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121.
Under the dry weather conditions in the typical steppe region of Inner Mongolia, the diurnal change curve of photosynthetic rate of Aneurolepidium chinense community is a curve of "double peaks" with midday depression. The photosynthetic rate in the morning is height than in the afternoon, which is related to the water condition at that time. The decrease range of community photosynthetic rate at noon is closely correlated with the low air relative humidity and soil moisture, the photosynthetic rate decreases less under better water condition.The instantaneous photosynthetic rate and diurnal net photosynthesis declined in dry condition, but they rised after irrigation or nitrogen-fertilization. Thus irrigation and fertilization is a effective way to improve grasslands and to raise grassland productivity. 相似文献
122.
C. Spence G. Ali C.J. Oswald C. Wellen 《Journal of the American Water Resources Association》2019,55(2):318-333
Lakes are landscape features that influence connectivity of mass and energy by being foci for the reception, mixing, and provision of water and material. Where lake fractions are high, they influence hydrological connectivity. This behavior was exemplified in the Baker Creek watershed in Canada's Northwest Territories during a two‐year drought in which many lake levels declined below outlet elevations. This study evaluated how lakes controlled surface runoff connectivity reestablishment following the drought using a new assessment method, T‐TEL (time scales — thresholds, excesses, losses). Analysis of daily data showed that during a summer period following the drought, connectivity occurred between 0% and 41% of the time. The size of run‐of‐the‐river lakes relative to their upstream watershed area, and the upstream lake fraction, are two factors for connectivity. These terms represent a lake's ability to control the size of storage deficits relative to rainfall, and evaporation and storage losses along pathways. The connectivity magnitude–duration curve only aligned with the watershed flow duration curve during high‐water conditions, implying lakes functioned as individuals rather than as part of a perennial watercourse during much of the study. The T‐TEL method can be used to quantify consistent metrics of hydrologic connectivity that can be used for regionalization exercises and understanding hydrologic controls on material transport. 相似文献
123.
Alexander Heeren Tapan B. Pathak Teenie Matlock Martha Conklin 《Journal of the American Water Resources Association》2019,55(6):1564-1571
While the exceptional drought in California ended in 2017, the state is expected to experience similar droughts in the future. Understanding how individuals perceive the causes and consequences of drought will help frame future communication and planning efforts. We surveyed a panel of Californian residents about their perceptions of the 2012–2017 drought. We found a major disconnect in how our respondents perceived drought and water use. Respondents perceived the drought as being caused primarily by climatic factors and underestimated the role human water use, particularly agricultural use, had in exacerbating drought. Comparing our respondents across the state and across socio‐demographics, there were few differences in concern about drought but several differences in how residents thought drought should be managed. Such research can help water managers communicate about the specific concerns the public has about future droughts, as well as address misperceptions about the relationship between drought and water use. 相似文献
124.
Ning Liu Jatin Kal Shirong Liu Vanessa Haver Bernard Dell Keith R.J. Smettem Richard J. Harper 《环境科学学报(英文版)》2020,32(4):262-274
Increasing atmospheric CO2 is both leading to climate change and providing a potential fertilisation effect on plant growth. However, southern Australia has also experienced a significant decline in rainfall over the last 30 years, resulting in increased vegetative water stress. To better understand the dynamics and responses of Australian forest ecosystems to drought and elevated CO2, the magnitude and trend in water use efficiency (WUE) of forests, and their response to drought and elevated CO2 from 1982 to 2014 were analysed, using the best available model estimates constrained by observed fluxes from simulations with fixed and time-varying CO2. The ratio of gross primary productivity (GPP) to evapotranspiration (ET) (WUEe) was used to identify the ecosystem scale WUE, while the ratio of GPP to transpiration (Tr) (WUEc) was used as a measure of canopy scale WUE. WUE increased significantly in northern Australia (p < 0.001) for woody savannas (WSA), whereas there was a slight decline in the WUE of evergreen broadleaf forests (EBF) in the southeast and southwest of Australia. The lag of WUEc to drought was consistent and relatively short and stable between biomes (≤3 months), but notably varied for WUEe, with a long time-lag (mean of 10 months). The dissimilar responses of WUEe and WUEc to climate change for different geographical areas result from the different proportion of Tr in ET. CO2 fertilization and a wetter climate enhanced WUE in northern Australia, whereas drought offset the CO2 fertilization effect in southern Australia. 相似文献
125.
