Annual Runoff Distribution Research Articles

The changes in the annual distribution of mountain runoff during the period of 1965–2018 in Hexi Corridor, Northwest China

The annual distribution characteristics of river runoff in arid regions have significant implications for water resource stability and management. Based on the mountain runoff data from 1965 to 2018, this study examines the annual change characteristics of monthly runoff of the Shiyang River Basin, Heihe River Basin, and Shule River Basin in the Hexi Corridor, Northwest China. Many indexes are used and analyzed, including the coefficient of variance, the complete regulation coefficient, the concentration degree and concentration period, the magnitude of change, the skewness coefficient, and the kurtosis coefficient of the annual distribution curves. The results reveal the following: (1) The inhomogeneity of annual runoff distribution in the Taolai River and the rivers to the west of it, except the Shiyou River, show an increasing trend. Conversely, the inhomogeneity of the rivers to the east of the Taolai River generally show a downward trend, but the coefficient of variance value is still very high. (2) In the Shiyang River Basin, the annual distribution of the concentration period is characterized by a relatively discrete pattern. Conversely, the Heihe River Basin exhibits a relatively concentrated pattern, and the distribution pattern of the Shule River Basin is quite different. Notably, all concentration periods in the three basins have shifted backward after the 2000s. (3) The Shiyang River Basin exhibits disordered annual distribution curves of runoff in different years. In contrast, the Heihe River Basin presents a typical ‘single-peak’ pattern with a prominent right-skewed. The Shule River Basin has regular distribution curves, with a gradually significant ‘double-peak’ pattern from east to west. Overall, there has been a slight change in runoff in the Shiyang River Basin, while the Heihe River Basin and Shule River Basin have experienced significant increases in runoff. The annual distribution curves of runoff in the Liyuan River and the rivers to the east of it exhibit a gentle peak pattern, and the appearance probability of extreme runoff during the year is low. Conversely, the rivers to the west of the Liyuan River, excluding the Danghe River, display a sharp peak and thick tail pattern, indicating that the appearance probability of extreme runoff during the year is high. These findings have practical implications for the planning and management of water resources in the Hexi Corridor. Moreover, they provide a solid foundation for predicting future changes in regional water resources.

Climate-Driven Dynamics of Runoff in the Dayekou Basin: A Comprehensive Analysis of Temperature, Precipitation, and Anthropogenic Influences over a 25-Year Period

Understanding runoff dynamics is vital for effective water management in climate-affected areas. This study focuses on the Dayekou basin in China’s Qilian Mountains, known for their high climate variability. Using 25 years of data (1994–2018) on river runoff, precipitation, and temperature, statistical methods were applied to explore the annual variations and climate change impacts on these parameters. Results reveal a significant variability in the river runoff (132.27 to 225.03 mm), precipitation (340.19 to 433.29 mm), and average temperature (1.38 to 2.08 °C) over the period. Decadal rising rates average 17 mm for runoff, 17 mm for precipitation, and 0.25 °C for temperature, with the peak precipitation and runoff occurring in 1998–2000, 2008, and 2016. The annual runoff distribution also exhibited a unimodal pattern, peaking at 39.68 mm in July. The cumulative runoff during low periods constituted only 13.84% of the annual total, concentrated in the second half of the year, particularly during the June-October flood season. The correlation analysis underscored a strong relationship between river runoff and precipitation (correlation coefficient > 0.80), while the temperature correlation was weaker (correlation coefficient < 0.80). This 25-year analysis provides valuable insights into runoff variation, elucidating the interconnected effects of temperature and precipitation in the Dayekou basin, with substantial implications for sustainable development amid climate challenges.

