Search

An accurate and complete rainfall record is prerequisite for climate studies. The purpose of this research study was to evaluate the homogeneity of the rainfall series for the Mae Klong River Basin in Thailand. Monthly rainfall data of eight stations in the Mae Klong River Basin for the period 1971–2015 were used. The double mass curve analysis was used to check the consistency of rainfall data, whereas the absolute homogeneity was assessed using the Pettitt test, standard normal homogeneity test, Buishand test, and von Neumann test at a 5% significance level. The results of these tests were qualitatively classified as ‘useful’, ‘doubtful’, and ‘suspect’ according to the null hypothesis. Results of the monthly time series indicated the rainfall data as ‘useful’ for 75% of the stations, while two stations’ data were classified as ‘doubtful’ (Stn130221) and ‘suspect’ (Stn376401). On an annual scale, seven out of eight stations data were classified as ‘useful,’ while one station (Stn376401) data were classified as ‘suspect’. Double mass curve analysis technique was used for the adjustment of inhomogeneous data. The results of this study can help provide reliable rainfall data for climate studies in the basin.

Runoff and sediment discharge have displayed great reductions due to climate change and enhanced various human activities during recent decades in the Jialing River, China, with significant environmental and social implications. The water balance equation, double mass curve, and linear regression analysis were employed to quantify the contributions of climate change and human activities to runoff and sediment discharge reductions in the Jialing River during 1960–2017. The results indicated that the annual runoff of the Jialing River exhibited a significant decreasing trend of − 2.75 × 108 m3 every year (P

A simple climate change assessment is carried out on annual air temperatures including average, maximum and minimum temperatures in Rendani, Manokwari for the period of 1993-2019. Parametric linear regression and nonparametric Mann-Kendall trend test (MK), Modified Mann-Kendall (MMK), Sen's Slope Estimator (SSE)are used to analyze trends and index numbers for analyzing the temperature changes. Homogenity test is performed using double mass curve and assumption of normality in the distribution is also investigated to meet the requirements of the linear regression trend test. There as a significant upward trend in the mean and minimum temperature with a slope of 0.029ºC/year and 0.069ºC/year, respectively. Meanwhile, the maximum temperature test shows no trend with a slope of 0.009ºC/year. Analysis of temperature changes using index numbers shows an increase in annual average temperature of 2.8% or 0.7°C, maximum temperature of 1.2% or 0.4°C, and minimum temperature of 3.1% or 0.8°C. The increase in annual air temperature in Manokwari City can generally be caused by several factors such as El Nino phenomenon, urbanization, population growth, and deforestation.

Quantifying the relative contributions of climate change and human activities to water and sediment variations is of great importance for regional resources and river basin management, which has become a hot topic in hydrology research. In this study, water discharge and sediment load in Xiangxi River basin of Three Gorges Reservoir area were investigated based on hydrometeorological time series since 1960s. The non-parametric Mann-Kendall (M-K) test was used to detect both the trends and abrupt changes in the time series. Double mass curve and sediment rating curve method were used to quantify and evaluate the climatic and anthropogenic effects on water discharge and sediment load. Results indicated that both water discharge and sediment load showed significant decreasing trends with annual decrement rate of –0.08 × 108 and ‒1.011 × 104 t/yr, respectively. The abrupt change points were observed in 1991 for water discharge and 1999 for sediment load by sequential M-K test and cumulative anomaly curve analysis. This study demonstrated that water discharge was mainly influenced by precipitation in 1990s while by human activities ever since 2000, and sediment load was predominantly influenced by human activities (relative contribution 86–98%, regardless of whether the effect is negative or positive). In this study, soil and water conservation as well as land use change were primarily responsible for water and sediment variations in Xiangxi river basin especially since 2000. Further studies need to be done to quantify the importance of a specific driving factor at multi-timescales.

Soil and water conservation are important measures in regulating runoff and sediment load on the Loess Plateau. Information on how land use and land cover changes, especially the implementation of the soil and water loss control project, can affect the sediment load dynamics and hydrological variables is important since large-scale eco-environmental governance programs are being implemented. In this study, an improved double mass curve and the decomposition method were used to assess the effects of different soil and water control measures on runoff and sediment load in the Lvergou, which is a small basin on the Loess Plateau in China, based on 60 years of data. We conclude that the total precipitation (P) was not statistically significantly different (p > 0.05), whereas heavy rain increased significantly (p

A Bacia Hidrográfica do Rio Una detém de um regime pluviométrico diversificado. Graças a sua extensão ela está inserida em duas mesorregiões Pernambucanas (Zona da Mata e Agreste) que apresentam padrões climáticos distintos. Nesse contexto, essa pesquisa visa analisar o comportamento pluviométrico espaço-temporal na Bacia Hidrográfica do Rio Una, por meio de uma análise de homogeneidade pelo algoritmo K-Mean, preenchimento de falhas com o vetor regional e espacialização dos dados médios mensais e anuais com o algoritmo do IDW. De acordo com o regime pluviométrico mensal o algoritmo Cluster K-Mean determinou coerentemente quatro clusters na Bacia hidrográfica do Rio Una. Quanto ao preenchimento de falhas pluviométricas, o método do vetor regional demonstrou bons resultados no preenchimento de falhas mensais. Com a curva de dupla massa, foi possível perceber consistência dos dados pluviométricos anuais. Na espacialização foi constatada uma grande variabilidade nas precipitações totais anuais e nos meses considerados úmidos, dos quais detêm a magnitude pluviométrica decrescente na direção Leste-Oeste (inversamente a altitude).

The Yom River is one of the four major sediment sources to the Chao Phraya River in Thailand. Human activities and changes in climate over the past six decades may have affected the discharge and sediment load to some extent. In the current study, the river discharge and sediment characteristics in the mainstream of the Yom River were investigated using the field observation data from 2011 to 2013 and the historical river flow and sediment data from 1954 to 2014 at six hydrological stations operated by the Royal Irrigation Department of Thailand (RID). The non-parametric Mann-Kendall test and double mass curve were used to analyze the sediment dynamics and temporal changes in the discharge of the Yom River. The results revealed that the sediment was mainly transported in suspension, and the bed-to-suspended sediment loads ratio varied between 0 and 0.05. The daily suspended sediment load (SSL) in the upper and middle basins had a strong correlation with the daily discharge and could be represented by power equations with coefficients of determination higher than 0.8. The daily suspended sediment load in the lower basin did not directly depend on the corresponding discharge because of the reduction in river slope and water diversion by irrigation projects. It also appeared that the river discharges and sediment loads were mainly influenced by climate variation (floods and droughts). Moreover, the average sediment transport of the upper, middle, and lower reaches were 0.57, 0.71, and 0.35 million t/y, respectively. The sediment load in the lower basin decreased more than 50% as a result of changes in the river gradient (from mountainous to floodplain areas). The results from sediment analysis also indicated that the construction of the Mae Yom Barrage, the longest diversion dam in Thailand, and land-use changes did not significantly affect the sediment load along the Yom River.

