Streamflow trends in Switzerland

Water Resources Research, 2010

1] Daily streamflow from stations close to five Swiss glaciers is analyzed for trends with the Mann-Kendall test. We consider a common period of record and longer periods based on data availability. The trend statistical significance is tested on annual and seasonal bases. We also examine changes in precipitation, temperature, and snow cover characteristics. Highly glacierized basins show statistically significant positive trends in annual streamflow caused by increasing streamflow in spring and summer. Trends are more numerous and stronger at lower and mid than at the upper quantiles. The basin characterized by lower glacier coverage, conversely, does not exhibit consistently statistically significant trends. Changes in precipitation are not sufficient to explain the observed streamflow trends. Air temperature sees an increase in mean, minimum, and maximum values at all sites. Variations in the seasonal snow accumulation and ablation process are evident. Solid precipitation is decreasing at all sites and trends may be due to a shift from snowfall into rainfall. Mean snow depth is also decreasing, and its duration is getting shorter because of a decrease in solid precipitation and enhanced melting. Trend magnitude attenuates with longer time series. Contrasting trends are detected for different subperiods in the last 70 years: statistically significant negative trends are observed in the periods 1944-1974 and 1954-1984 for Aletschgletscher, in contrast with the results for the common period. These trends are explained by different rates of ice volume changes, and the sign of trends is clearly related to phases of positive or negative glacier mass balance.

Water Resources Research, 2008

1] This paper describes regional methods for assessing field significance and regional consistency for trend detection in hydrological extremes. Four procedures for assessing field significance are compared on the basis of Monte Carlo simulations. Then three regional tests, based on a regional variable, on the regional average Mann-Kendall test, and a new semiparametric approach, are tested. The latter was found to be the most adequate to detect consistent changes within homogeneous hydro-climatic regions. Finally, these procedures are applied to France, using daily discharge data arising from 195 gauging stations. No generalized change was found at the national scale on the basis of the field significance assessment of at-site results. Hydro-climatic regions were then defined, and the semiparametric procedure applied. Most of the regions showed no consistent change, but three exceptions were found: in the northeast flood peaks were found to increase, in the Pyrenees high and low flows showed decreasing trends, and in the Alps, earlier snowmelt-related floods were detected, along with less severe drought and increasing runoff due to glacier melting. The trend affecting floods in the northeast was compared to changes in rainfall, using rainfall-runoff simulation. The results showed flood trends consistent with the observed rainfall. Citation: Renard, B., et al. (2008), Regional methods for trend detection: Assessing field significance and regional consistency, Water Resour. Res., 44, W08419,

Umweltwissenschaften und Schadstoff-Forschung, 2009

Zusammenfassung Hintergrund und Ziel Eine Abnahme der Forellenfangerträge in den Schweizer Fliessgewässern um 60 % in den Jahren 1980-2000 war Anlass für eine schweizweite Suche nach den möglichen Ursachen. Im Rahmen des dafür eingerichteten Projekts "Fischnetz" wurden 12 Hypothesen untersucht. Eine davon nimmt an, dass sich die globale Klimaveränderung nachteilig auf die Bachforellen der Schweizer Fliessgewässer auswirkt. Hier wird dargestellt, welche Parameter sich verändert haben und welche Konsequenzen der einheimischen Bachforelle daraus entstehen könnten. Material und Methoden Die vorhandene Literatur wird analysiert und eine Synthese versucht, die die Zusammenhänge zwischen den Faktoren in ihrer Wirkung untereinander und auf den Fisch veranschaulicht. Ergebnisse In den vergangenen 25 Jahren ist die Durchschnittstemperatur in den Fliessgewässern der Schweiz um etwa 1 °C gestiegen. Es gibt Hinweise, dass dieser Temperaturanstieg eine Vorverschiebung des Schlüpfzeitpunktes und eine Habitatverlagerung um 130 Höhenmeter flussaufwärts zur Folge hat. Häufigere Perioden mit Wassertemperaturen über 15 °C während 2-4 Wochen werden vermehrte klinische Ausbrüche der Nierenkrankheit PKD mit sich bringen. Das Niederschlagsmuster änderte sich und resultiert bereits in vermehrten Winterhochwassern und Erosion. Letztere trägt zu einem erhöhten Eintrag von Feinsedimenten bei, die

