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Badosa J.,Ecole Polytechnique - Palaiseau | Calbo J.,University of Girona | McKenzie R.,NIWA - National Institute of Water and Atmospheric Research | Liley B.,NIWA - National Institute of Water and Atmospheric Research | And 3 more authors.
Photochemistry and Photobiology | Year: 2014

Cloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern-hemisphere mid-latitude site where a 10-years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (<60%) and large SZA (>60°). Similarly, local short-time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%). Cloud effects on UV Index (UVI) and total solar radiation (TR) are assessed. The role of cloud cover and sunny conditions (from sky images) and of solar zenith angle is investigated. The analyses are undertaken for a southern-hemisphere mid-latitude site where a 10-years dataset is available. It is confirmed that clouds affect TR more than UVI, both in reducing and enhancing the cloud-free radiation. From the analyses, two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Methods' estimations are compared with measurements. © 2014 The American Society of Photobiology. Source


Wang X.-J.,Nanjing Hydraulic Research Institute | Wang X.-J.,Chinese Ministry of Water Resources | Zhang J.-Y.,Nanjing Hydraulic Research Institute | Zhang J.-Y.,Chinese Ministry of Water Resources | And 6 more authors.
Mitigation and Adaptation Strategies for Global Change | Year: 2012

Yellow River, is designated as "the cradle of Chinese civilization" and played a key role not only in the country's economic development but also in the historic and cultural identity of the Chinese people. With the rapid economic development and population growth, water demand for industry and households has increased significantly in the Yellow River basin; this has caused an increasing gap between water supply and demand. Competing water demands triggered conflicts between disparate water users on different scales such as the rich and the poor, or between different sectors and regions, such as domestic and agriculture, agriculture and industry, upstream and downstream, rural and urban areas, etc. Ensuring equity in water supply for conflicting water users is one of the major challenges that facing water managers and in particular water management in the Yellow River basin. In this paper, a method has been developed to calculate the Gini coefficient of water use as an indicator to measure the equality in domestic water supply. A dual domestic water use structure model is employed for this purpose. The developed method is subsequently applied to assess the equality in domestic water supply in the Yellow River. Data of population growth, domestic water use and economic development over the time period 1999-2006 are used to calculate the Gini coefficient of water use over the same length of period. The result shows a decreasing trend in Gini coefficient of domestic water use in the Yellow River basin after 2001 which means domestic water use is becoming more and more equitable in the basin. The study justifies that the Gini coefficient of water use can be used and recommended as a useful tool for the water management especially in the context of global change. © 2011 Springer Science+Business Media B.V. Source


Wang X.,Basin Water | Lian Y.,Basin Water | Huang C.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Wang X.,Nanjing Hydraulic Research Institute | And 7 more authors.
Mitigation and Adaptation Strategies for Global Change | Year: 2012

Due to freshwater supplement scarcity and heavy human activities, the fresh water wetland ecosystem in Yellow River Delta is facing disintegrated deterioration, and it is seriously affecting the health of the Yellow River ecosystem. This paper identifies the restoration objectives of wetland aiming to protect ecological and economic values and development as well as the water resources of the Yellow River. The hydraulic and groundwater coupling model and Landscape Ecological Decision and Evaluation Support System (LEDESS) of the Yellow River Delta were established to calculate environmental flows of degraded wetlands. LEDESS is a computer-based model developed and used to assess and evaluate the effects of land-use changes on nature. In this study, LEDESS is used to assess and evaluate the ecological effects and the restoration possibilities considering several environmental flows' supplement scenarios. This included the changes of suitable habitat conditions and its ecological carrying capacities for indicator species, e. g., Red-crowned crane (Grus japonensis), Oriental stork (Ciconia boyciana), and Saunder's gull (Larus relictus), and changing of ecological patterns. The results showed that replenishing fresh water to wetlands is one of the effective adaptive measures to mitigate wetland degradation and improve its habitat quality and carrying capacities. This study indicated that landscape ecology approach is not only considered as a good way to solve complex problems in ecosystem management but also can be used to decide on the environmental flows and assess its ecological effects in large-scale wetland rehabilitation. This integrated method could make environmental flows estimated and assessment more rational than the results of hydrologic methods. It could assist decision makers to "see" the ecological effects after water supplementing and so alleviate the contradictions between environmental flows and production water demands, and can facilitate the implementation of environmental flows in most countries with water resources shortage. © 2011 Springer Science+Business Media B.V. Source