Response of water and sediment generation to climate change and anthropogenic activities is becoming a hot topic in the middle reach of the Jinsha River Basin. In this research, coefficients of variation and concentration degree (i.e., Cᵥ and Cd) and double mass curve (DDC) were adopted to examine the changes in water and sediment discharge and their relationships with precipitation. The contribution rates of climatic and anthropogenic factors to water and sediment discharge were assessed through comparisons between the measured and predicted values in the baseline and postbaseline periods in the basin. The main results were: (a) the water and sediment discharges of the basin showed a decreasing trend from 2006 to 2014, with peak points of Cᵥ and Cd of sediment discharge of the basin in 2009 and 2010, respectively; (b) the precipitation had a major influence on water discharge variations, and the peak point of the DDC of the cumulative precipitation and sediment discharge was consistent with the cumulative water and sediment discharge; and (c) under annual and flooding season scales, the contribution rates of anthropogenic factors to water discharge were 63.060% and 70.457%, respectively. The contribution rates of anthropogenic factors on sediment discharge were 84.790% and 85.541%, respectively. The impacts of anthropogenic factors on water and sediment discharge were more significant than the impacts of precipitation, in which the construction and operation of cascade hydropower stations (CHS) were believed to play a crucial role.

Coal mining and soil-water conservation are the two major human interventions on the Loess Plateau in China. Analyzing their impacts on hydrological processes is of great significance for sustainable water resource management. Using hydrological simulation (Soil and Water Assessment Tool, SWAT) and a data-driven method (double mass curve, DMC), the contributions of these two human activities and climate change to the runoff decrease were analyzed in the upper Fenhe River. The runoff in the three affected periods (1967–1987, 1988–1994, and 1995–2017) decreased by 7.5%, 28.2%, and 24.1%, respectively, compared with the base period (1957–1966). In the first affected period (1967–1987), the amount of coal mining activities was small, human activities had little impact on runoff. In the second (1988–1994) and third (1995–2017) periods, as the coal mining and soil-water conservation intensified, their contributions to the runoff decrease rapidly increased. Due to the uncertainties in the model structure and parameters, in addition to the impact of the data accuracy, the results obtained from the two methods were different, but the proportions and the trends of the contribution rates in the different periods were consistent.

Determining the contributions of climate change and human activities to runoff variation is important for water resource management. An improved double mass curve method (IDMC), which can d...

The change in future climate will have a prominent impact on crop production and water requirement. Crop production is directly related to climatic variables. Temperature, solar radiation, wind, precipitation, CO2 concentration and other climatic variables dictate crop yield. This study, based on long-term historical data, investigates the patterns and changes in climatic variables (precipitation, temperature, and solar radiation) that would most significantly affect the future crop production in many parts of the world, and especially in India, where most farmers depend on rainfall for rice production. Statistical analyses—box and whisker plot, mean absolute error, Taylor diagram, double mass curve, Mann–Kendall trend test, and projected climate change—were used to assess the significance of the climatic factors for the purpose of agricultural modeling. Large variability in precipitation may cause the flash floods and affect the farming, and at the same time, increase in temperature from baseline period will lead to high water requirement by crops, and may cause drought if rainfall does not occur. Decrease in solar radiation will affect crop growth and development, and thus, would hamper the crop production. The results of this study would be useful in identifying the negative issues arising from climate change in future agricultural practices in Bihar, India. Furthermore, the results can also help in developing management strategies to combat the climate change impact on crop production.

The water resources in arid and semi-arid regions are critical to providing reliable sources of water for food production and ecosystem functioning. In this study, continuous wavelet transform and wavelet coherence were used to analyse the runoff periodicity and relationship with climate indices, respectively. Additionally, the double mass curve (DMCD), the slope changing ratio of cumulative quantity (SCRCQ) and the Choudhury–Yang equation (Budyko-CY) methods for different potential evapotranspiration data (E0(E0-20 cm, E0-PM, E0-H)) were used to separate the impacts of climate changes and anthropogenic activities on runoff variations. The results demonstrated that the flow regimes in high and low flow seasons were not obvious shifts, and that after implementation of the Ecological Water Diversion Project (EWDP), ecosystems were gradually restored in the downstream portion of the Heihe River Basin (DHRB). Periodicities of 1–7 years and 1–5.8 years were detected in Yingluoxia and Zhengyixia, respectively. Additionally, on a 1–148.2 month timescale, the monthly runoff with AO, NAO, PDO, and AMO had significant resonance periodicity and a 1–48 month Spearman's lag correlation. On the annual and high-flow, climate changes dominant determinant to an increase of runoff for the DMCD and Budyko-CY in period 2, SCRCQ and Budyko-CY in period 3 for different E0 in the upstream (UHRB). In the midstream (MHRB) region, anthropogenic activities played a dominant role in deducing the runoff by the SCRCQ and Budyko-CY methods for different E0 values in period 3. During the low-flow season, the impact of human activities in the UHRB and climate changes in the MHRB was significant for period 2 and 3. Therefore, the impacts of climate change and human activities on runoff changes caused by the introduction of different E0 on different timescales should be fully considered in the future.

The present study seeks to estimate the water balance that results as a product of the variation of precipitation and temperature over the Chaquilcay microcatchment, a natural system that intercepts with the surface of the Aguarongo Protected Forest in Gualaceo, Ecuador. Four meteorological stations of the National Institute of Meteorology and Hydrology (INAMHI) were studied, which are divided into climatological and pluviometric, with time series of over 30 years, (1982-2015 period). In order to quantify the contributions and losses of water, statistical analyzes of the time series and surveys of in situ information were carried out. The methods used are linear regression, streak test and double mass curve. To fill and validate the series of precipitation and temperature, reference temperatures of the isothermal raster of Ecuador were included in the pluviometric stations. Additionally, a digital elevation model (MDE) was used to predict the amount of sunshine, and the Thornthwaite evapotranspiration method (1948) was applied from the obtained data. The results show acceptance of the meteorological records, while in the soil analysis we obtained the following data: Humidity, 62.38%; organic matter, 21.29%; field capacity, 18.71 mm and a flow of 1.89 m³ / s during the month of May. Finally, the water balance indicates 843.7 mm of annual precipitation, a storage difference of 18.71 mm representing 2.22% of total precipitation, an surplus of 144.5 mm, and actual evapotranspiration of 680.5 mm, with 17.13% and 80.65%, respectively.

Human activities are increasingly recognized as having a critical influence on hydrological processes under the warming of the climate, particularly for dam-regulated rivers. To ensure the sustainable management of water resources, it is important to evaluate how dam construction may affect surface runoff. In this study, using Mann–Kendall tests, the double mass curve method, and the Budyko-based elasticity method, the effects of climate change and human activities on annual and seasonal runoff were quantified for the Yellow River basin from 1961–2018, additionally, effects on runoff were assessed after the construction of the Xiaolangdi Dam (XLD, started operation in 2001) on the Yellow River. Both annual and seasonal runoff decreased over time (p &lt, 0.01), due to the combined effects of climate change and human activities. Abrupt changes in annual, flood season, and non-flood season runoff occurred in 1986, 1989, and 1986, respectively. However, no abrupt changes were seen after the construction of the XLD. Human activities accounted for much of the reduction in runoff, approximately 75–72% annually, 81–86% for the flood season, and 86–90% for the non-flood season. Climate change approximately accounted for the remainder: 18–25% (annually), 14–19% (flood season), and 10–14% (non-flood season). The XLD construction mitigated runoff increases induced by heightened precipitation and reduced potential evapotranspiration during the post-dam period, the XLD accounted for approximately 52% of the runoff reduction both annually and in the non-flood season, and accounted for approximately −32% of the runoff increase in the flood season. In conclusion, this study provides a basic understanding of how dam construction contributes to runoff changes in the context of climate change, this information will be beneficial for the sustainable management of water resources in regulated rivers.