Regional Environmental Change, 2014

Floods in the northern foreland of the Tatra Mountains considerably contribute to the total flood damage in Poland. Therefore, the question whether the magnitude and frequency of floods have changed in this region is of high interest. This study aims at investigating the inter-decadal variability of magnitude, frequency and seasonality of floods since the mid-twentieth century, to better understand regional changes. The analysis was accomplished in a multi-temporal approach whereby trends are fitted to every possible combination of start and end years in a record. Detected trends were explained by estimating correlations between the investigated flood parameters and different large-scale climate indices for the northern hemisphere, and by trends found in intense precipitation indices, number of days with snow cover, cyclonic circulation types, temperature and moisture conditions. Catchment and channel changes that occurred in the region over the past decades were also considered. Results show that rivers in the area exhibit considerable inter-decadal variability of flows. The magnitude and direction of short-term trends are heavily influenced by this inter-decadal variability; however, certain patterns are apparent. More extreme, although perhaps less frequent floods are now likely to occur, with a shift in the seasonality, decreasing flood magnitudes in winter and increasing during autumn and spring. The identification of the factors contributing to the occurrence of flood events and their potential changes is valuable to enhance the flood management in the region and to improve the resilience of the population in this mountainous area.

Hydrological Processes, 2014

While many studies have been conducted in mountainous catchments to examine the impact of climate change on hydrology, the interactions between climate changes and land use components have largely unknown impacts on hydrology in alpine regions. They need to be given special attention in order to devise possible strategies concerning general development in these regions. Thus, the main aim was to examine the impact of land use and climate changes on hydrology by model simulations. For this purpose, the physically based WaSiM-ETH model was applied to the catchment of Ursern Valley in the central Alps (191 km2) over the period of 1983-2005. Modelling results showed that the reduction of the mean monthly discharge during the summer period is due primarily to the retreat of snow discharge in time and secondarily to the reduction in the glacier surface area together with its retreat in time, rather than the increase in the evapotranspiration due to the expansion of the green alder on the expense of grassland. The significant decrease in summer discharge during July, August, and September shows a change in the regime from b-glacio-nival to nivo-glacial. These changes are confirmed by the modeling results that attest to a temporal shift in snowmelt and glacier discharge towards earlier in the year: March, April and May for snowmelt and May and June for glacier discharge. It is expected that the change in the yearly total discharge due to the land use changes will be reduced by 0.6 % in the near future whereas, it will be reduced by about 5% if climate change is also taken into account.

Theoretical and Applied Climatology, 2014

Studying the long-term changes of streamflow is an important tool for enhancing water resource and river system planning, design, and management. The aim of this work is to identify the long-term variations in annual streamflow regime over a 50-year period from 1961 to 2010 in the Selangor River, which is one of the main tropical rivers in Malaysia. Initially, the data underwent preliminary independence, normality, and homogeneity testing using the Pearson correlation coefficient and Shapiro-Wilk and Pettitt's tests, respectively. The work includes a study and analysis of the changes through nine variables describing the annual streamflow and variations in the yearly duration of high and low streamflows. The analyses were conducted via two time scales: yearly and sub-periodic. The sub-periods were obtained by segmenting the 50 years into seven sub-periods by two techniques, namely the change-point test and direct method. Even though analysis revealed nearly negligible changes in mean annual flow over the study period, the maximum annual flow generally increased while the minimum annual flow significantly decreased with respect to time. It was also observed that the variables describing the dispersion in streamflow continually increased with respect to time. An obvious increase was detected in the yearly duration of danger level of streamflow, a slight increase was noted in the yearly duration of warning and alert levels, and a slight decrease in the yearly duration of low streamflow was found. The perceived changes validate the existence of long-term changes in annual streamflow regime, which increase the probability of floods and droughts occurring in future. In light of the results, attention should be drawn to developing water resource management and flood protection plans in order to avert the harmful effects potentially resulting from the expected changes in annual streamflow regime.

