Youpeng Xu

Hydrological Simulation by SWAT Model with Fixed and Varied Parameterization Approaches Under Land Use Change

Land use and land cover (LULC) change within a watershed is recognized as an important factor affecting hydrological processes and water resources. Modeling the hydrological effects of land-use change is important not only for after-the-fact analyses, but also for understanding and predicting the potential hydrological consequences of existing land-use practices. The main aim of the study is to understand and quantify the hydrological processes in a rapid urbanization region. The SWAT model and the Qinhuai River basin, one of the most rapidly urbanizing regions in China were selected to perform the study. In the study, a varied parameterization strategy was developed by establishing regression equations with selected SWAT parameters as dependent variables and catchment impermeable area as independent variable. The performance of the newly developed varied parameterization approach was compared with the conventional fixed parameterization approach in simulating the hydrological processes under LULC changes. The results showed that the model simulation with varied parameterization approach has a large improvement over the conventional fixed parameterization approach in terms of both long-term water balance and flood events simulations. The proposed modeling approach could provide an essential reference for the study of assessing the impact of LULC changes on hydrology in other regions.

Analysis of river health variation under the background of urbanization based on entropy weight and matter-element model: A case study in Huzhou City in the Yangtze River Delta, China

Maintaining the health of the river ecosystem is an essential ecological and environmental guarantee for regional sustainable development and one of the basic objectives in water resource management. With the rapid development of urbanization, the river health situation is deteriorating, especially in urban areas. The river health evaluation is a complex process that involves various natural and social components; eight eco-hydrological indicators were selected to establish an evaluation system, and the variation of river health status under the background of urbanization was explored based on entropy weight and matter-element model. The comprehensive correlative degrees of urban river health of Huzhou City in 2001, 2006 and 2010 were then calculated. The results indicated that river health status of the study area was in the direction of pathological trend, and the impact of limiting factors (such as Shannons diversity index and agroforestry output growth rate) played an important role in river health. The variation of maximum correlative degree could be classified into stationary status, deterioration status, deterioration-to-improvement status, and improvement-to-deterioration status. There was a severe deterioration situation of river health under the background of urbanization.

Relationship between changes of river-lake networks and water levels in typical regions of Taihu Lake Basin, China

The typical regions of the Taihu Lake Basin, China, were selected to analyze the variation characteristics of river-lake networks under intensive human activities. The characteristics of the fractal dimension of river networks and lakes for different periods were investigated and the influences of river system evolution on water level changes were further explored through the comparison of their fractal characters. The results are as follows: 1) River network development of the study area is becoming more monotonous and more simple; the number of lakes is reducing significantly, and the water surface ratio has dropped significantly since the 1980s. 2) The box dimension of the river networks in all the cities of the study area decreased slowly from the 1960s to the 1980s, while the decrease was significant from the 1980s to the 2000s. The variations of lake correlation dimension are similar to those of the river network box dimensions. This is unfavorable for the storage capacity of the river networks and lakes. 3) The Hurst exponents of water levels were all between 0.5 and 1.0 from the 1960s to the 1980s, while decreased in the 2000s, indicating the decline in persistence and increase in the complexity of water level series. The paper draws a conclusion that the relationship between the fractal dimension of river-lake networks and the Hurst exponents of the water level series can reveal the impacts of river system changes on flood disasters to some extent: the disappearance of river networks and lakes will increase the possibility of flood occurrence.

Impacts of urbanization on river system structure: a case study on Qinhuai River Basin, Yangtze River Delta

Stream structure is usually dominated by various human activities over a short term. An analysis of variation in stream structure from 1979 to 2009 in the Qinhuai River Basin, China, was performed based on remote sensing images and topographic maps by using ArcGIS. A series of river parameters derived from river geomorphology are listed to describe the status of river structure in the past and present. Results showed that urbanization caused a huge increase in the impervious area. The number of rivers in the study area has decreased and length of rivers has shortened. Over the 30 years, there was a 41.03% decrease in river length. Complexity and stability of streams have also changed and consequently the storage capacities of river channels in intensively urbanized areas are much lower than in moderately urbanized areas, indicating a greater risk of floods. Therefore, more attention should be paid to the urban disturbance to rivers.

