Search

The effects of climate change and population growth in recent decades are leading us to consider their combined and potentially extreme consequences, particularly regarding hydrological processes, which can be modeled using a generalized extreme value (GEV) distribution. Most of the GEV models were based on a stationary assumption for hydrological processes, in contrast to the nonstationary reality due to climate change and human activities. In this paper, we present the nonstationary generalized extreme value (NSGEV) distribution and use it to investigate the risk of Niangziguan Springs discharge decreasing to zero. Rather than assuming the location, scale, and shape parameters to be constant as one might do for a stationary GEV distribution analysis, the NSGEV approach can reflect the dynamic processes by defining the GEV parameters　as functions of time. Because most of the GEV model is designed to evaluate maxima (e.g. flooding, represented by positive numbers), and spring discharge cessation is a ‛minima', we deduced an NSGEV model for minima by applying opposite numbers, i.e. negative instead of positive numbers. The results of the model application to Niangziguan Springs showed that the probability of zero discharge at Niangziguan Springs will be 1/80 in 2025, and 1/10 in 2030. After 2025, the rate of decrease in spring discharge will accelerate, and the probability that Niangziguan Springs will cease flowing will dramatically increase. The NSGEV model is a robust method for analysing karst spring discharge. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This article explains the Global Energy and Water Cycle Experiment (GEWEX)-Asian Monsoon Experiment (GAME). GEWEX was conducted under the umbrella of the World Climate Research Program and was led by Professor Yasunari from Japan. GAME research focused on water and energy cycles of Eurasia. Intensive field work carried out in eastern Siberia, the Tibetan Plateau, Central China, and Thailand has resulted in new insights into hydrological and meteorological processes. The papers in this issue focus on the hydrological characteristics of the GAME region.

Understanding the dominant causes of streamflow alteration and effects of the current water diversion scheme is beneficial for sustainable management of water resources in an arid area. This study presents a quantitative attribution of the run‐off changes between headstreams and mainstream from 1960 to 2015 using the Choudhury–Yang equation and evaluates the effects of 18 times of ecological water conveyance in the lower reaches of the Tarim River Basin (TRB). Our results suggest that climate change was the primary determinant of increase of the streamflow in the headstreams from 2000 to 2015. While in the mainstream, human activities played a dominant role in deduction in the streamflow with the contribution of 54.8–355.6%. Eighteen episodes of ecological water conveyance have a positive effect on rising groundwater level and are highly related to seed falling time of Shrub and Perennial herbaceous and Annual herbaceous except for Arbor. It indicates that restoring the long‐term drying of the lower reaches through continuous water conveyance is feasible, although the existing programme has not restored the entire riparian system. Our study suggests that it is necessary to adopt an integrated approach for water resources allocation rather than relying on a single tributary contribution in the TRB. [ABSTRACT FROM AUTHOR]