Hydrological Sciences Journal, 2009

The main objective of this study is to compare the seasonality of selected precipitation and runoff characteristics in Austria and Slovakia. Monthly seasonality indices are analysed to interpret the long-term climatic behaviour, while the seasonality of extremes is analysed to understand flood occurrence. The analysis is based on mean monthly precipitation data at 555 (Austria) and 202 (Slovakia) stations, annual maximum daily precipitation at 520 (Austria) and 56 (Slovakia) stations, and mean monthly runoff and annual maximum floods at 258 (Austria) and 85 (Slovakia) gauging stations. The results suggest that the seasonality of the selected hydrological characteristics is an important indicator of flood processes, but varies considerably in space. The seasonality of extreme flood events and, hence flood processes, tends to change with the flood magnitude. This change is more pronounced in the lowland and hilly regions than it is in the mountains. Both in Austria and Slovakia, decades of flood seasonality exist.

Water

This study performs a simultaneous evaluation of gradual and abrupt changes in Australian annual maximum (AM) flood data using a modified Mann–Kendall and Pettitt change-point detection test. The results show that AM flood data in eastern Australia is dominated by downward trends. Depending on the significance level and study period under consideration, about 8% to 33% of stations are characterised by significant trends, where over 85% of detected significant trends are downward. Furthermore, the change-point analysis shows that the percentages of stations experiencing one abrupt change in the mean or in the direction of the trend are in the range of 8% to 33%, of which over 50% occurred in 1991, with a mode in 1995. Prominent resemblance between the monotonic trend and change-point analysis results is also noticed, in which a negative shift in the mean is observed at catchments that exhibited downward trends, and a positive shift in the mean is observed in the case of upward trends...

Water

The source region of the Indus River (SRIR), which is located in the Hindukush, Karakoram and Himalayan (HKH) mountainous range and on the Third Pole (TP), is very sensitive to climate change, especially precipitation changes, because of its multifarious orography and fragile ecosystem. Climate changes in the SRIR also have important impacts on social and economic development, as well as on the ecosystems of the downstream irrigation areas in Pakistan. This paper investigates the changes in precipitation characteristics by dividing the daily precipitation rate into different classes, such as light (0–10 mm), moderate (10.1–25 mm) and heavy precipitation (>25 mm). Daily precipitation data from gauging and non-gauging stations from 1961–2015 are used. The results of the analysis of the annual precipitation and rainy day trends show significant (p < 0.05) increases and decreases, respectively, while light and heavy precipitation show significant decreasing and increasing trends, ...

Environmental Geochemistry and Health

In the context of global climate change, understanding the relationships between climate and groundwater is increasingly important. This study in the NW Alps represents the first regional-scale investigation of the groundwater feature variation in mountain aquifers due to climate variability. The analysis of groundwater temperature and discharge in 28 natural mineral water springs and meteorological parameters (rainfall and air temperature) permitted us to evaluate the annual behaviour and possible trends of these parameters during the period from 2001 to 2018. The air temperature showed a positive trend almost everywhere, with a rise of up to 0.03 °C/year. In contrast, only ten springs showed a positive trend for groundwater temperature, but with the smallest rates of increase. Moreover, despite the substantial stability of the rainfall amount, 50% of the analysed springs showed a trend (29 and 21% for positive and negative trends, respectively) with low discharge variations. Final...

Hydrological Processes, 2011

One of the most significant consequences of climate warming is the likely change in streamflow as a result of warming air temperatures. Hydrologists have responded to the challenge of understanding these effects. Many recent studies quantify historical trends in streamflow and usually attribute these trends to climate warming, via altered evapotranspiration and snowpack (Figure 1.a). However, without questioning the fundamental reality of a warming climate, hydrologists should also consider biotic and social processes whose omission may produce misleading interpretations about climate change effects on hydrology. The aim of this commentary is to raise awareness of ecological and social processes that may confound the interpretation of climate effects on hydrology, to review how the geographic context of streamflow records affects interpretation of the climate signal, and to suggest a 'checklist' of working hypotheses that can be used to structure studies of streamflow responses to climate change. A wide variety of trends in streamflow have been detected and attributed to climate change and variability, but a few themes dominate the literature. The most common studies report earlier snowmelt, a shift to earlier streamflow timing, altered spring maximum flows, and/or intensified summer drought (

