Pluvial Regime Research Articles

A multi-proxy stalagmite record indicates a shift in forcing of twentieth century drought events in Normandy

Drought events are increasingly impacting Europe. The study of past droughts helps disentangle the different factors that trigger hydrological drought, helping to forecast future drought severity. Here we identify the historical drought events of the twentieth and twenty-first centuries in geochemical records of a stalagmite from Caumont cave in Northern France and develop a mechanistic understanding of their root causes. Subannually-resolved stable carbon isotope (δ13C) and trace element data are directly compared with historical climatic records. δ13C, Mg, and Sr peaks align well with most of the historical drought events of the twentieth and twenty-first centuries. The comparison reveals a good correspondence between summer effective rainfall and δ13C, Mg, and Sr concentrations. Further comparison of geochemical records with the precipitation-evapotranspiration index (SPEI) reveals a change in the drought forcings for the past two decades. During most of the twentieth century, droughts appear driven by a pluvial regime, whereas since the late 1990s, drought was driven by higher evapotranspiration due to increased temperature.

Physiological adaptations of red blood cells during aestivation in the south American lungfish Lepidosiren paradoxa

The South American lungfish Lepidosiren paradoxa inhabits areas with variable pluvial regimes. During aestivation (dormancy state observed in some species during dry seasons), the prolonged period of dryness imposes osmotic stress. We aimed to investigate the physiological and morphological adaptations of RBCs in Lepidosiren paradoxa during aestivation. Here, the lungfish were subjected to aestivation for 20 and 40 days and compared to a control group in an active period. The osmotic fragility, blood osmolality, and pH were measured. Blood smears were performed to assess morphological changes in the RBCs. Lepidosiren paradoxa presented lower hemolysis when compared with a teleost fish and tegu lizard. Hemolysis increased when the lungfish was subjected to 40 days of aestivation (from 6.04 % to 16.51 %; control vs 40-day aestivation). Hematocrit rose in both aestivation groups compared to the control (26.36 %, 41.36 % and 41 %, control, 20 and 40 days, respectively; p < 0.05) indicating changes in RBC volume and hydration status. Moreover, the results revealed increased osmolality in the 40-day aestivation group (244.4 vs 372.1 mmol/Kg; control vs 40-day aestivation). 40 days of aestivation led to a decrease in blood pH when compared to the control and 20-day aestivation groups. Both aestivation durations resulted in a reduction in the perimeter and cell diameters in at least one direction of the RBCs (24 % mean reduction in size from control to 40 days aestivation). These findings suggest that South American lungfish possess remarkable physiological and morphological adaptations in their RBCs during aestivation.

Assessing the impact of climate change on high return levels of peak flows in Bavaria applying the CRCM5 large ensemble

Abstract. ​​​​​​​Severe floods with extreme return periods of 100 years and beyond have been observed in several large rivers in Bavaria in the last 3 decades. Flood protection structures are typically designed based on a 100-year event, relying on statistical extrapolations of relatively short observation time series while ignoring potential temporal non-stationarity. However, future precipitation projections indicate an increase in the frequency and intensity of extreme rainfall events, as well as a shift in seasonality. This study aims to examine the impact of climate change on the 100-year flood (HF100) events of 98 hydrometric gauges within hydrological Bavaria. A hydrological climate change impact (CCI) modeling chain consisting of a regional Single Model Initial-condition Large Ensemble (SMILE) and a single hydrological model was created. The 50 equally probable members of the Canadian Regional Climate Model version 5 large ensemble (CRCM5-LE) were used to drive the hydrological model WaSiM (Water balance Simulation Model) to create a hydro-SMILE. As a result, a database of 1500 model years (50 members × 30 years) per investigated time period was established for extreme value analysis (EVA) to illustrate the benefit of the hydro-SMILE approach for a robust estimation of HF100 based on annual maxima (AM) and to examine the CCI on the frequency and magnitude of HF100 in different discharge regimes under a strong-emission scenario (RCP8.5). The results demonstrate that the hydro-SMILE approach provides a clear advantage for a robust estimation of HF100 using the empirical probability of 1500 AM compared to its estimation using the generalized extreme value (GEV) distribution of 1000 samples of typically available time series sizes of 30, 100, and 200 years. Thereby, by applying the hydro-SMILE framework, the uncertainty from statistical estimation can be reduced. The study highlights the added value of using hydrological SMILEs to project future flood return levels. The CCI of HF100 varies for different flow regimes, with snowmelt-driven catchments experiencing severe increases in frequency and magnitude, leading to unseen extremes that impact the distribution. Pluvial regimes show a lower intensification or even decline. The dynamics of HF100 driving mechanisms depict a decline in snowmelt-driven events in favor of rainfall-driven events, an increase in events driven by convective rainfall, and almost no change in the ratio between single-driver and compound events towards the end of the century.