The damming of rivers has altered their hydrological regimes. The current study evaluated the impacts of major hydrological interventions of the Zhikong and Pangduo hydropower dams on the Lhasa River, which was exposed in the form of break and change points during the double-mass curve analysis. The coefficient of variability (CV) for the hydro-meteorological variables revealed an enhanced climate change phenomena in the Lhasa River Basin (LRB), where the Lhasa River (LR) discharge varied at a stupendous magnitude from 2000 to 2016. The Mann–Kendall trend and Sen’s slope estimator supported aggravated hydro-meteorological changes in LRB, as the rainfall and LR discharge were found to have been significantly decreasing while temperature was increasing from 2000 to 2016. The Sen’s slope had a largest decrease for LR discharge in relation to the rainfall and temperature, revealing that along with climatic phenomena, additional phenomena are controlling the hydrological regime of the LR. Reservoir functioning in the LR is altering the LR discharge. The Soil and Water Assessment Tool (SWAT) modeling of LR discharge under the reservoir’s influence performed well in terms of coefficient of determination (R2), Nash–Sutcliffe coefficient (NSE), and percent bias (PBIAS). Thus, simulation-based LR discharge could substitute observed LR discharge to help with hydrological data scarcity stress in the LRB. The simulated–observed approach was used to predict future LR discharge for the time span of 2017–2025 using a seasonal AutoRegressive Integrated Moving Average (ARIMA) model. The predicted simulation-based and observation-based discharge were closely correlated and found to decrease from 2017 to 2025. This calls for an efficient water resource planning and management policy for the area. The findings of this study can be applied in similar catchments.

The climate is becoming warmer and more humid in the inland area of northwestern China. In addition, human activities have changed the underlying surface of the river basin, and the instability of the runoff changes has intensified. As a component of river runoff, the base flow reflects the impacts of climate change and human activities. Therefore, it is necessary to carry out research on the change in the base flow and its influencing factors in the context of climate change and human activities. In this study, a base flow method suitable for the inland rivers in northwestern China was assessed, and the variation rules and influencing factors of the base flow were analyzed. The results reveal that since the 1980s, the base flow of the Hexi inland rivers has exhibited an increasing trend, and the growth rate has exhibited the following order: western &gt, central &gt, eastern. The Base Flow Index (the proportion of the base flow to the total runoff in a period) values are in the range of 0.45–0.65. Overall, the change in the base flow of the Hexi inland rivers is the result of the coupling of climate factors and land-use change. The influence of land-use change on the base flow of the Hexi inland rivers gradually weakens from east to west, except for the Xiying River, while the influence of climate change gradually increases. The contribution rates of land-use change to the base flow in the eastern, central, and western regions were 75%, 55%, and 27%. Temperature and precipitation are the main climate factors affecting the change in the base flow in the western and central regions, respectively.

Human activities have substantially altered present-day flow regimes. The Headwater Area of the Yellow River (HAYR, above Huanghe’yan Hydrological Station, with a catchment area of 21,000 km2 and an areal extent of alpine permafrost at ~86%) on the northeastern Qinghai-Tibet Plateau, Southwest China has been undergoing extensive changes in streamflow regimes and groundwater dynamics, permafrost degradation, and ecological deterioration under a warming climate. In general, hydrological gauges provide reliable flow records over many decades and these data are extremely valuable for assessment of changing rates and trends of streamflow. In 1998–2003, the damming of the Yellow River by the First Hydropower Station of the HAYR complicated the examination of the relations between hydroclimatic variables and streamflow dynamics. In this study, the monthly streamflow rate of the Yellow River at Huanghe’yan is reconstructed for the period of 1955–2019 using the double mass curve method, and then the streamflow at Huagnhe’yan is forecasted for the next 20 years (2020–2040) using the Elman neural network time-series method. The dam construction (1998–2000) has caused a reduction of annual streamflow by 53.5–68.4%, and a more substantial reduction of 71.8–94.4% in the drier years (2003–2005), in the HAYR. The recent removal of the First Hydropower Station of the HAYR dam (September 2018) has boosted annual streamflow by 123–210% (2018–2019). Post-correction trends of annual maximum (QMax) and minimum (QMin) streamflow rates and the ratio of the QMax/QMin of the Yellow River in the HAYR (0.18 and 0.03 m3·s−1·yr−1 and −0.04 yr−1, respectively), in comparison with those of precorrection values (−0.11 and −0.004 m3·s−1·yr−1 and 0.001 yr−1, respectively), have more truthfully revealed a relatively large hydrological impact of degrading permafrost. Based on the Elman neural network model predictions, over the next 20 years, the increasing trend of flow in the HAYR would generally accelerate at a rate of 0.42 m3·s−1·yr−1. Rising rates of spring (0.57 m3·s−1·yr−1) and autumn (0.18 m3·s−1·yr−1) discharge would see the benefits from an earlier snow-melt season and delayed arrival of winter conditions. This suggests a longer growing season, which indicates ameliorating phonology, soil nutrient availability, and hydrothermal environments for vegetation in the HAYR. These trends for hydrological and ecological changes in the HAYR may potentially improve ecological safety and water supplies security in the HAYR and downstream Yellow River basins.

Global climate change and human activities have important effects on the water discharge and sediment load of the Pearl River. In this study, the water discharge and sediment load were investigated by using hydro-meteorological data from 1954 to 2018. The linear regression, Mann–Kendall abrupt test and double mass curve were employed to detect trends and abrupt change-points in water discharge and sediment load and to quantify the effects of climate change and human activities on water discharge and sediment load. The results revealed that the annual sediment load exhibited a significant decreasing trend at a rate of − 2.24 × 104 t/year, regardless of water discharge, and an abrupt change occurred in 1998. Human activities, especially dam construction contributed 96% to this change, while 4% was due to climate change. El Niño/Southern Oscillation (ENSO) events are often associated with low precipitation, resulting in low water discharge and sediment load, indicating that changes in ENSO periodicity could affect the inter-annual periodic variations of water discharge and sediment load. As population and economy boom, more dams are being built in the Pearl River basin, and special attention should be paid to the management and mitigation of the effects of dams on sediment load.

The impact of human activities and rainfall variability on river discharge is of main concern for policymakers in the Komadugu-Yobe Basin (KYB), Lake Chad area. The KYB is of strategic importance because its rivers contribute significantly to the recharge of Lake Chad whose shrinkage has been of concern to policymakers and the international society. This study investigates the variations in river discharge of the KYB as a result of the contributory effects of rainfall variability and human influences, using daily rainfall and discharge data between 1971 and 2013. In order to partition the impacts of rainfall variability and human activities on river discharge, breakpoints related to abrupt environmental changes caused by human activities are identified using the generalized variance (GV), double mass curve (DMC) and the wavelet spectral methods. Breakpoints are found in 1974 and 1993, which correspond to times when major dams in the basin became operational. These breakpoints may also be related to LULC changes. The land-use land-cover (LULC) analysis shows an increase in bare surface, plantation, settlements and water bodies from 1975 to 2013, in association with a decrease in the forest and grassland coverage. Overall, the mean discharge between the pre-break and post-break periods increased by 24%. This increment in discharge was caused by approximately 50% rainfall variability and 50% human activities. Hence, the effects of human activities appear to be as important as the effect of natural rainfall variability on the river discharge changes in the KYB.