Hydrological Processes

Fluvial flood events have substantial impacts on humans, both socially and economically, as well as on ecosystems (e.g., hydroecology and pollutant transport). Concurrent with climate change, the seasonality of flooding in cold environments is expected to shift from a snowmelt-dominated to a rainfall-dominated flow regime. This would have profound impacts on water management strategies, that is, flood risk mitigation, drinking water supply, and hydro power. In addition, cold climate hydrological systems exhibit complex interactions with catchment properties and largescale climate fluctuations making the manifestation of changes difficult to detect and predict. Understanding a possible change in flood seasonality and defining related key drivers therefore is essential to mitigate risk and to keep management strategies viable under a changing climate. This study explores changes in flood seasonality across near-natural catchments in Scandinavia using circular statistics and trend tests. Results indicate strong seasonality in flooding for snowmelt-dominated catchments with a single peak occurring in spring and early summer (March through June), whereas flood peaks are more equally distributed throughout the year for catchments located close to the Atlantic coast and in the south of the study area. Flood seasonality has changed over the past century seen as decreasing trends in summer maximum daily flows and increasing winter and spring maximum daily flows with 5-35% of the catchments showing significant changes at the 5% significance level. Seasonal mean daily flows corroborate those findings with higher percentages (5-60%) of the catchments showing statistically significant changes. Alterations in annual flood occurrence also point towards a shift in flow regime from snowmelt-dominated to rainfall-dominated with consistent changes towards earlier timing of the flood peak (significant for 25% of the catchments). Regionally consistent patterns suggest a first-order climate control as well as a local second-order catchment control, which causes inter-seasonal variability in the streamflow response.

Climate, 2021

This study investigated the trends and variability of seasonal and annual rainfall and temperature data over southern Ethiopia using time series analysis for the period 1983–2016. Standard Anomaly Index (SAI), Coefficient of Variation (CV), Precipitations Concentration Index (PCI), and Standard Precipitation Index (SPI) were used to examine rainfall variability and develop drought indices over southern Ethiopia. Temporal changes of rainfall trends over the study period were detected using Mann Kendall (MK) trend test and Sen’s slope estimator. The results showed that the region experienced considerable rainfall variability and change that resulted in extended periods of drought and flood events within the study period. Results from SAI and SPI indicated an inter-annual rainfall variability with the proportions of years with below and above normal rainfall being estimated at 56% and 44% respectively. Results from the Mann Kendall trend test indicated an increasing trend of annual rai...

Regional Environmental Change

Planning for the future requires a detailed understanding of how climate change affects a wide range of systems at spatial scales that are relevant to humans. Understanding of climate change impacts can be gained from observational and reconstruction approaches and from numerical models that apply existing knowledge to climate change scenarios. Although modeling approaches are prominent in climate change assessments, observations and reconstructions provide insights that cannot be derived from simulations alone, especially at local to regional scales where climate adaptation policies are implemented. Here, we review the wealth of understanding that emerged from observations and reconstructions of ongoing and past climate change impacts in Switzerland, with wider applicability in Europe. We draw examples from hydrological, alpine, forest, and agricultural systems, which are of paramount societal importance, and are projected to undergo important changes by the end of this century. For each system, we review existing model-based projections, present what is known from observations, and discuss how empirical evidence may help improve future

Remote Sensing

In the Alps, understanding how climate change is affecting evapotranspiration (ET) is relevant due to possible implications on water availability for large lowland areas of Europe. Here, changes in ET were studied based on 20 years of MODIS data. MOD16 and operational Simplified Surface Energy Balance (SSEBop) products were compared with eddy-covariance data and analyzed for trend detection. The two products showed a similar relationship with ground observations, with RMSE between 0.69 and 2 mm day−1, and a correlation coefficient between 0.6 and 0.83. A regression with the potential drivers of ET showed that, for climate variables, ground data were coherent with MOD16 at grassland sites, where r2 was 0.12 for potential ET, 0.17 for precipitation, and 0.57 for air temperature, whereas ground data agreed with SSEBop at forest sites, with an r2 of 0.46 for precipitation, no correlation with temperature, and negative correlation with potential ET. Interestingly, ground-based correlatio...

