateau (TP) in China continues to increase with climate change. Rainfall erosivity is one of the most widely used indicators to assess the potential impact of rainfall events on water erosion. However, limited by the scarcity of historical in situ precipitation observations with sufficient spatiotemporal resolution, the estimates of rainfall erosivity over the TP have much larger biases than those of other regions in China. To accurately investigate the spatiotemporal evolution of rainfall erosivity, empirical models were first established to estimate monthly rainfall erosivity using 1-minute in situ precipitation observations from 1711 meteorological stations on the TP. The independent assessment showed that the correlation correction values between the observed and estimated monthly values were greater than 0.81 for all months. The annual rainfall erosivity data were then produced with a 0.1° spatial resolution for the 1979–2018 period based on the China Meteorological Forcing Dataset (CMFD) precipitation data using newly established estimation models. Our results show that the CMFD-based estimates successfully captured the decreasing spatial pattern of the multiyear average annual rainfall erosivity from the southeast to northwest of the TP. In addition, the CMFD-based annual rainfall erosivity had a good linear relationship with the observed values but with a certain overestimation. Therefore, standardized annual rainfall erosivity values were used to detect the changes in rainfall erosivity. For most regions on the TP, annual rainfall erosivity values have exhibited significant increasing trends over the last 40 years. This study provides a theoretical basis and reference for controlling water erosion and climate adaptation on the TP. [ABSTRACT FROM AUTHOR]

The Yunnan Plateau (YP), southwest China, is a typical plateau mountain region characterized by a monsoon climate. Soil erosion in the YP is recognized as a major environmental problem. Rainfall is abundant in the YP but distributed unevenly on a spatiotemporal scale. However, little published work is available on rainfall erosivity (R factor) in the YP, an important basic parameter for representing the potential ability of precipitation and runoff to erode soil in the Universal Soil Loss Equation. This study integrates the trend coefficient and climate tendency rate indicators and Mann-Kendall nonparametric statistical test to identify the spatial distribution and temporal variation of the R factor in the YP. The daily rainfall records from 1960 to 2012 in the YP were collected from 115 national meteorological observatory stations. The result shows that the average annual R factor was 4382.65 MJ·mm·ha − 1 ·h − 1 in the YP, and > 80% of the annual R was concentrated in the summer and autumn. The spatial distribution of annual, summer and autumn R was greater in the south than in the north while the northwest surpassed other regions for winter and spring R factor. There was significant variability in temporal trends from station to station, in general, the annual and autumn R showed a distribution pattern of an increase in the western YP and a reduction in the eastern YP. The temporal variance of winter R showed a pattern opposite of that of annual and autumn R, indicating an increase in the eastern YP and a reduction in the western YP over recent decades. [ABSTRACT FROM AUTHOR]