Divergent runoff regime revealed by hydrological simulations with corrected precipitation in the upper Indus

The upper Indus basin (UIB) supplies water for the largest irrigation system in Asia and for the livelihoods of millions of people downstream. Yet a large gap still remains in the current knowledge of the hydrological processes in this region due to data scarcity, especially at sub-basin scales. In this work, we evaluated eight precipitation datasets and screened out an optimized (MERRA-2) to be inversely corrected through the Variable Infiltration Capacity (VIC)-glacier hydrological model across the UIB. Divergent runoff regimes, changes, and their attributions were quantified at sub-basin scales based on corrected MERRA-2 precipitation and the well-constrained VIC-glacier model against observed streamflow and glacier/snow changes. Spatial variations exist in the corrected precipitation over the UIB with the lowest mean annual average of 414 mm in the Kharmong and the highest of 1318 mm in the Astore, and a mean of 646 mm over the entire basin in 1980–2013. Three runoff regimes were identified across the UIB basins, including the glacial regime of Shigar, Hunza, and Shyok with glacier runoff dominating (41.6%–53.4%), nival-pluvial regime of Astore and Gilgit with rainfall (46.9%–51.9%) and snowmelt (33.1%–40.7%) runoff dominating, and pluvial regime of UIB-M and Kharmong with rainfall runoff (56.7%–60.9%) dominating. Total runoff generally exhibited stable or insignificant positive tendencies over the UIB basins during 1980–2013. Runoff increases in the glacial regime basins were mainly controlled by the increased glacier runoff, while runoff changes in the non-glacial regime basins were mostly attributed to the changes of precipitation-induced runoff from non-glacierized areas. The increased glacier runoff served as a buffer against hydrological drought by offsetting the non-glacierized runoff decrease caused by the overall decreased precipitation. This study is expected to further the understanding of divergent hydrological regimes in the UIB, and provide essential information for policy decisions on sustainable water resource management in this water-stressed area.

Применение биотического индекса &lt;i&gt;Qmci&lt;/i&gt; для оценки загрязнения рек горной, предгорной и прибрежной территории курорта Сочи

This paper discusses the QMCI biotic index application, developed for the regions with tropical and subtropical climate and adapted to the studied area, in order to assess the aquatic environment quality within the river sections in the mountain, submountain and coastal clusters on the example of the river Mzymta and its tributaries. Index values were determined on the basis of qualitative and quantitative characteristics of macroinvertebrates communities. For the index adjustment to the region's conditions, the individual tolerance of each aquatic organisms' taxon (genus, species) found in the studied watercourses was identified using the Chessman-Stark approach, taking into account the Caucasus endemics. It was revealed that the biotic index QMCI is a reliable biomarker of various degrees water pollution caused primarily by excessive input of organic eutrophication agents, taking into account specific conditions of biocenoses development in the pluvial regime rivers. The research demonstrates the index values dynamics changes from upstream stations located in the specially protected areas (reference samples), to stations experiencing occasional impact, and further to the river's mouth stations, where the anthropogenic pressure has a complex and stable character. The QMCI biotic index can serve as a tool for introducing regional environmental standards of natural waters quality assessment on the Russian Black Sea coast and adjacent mountain territories, as it has some advantages over analogous biotic indices developed for watercourses of other geographical regions: the possibility of adaptation to different types of river biotopes and seasonal variations.