Hydrological Processes, 2013

Rainfall is the key climatic variable that governs the regional hydrologic cycle and availability of water resources. Recent studies have analyzed the changes in rainfall patterns at global as well as regional scales in Australia. Recent studies have also suggested that any analysis of hydro-climatic variables should be done at the local scale rather than at a large or global scale because the trends and their impacts may be different from one location to the other. Since, no studies were found specific to the Yarra River catchment, which is an important catchment in Victoria (Australia), this study performs a spatio-temporal trend analysis on long-term rainfall records at 15 measuring stations within the catchment. The Mann-Kendall test was used to detect trends and Sen"s slope estimator was used to calculate the slopes in both monthly and annual rainfall. Moreover, cumulative summation technique was used to identify the trend beginning year and pre-whitening criteria were tested to check for autocorrelation in the data. The results showed that the monthly rainfall has generally decreasing trends except in January and June. Significant decreasing rainfall trends were observed in May (amongst the autumn months of March, April and May) at majority of the stations and also in some other months at several stations. Decreasing trend was also observed in the annual rainfall at all stations. This study indicates that there has been a consistent reduction in rainfall over the catchment, both spatially and temporally over the past 50 years, which will have important implications for future management of water resources.

Theoretical and Applied Climatology, 2015

The study of precipitation trends is critically important for a country like India whose food security and economy are dependent on the timely availability of water such as 83 % water used for agriculture sector, 12 % for industry sector and only 5 % for domestic sector. In this study, the historical rainfall data for the periods 1901-2002 and 1942-2002 of the Sindh river basin, India, were analysed for monthly, seasonal and annual trends. The conventional Mann-Kendall test (MK) and Mann-Kendall test (MMK), after the removal of the effect of all significant autocorrelation coefficients, and Sen's slope estimator were used to identify the trends. Kriging technique was used for interpolating the spatial pattern using Arc GIS 9.3. The analysis suggested significant increase in the trend of rainfall for seasonal and annual series in the Sindh basin during 1901-2002.

Climatic Change, 2011

Climate change has affected the temperature and rainfall characteristics worldwide. However, the changes are not equal for all regions and have localized intensity and must be quantified locally to manage the natural resources. Orissa is an eastern state in India where agricultural activities mainly depends on the rainfall and thus face problems due to changing patterns of rainfall due to changing climate. In the present study, attempts were made to study temporal variation in monthly, seasonal and annual rainfall over the state during the period from 1871 to 2006. Long term changes in rainfall characteristics were determined by both parametric and non-parametric tests. The analysis revealed a long term insignificant decline trend of annual as well as monsoon rainfall, where as increasing trend in post-monsoon season over the state of Orissa. Rainfall during winter and summer seasons showed an increasing trend. Statistically monsoon rainfall can be considered as very dependable as the coefficient of variation is 14.2%. However, there is decreasing monthly rainfall trend in June, July and September, where as increasing trend in August. This trend is more predominant in last 10 year. Based on departure from mean, rainfall analysis also showed an increased number of dry years compared to wet years after 1950. This changing rainfall trend during monsoon months is major concern for the rain-fed agriculture. More over, this will affect hydro power generation and reservoir operation in the region.

Stochastic Environmental Research and Risk Assessment, 2013

The objectives of this study are to investigate the changes of runoff and sediment load and their potential influencing factors in the Huangfuchuan catchment. The Mann-Kendall test and accumulative anomaly methods were, respectively, applied to examine the changing trends and abrupt changes. Both annual runoff and sediment load demonstrated significant reduction (< 0.05) with decreasing rates of −3.2 × 10 6 m 3 /a and −1.09 Mt/a, respectively. The abrupt changes were detected in 1979 and 1996 for the runoff and sediment load. All the runoff and sediment indices (runoff, sediment load, runoff coefficient, and sediment concentration) exhibited remarkable reduction (< 0.01). The climate variability contributed 24.4% and 25.1% during 1980-1996 and 1997-2010 to annual runoff decrease, respectively, and human activities accounted for the remaining 75.6% and 74.9%. In contrast, changes in precipitation accounted for 43.5% and 20.2% of sediment load reduction during 1980-1996 and 1997-2010, whereas the human activities contributed 56.5% and 79.8%, respectively. The relative contributions from climate variability and human activities to runoff and sediment load changes at annual scale were different from that at flood season scale. Results suggested the dominant role of soil and water conservations in the variation of runoff and sediment load in the catchment.

Advances in Meteorology

Understanding hydroclimatic variability and trend for the past four decades in the Upper Tekeze River basin is significant for future sustainable water resource management as it indicates regime shifts in hydrology. Despite its importance for improved and sustainable water allocation for water supply-demand and food security, varying patterns of streamflow and their association with climate change are not well understood in the basin. The main objective of this study was to characterize, quantify, and validate the variability and trends of hydroclimatic variables in the Upper Tekeze River basin at Ghba subbasin using graphical and statistical methods for homogeneous stations for the time period from 1953 to 2017, not uniform at all stations. The rainfall, temperature, and streamflow trends and their relationships were evaluated using the regression method, Mann–Kendall (MK) test, Spearman’s rho (SR) test, Sen’s slope, and correlation analysis. The analysis focused on rainfall, tempe...