It is critical to determine soil erosion rates and sediment yields under ecological restoration conditions on the Loess Plateau. Sediments retained in check-dams document the soil erosion history in a small watershed. We selected the check-dam systems to reconstruct the long-term sediment yield in a restored agricultural catchment on the Loess Plateau. The storage capacity curve method was applied to estimate the total sediment deposition of check-dam systems, and 725.82 thousand tons of sediment was trapped in the check-dams systems from 1975 to 2013. Two abrupt change points were detected in 1987 and 2003 using the double mass curve method; the average catchment sediment yields were 5,273.63 t/(km2·a) in Stage-1 (1975–1987), 1,734.09 t/(km2·a) in Stage-2 (1988–2003), and 2,653.10 t/(km2·a) in Stage-3 (2004–2013), represented intense erosion, mild erosion, and moderate erosion, respectively. In Stage-2, the sediment yield variation in the Fangta catchment was mainly affected by human activities, and its contribution reached 97%. According to the hierarchical cluster analysis, the soil erosion intensity changed gradually from mild to moderate and then to intense when the average annual erosive rainfall reached approximately 300, 350, and 400 mm in the Fangta catchment of the loess hilly-gully region. Approximately 6.1–42.6 % of the sediment was deposited along the way since 2003 when the sediments generated by erosion in small watersheds were gradually transported to the downstream river network. Therefore, check-dam systems are important carriers for reconstructing the historical sediment yield in small and ungauged watersheds. The results of this study not only serve as a basis for obtaining reliable information on erosion and sediment yield in small dam-controlled catchments, but also provide a useful reference for implementing sustainable ecological restoration in the future.

Climate change and human activities have substantially changed hydrological and geomorphologic processes, particularly in upper mountainous catchments. The Jinsha River Basin (JRB), the uppermost region of the Yangtze River and the largest hydropower production region in China, was chosen to investigate the sediment load responses to climate variations and human activities. The non-parametric Mann-Kendall test and double mass curve were used to explore the spatial-temporal variations of hydro-meteorological variables and quantify the contributions of climate variation and human activities to changes in discharge and sediment load in the JRB from the 1950s to 2015. The results indicate that human activities, in particular cascade damming, were the governing factor for sediment load changes, while climate variations (increasing precipitation and snow and glacier melt) dominated the discharge changes in the JRB. The average annual sediment load at the Panzhihua (PZH) station increased by 42.4% from 1966–1984 to 1985–2010, mainly due to mineral extraction and deforestation, followed by a decrease of 75.9% in 2011–2015 because of the operation of the cascade reservoirs in the middle JRB since 2010. The construction of new dams like the Xiangjiaba Reservoir (2012) and the Xiluodu Reservoir (2013) in the lower JRB and many other cascade reservoirs since 2010 in the middle JRB further decreased the sediment load by 58.5% (BHT) and 83.8% (XJB) in the recent five years from 2011 to 2015. Although channel erosion downstream of the XJB Dam can provide new sediment to the Three Gorges Reservoir (TGR), the sedimentation rate of the TGR has decreased rapidly and will continue to be reduced due to the construction of more dams in the future.

Water resources and engineering projects are of major importance due to great demand of water and power supplies, irrigation needs, drought mitigation and flood control. In order to plan and design these projects, complete and reliable hydrological datasets are required. Missing data can severely compromise data quality and utility. The Rufiji Water Basin Office has developed and kept a database of daily streamflow records from 1950s to-date for at least 87 gauging stations. While the majority of the records are complete, data checks revealed significant gaps. Some stations are experiencing large gaps of up to 19 consecutive years. There is no dedicated study that looked at assessment of suitable methods for infilling such gaps. This study therefore made a contribution by appraising empirical and regression rainfall runoff based methods in the Little Ruaha River catchment, a sub-catchment of the Great Ruaha River sub-basin both within the Rufiji River Basin. The methods employed included simple linear regression (with untransformed and log-transformed data), multiple linear regression (with untransformed and log-transformed data), rainfall-runoff relationship using double mass curve technique, flow duration matching and drainage-area ratio. In addition, rainfall runoff modeling using HBV-Light was done for further comparison. With exception to the rainfall-runoff relationship and HBV-Light model, all other methods relied upon data transfer from donor stations (upstream & downstream station(s)) for infilling a downstream/upstream station. Data quality and consistency checks were performed, and performances of infilling methods were evaluated based on three performance criteria namely Nash-Sutcliffe efficiency coefficient (NSE), Coefficient of determination (R2) and standard error of estimate (SE) during calibration and validation periods. Four gauging stations (2 each upstream and downstream) were separately used to infill artificially created gaps to the target station. Overall, the calibration and validation daily results at 1KA21A indicated that the flow duration matching technique and multiple linear regression methods performed better than other methods with NSE (71%; 93%) and NSE (55%; 75%) respectively. These results have a potential for wide application in other basins of Tanzania for hydrological analysis and water resource management, where missing data is very common.

Analyzing intra-annual stream flow can reveal the main causes for runoff changes and the contributions of climate variability and human activities. For this purpose, the Mann–Kendall and cumulative rank difference (CRD) tests, and the double mass curve method, were applied to a time series of hydro-meteorological variables from 1971 to 2010 in the Tajan River basin in Iran. Results indicated that runoff changes in the wet and dry seasons after 1999 had significant respective decreasing and increasing trends, at the 0.01 confidence level, due to dam construction. In the pre-dam period (1991–1998), the results of the double mass curve method showed that climate variability and human activities contributed 57.76% and 42.24%, respectively, to the runoff decrease during the wet season. For the post-dam period (1999–2010), climate variability and anthropogenic activities contributed 24.68% and 75.32%, respectively, to the wet season runoff decrease of 116.55 mm. On the other hand, in the same period during the dry season, climate variability contributed −30.68% and human activities contributed 130.68% to the runoff increase of 41.45 mm. It is evident that runoff changes in both wet and dry seasons were mainly due to human activities associated with dam construction to meet water supply demands for agriculture.

Climate change and land use and cover change (LUCC) have had great impacts on watershed hydrological processes. Although previous studies have focused on quantitative assessment of the impacts of climate change and human activities on decreasing run‐off change, few studies have examined regions that have significant increasing run‐off due to both climate variability and land cover change. We show that annual run‐off had a significant increasing trend from 1956 to 2014 in the U.S. lower Connecticut River Basin. Abrupt change point years of annual run‐off for four subbasins are detected by nonparametric Mann–Kendall–Sneyers test and reconfirmed by the double mass curve. We then divide the study period into 2 subperiods at the abrupt change point year in the early 1970s for each subbasin. The Choudhury–Yang equation based on Budyko hypothesis was used to calculate precipitation and potential evapotranspiration, and landscape elasticities of run‐off. The results show that the difference in mean annual run‐off between 2 subperiods for each subbasin ranged from 102 to 165.6 mm. Climate variations were the primary drivers of increasing run‐off in this region. Quantitative contributions of precipitation and potential evapotranspiration in all subbasins are 106.5% and −3.6% on average, respectively. However, LUCC contributed both positively and negatively to run‐off: −18.6%, −13.3%, and 10.1% and 9.9% for 4 subbasins. This may be attributed to historical LUCC occurring after the abrupt change point in each subbasin. Our results provide critical insight on the hydrological dynamics of north‐east tidal river systems to communities and policymakers engaged in water resources management in this region.

