Variations In Hydrological Cycle Research Articles

Influence of Land Use Change on Hydrological Cycle: Application of SWAT to Su-Mi-Huai Area in Beijing, China

The human activities and urbanization process have changed the underlying surface of urban areas, which would affect the recharge of groundwater through rainfall infiltration and may further influence the groundwater environment. Accordingly, it is imperative to investigate the variation of hydrological cycle under the condition of underlying surface change. Based on the high-precision remote sensing data of 2000, 2005, 2010 and 2015, and Soil and Water Assessment Tool (SWAT) model, this work firstly studied the land use change and the corresponding changes in runoff generation mechanism and rainfall infiltration coefficient in Su-Mi-Huai area, Beijing, China. Meanwhile, SWAT-MODFLOW semi-loose coupling model was applied to analyze the water balance in the study area in typical hydrological years. The results showed that the area of the construction land (urban and rural residential land) increased by 1.04 times from 2000 to 2015, which is mainly attributed to the conversion of cultivated land to construction land in the plain area. This change caused the runoff in the area to increase by 7 × 106 m3, the runoff coefficient increased by 17.9%, and the precipitation infiltration coefficient was less than the empirical value determined by lithology. Compared with 2000, the average annual precipitation infiltration coefficient in 2018 decreased by 6.5%. Under the influence of urbanization process, the maximum reduction rate of precipitation infiltration recharge is up to 38%. The study investigated the response of surface runoff and precipitation infiltration recharge to land use change, which can provide helps for water resources managers to coordinate the relationship between land use change and rational water resources planning.

An assessment of the factors determining rotifer assemblage in river-lake systems: the effects of seasonality and habitat

Zooplankton exhibit several trends of variation in space and time, and these trends can be more evident in natural environments without anthropic perturbations. Examples of anthropic factors are climate change, eutrophication and construction of reservoirs. This study evaluated the influence of three factors – seasonality, type of environment and the presence of aquatic macrophytes – on various ecological attributes of rotifers in a river-lake system located in the Paraná River floodplain. Monthly samplings were conducted during 1993 and 1994. The mean species richness per sample was 60 species. The seasonality and the type of environment influenced the ecological attributes of rotifer assemblages, while the presence or absence of aquatic macrophytes did not. Species richness was highest in the lake system and during the months when water levels were low. Multivariate analysis indicates a small group of species associated with the low water-level phase. In contrast, many species were associated with high water levels or increasing water levels. The seasonal variation of hydrological cycle and the type of environment are the most important factors for rotifer structure in natural conditions.

水循环改变的生态影响评价研究进展

淡水循环是流域尺度内坡面植被、河流、湖沼湿地以及河口近岸海域四大类生态系统的重要环境因子，改变水循环会不同程度地影响流域内各类生态系统。本文从生态系统过程、结构和功能三方面梳理了国内外有关水循环改变生态系统的影响评价工作；指出我国水资源开发力度大使流域水循环显著改变，以及未来发展对水资源与健康生态的双重需要，将会使围绕流域水循环的生态影响评价有更广泛的需求。目前存在的主要问题是生物本底信息缺乏、生态水文过程不清晰、生态恢复工程人为调控因素被忽略，需要基于生态站有限的信息建立分区生态基准，应加强各类生态系统生态水文过程的研究，开展生态系统的动态影响评价。 Freshwater cycle is the major environmental factor for four ecosystems including slope vegetation, river, lake or wetland and estuary in watershed scale. Variation of hydrological cycle will affect each ecosystem to different extent. By analyzing ecosystem’s process, structure and function, the impact assessment research both at home and abroad for how hydrological cycle affect ecosystem was summarized in this article. The article also indicated that in China more and more extensive water resources’ development by the government has changed hydrological cycle obviously and future economic development needs both water resources and healthy ecosystem. They will make the study on ecological impacting assessment caused by hydrological cycle variation in watershed become more desired. The main problems were summarized as follow: a) There is a lack of original biological information; b) Processes between hydrology and ecology in aquatic ecosystem are not clear enough; c) Influences of artificial controlling for ecosystem restoration are ignored. The main suggested methods are to construct ecological basis in different area based on limited ecological monitoring station, enhance research on eco-hydrological process and take dynamic assessment for different ecosystems.