Hydrology, 2016

The study focused on investigating the presence of change patterns in 600 unimpaired streamflow stations across the continental U.S. at different time intervals to understand the change patterns that can provide significant insight regarding climate variability and change. Each station had continuous streamflow data of at least 30 years (the entire dataset covered a range of 109 years). Presence of trends and shifts were detected in water year and the four seasons (fall, winter, spring, and summer) analyzing the water year and seasonal mean flows. Two non-parametric tests, namely, the Mann-Kendall test and the Pettitt's test were used to identify the trends and the shifts, respectively. The results showed an increasing trend in the northeast and upper-mid regions, whereas southeast and northwest regions underwent a decrease. Shifts followed similar patterns as trends with higher number of stations with significant change. Fall and spring showed the highest number of stations with increasing and decreasing change, respectively, in the seasonal analyses. Results of this study may assist water managers to understand the streamflow change patterns across the continental U.S., especially at the regional scale since this study covers a long range of years with a large number of stations in each region.

Water, 2022

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 wat...

Stochastic Environmental Research and Risk Assessment, 2020

The 100 year discharge series of the Caposele karst spring in southern Italy enables insight into variations in water resource availability under climate change, given the length of the series, the systematic quality of the records and the absence of human-made alteration of the natural conditions of the aquifer. With this scope, frequency and trend analyses of hydrometeorological variables were conducted. Various three-parameter probability distribution functions were fitted to the data to calculate the Standardized Discharge Index, which describes spring discharge variations in a standardized manner. Common goodness-of-fit tests were applied to evaluate the performance of each distribution. In addition, a new criterion based on the frequency of events exceeding specific extreme Z values is proposed to quantify the deviation of the calculated index from the theoretical Standard Normal Distribution. The Weibull distribution was found to be best for calculating standardized series of spring discharge as it fits the extreme values of both tails well. The relationship between spring discharge and climatic variables was investigated by using least square linear regression, Mann-Kendall and Sen's slope trend detection tests, applied to the entire series and to 30-year moving time series. A statistically significant decrease of spring discharge of-0.0045 m 3 s-1 /year has occurred over the last 100 years, whereas no statistically significant trends were found in annual or seasonal precipitation series. However, temperature has constantly been above the mean during the past two decades. An analysis of trends in the moving time series of all variables suggests a connection between the observed spring discharge decay and temperature increase, which can be considered common to other areas of centralsouthern Italy.

Encyclopedia of Earth Sciences Series, 2011

Synonyms Brininess; Salinity; Salt; Saltiness Definition Concentration of dissolved salts found in a sample of water. It is measured as the total amount of dissolved salts in parts per 1,000. Seawater has an average salinity of about 35 parts/1,000. Nearly all water contains dissolved chemicals, even rainwater. These dissolved chemicals are called salts. The salinity of normal ocean water is about 35 parts per 1,000, total dissolved solids. This is written as 35% or 35 ppth. A salinity of 35% is the same as 3.5%. The symbol resembles a percentage sign (%), but percent means per 100. But the symbol with two zeros on the bottom of the fraction (%) means per 1,000. Salinity varies slightly from place to place around the world, and also varies somewhat with the seasons (affected by temperature and precipitation). The salinity of seawater ranges from about 30% to 40%. Warm temperatures and high evaporation rates (particularly in shallow seas) raise the salinity. Warmer waters will tend to have higher salinity than cooler waters. Water of salinity between freshwater and seawater is called brackish. Brackish water can be found in estuaries. Water with salinity greater than normal seawater is called hypersaline. For example, the Great Salt Lake, Utah, and the Dead Sea are hypersaline. Hypersaline lakes tend to occur in arid areas. They are landlocked basins with no outlet for the waters to flow from the lake. The salts are concentrated as a result of evaporation. Evaporation is so extreme in some lakes (ephemeral lakes or playa lakes) that they dry up completely every few years, leaving a saltpan. Freshwater input (rivers, precipitation, or melting ice) lowers the salinity. In polar areas where glaciers and ice caps are melting, the seawater has lower salinity.