Historical and projected future runoff over the Mekong River basin

Abstract. The Mekong River (MR) crosses the borders and connects six countries, including China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. It provides critical water resources and supports natural and agricultural ecosystems, socioeconomic development, and the livelihoods of the people living in this region. Understanding changes in the runoff of this important international river under projected climate change is critical for water resource management and climate change adaptation planning. However, research on long-term runoff dynamics for the MR and the underlying drivers of runoff variability remains scarce. Here, we analyse historical runoff variations from 1971 to 2020 based on runoff gauge data collected from eight hydrological stations along the MR. With these runoff data, we then evaluate the runoff simulation performance of five global hydrological models (GHMs) forced by four global climate models (GCMs) under the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP). Furthermore, based on the best simulation combination, we quantify the impact of future climate change on river runoff changes in the MR. The result shows that the annual runoff in the MR has not changed significantly in the past 5 decades, while the establishment of dams and reservoirs in the basin visibly affected the annual runoff distribution. The ensemble-averaged result of the Water Global Assessment and Prognosis version 2 (WaterGAP2; i.e. GHM) forced by four GCMs has the best runoff simulation performance. Under Representative Concentration Pathways (RCPs; i.e. RCP2.6, RCP6.0 and RCP8.5), the runoff of the MR is projected to increase significantly (p<0.05); e.g. 3.81 ± 3.47 m3s-1a-1 (9 ± 8 % increase in 100 years) at the upper reach under RCP2.6 and 16.36 ± 12.44 m3s-1a-1 (13 ± 10 % increase in 100 years) at the lower reach under RCP6.0. In particular, under the RCP6.0 scenario, the increase in annual runoff is most pronounced in the middle and lower reaches, due to increased precipitation and snowmelt. Under the RCP8.5 scenario, the runoff distribution in different seasons varies obviously, increasing the risk of flooding in the wet season and drought in the dry season.

Historical and future runoff changes and their impacts on stormflow characteristics in the upper Yangtze River basin, China

Identifying the contributions of climate- and human-induced impacts on runoff change have aroused broad attention globally in the hydrological cycles and water resource management. However, a systematic quantitative assessment of the impact of climate changes and human activities on historical and future runoff changes in the upper Yangtze River (UYR) and the effects of runoff variation on stormflow characteristics (e.g., annual runoff distribution) remain unclear. Here, we quantified runoff variations and simulated runoff in the UYR using the Soil and Water Assessment Tool (SWAT) hydrologic model and statistical methods. Our main findings include: (1) climate variability played a dominant role in runoff decline in the UYR from 1972 to 2016 (Slope: –0.10 mm/a, P–value < 0.05), accounting for 43.34 % of the total decrease, while anthropogenic activities accounted for 4.82 %; (2) runoff in the upcoming period of 2020–2059 under RCP 2.6, RCP 4.5, and RCP 8.5 will increase significantly (P–value < 0.05) at a rate of 0.14 mm, 0.13 mm, and 0.27 mm per year, respectively; (3) water yield and hydrological drought are all projected to decrease in the entire UYR, but flood frequency will increase under the 1.5 ℃ and 2.0 ℃ global warming. This study provides a new perspective for understanding the status of water resources in the UYR and offers great implications for flood control and effective water resources management over the UYR in the future.

Quantitative Analysis of the Influence of the Xiaolangdi Reservoir on Water and Sediment in the Middle and Lower Reaches of the Yellow River

The Xiaolangdi Reservoir is the second largest water conservancy project in China and the last comprehensive water conservancy hub on the mainstream of the Yellow River, playing a vital role in the middle and lower reaches of the Yellow River. To study the effects of the construction of the Xiaolangdi Reservoir (1997-2001) on the runoff and sediment transport in the middle and lower reaches of the Yellow River, runoff and sediment transport data from 1963 to 2021 were based on the hydrological stations of Huayuankou, Gaocun, and Lijin. The unevenness coefficient, cumulative distance level method, Mann-Kendall test method, and wavelet transform method were used to analyze the runoff and sediment transport in the middle and lower reaches of the Yellow River at different time scales. The results of the study reveal that the completion of the Xiaolangdi Reservoir in the interannual range has little impact on the runoff in the middle and lower reaches of the Yellow River and a significant impact on sediment transport. The interannual runoff volumes of Huayuankou station, Gaocun station, and Lijin station were reduced by 20.1%, 20.39%, and 32.87%, respectively. In addition, the sediment transport volumes decreased by 90.03%, 85.34%, and 83.88%, respectively. It has a great influence on the monthly distribution of annual runoff. The annual runoff distribution is more uniform, increasing the runoff in the dry season, reducing the runoff in the wet season, and bringing forward the peak flow. The runoff and Sediment transport have obvious periodicity. After the operation of the Xiaolangdi Reservoir, the main cycle of runoff increases and the second main cycle disappears. The main cycle of Sediment transport did not change obviously, but the closer it was to the estuary, the less obvious the cycle was. The research results can provide a reference for ecological protection and high-quality development in the middle and lower reaches of the Yellow River.