Modelling Subarctic watershed dissolved organic carbon response to hydroclimatic regime

Shifts in hydroclimatic regimes associated with global climate change may impact freshwater availability and quality. In high latitudes of the northern hemisphere, where vast quantities of carbon are stored terrestrially, explaining landscape-scale carbon (C) budgets and associated pollutant transfer is necessary for understanding the impact of changing hydroclimatic regimes. We used a dynamic modelling approach to simulate streamflow, DOC concentration, and DOC export in a northern Canadian catchment that has undergone notable climate warming, and will continue to for the remainder of this century. The Integrated Catchment model for Carbon (INCA-C) was successfully calibrated to a multi-year period (2012–2016) that represents a range in hydrologic conditions. The model was subsequently run over 30-year periods representing baseline and two future climate scenarios. Average discharge is predicted to decrease under an elevated temperature scenario (22–27 % of baseline) but increase (116–175 % of baseline) under an elevated temperature and precipitation scenario. In the latter scenario the nival hydroclimatic regime is expected to shift to a combined nival and pluvial regime. Average DOC flux over 30 years is predicted to decrease (24–27 % of baseline) under the elevated temperature scenario, as higher DOC concentrations are offset by lower runoff. Under the elevated temperature and precipitation scenario, results suggest an increase in carbon export of 64–81 % above baseline. These increases are attributed to greater connectivity of the catchment. The largest increase in DOC export is expected to occur in early winter. These predicted changes in DOC export, particularly under a climate that is warmer and wetter could be part of larger ecosystem change and warrant additional monitoring efforts in the region.

Runoff Regime, Change, and Attribution in the Upper Syr Darya and Amu Darya, Central Asia

Abstract The upper Syr Darya (USD) and Amu Darya (UAD) basins are the two biggest flow formation zones in central Asia and the only water supply sources for the Aral Sea. Upstream snow and ice reserves of those two basins, important in sustaining seasonal water availability, are highly sensitive and prone to climate change, but their importance and changes are still uncertain and poorly understood due to data scarcity, inaccessibility, harsh climate, and even geopolitics. Here, an improved forcing dataset of precipitation and temperature was developed and used to drive a physically based hydrological model, which was thoroughly calibrated and validated to quantify the contributions of different runoff components to total flow and the controlling factors for total runoff variations for 1961–2016. Our analysis reveals divergent flow regimes exist across the USD and UAD and an ongoing transition from nival–pluvial toward a volatile pluvial regime along with rising temperatures. Annual total runoff has weakly increased from 1961 to 2016 for the entire USD and UAD, while the subbasins displayed divergent flow changes. Spring runoff significantly increased in all the USD and UAD basins primarily due to increased rainfall and early snow melting, tending to shift the peak flow from June–July to April–May. In contrast, distinct runoff changes were presented in the summer months among the basins primarily due to the trade-off between the increase in rainfall and the decrease in snowmelt and glacier runoff. These findings are expected to provide essential information for policymakers to adopt strategies and leave us better poised to project future runoff changes in ongoing climate change.

Interpreting Deep Machine Learning for Streamflow Modeling Across Glacial, Nival, and Pluvial Regimes in Southwestern Canada

The interpretation of deep learning (DL) hydrological models is a key challenge in data-driven modeling of streamflow, as the DL models are often seen as “black box” models despite often outperforming process-based models in streamflow prediction. Here we explore the interpretability of a convolutional long short-term memory network (CNN-LSTM) previously trained to successfully predict streamflow at 226 stream gauge stations across southwestern Canada. To this end, we develop a set of sensitivity experiments to characterize how the CNN-LSTM model learns to map spatiotemporal fields of temperature and precipitation to streamflow across three streamflow regimes (glacial, nival, and pluvial) in the region, and we uncover key spatiotemporal patterns of model learning. The results reveal that the model has learned basic physically-consistent principles behind runoff generation for each streamflow regime, without being given any information other than temperature, precipitation, and streamflow data. In particular, during periods of dynamic streamflow, the model is more sensitive to perturbations within/nearby the basin where streamflow is being modeled, than to perturbations far away from the basins. The sensitivity of modeled streamflow to the magnitude and timing of the perturbations, as well as the sensitivity of day-to-day increases in streamflow to daily weather anomalies, are found to be specific for each streamflow regime. For example, during summer months in the glacial regime, modeled daily streamflow is increasingly generated by warm daily temperature anomalies in basins with a larger fraction of glacier coverage. This model's learning of “glacier runoff” contributions to streamflow, without any explicit information given about glacier coverage, is enabled by a set of cell states that learned to strongly map temperature to streamflow only in glacierized basins in summer. Our results demonstrate that the model's decision making, when mapping temperature and precipitation to streamflow, is consistent with a basic physical understanding of the system.