Hydrology, 2016

Several trend studies have shown that hydrological conditions are changing considerably in the Alpine region. However, the reasons for these changes are only partially understood and trend analyses alone are not able to shed much light. Hydrological modelling is one possible way to identify the trend drivers, i.e., to attribute the detected streamflow trends, given that the model captures all important processes causing the trends. We modelled the hydrological conditions for two alpine catchments in western Austria (a large, mostly lower-altitude catchment with wide valley plains and a nested high-altitude, glaciated headwater catchment) with the distributed, physically-oriented WaSiM-ETH model, which includes a dynamical glacier module. The model was calibrated in a transient mode, i.e., not only on several standard goodness measures and glacier extents, but also in such a way that the simulated streamflow trends fit with the observed ones during the investigation period 1980 to 2007. With this approach, it was possible to separate streamflow components, identify the trends of flow components, and study their relation to trends in atmospheric variables. In addition to trends in annual averages, highly resolved trends for each Julian day were derived, since they proved powerful in an earlier, data-based attribution study. We were able to show that annual and highly resolved trends can be modelled sufficiently well. The results provide a holistic, year-round picture of the drivers of alpine streamflow changes: Higher-altitude catchments are strongly affected by earlier firn melt and snowmelt in spring and increased ice melt throughout the ablation season. Changes in lower-altitude areas are mostly caused by earlier and lower snowmelt volumes. All highly resolved trends in streamflow and its components show an explicit similarity to the local temperature trends. Finally, results indicate that evapotranspiration has been increasing in the lower altitudes during the study period.

Computational Urban Science

Bhubaneswar is the first designed ‘smart city’ in India and has experienced rapid urbanization since 2000. The question undertaken in this study is to assess if there is a change in the rainfall over this rapidly urbanizing region, and if so, what are the characteristics of the change? The broader intent is to understand if the change in urbanization and rainfall are interlinked? The India Meteorological Department (hourly station and daily gridded) and Tropical Rainfall Measurement Mission (3-hourly) datasets are analyzed for the 1980–2018 period (39 years) for different seasons separately. Wavelet and trend analysis reveal that precipitation intensity has increased over the study period. The assessments of the hourly rainfall data show an interesting feature. There is a decrease in the midnight to early-morning rain, with a corresponding increase in the late-afternoon to midnight rainfall. The increase in the rainfall is preferentially downwind and on the east side of the city. A ...

Water

In southern Europe, climate change is expected to aggravate water scarcity conditions and challenge current water management practices. The present paper evaluates the impacts of climate change in the highly regulated Tagus River basin and assesses various adaptation options, quantifying the effort needed to maintain the ability to sustain current water uses. A water management and allocation model covering surface and groundwater resources is used to evaluate available and renewable water resources for different climate scenarios. Additionally, the Water Exploitation Index Plus (WEI+) and water supply reliability criteria are used to quantify water scarcity and the ability to satisfy water demands, respectively. The results show that climate change will significantly change the stream flow regime and reduce water availability in the Tagus River basin, but the existing reservoir infrastructure will alleviate some of these impacts, especially in the dry half-year. Until the end of th...

The two major factors influencing river flow change in basins are anthropogenic activities and climate change (AACC), and separating the attribution of each can be crucial for managing water resources as well as economic, political, and social activities. In this study, a hydrologic model simulation was used to separate AACC attributions to river flow change in the southwest of Iran&#39;s Karkheh basin. The trend of annual potential evapotranspiration, precipitation, river flow, and air temperature was determined by the Mann-Kendall (MK) test. Multivariate dependence analysis was performed for precipitation changes, river flow changes, attributions of AACC to river flow change by different copula functions. The finding showed that the point of change in the annual river flow series by the double cumulative curve (DCC) and Pettitt test occurred in 1999. Thus, the pre-and post-change periods are before and after 1999, respectively. When compared to the pre-change period, the average a...