СУЧАСНА ТРАНСФОРМАЦІЯ СЕЗОННОГО РОЗПОДІЛУ СТОКУ ВОДИ РІЧОК БАСЕЙНУ СІВЕРСЬКОГО ДІНЦЯ

The annual runoff distribution of the Siverskyi Donets River Basin in the period of modern climate change was estimated. The annual runoff distribution of the Siverskyi Donets Basin was researched for two characteristic periods (from the beginning of observations to 1988 and from 1989 to 2018). The assessment was performed for three water year types: wet year, average year and dry year. The research was performed for three groups of rivers depending on their affiliation to a particular part of the Basin. During the research, the average monthly runoff of the hydrological gauges, which we selected for the study were averaged. The annual runoff distribution was leveled in the current period. The Siverskyi Donets Basin is characterized by the peculiar physico-geographical conditions, so the annual runoff distribution is somewhat different for different part of the Basin. Differences in the annual runoff distribution of the right-bank tributaries, the left-bank tributaries and the Siverskyi Donets River were revealed. For the left-bank tributaries, which are less affected by anthropogenic load, climate change has led to a significant increase in runoff of the winter and summer-autumn low period. For the right-bank tributaries of the Siverskyi Donets, flowing within the industrial part of Donbas, the share of low period runoff has not changed, or even decreased. This is due to the reduction of mine drainage, due to the reduction of industrial production in the region. Instead, the share of autumn-winter period in the annual runoff has increased for the right-bank tributaries and the Siverskyi Donets River itself. It is established that the share of spring floods from the annual volume of runoff has significantly decreased and the share of the summer-autumn period for the rivers of the Siverskyi Donets Basin in the modern period has increased. The winter runoff of the left-bank tributaries of the modern period is characterized by an increase. The right-bank tributaries of the Basin are characterized by a decrease in winter runoff. Currently, in dry years, spring flood is practically not allocated on the annual hydrograph; the share of runoff in the limited months has significantly increased. At the present stage of climate change, the annual runoff distribution of the Siverskyi Donets River Basin has undergone significant changes.

Analysis on the LUCC on Annual Distribution of Runoff in Liusha River Basin

Natural tropical forests in the Liusha river basin of xishuangbanna have been replaced by artificial economic forests such as rubber and tea trees since1976. Land use/cover change has affected the annual distribution characteristics of river runoff in the basin. This paper based on Liusha river basin in Menghai hydrology station monthly runoff data from 1963 to 2015. It analyzed the watershed runoff annual distribution of each seasons and month under land use and cover change analyzing the characteristics of distribution of annual runoff by Non-uniform Coefficient Cu, Concentration Ratio Cd, Absolute change ΔR and Relative changes Cm. The Cumulated filter method, Mann Kendall method and R/S analysis method also are used to study the historical and future trends of runoff and its characteristic indexes. Results show that the decade and annual runoff of Liusha river of each season are large difference. The current and future monthly runoff differences are gradually reduced and the annual runoff distribution tends to be concentrated. It can optimize the utilization of water resources and guarantee the regional water security to study the characteristics of land use and cover change on the annual distribution change of river runoff.

Impact of Possible Climate Change on Extreme Annual Runoff from River Basins Located in Different Regions of the Globe

For 11 large river basins (the Rhine, Tagus, Ganges, Lena, Upper Yellow, Upper Yangtze, Niger, Mackenzie, Upper Mississippi, Upper Amazon and Darling) located on different continents under a wide variety of natural conditions, series of annual river runoff were calculated by means of the land surface model SWAP for the period of 1962–2099. For the historical (base) period (1962–2005), meteorological forcing data were taken from the global WATCH data set. For the projection period (2006–2099), the results of simulations from five Atmosphere and Ocean General Circulation Models (AOGCMs: HadGEM2-ES, IPSL-CM5A -LR, MIROC-ESM-CHEM, GFDL-ESM2M, and NorESM1-M) obtained for four climate change scenarios of the RCP-family were applied. The obtained series of annual runoff for each river basin were used to calculate climatic values and standard deviations of annual runoff for four climatic periods (1962–2005, 2006–2035, 2036–2065 and 2066–2099), which were then averaged over all AOGCMs and RCP-scenarios and used to construct distribution functions of annual runoff (for each river basin and climatic period) approximated by the lognormal distribution function of random variables. The constructed annual runoff distribution functions were applied for estimating the probabilities of occurrence of extremely high and extremely low values of annual runoff for each river and climatic period.