Accelerated soil erosion exerts adverse effects on water and soil resources. Rainfall erosivity reflects soil erosion potential driven by rainfall, which is essential for soil erosive risk assessment. This study investigated the spatiotemporal variation of rainfall erosivity and its impacts on sediment load over the largest freshwater lake basin of China (the Poyang Lake Basin, abbreviate to PYLB). The spatiotemporal variations of rainfall erosivity from 1961 to 2014 based on 57 meteorological stations were detected using the Mann–Kendall test, linear regression, and kriging interpolation method. The sequential t test analysis of regime shift (STARS) was employed to identify the abrupt changes of sediment load, and the modified double mass curve was used to assess the impacts of rainfall erosivity variability on sediment load. It was found that there was significant increase (P

Homogeneous time series of meteorological variables are necessary for hydrologic and climate studies. Dependability of historical precipitation data is subjected to keen evaluation prior to every study in water resources, hydrology, and climate change fields. This study aims to characterize the homogeneity of long-term Turkish precipitation data in order to ensure that they can be reliably used. The homogeneity of monthly precipitation data set was tested using the standard normal homogeneity test, Buishand test, Von Neumann ratio test, and Pettitt test at the 5% significance level across Turkey. Our precipitation records including the most updated observations, extracted from 160 meteorological stations, for the periods 1974–2014 were analyzed by all the four homogeneity tests. According to the results of all tests, five out of 160 stations have an inhomogeneity. With regard to our strict confirmation rule, 44 out of 160 stations are said to be inhomogeneous since they failed from at least one of the four tests. The breaks captured by the Buishand and Pettitt tests usually tend to appear in the middle of the precipitation series, whereas the ability of standard normal homogeneity test is in favor of identifying inhomogeneities mostly at the beginning or at the end of the records. Our results showed that 42 out of 44 inhomogeneous stations passed all the four tests after applying a correction procedure based on the double mass curve analysis. Available metadata was used to interpret the detected inhomogeneity.

Mo, S.; Li, Z.; Gou, K.; Qin, L., and Shen, B., 2018. Quantifying the effects of climate variability and direct human activities on the change in mean annual runoff for the Bahe River (Northwest China). Evaluating the impacts of climate change and human interference on runoff is critically important for regional water security. This study investigated the effects of climate variability and direct human activities on the change in mean annual runoff for the Bahe River in Northwest China. Precipitation, evaporation, and runoff data from 1959 to 2010 were analyzed at the Luolicun and Maduwang hydrologic gauge stations, and their temporal trends were explored using the Mann-Kendall test. A Mann-Kendall-Sneyers test and the double mass curve were applied to detect the statistically significant transition points in the hydrometeorological records. Results indicated no change point in upstream runoff in the Bahe River from 1959 to 2010; however, a clear transition point existed in midstream runoff in 19...

Identifying the individual contributions of factors impacting the water resources in Beijing plays crucial roles in planning water management for resolving water shortage problems and for the sustainable utilization of water resources. In this study, four statistical methods, the Mann-Kendall test, double mass curve method, modified slope changing ratio of accumulative quantity method, and generalized linear model, were employed to detect the individual contributions of climate change and human activities on the variation of runoff in Beijing from 1961 to 2017. Our results showed that the annual runoff declined significantly during the entire study period. The mean temperature increased significantly, while the annual precipitation did not change significantly, over the entire study period. An abrupt change was detected in 1977 with a change in runoff. During the period of change, climate change contributed 20.0% to the increase in runoff, while human activities contributed 120% to the decline in runoff from 1978 to 2017. Furthermore, we partitioned the contributions of human activities into eight social and economic factors. These factors explained 55.29% of the total contributions of human activities. The economic factors, the changes in the arable land area and accumulative construction area, and the change in urbanization rate contributed 15.94%, 18.37%, and 6.05% to the total variation in runoff, respectively. Finally, the South-to-North Water Transfer Project contributed 5.19% of the change in runoff. Our study provides the individual contributions of the specific impact factors to runoff in Beijing and may help policy-makers to devise targeted water resource management plans.

To evaluate the evolution of river water quality in a changing environment, measuring the objective water quality is critical for understanding the rules of river water pollution. Based on the sample entropy theory and a nonlinear statistical method, this study aims to identify the spatiotemporal dynamics of water quality and its complexity in the Yangtze River basin using time series data, to separate the contributions of human activity and climate change to water quality, and to establish a data-driven risk assessment framework for the spatial (potential risk) and temporal (direct risk) aspects of water pollution. The results demonstrate that the spatiotemporal dynamics of water quality and sample entropy in each monitoring section are closely related to the characteristics of the corresponding location. The water quality of the main stream is superior, and its complexity is less than that of the tributaries. Cascade reservoir operation and vegetation status, agricultural production, and rainfall patterns exert great influences in the upper, middle, and lower reaches, respectively. Dam construction, urban agglomeration development, and interactions between river and lake are also influencing factors. An attributional analysis found that climate change and human activities negatively contributed to the evolution of NH3-N concentration in most of the monitored sections, and the average relative contribution rates of human activities to changes in water quality in the main and tributary streams were -55.46% and -48.49%, respectively. In addition, the construction of data-driven risk assessment framework can efficiently and accurately assess the potential and direct water pollution risks of rivers.

The water discharge and sediment load of rivers are changing substantially under the impacts of climate change and human activities, becoming a hot issue in hydro-environmental research. In this study, the water discharge and sediment load in the mainstream and seven tributaries of the Yangtze River were investigated by using long-term hydro-meteorological data from 1953 to 2013. The non-parametric Mann-Kendall test and double mass curve (DMC) were used to detect trends and abrupt change-points in water discharge and sediment load and to quantify the effects of climate change and human activities on water discharge and sediment load. The results are as follows: (1) the water discharge showed a non-significant decreasing trend at most stations except Hukou station. Among these, water discharge at Dongting Lake and the Min River basin shows a significant decreasing trend with average rates of -13.93×108m3/year and -1.8×108m3/year (P

Design of urban drainage infrastructure depends on the rainfall pattern and runoff volumes. Under the current impacts of urbanization and industrialization in the Kingdome of Saudi Arabia (KSA), there is a need to review the guidelines for design of drainage infrastructure. In this study, a methodology is developed to investigate the impact of variations in rainfall on the capacity of drainage infrastructure for the city of Madinah (Taibah), KSA. Rainfall data collected from Madinah Municipality was analyzed to determine the normal annual rainfall (average of the annual rainfall for 30 years). Data consistency was checked using double mass curve technique, and the design rainfall (DR) was estimated by Gumbel Extreme Value Distribution. The Mann-Kendall test was run at 5% significance level on rainfall time series over the period 1985–2015; however, no significant trend was observed. Urban drainage schemes are designed for peak flows based on DR. The true values of DR are difficult to estimate due to uncertainties associated with variations in estimation procedures and data limitations. An attempt is made to elaborate the impact of data errors (both systematic and random) on DR to facilitate engineers in selecting safety factor for design of urban drainage infrastructure. The stormwater trunk-sewer was designed to safely convey the runoff for an area around the Masjid-e-Al-Nabawi. Rainfall–runoff modeling was performed by Rational Method to find the peak flow and Nash GIUH. It was found that there is about 20% change in diameter of trunk sewer for change in return period from 2 to 10 years.