Wang X.-J.,Nanjing Hydraulic Research Institute | Wang X.-J.,Chinese Ministry of Water Resources | Zhang J.-Y.,Nanjing Hydraulic Research Institute | Zhang J.-Y.,Chinese Ministry of Water Resources | And 6 more authors.
IAHS-AISH Publication | Year: 2011

A System Dynamics (SD) approach, focusing on water demand forecasting, was applied and developed based on the analysis of dynamic interactions among physical elements (natural runoff, groundwater recharge), environmental (water quality, ecosystem preservation) and socio-economic (population growth, water consumption, policy and management) aspects of water management elements in a regional water resources system. Through the analysis of multi-feedbacks and nonlinear interactions among system elements, a complex SD model was developed and applied in Tuwei River in the middle reaches of the Yellow River using water demand theory. The practical verification of the model shows that the relative error is small; therefore the model is reasonable structured to mimic the actual situation. Furthermore, total water demand of the whole basin can be also forecasted under the future changes of population, economic and climate scenario, and then propose the sustainable strategy for water demand management to achieve the goal of sustainable development in the whole basin. Copyright © 2011 IAHS Press. Source


Xiao-jun W.,Nanjing Hydraulic Research Institute | Xiao-jun W.,Chinese Ministry of Water Resources | Jian-yun Z.,Nanjing Hydraulic Research Institute | Jian-yun Z.,Chinese Ministry of Water Resources | And 7 more authors.
Urban Water Journal | Year: 2011

Climate change and human activities have changed a number of characteristics of river flow in the northwest of China. Numerous problems such as water resource shortage, drying up of rivers, water pollution are the direct consequences of these changes. In this paper, we used the example of Yulin city in northwest China to assess the spatio-temporal characteristics and driving forces of annual river flow changes. Our research was based on the long-term time series of hydrological data from 1956 to 2005, to analyse annual flow in four main rivers (Kuye River, Tuwei River, Wuding River and Jialu River). The river flow depends upon the runoff characteristics of the river catchment, therefore we used variation ratio, variation index, unevenness, Runoff-Concentration Degree (RCD) and Runoff-Concentration Period (RCP) to determine the change in runoff characteristics of the four main rivers flows of the Yulin city. We tested the tendency of runoff by the Mann-Kendall non-parameter statistical method to obtain the temporal evolution law. At the same time, Kriging spatial interpolation and GIS were used to derive the spatial evolution law. The dates of climate change (precipitation) and human activities were also used to calculate the driving forces for annual runoff changes of the rivers' catchments. Through the accumulation curves and multi-recursive techniques, we built the correlation between precipitation and runoff. The driving factors for annual runoff change were then calculated by using the runoff coefficient method. Results showed that the distribution of annual runoff was uneven and had a small accumulation in July and August, especially in Kuye River, and there seemed to be a significant reducing trend in annual runoff. Isolines and the thematic map of Mann-Kendall tests U(R) revealed that the Tuwei River's catchment is the most affected catchment, with annual runoff substantially changed. At the 5% significance level, precipitation did not significantly drop compared with annual runoff. We also found that precipitation is not the only factor responsible for the decreased annual runoff. Therefore we included human activities affect in this case study by using the past 25 years land use, water conservancy and urbanisation data. We discriminated the impacts of climate change and human activities on the surface runoff by multi-recursive analysis method and runoff coefficient method. The results showed that human activities are the direct cause for the changes of river runoff. The results of the study also revealed that the Wuding and Jialu rivers had the most and the least changes in the runoff respectively; this phenomenon should be seriously considered for future water resources planning and management. © 2011 Copyright Taylor and Francis Group, LLC. Source

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