Assessment of Hydrological Changes and Their Influence on the Aquatic Ecology over the last 58 Years in Ganjiang Basin, China

Runoff is the key driving factor of the Ganjiang River ecosystem. Human activities such as reservoir construction have greatly changed the state of runoff. In order to analyze the influence of Ganjiang Reservoir on the hydrological regime, the following paper is based on the daily precipitation data of 53 rainfall stations in Ganjiang River Basin from 1959 to 2016, and the daily runoff data of three stations in Dongbei, Ji’an, and Waizhou from 1959 to 2016. The Mann–Kendall test (MK) was used to analyze the trend of precipitation and runoff in Ganjiang River Basin. The Sliding t-Test (ST) was used to determine the abrupt change time of runoff in flood season within typical cross-sections of upper, middle, and lower reaches of Ganjiang River Basin, Ji’an, and Waizhou. Indicators of hydrological change (IHA), range of variability approach (RVA), and other methods were used to analyze the changes of 32 hydrological indicators in Ganjiang River Basin. The results showed that (1) The annual and flood season precipitation in Ganjiang River Basin increased from 1992 to 2016, but it did not reach a significant level. The change of annual runoff at Dongbei and Waizhou Stations was the same as that of the annual precipitation in Ganjiang River Basin. The runoff of Dongbei Station in flood season decreased from 1986 to 2016, and the runoff of Waizhou Railway Station in flood season decreased from 2008 to 2016. It showed that precipitation had a great influence on annual runoff, and human activities made the annual runoff distribution process more uniform; (2) The abrupt changes of runoff in flood season at three hydrological stations in Ganjiang River Basin occurred in 1991, and reached a significant level of 0.01; (3) There were five hydrological indicators of Dongbei Station which had reached height change. The change degree of low (l) pulse duration was −92.24%, the change degree of high (h) pulse count was −86.8%, the change degree of flow rise rate was 87.06%, the change degree of fall rate was −92.24%, and the change degree of number of reversals was −100%. Four hydrological indicators of Ji’an Station had reached high change degree, the count and duration of high pulse changes were −73.33% and −73.65%, the change degree of fall rate was −79%, and the change degree of number of reversals was −100%. Waizhou Station did not reach the high change indicator. The hydrological regime of the upper and middle reaches of Ganjiang River has changed greatly, while the hydrological regime of the lower reaches has changed little. The hydrological regime in the upper and middle reaches of Ganjiang River Basin has been highly changed by human activities such as dam construction. The change of hydrological conditions in the upper and middle reaches of Ganjiang River Basin may reduce the area of aquatic organisms’ habitat, be harmful to the spawning, migration, and survival of aquatic organisms, reduce the interception of organic matter in floodplains, and increase the drought pressure of plants. The reservoir ecological operation of rivers with numerous reservoirs should be considered, joint reservoir dispatching schemes should be formulated for the study area so as to maximize the comprehensive benefits. This study provides a reference for water resources management and reservoir operation in Ganjiang River Basin. The next step is to use a habitat model to simulate the habitat of Ganjiang River Basin.

Impacts of Hydrological Changes on Annual Runoff Distribution in Seasonally Dry Basins