Co-occurrence probability of water balance elements in a mountain catchment on the example of the upper Nysa Kłodzka River

Conditions of the formation of key elements of the water balance, such as precipitation and runoff, and relations between them in the mountain catchment area are very complicated, conditioned both by the climatic factor and the physiographic characteristics of the catchment area. The aim of the study is to determine relations between precipitation and runoff in the Kłodzka Valley (KV) located in mountain areas of south-western Poland. Analyzes were based on precipitation in KV and discharges of the Nysa Kłodzka River and its tributaries, recorded in hydrological years 1974–2013. The bivariate Archimedean copulas were used to describe the degree of synchronicity between these variables. The study area shows a considerable variability in the conditions of transformation of precipitation into runoff. It is conditioned both by the pluvial regime and the physical-geographical characteristics of the catchment area. As a result, sub-catchments with diversified hydrological activity and their role in the formation of water resources of the entire KV were identified. Among them, the Biała Lądecka River sub-catchment was found to be the most hydrologically active, and the sub-catchment of Bystrzyca Dusznicka River the most inert, despite e.g. quite similar synchronicity of precipitation compared to the average precipitation in KV. At the same time, the KV rivers are characterized by different types of runoff regime and characteristic of the water balance structure. The methodology presented can be useful in determining dependencies between selected elements of the water balance and evaluation of water resources availability in source areas of mountain rivers.

Analysis of the Relative Importance of the Main Hydrological Processes at Different Temporal Scales in Watersheds of South-Central Chile

In Chile in recent years, changes in precipitation and temperatures have been reported that could affect water resource management and planning. One way of facing these changes is studying and understanding the behavior of hydrological processes at a regional scale and their different temporal scales. Therefore, the objective of this study is to analyze the importance of the hydrological processes of the HBV model at different temporal scales and for different hydrological regimes. To this end, 88 watersheds located in south-central Chile were analyzed using time-varying sensitivity analysis at five different temporal scales (1 month, 3 months, 6 months, 1 year, and 5 years). The results show that the model detects the temporality of the most important hydrological processes. In watersheds with a pluvial regime, the greater the temporal scale, the greater the importance of soil water accumulation processes and the lower the importance of surface runoff processes. By contrast, in watersheds with a nival regime, at greater temporal scales, groundwater accumulation and release processes take on greater importance, and soil water release processes are less important.

Rain on snow induced urban floods in cold maritime climate: Risk, indicators and trends

AbstractUrban floods pose a societal and economical risk. This study evaluated the risk and hydro‐meteorological conditions that cause pluvial flooding in coastal cities in a cold climate. Twenty years of insurance claims data and up to 97 years of meteorological data were analysed for Reykjavík, Iceland (64.15°N; &lt;100 m above sea level). One third of the city's wastewater collection system is combined, and pipe grades vary from 0.5% to 10%. Results highlight semi‐intensive rain (&lt;7 mm/h; ≤3 year return period) in conjunction with snow and frozen ground as the main cause for urban flood risk in a climate which undergoes frequent snow and frost cycles (avg. 13 and 19 per season, respectively). Floods in winter were more common, more severe and affected a greater number of neighbourhoods than during summer. High runoff volumes together with debris remobilized with high winds challenged the capacity of wastewater systems regardless of their age or type (combined vs. separate). The two key determinants for the number of insurance claims were antecedent frost depth and total precipitation volume per event. Two pluvial regimes were particularly problematic: long duration (13–25 h), late peaking rain on snow (RoS), where snowmelt enhanced the runoff intensity, elongated and connected independent rainfall into a singular, more voluminous (20–76 mm) event; shorter duration (7–9 h), more intensive precipitation that evolved from snow to rain. Closely timed RoS and cooling were believed to trigger frost formation. A positive trend was detected in the average seasonal snow depth and volume of rain and snowmelt during RoS events. More emphasis, therefore, needs to be placed on designing and operating urban drainage infrastructure with regard to RoS co‐acting with frozen ground. Furthermore, more detailed, routine monitoring of snow and soil conditions is important to predict RoS flood events.