Water Resources Research, 2018

Recent climatic warming and associated glacial retreat may have a large impact on sediment release and transfer in Alpine river basins. Concurrently, the sediment transport capacity of many European Alpine streams is affected by hydropower exploitation, notably where flow is abstracted but the sediment supply downstream is maintained. Here, we investigate the combined effects of climate change and flow abstraction on morphodynamics and sediment transfer in the Borgne River, Switzerland. From photogrammetrically derived historical Digital Elevation Models (DEMs), we find considerable net aggradation of the braided river bed (up to 5 m) since the onset of flow abstraction in 1963. Reaches responded through bed level steepening which was strongest in the upper most reach. Widespread aggradation however did not commence until the onset of glacier retreat in the late 1980s and the dry and warm years of the early 1990s. Upstream flow intake data shows that this aggradation coincided with an increase in sediment supply, although aggradation accounts for no more than 25% of supplied material. The remainder was transferred through the studied reaches. Estimations of bed load transport capacity indicate that flow abstraction reduces transport capacity by 1-2 orders of magnitude. While residual transport rates vary with morphological evolution, they are in the same order of magnitude as the sediment supply rates, which is why significant transport remains. However, the reduction in transport capacity makes the system more sensitive to short-term (annual) changes in climate-driven hydrological variability and climate-induced changes in intake management and sediment delivery rates.

World Environmental and Water Resources Congress 2017, 2017

The trend and shift in the seasonal temperature, precipitation and streamflow time series across the Midwest have been analyzed, for the period 1960-2013, using the statistical analyses (Mann-Kendall test with and without considering short term persistence (MK2 and MK1, respectively) and Pettitt test). The paper also utilizes a relatively new approach, wavelet analysis, for testing the existence of trend and shift in the time series. The method has the ability to decompose a time series in to lower (trend) and higher frequency components (noise). Discrete wavelet transform (DWT) has been employed in the present study with an aim to find which periodicities are mainly responsible for trend in the original data. The combination of MK1, MK2 and DWT along with Pettitt test hasn't been extensively used up to this time, especially in detecting trend and shift in the Midwest. The analysis of climate division temperature and precipitation data and USGS naturalized streamflow data revealed the presence of periodicity in the time series data. All the incorporated time series data were seasonal to analyze the trends and shifts for four seasons-winter, spring, summer and fall independently. D3 component of DWT were observed to be influential in detecting real trend in Temperature, precipitation and streamflow data, however unlike temperature, precipitation and streamflow showed decreasing trend as well. Shift was relatively observed more than trend in the region with dominance of D3 component in the data. The result indicate the significant warming trend which agrees with the "increasing temperature" observations in the past two decades, however a clear explanation for precipitation and streamflow is not obvious.

Hydrology

Rainfall is one of the dominating climatic parameters that affect water availability. Trend analysis is of paramount significance to understand the behavior of hydrological and climatic variables over a long timescale. The main aim of the present study was to identify trends and analyze existing linkages between rainfall and streamflow in the Nilwala River Basin (NRB) of Southern Sri Lanka. An investigation of the trends, detection of change points and streamflow alteration, and linkage between rainfall and streamflow were carried out using the Mann–Kendall test, Sen’s slope test, Pettitt’s test, indicators of hydrological alteration (IHA), and Pearson’s correlation test. Selected rainfall-related extreme climatic indices, namely, CDD, CWD, PRCPTOT, R25, and Rx5, were calculated using the RClimdex software. Trend analysis of rainfall data and extreme rainfall indices demonstrated few statistically significant trends at the monthly, seasonal, and annual scales, while streamflow data ...

Water Resources Research, 2015

Many watershed models used within the hydrologic research community assume (by default) stationary conditions, that is, the key watershed properties that control water flow are considered to be time invariant. This assumption is rather convenient and pragmatic and opens up the wide arsenal of (multivariate) statistical and nonlinear optimization methods for inference of the (temporally fixed) model parameters. Several contributions to the hydrologic literature have brought into question the continued usefulness of this stationary paradigm for hydrologic modeling. This paper builds on the likelihood-free diagnostics approach of Vrugt and Sadegh (2013) and uses a diverse set of hydrologic summary metrics to test the stationary hypothesis and detect changes in the watersheds response to hydroclimatic forcing. Models with fixed parameter values cannot simulate adequately temporal variations in the summary statistics of the observed catchment data, and consequently, the DREAM (ABC) algorithm cannot find solutions that sufficiently honor the observed metrics. We demonstrate that the presented methodology is able to differentiate successfully between watersheds that are classified as stationary and those that have undergone significant changes in land use, urbanization, and/or hydroclimatic conditions, and thus are deemed nonstationary.