Runoff is expected to change due to climate and land use change. Because it constitutes a large component of the terrestrial water budget, we need to develop new policies for managing regional water resources. To do so, we must first attribute changes in the natural flow regime to either climate or land use change. In this context, the Budyko’s curve has previously been adopted to separate the impacts of climate and land use change on runoff by using long term hydrological variables. In this study, a framework based on Fu’s equation (which describes Budyko’s curve) is used to separate the impacts of climate and land use change on annual runoff distributions. Specifically, this framework is based on a recently developed method to obtain annual runoff probability density function (pdf) in seasonally dry basins—such as those in Mediterranean regions—from climate statistics and Fu’s equation parameter ω. The effect of climate change is captured through variations in the first order statistics of annual rainfall and potential evapotranspiration, while land use change is represented by changes in Fu’s equation parameter ω. The effects of these two drivers (i.e., climate and land use change) are analyzed by reconstructing the annual runoff pdfs for the current period and for likely future scenarios, based on predictions from global circulation models and urbanization trajectories. The results show that climate change can lead to a strong reduction in mean annual runoff, a shift of the runoff pdf toward lower values, and a decrease in its variance. Concurrent changes in climate and land use almost always result in a reduction in the mean annual runoff, due to the greater impact of climate change on the runoff pdf.

Comparison of First-Order and Second-Order Derived Moment Approaches in Estimating Annual Runoff Distribution

AbstractThe first-order second-moment approximation (FOSM) has been proposed to estimate the annual runoff (Q) distribution from the statistical information of annual precipitation (P), annual pote...

Budyko’s Based Method for Annual Runoff Characterization across Different Climatic Areas: an Application to United States

Runoff data knowledge is of fundamental importance for a wide range of hydrological, ecological, and socioeconomic applications. The reconstruction of annual runoff is a fundamental task for several activities related to water resources management, especially for ungauged basins. At catchment scales, the Budyko’s framework provides an extremely useful and, in some cases, accurate estimation of the long-term partitioning of precipitation into evapotranspiration and runoff as a function of the prevailing climatic conditions. Recently the same long-term partitioning rules have been successfully used to describe water partitioning also at the annual scale and calculate the annual runoff distribution within a simple analytic framework in arid and semi-arid basins. One of the main advantages of the latter method is that only annual precipitation and potential evapotranspiration statistics, and the Fu’s equation parameter ω are required to obtain the annual runoff probability distribution. The aim of this study is to test the limit and potentialities of the aforementioned method under different climatic conditions. To this aim, the model is applied to more than four hundred basins located in the United States. Catchments were grouped into five different samples, following the subdivision of the continental region in five homogeneous climatic zones according to Koppen-Geiger classification. The theoretical probability distribution of annual runoff at each basin has been compared with that derived from historical observations. The results confirm the capability of the tested technique to reproduce the empirical annual runoff distributions with similar and satisfactory performances across different areas, revealing a good option also in cases characterized by climate and hydrological conditions very different from those hypothesized during the original analytical model design, thus extending the geographical and conceptual limits of applicability of the framework.

Peculiarities of annual internal distribution of small rivers’ runoff (on example of the Udy river)

Formulation of the problem. Water is the basis of life and, therefore, the questions regarding the definition of annual runoff distribution as a whole in Kharkiv region and in the context of individual river basins remain actual. The study of the domestic annual runoff is due to the fact that the Udy River basin belongs to the poorly watered areas, and in recent years climate change leads to a decrease in drainage during the year, including seasonal runoff changes, which may cause water supply problems in the economic sphere. The purpose of the article is to study modern features of the annual distribution of the water runoff of the Udy River basin. Presenting main material. The article deals with the peculiarities of the formation and changes in the annual flow of the river Udy basin for 35 years (1991-2015). Having analyzed the average monthly water consumption in the Udy basin, it can be noted that the annual distribution of drainage for this period is close to all rivers - typical spring flood (March), summer (August, September) and winter (December, January) months. However, the share of spring water in the Udy basin in the annual volume of drainage has decreased and the supply of rivers has changed. In connection with climatic changes, namely, the decrease in winter rainfall, there was an increase in the share of underground supply which contributed to its alignment with the share of snow intra-annual distribution. Conclusions. Having studied annual distribution of the river basin’s flow in the Udy River, it has been found that the share of spring water in the annual volume of drainage decreased from 42-36 to 36-25 %. In recent years, there has been less precipitation in winter and, therefore, snow supply is not prevailing, and there is an increase in the share of underground supply.