Quantitative assessment of the hydrological response to urbanization has been a major concern in hydrology and water resources management. In this study, a procedure combining different statistical methods and a hydrological model to quantify annual runoff response to spatial and temporal variations of impervious surface areas was proposed and applied to the Qinhuai River basin, an urbanized basin located in southeastern China, over the period from 1986 to 2013. The landscape indicators, such as impervious area and number of impervious patches were used to measure the spatial configuration of urbanization and quantify the runoff response to urbanization. Impervious area data were derived from the Landsat images using superior ensemble learning method of rotation forest. The Mann–Kendall test, Sen's estimator, Pettitt test and double mass curve method were applied to examine gradual trend and abrupt changes for hydro-meteorological data series. A hydrological model based on stepwise regression analysis was built and used to explore the relation among annual runoff and precipitation, potential evapotranspiration and landscape indicators. The results showed that annual runoff and runoff coefficient had significant increasing trends and an abrupt change after year 2001 when the watershed impervious area reached 8.6%. The average annual runoff increased by 60%, of which, urbanization was responsible for 59% of the increase, while precipitation changes were responsible for the remaining 1% in the study region. The annual runoff response to impervious area showed a nonlinear relationship, and was more sensitive in dry years than wet years. The changes of impervious area were more remarkable in connecting the existed impervious patches than in developing the new ones beginning in the early 2000s, which increased the watershed's drainage capacity and resulted in the abrupt change of runoff response. The study demonstrated that the proposed procedure was efficient to quantify the runoff responses to urbanization using landscape metrics of impervious surface.

Quantification of runoff is critical to estimate and control water pollution in urban regions, but variation in impervious area and land-use type can complicate the quantification of runoff. We quantified the streamflow contributions of subwatersheds and the historical changes in streamflow in a flood prone urbanizing watershed in US Midwest to guide the establishment of a future pollution-control plan. Streamflow data from five nested hydrological stations enabled accurate estimations of streamflow contribution from five subwatersheds with variable impervious areas (from 0.5% to 26.6%). We corrected the impact of Missouri river backwatering at the most downstream station by comparing its streamflow with an upstream station using double-mass analysis combined with Bernaola-Galvan Heuristic Segmentation approach. We also compared the streamflow of the urbanizing watershed with seven surrounding rural watersheds to estimate the cumulative impact of urbanization on the streamflow regime. The two most urbanized subwatersheds contributed >365 mm streamflow in 2012 with 657 mm precipitation, which was more than fourfold greater than the two least urbanized subwatersheds. Runoff occurred almost exclusively over the most urbanized subwatersheds during the dry period. The frequent floods occurred and the same amount of precipitation produced ~100 mm more streamflow in 2008–2014 than 1967–1980 in the urbanizing watershed; such phenomena did not occur in surrounding rural watersheds. Our approaches provide comprehensive information for planning on runoff control and pollutant reduction in urban watersheds.

In this study, we updated the hydrological data from the 1950s to 2012 and analysed the temporal variations in the hydrological series of the Pearl River using the wavelet transform method. Furthermore, we quantified the climatic and anthropogenic effects on the changes in the hydrological processes in the Pearl River. The results of the combined methods of the wavelet transform method and the Mann-Kendall (MK) trend test (i.e., wavelet trend test) reveal that the water discharge series exhibited a statistically insignificant changing trend since the 1950s; however, the sediment load series displayed a statistically significant decreasing trend. Comparisons of the results of the MK trend test and the wavelet trend test indicate that annual and inter-annual periodic oscillations affect the trend changes in the hydrological series. Statistical analysis and the double mass curve indicate that climatic change dominates changes in water discharge, such as the El Nino Southern Oscillation (ENSO), and human activities were mainly responsible for the phase changes in the sediment load. From 1973 to 1986, deforestation in the basin dominated the sediment variability and caused 83.2% of the increase in the sediment load compared to the reference period of 1957–1972. Even though water and soil conservation projects have been carried out since the early 1990s, the vegetation cover in the catchment area decreased by 6.5 × 10 4 km 2 from the late 1980s to the late 2000s, as detected by Landsat TM images, and water and soil conservation projects had little effect on the sediment reduction. Since the 1990s, dam construction has dominated sediment variability. Compared to the reference period, the sediment load due to dam construction decreased by 83.4 kg/s and 993.3 kg/s in the periods of 1987–1998 and 1998–2006, respectively, and the reduction in the sediment load increased to 1329.5 kg/s in the period of 2007–2012, indicating the intensifying impact of dam construction on the sediment reduction. The sediment sources in the Pearl River basin have changed, and scouring of the river channel has become a new sediment source in response to dam construction. The alteration of hydrological processes in the Pearl River will continue to occur in the future in the context of global climatic change, which is becoming increasingly important for river management in the Pearl River basin.

Hydrological frequency analysis (HFA) is commonly used for the assessment of the risk associated to hydrological events. HFA is generally based on the assumptions of homogeneity, independence and stationarity of the hydrological data. Hydrological events are often described through a number of dependent characteristics, such as peak, volume and duration for floods. Unfortunately, in this multivariate setting, the verification of the above assumptions is often neglected. When a shift occurs in a data series, it can affect the stationarity and the homogeneity of the data. The objective of this paper is to study tests for shift detection in multivariate hydrological data. The considered shift tests are mainly based on the notion of depth function, except for one test that is considered for comparison purposes. A simulation study is performed to evaluate and compare the power of all these tests with hydrological constraints. A flood analysis application is also carried out to show the practical aspects of the considered tests. The power of the considered tests is influenced by a number of factors, including the sample size, the shift amplitude, the magnitude of the series and the location of the shift in the series.

As one of the fastest developing regions in China, the middle-lower Yangtze River (MLYR) is vulnerable to floods and droughts. With obtained time series of annual highest water level (HWL), annual lowest water level (LWL) and the corresponding river discharges from three gauging stations in MLYR that covering the period 1987–2011, the current study evaluated the change characteristics of annual extreme water levels and the correlation with river discharges by using the methods of trend test, Mann-Whitney-Pettitt (MWP) test and double mass analysis. Major result indicated a decreasing/increasing trend for annual HWL/LWL of all stations in MLYR during the study period. A change point in 1999 was identified for annual HWL at the Hankou and Datong stations. The year 2006 was found to be the critical year that the relationship between annual extreme water levels and river discharges changed in the MLYR. With contrast to annual LWL in MLYR, further investigation revealed that the change characteristics of annual HWL were highly consistent with regional precipitation in the Yangtze River Basin, while the linkage with Three Gorges Dam (TGD) operation is not strong. Our observation also pointed out that the effect of serious down cutting of the riverbed and the enlargement of the cross-section area during the initial period of TGD operation caused the downward trend of the relationship between annual LWL and river discharge. Whereas, the relatively raised river water level before the flood season due to TGD regulation since 2006 explained for the changing upward trend of the relationship between annual HWL and river discharge.