Impacts of Land Cover Changes on Hydrologic Responses: A Case Study of Chi River Basin, Thailand

Land use and land cover (LULC) have been continuously changing, through human activities, leading to variations in hydrological cycle. In this study, we applied SWAT model to investigate potential impacts of LULC on water budget of the Chi river basin in Thailand. Five plausible scenarios of land use change were evaluated, including an conversion of forested area, expansion of farmland, switching of rice paddy fields to energy crops and two scenarios involving conversion of farmland to rice and sugarcane plantation. The results indicated that different land use scenarios contributed to various effects in annual and seasonal water yield and evapotranspiration (ET). Conversion of forested area and farmland showed slightly small changes on water flows and ET. Substitution of paddy fields by sugarcane plantation showed clearly reduced water flows and increased ET by almost 5.0% in dry season. Particularly, in case of expansion of rice paddy fields to farmland, small changes occur on annual flow and ET but more significant effect occur on seasonal flows. The results showed decrease in ET by nearly 12.0%, leading to increase of water yield by up to 5.1% during dry season. Finally, conversion of farmland to sugarcane plantation for biofuel production showed significant effect on seasonal ET, mainly decreasing in dry season by 4.5 % but small changes were detected on water yields.

Low-Frequency Variations in the Atmospheric Branch of the Global Hydrological Cycle

According to the atmospheric water balance equation, the divergence of the water vapor flux is responsible for the exchange of water vapor between its source and sink regions. Because the water vapor flux divergence is primarily determined by the divergent circulation, time variations of the global hydrological cycle reflect the pronounced low-frequency modes of the global divergent circulation, that is, the annual and intraseasonal (30–60 day) modes. The annual variation of the hydrological cycle is illustrated in terms of hemispheric-mean hydrological variables for the Northern and Southern Hemispheres, while the intraseasonal variations of the global hydrological cycle are illustrated with mean values over two hemispheres that form an east-west partition of the globe. This partition is defined by the 60°E–120°W great circle and was chosen so that the mean precipitation difference and the divergent water vapor transport between the two hemispheres was maximized. Two years (1979–80) of daily precipitation estimates from the Goddard Laboratory for Atmospheres and 14 years (1979–92) of upper-air data generated by the Global Data Assimilation System at the National Meteorological Center are used in making quantitative estimates of the annual and intraseasonal variations in the global hydrological cycle. The annual variations in hemispheric-mean precipitation [P̂] and water vapor flux divergence [∇ · Q̂ ] for the Northern and Southern Hemispheres are comparable with amplitudes of about 0.5 ∼ 0.7 mm day−. Both [P̂] and [∇ · Q̂] vary annually in a coherent way in each hemisphere so that water vapor diverges from the winter hemisphere, where [P̂] reaches its minimum, to the summer hemisphere, where [P^] attains its maximum. In fact, the hemispheric-mean divergence of water vapor flux changes sign during the annual cycle. Intraseasonal variations of hemispheric-mean precipitation 〈P̃〉, evaporation 〈Ẽ〉, and water vapor flux divergence 〈∇ · Q̃〉 in the two hemispheres in the cast-west direction are comparable with amplitudes of about 0.1 ∼ 0.2 mm day−1, although amplitudes in some cases exceed 0.3 mm day−1. Hemispheric-mean precipitation 〈P̃〉 varies coherently in opposite phase for the two hemispheres, while 〈∇ · Q̃ 〉 varies so that water vapor diverges from the hemisphere of maximum 〈P̃〉 to the hemisphere of minimum 〈P〉. Intraseasonal variations of 〈P̃〉, 〈Ẽ〉 and 〈∇ · 〉 are in accord with the eastward propagation of the intra seasonal global divergent circulation.