Ecological Conditions of Watercourses in the Middle Amur Lowland in the Areas of Drainage Reclamation

The effect of land reclamation on the migration and accumulation of heavy metals and some pollutants in small rivers is determined. The study was conducted in the Middle Amur lowland in different phases of hydrological regime and at different extent of floodplain inundation. The formation of the hydrological regime in small rivers in this area is governed by the irregular annual runoff distribution. The seasonal character of flood periods requires water samples to be taken before spring flood (April) and after floods have passed (September–October), and at various extent of floodplain inundation. The field studies of water-courses were carried out in 2009–2014. The water samples were analyzed to determine the concentrations of heavy metals (iron, manganese, copper, nickel, cobalt, lead and zinc), suspended substances, organic carbon (total, dissolved, and suspended), humic and fulvic acids, and volatile organic compounds. The mobility of heavy metals in surface watercourses was shown to reflect the effect of drainage and surface runoff from soil horizons, an increase in the concentrations of suspended and organic compounds, especially, fulvic acids, which enhance their geochemical mobility. During floods, an increase in heavy metals washout from floodplain soils and the dilution of their concentrations causes the formation of a single-type concentration series of heavy metals. In addition, the processes of pollutants migration show an effect of changes in the geomorphological characteristics of floodplain–channel complexes and a decrease in flow velocity in watercourses in the areas where land reclamation was applied. Thus, all factors mentioned above lead to a decrease in water pollution index in the river.

In vitro evaluation of cell signalling processes associated with the potential genotoxicity of metal oxide nanoparticles

The assessment of the mean annual runoff and its interannual variability in a basin is the first and fundamental task for several activities related to water resources management and water quality analysis. The scarcity of observed runoff data is a common problem worldwide so that the runoff estimation in ungauged basins is still an open question. In this context, the main aim of this work is to propose and test a simple tool able to estimate the probability distribution of the annual surface runoff in ungauged river basins in arid and semi-arid areas using a simplified Fu's parameterization of the Budyko's curve at regional scale. Starting from a method recently developed to derive the distribution of annual runoff, under the assumption of negligible inter-annual change in basin water storage, we here generalize the application to any catchment where the parameter of the Fu's curve is known. Specifically, we provide a closed-form expression of the annual runoff distribution as a function of the mean and standard deviation of annual rainfall and potential evapotranspiration, and the Fu's parameter. The proposed method is based on a first order Taylor expansion of the Fu's equation and allows calculating the probability density function of annual runoff in seasonally dry arid and semi-arid geographic context around the world by taking advantage of simple easy-to-find climatic data and the many studies with estimates of the Fu's parameter worldwide. The computational simplicity of the proposed tool makes it a valuable supporting tool in the field of water resources assessment for practitioners, regional agencies and authorities.

Analytical estimation of annual runoff distribution in ungauged seasonally dry basins based on a first order Taylor expansion of the Fu's equation

Abstract The assessment of the mean annual runoff and its interannual variability in a basin is the first and fundamental task for several activities related to water resources management and water quality analysis. The scarcity of observed runoff data is a common problem worldwide so that the runoff estimation in ungauged basins is still an open question. In this context, the main aim of this work is to propose and test a simple tool able to estimate the probability distribution of the annual surface runoff in ungauged river basins in arid and semi-arid areas using a simplified Fu's parameterization of the Budyko's curve at regional scale. Starting from a method recently developed to derive the distribution of annual runoff, under the assumption of negligible inter-annual change in basin water storage, we here generalize the application to any catchment where the parameter of the Fu's curve is known. Specifically, we provide a closed-form expression of the annual runoff distribution as a function of the mean and standard deviation of annual rainfall and potential evapotranspiration, and the Fu's parameter. The proposed method is based on a first order Taylor expansion of the Fu's equation and allows calculating the probability density function of annual runoff in seasonally dry arid and semi-arid geographic context around the world by taking advantage of simple easy-to-find climatic data and the many studies with estimates of the Fu's parameter worldwide. The computational simplicity of the proposed tool makes it a valuable supporting tool in the field of water resources assessment for practitioners, regional agencies and authorities.