Watershed delineation is a required step when conducting any spatially distributed hydrological modelling. Automated approaches are often proposed to delineate a watershed based on a river network extracted from the digital elevation model (DEM) using the deterministic eight-neighbour (D8) method. However, a realistic river network cannot be derived from conventional DEM processing methods for a large flat area with a complex network of rivers, lakes, reservoirs, and polders, referred to as a plain river network region (PRNR). In this study, a new approach, which uses both hydrographic features and DEM, has been developed to address the problems of watershed delineation in PRNR. It extracts the river nodes and determines the flow directions of the river network based on a vector-based hydrographic feature data model. The river network, lakes, reservoirs, and polders are then used to modify the flow directions of grid cells determined by D8 approach. The watershed is eventually delineated into four types of catchments including lakes, reservoirs, polders, and overland catchments based on the flow direction matrix and the location of river nodes. Multiple flow directions of grid cells are represented using a multi-direction encoding method, and multiple outflows of catchments are also reflected in the topology of catchments. The proposed approach is applied to the western Taihu watershed in China. Comparisons between the results obtained from the D8 approach, the 'stream burning' approach, and those from the proposed approach clearly demonstrate an improvement of the new approach over the conventional approaches. This approach will benefit the development of distributed hydrological models in PRNR for the consideration of different types and multiple inlets and outlets of catchments. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of river runoff variation is important for the effective management of water resources in arid and semi-arid regions. This study uses long-term observational data as a basis for examining the effects of human activities and climate change on the runoff variation of Jinghe River Basin, a typical arid inland basin in northwest China. A distributed hydrological model called the Soil and Water Assessment Tool, combined with a sequential cluster method and a separation approach, was used to quantify and distinguish the effects of human activities and climate change on runoff. The hydrological sequence before 1981 can be considered natural. However, human activities have significantly affected runoff since 1981. The runoff reduction caused by human activities between 1981 and 2008 accounted for 85.7% of the total reduction in the downstream of Jinghe River, whereas that caused by climatic variation was only 14.3%. This observation suggests that human activities are the major driver of runoff variation in the basin. Although the role of climate change in driving runoff variation has been identified to be prevalent and dominant in arid regions, this study highlights the importance of human activities. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Shallow groundwater is an important source of water for the maintenance and restoration of ecosystems in arid environments, which necessitates a deeper understanding of its complex spatial and temporal dynamics driven by hydrological processes. This study explores the dominant hydrological processes that control the shallow groundwater dynamics in the Gobi Desert-riparian-oasis system of the lower Heihe River, a typical arid inland river basin located in northwestern China. The groundwater level and temperature were monitored in 14 shallow wells at 30-min intervals during the 2010-2012 period. After combining this information with meteorological and hydrological data, a comprehensive analysis was conducted to understand the dynamic behaviour of the shallow groundwater system and to determine the dominant factors that control the groundwater flow processes. The results of the study indicate notably large temporal and spatial variations in both the groundwater level and temperature. Noticeable fluctuations in the groundwater level (0.5-1 m) and temperature (4-8 °C) were observed in the riparian zone, evidencing a clear river influence. In comparison, the groundwater fluctuations in the Gobi Desert were more stable (the annual variations of the water table were less than 0.5 m, and the water temperature varied by no more than 2 °C). Strong variations in the groundwater table (1.5-5.0 m/year) and temperature (1.5-6.5 °C), mainly caused by surface flood irrigation and groundwater pumping, were observed in the oasis area. The investigated sites were categorized into three types that reflect the dominant hydrological processes: (1) the riparian zone, dominated by riverbank filtration and groundwater evapotranspiration; (2) the Gobi Desert area, controlled by groundwater evaporation and lateral recharge; and (3) the oasis area, dominated by groundwater evapotranspiration as well as surface-groundwater interactions caused by human activities. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hydrological processes change from the impacts of climate variability and human activities. Runoff in the upper reaches of the Hun-Taizi River basin, which is mainly covered by forests in northeast China, decreased from 1960 to 2006. The data used in this study were based on runoff records from six hydrological stations in the upper reaches of the Hun-Taizi River basin. Nonparametric Mann-Kendall statistic was used to identify change trends and abrupt change points and consequently analyze the change characteristics in hydrological processes. The abrupt change in the annual runoff in most subcatchments appeared after 1975. Finally, the effects of climate change and land cover change on water resources were identified using regression analysis and a hydrology model. Results of the regression analysis suggest that the correlation coefficients between precipitation and runoff prior to the abrupt change were higher compared with those after the abrupt change. Moreover, using hydrology model analysis, the water yield was found to increase because of the decrease in forest land. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Hydrological Processes is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article presents a study which analyzed hydrological daily discharge time series of the Shaligunlanke Station in China based on data mining theory and technology. Results showed that the annual process of the daily discharge can be divided into five segments. Dynamic time warping (DTW) was used to look for similarities in the discharge process. The study also showed that data mining is a feasible approach to discover hidden information in the historical hydrological data.

The article presents a study on the shift trend and step changes for runoff time series in the Shiyang River basin in northwest China. It states that seven statistical test approaches were used to determine the shift trends and step changes in the study. It discusses that Mann-Kendall test, Spearman's Rho test, linear regression and Hurst exponent were utilized to detect past and future shift trends for runoff time series, while the distributed-free CUSUM test, cumulative deviations and the Worsley likelihood ratio test were employed to detect step changes for the same time series. Results showed that the annual runoff from Zamu, Huangyang and Gulang rivers demonstrate statistically significant decreasing trends.

The article presents a comparison of three methods for examining vineyard evapotranspiration (ET) in the arid desert regions of China. The methods compared include field Water Balance (WB), Eddy Covariance (EC) and Bowen Ratio-Energy Balance (BREB). The variations of the total ET estimated by EC and BREB are similar at hourly or daily timescale with a slight difference in values. Results show that these methods provided similar estimate of the total ET at various timescales and can be used to estimate ET from vineyards in arid conditions.

The article presents a study which focuses on the improvement of the peak flow rate equation used in the Chemicals, Runoff, and Erosion from Agricultural Management Systems (CREAMS) model, to be used in the Loess Plateau in China. The significance of the measure of the peak flow rates in CREAMS in soil conservation plans and engineering projects are discussed. The methods and results of the study and observations are also discussed. The new equation for the peak flow rate in CREAMS is also presented.