The Kwakshua Watersheds Observatory, central coast of British Columbia, Canada

AbstractThe Kwakshua Watersheds Observatory (KWO) is an integrative watersheds observatory on the coastal margin of a rain‐dominated bog‐forest landscape in British Columbia (BC), Canada. Established in 2013, the goal of the KWO is to understand and model the flux of terrestrial materials from land to sea – the origins, pathways, processes and ecosystem consequences – in the context of long‐term environmental change. The KWO consists of seven gauged watersheds and a network of observation sites spanning from land to sea and along drainage gradients within catchments. Time‐series datasets include year‐round measurements of weather, soil hydrology, streamflow, aquatic biogeochemistry, microbial ecology and nearshore oceanographic conditions. Sensor measurements are recorded every 5 min and water samples are collected approximately monthly. Additional observations are made during high‐flow conditions. We used remote sensing to map watershed terrain, drainage networks, soils and terrestrial ecosystems. The watersheds range in size from 3.2 to 12.8 km2, with varying catchment characteristics that influence hydrological and biogeochemical responses. Despite local variation, the overall study area is a global hotspot for yields of dissolved organic carbon, dissolved organic nitrogen and dissolved iron at the coastal margin. This observatory helps fill an important gap in the global network of observatories, in terms of spatial location (central coast of BC), climate (temperate oceanic), hydrology (very high runoff, pluvial regime), geology (igneous intrusive, glacially scoured), vegetation (bog rainforest) and soils (large stores of organic carbon).

Equation for rainwater tank efficiency: Considering demand, roof area, tank size and pluvial regime

A rainwater harvesting system (RWHS) is essential to meet the water domestic needs for many semi-urban, remote communities, where there is no centralized potable water supply system. This research evaluated the behavior of rainwater tanks sized by the modified Rippl method applied in regions of different rainfall regimes in Rio Grande do Norte (Brazil) and developed two empirical equations: one to determine the rainwater tank volume and the other to determine its efficiency. The independent variables studied were the roof area, demand, annual precipitation, critical precipitation, and precipitation concentration degree. The general empirical equation developed to determine the volume considering the entire study area proved to be adequate, with no need to divide the area into homogeneous sub-regions. In the case of efficiency, obtaining a general equation proved to be feasible, but it was necessary to exclude the eastern region during the acquisition, due to the high discrepancy in the rainfall regime in that region in relation to the others. Using a general tank efficiency equation, it is possible to evaluate the behavior of tanks of different sizes, not only measured by the Rippl method. This study also examined the behavior of rainwater tanks sized by the Rippl method, but the emphasis was on the study of reservoirs efficiencies. It argues the necessity to study the rainwater tanks by efficiencies indexes, as this approach provides essential information so that the users can choose the best size considering their RWHS degree of dependence in meeting their demands.

MULTIVARIATE MODELS FOR PREDICTING RAINFALL EROSIVITY FROM ANNUAL RAINFALL AND GEOGRAPHICAL COORDINATES IN A REGION WITH A NON- UNIFORM PLUVIAL REGIME

Soil erosion by water is a major land degradation problem because it threatens the farmer’s livelihood and ecosystem's integrity. Rainfall erosivity is one of the major controlling factors inducing this process. One obstacle of estimating the R-factor is the lack of detailed rainfall intensity data worldwide. To overcome the problem of data scarceness for individual analysis of storm events for developing the country with a non-uniform pluvial regime like the upper part of Iraq, multivariate models were derived for estimating annual rainfall erosivity. They were based on annual rainfall data and geographical coordinates of a group of meteorological stations distributed over the study area. A host of statistical indices were selected to evaluate adequately the model's performance. Further, the models were cross-validated using k-fold procedure and unseen data. Subsequently, four linear models were proposed for estimating the annual erosivity for the study area. Good correspondence was found between the measured and predicted values. Among the proposed models, the model with the combination of annual rainfall, latitude and longitude outperformed the remaining proposed ones. After calculating the annual, the ArcMap software ver. 10.2 was applied to map the spatial variability of the R-factor over the study region.

Analysis of the Relative Importance of Model Parameters in Watersheds with Different Hydrological Regimes

Depending on the purpose of the study, aggregated hydrological models are preferred over distributed models because they provide acceptable results in terms of precision and are easy to run, especially in data scarcity scenarios. To obtain acceptable results in terms of hydrological process representativeness, it is necessary to understand and assess the models. In this study, the relative importance of the parameters of the Hydrologiska Byråns Vattenbalansavdelning (HBV) model is analyzed using sensitivity analysis to detect if the simulated processes represent the predominant hydrological processes at watershed scale. As a case study, four watersheds with different hydrological regimes (glacial and pluvial) and therefore different dominant processes are analyzed. The results show that in the case of the rivers with a glacial regime, the model performance depends highly on the snow module parameters, while in the case of the rivers with a pluvial regime, the model is sensitive to the soil and evapotranspiration modules. The results are directly related to the hydrological regime, which indicates that the HBV model, complemented by sensitivity analysis, is capable of both detecting and representing hydrological processes at watershed scale.