Corey D. Wallace Ryan T. Bailey 《Journal of the American Water Resources Association》2015,51(1):185-199
Atoll island communities rely on rainwater catchment systems (RWCS) as a primary method of storing freshwater. However, stored freshwater can be depleted during times of drought, requiring importation of water to sustain community living. To maintain adequate water supply under future climatic conditions, the functioning of RWCS for atoll communities must be analyzed and optimal designs must be adopted. In this study, a quantitative analysis of stored daily water volumes is provided for atoll islands within the Federated States of Micronesia (FSM), with Nikahlap Island, Pakein Atoll, and a generic island in western FSM used as representative cases. Using a daily water balance model for the RWCS, baseline conditions are simulated for the 1997‐1999 time period, during which an intense El Niño‐induced drought occurred, and a sensitivity analysis is performed to quantify the influence of RWCS features on water system outputs, whereupon an optimal RWCS design using existing infrastructure is analyzed. Results indicate the strong influence of catchment area, system efficiency, and storage capacity on water volumes and the depletion of water during dry seasons and drought periods using current RWCS infrastructure. Adequate storage can be maintained during a major drought if unused RWCS features are employed and if minimal rationing is adopted. Study results provide water resource managers and government officials with valuable data for consideration in water security measures. 相似文献
126.
生态破坏诱发中国水旱灾害程度及计量——以90年代为例 总被引:4,自引:1,他引:3
徐嵩龄 《中国人口.资源与环境》1999,9(4):46-51
生态破坏表现为植被破坏、水土流失、水系统淤塞,利用自然致灾因子和生态破坏因子可以构建水旱灾害的致灾函数。本文利用灾函数计算了生态破坏对中国90 年代水旱灾害的致灾影响度 相似文献
127.
Yuliang Zhou Dong Zhang Ping Zhou Zhaoli Wang Pan Yang Juliang Jin Yi Cui Shaowei Ning 《Journal of the American Water Resources Association》2023,59(3):571-583
In univariate frequency analysis, the return period of an event has a one-to-one correspondence with its characteristic value, and the response of the hydraulic structure to hydrological load expressed by the hydrological event is monotonic. Thus, the design criteria of the hydraulic structure can be equivalently represented by the return period of the hydrological event, and consequently, design event-based design parameters evaluated have been widely used in practical engineering. However, the monotonic correspondence between the return period of the hydrological event and the response of the hydraulic structure does not exist in the multivariate context, and hydrological load with a larger joint return period does not always produce a more unsafe response. Misunderstandings of concepts of return periods of hydrological event, and estimation of hydrological design events usually take place in multivariate frequency analysis. This study theoretically derives the relations between different types of joint return periods, joint return period and its marginal return periods, the occurrence of bivariate extreme events and their return periods, and then the theoretical framework is tested. Results from the case contribute to the understanding of bivariate return periods of hydrological event, and the results demonstrate that design criteria cannot be equivalently represented by joint return periods of hydrological load, and design parameters of the hydraulic structure should not be determined by multivariate hydrological design events. 相似文献
128.
ABSTRACT: Temporary transfers of water for dry year water supply are analyzed for cost and operational feasibility. The temporary transfer is implemented as part of a water rights option agreement (WROA) between a lesson and a lessee. First, engineering analysis determines the technical feasibility and operations plan under the Colorado doctrine of prior appropriation. The cost of the WROA to a water utility is estimated. Other considerations in the agreement are discussed. The WROA is compared to other dry-year supply alternatives using a water system simulation model to obtain expected cost and operational performance characteristics. 相似文献
129.
Raymond L. Anderson Thomas A. Miller Monty C. Washburn 《Journal of the American Water Resources Association》1980,16(4):642-645
ABSTRACT: During the drought year of 1977, unusually low river flows during the summer caused the City of Fort Collins, Colorado, to institute lawn watering restrictions for six weeks as a conservation measure. Water use during the restriction period decreased 41 percent below the previous year. The effectiveness of the restrictions, however, has been unclear because abnormally wet weather also appeared to reduce evapotranspiration rates during the period the restrictions were in effect. The statistical analysis indicates that the reduction in water use due to lawn watering restrictions was 603 acre-feet and that abnormal weather reduced use by an additional 659 acre-feet during the same period. During a period of normal evapotranspiration rates, such restrictions would be expected to reduce Fort Collins municipal water usage by 19.7 percent. 相似文献
130.
William Whipple 《Journal of the American Water Resources Association》1981,17(5):814-819
Water conservation is a much emphasized policy of the Federal government. Discussion of water conservation proposals often involves confusion between a conservation “ethic,” which is an end in itself, and conservation as a means for attaining various economic objectives. Analysis indicates that outside of ground water “mining.” water is usually a renewable and reusable resource. During periods of normal precipitation, water conservation should be employed only when the value of the water saved exceeds the cost of effecting the savings. Water conservation is most valuable as a drought contingency tactic. Water conservation as a substitute for structural provision to meet normal water demand growth is apt to prove shortsighted. 相似文献