This article presents a study regarding the isotropic variation in the lake water balance at the Yamdruk-tso basin found in southern Tibetan Plateau. It discusses that the use of stable isotopes is a practical tool in the study of the lake water budget, which is one way to study the hydrological cycle in the large numbers of inland lakes on the Tibetan Plateau. It mentions that the isotope record of the sediments at the Tibetan Plateau is believed to reflect the climatic and environmental changes.

The article presents a study on an automatic mapping of snow cover depletion curves using remote sensing data under conditions of frequent cloud cover and temporary snow. The study formulates a methodology to produce accurate snow cover depletion curves automatically using high temporal resolution optical remote sensing data such as Terra Moderate Resolution Imaging Spectroradiometer (MODIS). Moreover, the said method based on Terra MODIS was used in a case study carried in the lower and middle reaches of the Kaidu River Watershed in China. Results of the case study suggest that the approach in making accurate snow cover depletion curves automatically under conditions of frequent cloud cover and temporary snow cover using high temporal resolution optical sensing data, were successful.

This article discusses a study which estimated the evolution of vegetation cover and its hydrological impact in the Mekong River basin in the 21st century. The researchers used climatic predictions, a dynamic global vegetation model, terrestrial biogeochemical model, and the distributed hydrological model. They indicated a significant change in vegetation type mainly on the Tibetan Plateau in China and in mountainous areas, with the degree of change differing for each special report on emissions scenario. They suggested that changes in river discharge will be slowed due to changes in evapotranspiration.

The Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME) reanalysis datasets are the products of four-dimensional data assimilations (4DDA) of meteorological observations made from April 1998 to October 1998. These datasets were created using the most recently updated 4DDA schemes of the Japan Meteorological Agency (JMA) during the GAME reanalysis project (1999-2001) as well as radiosonde observations made during the intensive observation period of the GAME project (April 1998-October 1998). Two versions of reanalyses products have been released officially: Ver. 1.1 and Vet. 1.5. One of the greatest differences between the two versions is the representation of snow cover: Ver. 1.1 used climatological snow data, while Vet. 1.5 used satellite-derived snow information. Here, we describe how snow cover modifications and land surface schemes differ between the two versions and how changes in surface processes affect surface fluxes. The use of satellite-derived snow information produced a difference in surface fluxes over the Tibetan Plateau, especially for May. We also compare surface fluxes estimated by the long-term reanalysis (JRA25) product of the JMA as well as GAME reanalysis product with in situ observations by the Asian Automatic Weather Station (AWS) Network (AAN). Radiosonde observations made 4 times daily were incorporated into the atmospheric field of the 4DDA GAME reanalysis and resulted in a good correspondence between the reanalyses products and surface observations, especially for July. The use of satellite-derived snow information as a boundary condition also had improved flux results over the Tibetan Plateau in May. [ABSTRACT FROM AUTHOR]

The hydrological response to climate change in the Tarim River Basin was investigated by analysing the hydrological, temperature and precipitation data of the past 50 years. The long-term trend of the hydrological time-series, including air temperature, precipitation, and streamflow, was examined by using both parametric and non-parametric techniques and the plausible association between streamflow and climate change by the method of grey correlation analysis. The results show that the study area became warmer in the last few decades. The air temperature experienced a significant monotonic increase by 5%; the precipitation showed a significant decrease in the 1970s and then a major increase in the 1980s and 1990s, with average annual precipitation up by 6-8 mm per decade. A step change occurred in both temperature and precipitation around 1986, with mean temperature and precipitation increasing from 67°C and 146 mm before 1986 to 7.3°C and 180 mm respectively after 1986. The temperature has risen by nearly 1 °C over the past 50 years, possibly resulting from the impact of global climate change. Streamflows in the Aksu River and the Yarkant River have shown a significant (P < 0.05) tendency of increase. This is particularly the case for the Aksu River. The coefficients of streamflow increase in the Aksu and Yarkant Rivers are 0.41 and 0.13 respectively. The results of grey correlation analysis show that in the Aksu River, which is located in the northwest of the basin, the impact of precipitation on streamflow is much greater than that of temperature. However, in the Hotan River, which is located in the southwest of the basin, the impact of temperature on streamflow is much greater than that of precipitation. This is likely to be related to the geographic distribution of the headstreams of the rivers. [ABSTRACT FROM AUTHOR]