A process‐based insight into nonstationarity of the probability distribution of annual runoff

AbstractIn this paper, a process‐based analytical derivation approach is proposed to perform a nonstationary analysis for annual runoff distribution by taking into account the information of nonstationarities in both hydrological inputs and runoff generation processes. Under the Budyko hypothesis, annual runoff is simulated as a formulation of hydrological inputs (annual precipitation and potential evaporation) using an annual runoff model based on the Fu equation with a parameter w accounting for the runoff generation processes. The nonstationarity of the runoff generation process is captured by the dynamic Fu‐equation parameter w. Then the multivariate joint probability distribution among the hydrological inputs, the Fu‐equation parameter w, and the runoff model error k is constructed based on the nonstationary analysis for both the hydrological inputs and w. Finally, the annual runoff distribution is derived by integrating the multivariate joint probability density function. The derived distribution by the process‐based analytical derivation approach performs well in fitting distributions of the annual runoffs from both the Yangtze River and Yellow River, China. For most study watersheds in these two basins, the derived annual runoff distributions are found to be nonstationary, due to the nonstationarities in hydrological inputs (mainly potential evaporation) or the Fu‐equation parameter w.

Annual runoff assessment in arid and semiarid Mediterranean watersheds under the Budyko's framework

AbstractThe solution of many practical water problems is strictly connected to the availability of reliable and widespread information about runoff. The estimation of mean annual runoff and its interannual variability for any basin over a wide region, even if ungauged, would be fundamental for both water resources assessment and planning and for water quality analysis. Starting from these premises, the main aim of this work is to show a new approach, based on the Budyko's framework, for mapping the mean annual surface runoff and deriving the probability distribution of the annual runoff in arid and semiarid watersheds. As a case study, the entire island of Sicily, Italy, is here proposed. First, time series data of annual rainfall, runoff, and reconstructed series of potential evapotranspiration have been combined within the Budyko's curve framework to obtain regional rules for rainfall partitioning between evapotranspiration and runoff. Then this knowledge has been used to infer long‐term annual runoff at the point scale by means of interpolated rainfall and potential evapotranspiration. The long‐term annual runoff raster layer has been obtained at each pixel of the drainage network, averaging the upstream runoff using advanced spatial analysis techniques within a GIS environment.Furthermore, 2 alternative methods are here proposed to derive the distribution of annual runoff, under the assumption of negligible interannual variations of basin water storage. The first method uses Monte Carlo simulations, combining rainfall and potential evapotranspiration randomly extracted from independent distributions. The second method is based on a simplification of the Budyko's curve and analytically provides the annual runoff distribution as the derived distribution of annual rainfall and potential evapotranspiration. Results are very encouraging: long‐term annual runoff and its distribution have been derived and compared with historical records at several gauged stations, obtaining satisfactory matching.

Space and time variations of the runoff of Kamchatka Krai rivers

The current features of the space and time variations of river runoff in Kamchatka Krai have been considered. Two relatively long cycles have been shown to exist in water runoff variations in the major portion of the examined rivers. The renewable water resources were increasing until 1970–1980, while in the following years (up to 2010), they were gradually decreasing. Current data on river runoff were used to prove the existence of three zonal types of water regime in Kamchatka Krai; five azonal types of annual runoff distribution are characterized. One of them (nearly uniform annual distribution caused by the predominance of groundwater recharge) has been theoretically predicted in the classification proposed by M.I. L’vovich, though without factual confirmation. The specific features of water regime of rivers whose basins lie on the slopes of active volcanoes are considered for the first time. This type of regime typically shows alternating periods of the presence and absence of surface runoff in river channels, corresponding to the inflow of snowmelt or rainfall runoff at high level of subsoil water (when channel deposits are fully saturated with water) or at its low position (when moisture is deficient).

Spatial and temporal changes in runoff and sediment loads of the Lancang River over the last 50 years

Non-parametric Mann-Kendall, double mass curve analysis and annual variation analysis were used to analyze the spatial and temporal changes in runoff and sediment loads at the Jiuzhou, Jiajiu and Yunjinghong hydropower stations in the Lancang River from 1964 to 2010. The results indicate that the inter-annual and annual distributions of sediment have significantly changed since the 1990s, and that sediment discharge has increased at the Jiuzhou station, while sediment discharge has declined at the Jiajiu and Yunjinghong stations. Overall, annual runoff distribution patterns have been consistent since the 1990s. Spatial and temporal changes in runoff and sediment loads in the Lancang River have been attributed to the construction of hydropower stations, changes in land use and precipitation patterns. The results can provide guidance for the environmental protection and ecological restoration of rivers in the Southwest of China.