Impact of Climate Change on the Hydrological Regimes in Bavaria

This study assesses the change of the seasonal runoff characteristics in 98 catchments in central Europe between the reference period of 1981–2010, and in the near future (2011–2040), mid future (2041–2070) and far future (2071–2099). Therefore, a large ensemble of 50 hydrological simulations featuring the model WaSiM-ETH driven by a 50-member ensemble of the Canadian Regional Climate Model, version 5 (CRCM5) under the emission scenario Representative Concentration Pathway (RCP 8.5) is analyzed. A hierarchical cluster analysis is applied to group the runoff characteristics into six flow regime classes. In the study area, (glacio-)nival, nival (transition), nivo-pluvial and three different pluvial classes are identified. We find that the characteristics of all six regime groups are severely affected by climate change in terms of the amplitude and timing of the monthly peaks and sinks. According to our simulations, the monthly peak of nival regimes will occur earlier in the season and the relative importance of rainfall increases towards the future. Pluvial regimes will become less balanced with higher normalized monthly discharge during January to March and a strong decrease during May to October. In comparison to the reference period, 8% of catchments will shift to another regime class until 2011–2040, whereas until 2041–2070 and 2071–2099, 23% and 43% will shift to another class, respectively.

UNA SEQUENZA PALINOLOGICA DI ETA' RUSCINIANA NEI SEDIMENTI LACUSTRI BASALI DEL BACINO DI AULLA-OLIVOLA (VAL DI MAGRA)

Palynological investigations were carried out on the basal sediments of the Aulla-Olivola basin, precisely on the Aulla lacustrine deposit, which underlies by about 200 m, both stratigraphically and geometricall", the Olivola village, known for its famous Villafranchian fauna.&#x0D; This research has revealed;&#x0D; &#x0D; a very rich palynoflora and a long, complex, vegetational succession. dominated by arboreal formations, with high abundance of exotic taxa, including also tropical-subtropical elements;&#x0D; a climatic Sequence characterized by oscillations reflecting seasonality, especially in pluvial regime. A most evident climatic change occurs in the middle of the sequence.&#x0D; &#x0D; Moreover, the palynological sequence made it possible:&#x0D; &#x0D; to assign the examined sequence to the Pliocene, because of the abundance of "Tertiary" elements (Taxodium-type, Sciadopitys, Sequoia-type, Nyssa, Palmae, etc.);&#x0D; to-ascertain the rather archaic character of the Aulla pollenflora because of the significant occurrence Of pollen assemblages mainly confined to pre-Pliocene and early Pliocene (Symplocos, Sapotaceae, Clethraceae/Cyrillaceae-type, Magnolia-type, Sapindaceae- type, Sterculiaceae, cfr. Castanopsis, Tricolporopollenites sp. of archaic-type, etc.);&#x0D; to compare the Aulla pollenflora with Other Pliocene pollen microfloras from Italy and Other areas and to evidence affinities and differences.&#x0D; &#x0D; From these comparisons it appears clearly that the Aulla lacustrine episode represents the most ancient continental Pliocene deposit discovered in Italy by means of pollen analyses so far. In fact, the palynological and climatic features indicate that the pollen sequence of Aulla is certainly older than the establishement of glacial/interglacial climatic cycles in the Northern Hemisphere (—2,5 Ma). Also the Villafranca d'Asti deposit (Early Villafranchian in age) is older than 2,5 Ma on the base of the paleomagnetic data. But the pollen floras of Villafranca d'Asti (Fornace R.D.B.) do not include the pre- Pliocene and early Pliocene elements, which characterize the Aulla pollen records.&#x0D; All these considerations lead to Suggest an older chronostratigraphic collocation of the Aulla sequence, most likely in a pre-Vilafranchian interval, i.e., in the Ruscinian stage interval. The large floristic affinities with the pollen zones of the Brunssumian of the Netherlands, entirely included in the Ruscinian stage, and also the pollen affinities with the continental middle-Pliocene western-alpine deposits support the chronostratigraphical assignation of the Aulla deposit to a (probably late) Ruscinian phase.&#x0D; Finally, the pollen record of Aulla represents a particular uniform floristic biozone, which is named here "Macrian" phase, easily distinguished from the contiguous vegetational biozones.&#x0D; The results reported above allow to extend the chronostratigraphic scheme of the paleofloristic evolution in Northern-Central Italy during the Pliocene.