Alpine glaciers and perennial snow fields are important hydrologic elements in many mountain environments providing runoff during the late summer and during periods of drought. Because relatively long records of glacier mass-balance data are absent from many glacierized catchments, it remains unclear to what extent shrinking perennial snow and glaciers have affected runoff trends from these watersheds. Here we employ a hydrograph separation technique that uses a double mass curve in an attempt to isolate changes in runoff due to glacier retreat and disappearance of perennial snow. The method is tested using hydrometric data from 20 glacierized and 16 non-glacierized catchments in the Columbia Basin of Canada. The resulting estimates on cryosphere storage contribution to streamflow were well correlated to other regional estimates based on measurements as well as empirical and mechanistic models. Annual cryosphere runoff changed from +19 to -55% during the period 1975-2012, with an average decline of 26%. For August runoff, these changes ranged from +17 to -66%, with an average decrease of 24%. Reduction of cryosphere contributions to annual and late summer flows are expected to continue in coming decades as glaciers and the perennial snow patches shrink. Our method to isolate changes in late summer cryospheric storage contributions can be used as a first order estimate on changes in glacier contributions to flow and may help researchers and water managers target watersheds for further analysis.

Hydrological models are used for various purposes, including flow forecasting, flood forecasting and short and long term water management. However, models suffer from uncertainties from different sources, such as parameterisation, input data errors and process descriptions. The choice of a hydrological model depends on the purpose of its utilisation and data availability. The objectives of this study are, firstly, to investigate the consequences (uncertainty) of using simple versus a complex hydrological model to predict discharge and to quantify the uncertainty of results owing to differences between hydrological models, and secondly, to investigate the effects of using simple versus complex hydrological models in climate change studies. The complexity of each hydrological model is defined based on input data requirements, number of parameters and the level of description of the hydrological processes in the model. Model responses are compared using five hydrological models, ranging from conceptual-lumped to physically-based fully-distributed (HYMOD, HBV, HydroMAD, TopNet WaSiM-ETH) employing data from the Waiokura catchment, in the North Island of New Zealand. Climate change scenarios for three emission scenarios (B1, A1B and A1F1) have been assessed and using the models for three different time periods: “current” (1980–1999), “2040 condition” (2030–2049) and “2090 condition” (2080–2099). It was found that different models need different amounts of input data and time for the set up and the calibration and validation. The analysis of the climate change scenarios shows that the resulting discharges differ significantly between the selected models. This uncertainty indicates a need to carefully choose the model for a given application. Based on the results from the different scenarios, we conclude that a simple to moderately complex model is probably sufficient for most climate change studies; for more realistic results, using a multi-model ensemble is preferable, as it will reduce uncertainty due to model structure and complexity.

Forests and water are closely related to each other. Thus, forest management is crucial for the sustainable clean water supply. Forest thinning is one of the fundamental forest management practices, as it can change runoff by controlling the density of trees. In this study, the effect of forest thinning on long-term runoff changes was evaluated, based on the long-term rainfall-runoff data of a coniferous plantation forest catchment in Korea. From the double mass curve and Pettitt&rsquo, s test, a statistically significant increase in runoff rates was identified. A simple linear regression model of the double mass curve can successfully quantify the net effect of forest thinning on the runoff increase. Furthermore, it was also confirmed that forest thinning does not significantly increase the risk of flooding. About ten years after forest thinning, crown closure rates of the coniferous plantation forest reached a level similar to the pre-thinning period, and runoff rates returned to the pre-thinning level, due to forest growth. As a result of this study, a proposed direction for Korea&rsquo, s forest policy for water resource management is presented for the future.

Identifying the changes in precipitation and temperature at a regional scale is of great importance for the quantification of climate change. This research investigates the changes in precipitation and surface air temperature indices in the seven irrigation zones of Punjab Province during the last 50 years, this province is a very important region in Pakistan in terms of agriculture and irrigated farming. The reliability of the data was examined using double mass curve and autocorrelation analysis. The magnitude and significance of the precipitation and temperature were visualized by various statistical methods. The stations&rsquo, trends were spatially distributed to better understand climatic variability across the elevation gradient of the study region. The results showed a significant warming trend in annual Tmin (minimum temperature) and Tmean (mean temperature) in different irrigation zones. However, Tmax (maximum temperature) had insignificant variations except in the high elevation Thal zone. Moreover, the rate of Tmin increased faster than that of Tmax, resulting in a reduction in the diurnal temperature range (DTR). On a seasonal scale, warming was more pronounced during spring, followed by that in winter and autumn. However, the summer season exhibited insignificant negative trends in most of the zones and gauges, except in the higher-altitude Thal zone. Overall, Bahawalpur and Faisalabad are the zones most vulnerable to warming annually and in the spring, respectively. Furthermore, the elevation-dependent trend (EDT) indicated larger increments in Tmax for higher-elevation (above 500 m a.s.l.) stations, compared to the lower-elevation ones, on both annual and seasonal scales. In contrast, the Tmin showed opposite trends at higher- and lower-elevation stations, while a moderate increase was witnessed in Tmean trends from lower to higher altitude over the study region. An increasing trend in DTR was observed at higher elevation, while a decreasing trend was noticed at the lower-elevation stations. The analysis of precipitation data indicated wide variability over the entire region during the study period. Most previous studies reported no change or a decreasing trend in precipitation in this region. Conversely, our findings indicated the cumulative increase in annual and autumn precipitation amounts at zonal and regional level. However, EDT analysis identified the decrease in precipitation amounts at higher elevation (above 1000 m a.s.l.) and increase at the lower-elevation stations. Overall, our findings revealed unprecedented evidence of regional climate change from the perspectives of seasonal warming and variations in precipitation and temperature extremes (Tmax and Tmin) particularly at higher-elevation sites, resulting in a variability of the DTR, which could have a significant influence on water resources and on the phenology of vegetation and crops at zonal and station level in Punjab.

National large-scale soil and water conservation controls on the Gangjiang River basin have been documented, but the effect of governance on regional watershed hydrology and how the main driving factors act have not been systematically studied yet. To do this, this study evaluated changing trends and detected transition years for both streamflow and sediment discharge using long-term historical records at seven hydrological stations in the Ganjiang River basin over the past 50 years. The double mass curve (DMC) method was used to quantify the effects of both climate change and human activities on hydrological regime shifts. The results showed that the distributions of precipitation, streamflow, and sediment discharge within a year are extremely uneven and mainly concentrated in the flood season of Jiangxi Province. None of the stations showed significant trends over time for either annual precipitation or streamflow, while the annual sediment discharge at most stations decreased significantly over time. The estimation of sediment discharge via DMC indicated that after the transition years, there were rapid reductions in sediment discharge at all hydrological stations, and the average decline degree of midstream and downstream were much larger than that of upstream. Human activities, especially the increase of vegetation cover and construction of large and medium-sized reservoirs, provided a significantly greater contribution to the reduction of sediment discharge than did precipitation changes. As a case study of river evolution under global change environment, this study could provide scientific basis for the control of soil erosion and the management of water resources in Ganjiang River, as well as for the related research of Poyang Lake and the Yangtze River basin of China.

The spatiotemporal patterns prevailing at regional scale can be significantly different from the patterns observed at basin or country scale. The present study aims to analyse regional-scale trends (spatial and temporal) in monthly, seasonal and annual time series, and change point in annual time series of temperature (Tmax, Tmean and Tmin), rainfall, runoff and evapotranspiration in Kesinga sub-catchment of Mahanadi basin over the period 1970–2015. Non-parametric Mann–Kendall (MK) test and Sen’s slope test have been applied to assess the significance and magnitude of the trends, respectively. In the results, increasing trends are observed in Tmax, whereas, Tmean- and Tmin are following insignificant decreasing trend. Rainfall exhibits significant increasing trend in monsoon and annual time series, whereas, insignificant decreasing trend prevails in post-monsoon and winter season. On the contrary, significant increasing trends are observed in runoff at the catchment outlet and evapotranspiration in all the seasons. The change point in annual rainfall and runoff as identified using non-parametric Pettitt test is found to be in the year 2000 which is further verified using sequential MK test. The significant change in LULC of the region from forest, swamp and fallow land to cropland over time has been found to be the possible reason for the breakpoint observed in double mass curve and discrepancies in the trend of rainfall and runoff during non-monsoon season. Overall, the influence of climate variability is mainly evident in annual and monsoon series, whereas, the effect of anthropogenic variables is confined to non-monsoon seasons.

Yongding River is the largest river flowing through Beijing, the capital city of China. In recent years, Yongding River Basin (YDRB) has witnessed increasing human impacts on water resources, posing serious challenges in hydrological and ecological health. In this study, remote sensing techniques and statistical time series approaches for hydrological studies were combined to characterize the dynamics and driving factors of reservoir water extents in YDRB during 1985–2016. First, 107 Landsat 4, 5, 7 and 8 images were used to extract surface water extents in YDRB during 1985–2016 using a combination of water indices and Otsu threshold algorithm. Significant positive correlation was found between water extents and the annual inflow for the two biggest reservoirs, the downstream Guanting and upstream Cetian reservoirs, proving their representativeness of surface water availability in this basin. Then, statistical time series approaches including trend-free pre-whitening Mann-Kendall trend test, Pettit change-point test and double mass curve method, which are frequently used in hydrological studies, were adopted to quantify the trend of reservoir water extents dynamics and the relative contributions of climate variability and human activities. Results showed that the water extents in both reservoirs exhibited significant downward trend with change point occurring in 2001 and 2005 for Guanting and Cetian, respectively. About 74%~75% of the shrinkage during the post-change period can be attributed to human activities, among which GDP, population, electricity power production, raw coal production, steel and crude iron production, value of agriculture output, and urban area were the major human drivers. Hydrological connectivity between the upstream Cetian and downstream Guanting reservoirs declined during the post-change period. Since 2012, water extents in both reservoirs recovered as a result of various governmental water management policies including the South-to-North Water Diversion Project. The methodology presented in this study can be used for analyzing the dynamics and driving mechanism of surface water resources, especially for un-gauged or poorly-gauged watersheds.

In northern Iran’s Haraz River basin between 1975 and 2010, hydrological sensitivity, double mass curve, and Soil and Water Assessment Tool (SWAT) methods were applied to monitoring and analysing changes in stream flow brought on by climatic variability and human activities. Applied to analyse trends in annual and seasonal runoff over this period, the sequential MK test showed a sudden change point in stream flow in 1994. The study period was, therefore, divided into two sub-periods: 1975–1994 and 1995–2010. The SWAT model showed obvious changes in water resource components between the two periods: in comparison to the period of 1975–1994, sub-watershed-scale stream flow and soil moisture decreased during 1995–2010. Changes in evapotranspiration were negligible compared to those in stream flow and soil moisture. The hydrological sensitivity method indicated that climatic variability and human activities contributed to 29.86% and 70.14%, respectively, of changes in annual stream flow, while the SWAT model placed these contributions at 34.78% and 65.21%, respectively. The double mass curve method indicated the contribution of climatic variability to stream flow changes to be 57.5% for the wet season and 22.87% for the dry season, while human activities contributed 42.5% and 77.13%, respectively. Accordingly, in the face of climatic variability, measures should be developed and implemented to mitigate its impacts and maintain eco-environmental integrity and water supplies.

The Shiyang River Basin is a typical arid watershed in Northwest China. Scientific understanding of the driving mechanism of runoff change is the basis of scientific utilization of water resources and regional sustainable development. In this study, runoff changes at different time scales were analyzed for the period 1960–2018, and the impacts of climate variability and human activities on runoff were investigated in the middle and lower reaches of the Shiyang River Basin (SRB). A combination of mutation analysis and human-designed analysis was adopted to divide the study period into the baseline period and the variation period. The Mann–Kendall test (M−K) and Double Mass Curve method (DMC) were used to detect abrupt changes and quantify the relative effects of climate change and human activities on runoff. The results reveal a significant declining trend in annual runoff on the whole in the middle and lower reaches of the SRB, and there was an obvious recovery trend after the implementation of the Comprehensive Treatment Program of the SRB (CTSRB) in 2007. Abrupt changes occurred in 1976, 1991 and 2007, which divided the study period into the baseline period (1960–1975), the Variation Ⅰ period (1976–1990), the Variation Ⅱ period (1991–2006) and the Variation III period (2007–2018). The contribution of human activities to runoff reduction was 88.72%, whereas the contribution of climate change to runoff reduction was only 11.28%. Furthermore, the contribution of human activities to runoff reduction in the Variation Ⅰ period, Variation Ⅱ period and Variation III period was 89.44%, 93.02% and 83.69%, respectively. Therefore, human activities played the most dominant role in the variation of runoff, followed by climate change and upstream runoff. Further analysis of the impact of human activities on runoff indicated that agricultural irrigation was the dominant factor of runoff reduction. This study can provide detailed information on water resources and a scientific basis for the development and utilization of water resources in the future.

In the context of global warming, precipitation (P) and temperature (T) are the most important climate indicators playing important roles in the hydrological cycle. Nevertheless, the response of their dependency structures to the changing environment is not clearly revealed on a regional or global scale. To this end, the non-stationarity of the precipitation-temperature (P-T) dependency structure was identified via the Copula-based Likelihood-ratio (CLR) method, which further verified through the frequently used double mass curve method. Furthermore, local meteorological factors (e.g. wind speed (WS), sunshine duration (SD), relative humidity (RH) and vapour pressure (VP)) and teleconnection factors (e.g. the Arctic Oscillation (AO), Pacific Decadal Oscillation (PDO), El Nino-Southern Oscillation (ENSO) and Sunspots) were selected to explore possible driving forces and mechanism of the P-T dependency structure dynamics. The Datong River Basin (DRB), located in the Qinghai-Tibet Plateau, one of the climate change-sensitive and eco-sensitive areas worldwide, was selected as a case study. Results showed that: (1) the CLR method simultaneously capturing bivariate linear and nonlinear information is more superior than the double mass curve in detecting the non-stationarity of bivariate dependency structure; (2) change points of P-T dependency structure were identified at Qilian and Minhe stations, indicating that its non-stationarity occurred in the DRB; (3) in terms of local meteorological factors, the P-T dependency structure dynamics were directly driven by the VP, which was closely associated with the Clausius-Clapeyron (CC) equation where P and T would be theoretically linked by the atmospheric moisture; (4) in terms of teleconnection factors, the impacts of AO and PDO on local meteorological (VP, WS, and RH) are dominant, which further leads to the change in the P-T dependency structure dynamics. Generally, this study provides important insights into the response of the P-T dependency structure dynamics to a changing environment, where the proposed research framework could be extended to any other watershed and any bivariate hydro-meteorological elements.