A CONTRIBUTION TO THE HYDROCHEMISTRY AND WATER TYPOLOGY OF THE AMAZON RIVER AND ITS TRIBUTARIES

The geological diversity of the Amazon Basin, as well as the pluvial regime, influences the characteristics of the waters. To know the water types of the rivers of the Amazon basin, 288 superficial water samples were collected, 94 of them along the Amazon River and 194 in their tributaries, from March 2009 to September 2012. The physical, chemical, and physicochemical properties were analyzed. Rivers with pH between 6.5 and 7.6 and electrical conductivity (40.00 - 80.00 μS cm-1) are water bodies that are influenced by the Andean region (e.g., the Amazon River and some of its right bank tributaries). On the other hand, the rivers with pH in the range of 3.5 to 5.5 and conductivity &lt;30.00 μS cm-1, which are Amazon River’s left bank tributaries, reflect the characteristics of the Guiana Shield. The rivers with pH (6.0 to 7.0), low ionic charge, and conductivity &lt;40.0 μS cm-1, such as the lower Amazon River’s right bank tributaries (Tapajos and Xingu) which are influenced by the Central Brazilian Shield, and also the middle/upper Amazon River’s right bank tributaries (Tefé, Coari and Jutaí).

Flow regime aspects in determining environmental flows and maximising energy production at run-of-river hydropower plants

This study investigates the influence of the river flow regime type on the e-flows releases and hydropower production, constrained by eight hydrologically-based e-flows methods. For this purpose, 20 run-of-river hydropower plants up to 10 MW, from five Iberian Peninsula basins, located in regions with pluvial highly fluctuating, pluvial stable, pluvial winter, and pluvio-nival flow regimes were analysed. We integrated a hydropower model with a hydrological model, and eight e-flows methods to estimate mean daily hydropower production, e-flows, and hydrologic alteration. The results demonstrate little influence on hydropower production and e-flows releases for the pluvial regime type, notably, pluvial stable regime river reaches. Pluvio-nival regime provides unstable hydropower production and comparatively high e-flows alteration. Overall, hydrologic parameters represented by five global indices derived from Indicators of Hydrologic Alteration were affected differently for the e-flows releases regime induced by tested e-flows methods. In general, e-flows methods that involve annual minimum flow and indices of flow duration curve show inconsistent results among all study cases and hydrological regimes types; either they result in high e-flows releases while sharply reducing hydropower production or vice versa. However, so-called dynamic approaches demonstrate consistent results and are more suitable, both in terms of hydropower production and e-flows releases by therefore providing 10–35% more energy production while having little impact in several hydrological parameters. The findings of this study may serve as a starting point to initiate a new discussion on the methods and criteria that should be established regarding e-flows determination at run-of-river hydropower plants.

Changes in flood events inferred from centennial length streamflow data records

Abstract This research examines ways that climate change may alter the risk of flooding in cold regions focusing on changes in the flood regimes and changes and shifts in the dominant flood generating processes at 27 natural watersheds across Canada and the northern United States. Changes in flood regimes are examined using data from long term hydrometric reference streamflow gauging stations whose data record spans the past 100 years; stations included are considered to have good quality data and were screened to avoid the influences of regulation, diversions, or land use change. Changes in flood regimes are complex and require different approaches to properly characterize the variety of changes that have occurred and are likely to occur in the future. Peaks over threshold data are used to explore changes to the magnitude, timing, volume and duration of threshold exceedences. Circular statistics are used to explore changes in the nature of the flood regime based on changes in the timing and regularity of flood threshold exceedences. All flood regimes show an increased number of threshold exceeding events. An increased prevalence of rainfall flood responses is observed as flood events occur more often during the rainfall dominated portion of the seasonal cycle resulting in a shift for nival regime stations to a more mixed regime and for mixed regime stations towards a more pluvial regime. The results support viewing hydrologic regime as a continuum from nival to pluvial with several stations shifting towards the pluvial end.