Degrading river network due to urbanization in Yangtze River Delta

Evolution of river systems under the background of human activities has been a heated topic among geographers and hydrologists. Spatial and temporal variations of river systems during the 1960s–2010s in the Yangtze River Delta (YRD) were investigated based on streams derived from the topographic maps in the 1960s, 1980s and 2010s. A list of indices, drainage density (Dd), water surface ratio (WSR), ratio of area to length of main streams (R), evolution coefficient of tributaries (K) and box dimension (D), were classified into three types (quantitative, structural, and complex indices) and used to quantify the variations of stream structure. Results showed that: (1) quantitative indices (Dd, WSR) presented decreasing trend in the past 50 years, and Dd in Wuchengxiyu, Hangjiahu and Yindongnan have decreased most, about 20%. Structurally, the Qinhuai River basin was characterized by significant upward R, and K value in Hangjiahu went down dramatically by 46.8% during the 1960s–2010s. Decreasing tendency in D was found dominating across the YRD, and decreasing magnitude in Wuchengxiyu and Hangjiahu peaks for 7.8% and 6.5%, respectively in the YRD. (2) Urbanization affected the spatial pattern of river system, and areas with high level of urbanization exhibited least Dd (2.18 km/km2), WSR (6.52%), K (2.64) and D (1.42), compared to moderate and low levels of urbanization. (3) Urbanization also affected the evolution of stream system. In the past 50 years, areas with high level of urbanization showed compelling decreasing tendency in quantitative (27.2% and 19.3%) and complex indices (4.9%) and trend of enlarging of main rivers (4.5% and 7.9% in periods of the 1960s–1980s and the 1980s–2010s). In the recent 30 years, areas with low level of urbanization were detected with significant downward trend in Dd and K. (4) Expanding of urban land, construction of hydraulic engineering and irrigation and water conservancy activities were the main means which degraded the river system in the YRD.

Impacts of Urbanization on Precipitation in Taihu Lake Basin, China

AbstractTaking Suxichang and Hangjiahu urban agglomerations in Taihu Lake Basin as study areas, the authors explore differences in annual precipitation, flood season precipitation, annual maximum daily precipitation, and rainfall days of different types between cities and suburbs from 1961 to 2006. The authors also investigate the trends of precipitation change by means of Mann-Kendall test and rescaled range analysis. The results show that the amount of precipitation increased with the level of urbanization at spatial and temporal scales. The maximum daily precipitation and the number of rainstorms in urban areas also increased. With further development of urbanization, the increase would continue in the future. The two urban agglomerations with similar level of urbanization and climatic conditions are consistent in terms of all research indicators applied in this paper. The results are basically consistent with many previous studies, while the study area has its own characteristics in that the maximum r...

Temporal and spatial variation of water level in urbanizing plain river network region

As one of the most developed regions in China, the plain of East China is undergoing gradually increased flooding under the obvious urbanization process. This paper mainly analyses the trend of water level time series in the region during the past decades, and assesses the temporal and spatial variation of water level and indicators of hydrological alteration. The results show that there is a trend of increasing water level. Bigger slope and higher significant level can be observed in monthly minimum than in monthly maximum water level, in peri-urban than in urban areas. Meanwhile, it is observed that the mean monthly minimum and maximum water level increased in both urban and peri-urban regions, while decreased coefficients of variation (Cv) in urban and increased Cv in peri-urban regions were calculated. Most indicators of hydrologic alteration in urban stations are concentrated to the range of variability approach target, while most indicators are discrete in peri-urban stations. And the degree of hydrologic alteration is higher in peri-urban than in urban regions.

Flood Simulation with Distributed Hydrological Approach Using DEMs and Remotely Sensed Data

The spatial variability of both meteorological and geographic features has a great influence on rainfall runoff process. When making flood forecasting, the influence of this variability on runoff should be considered. In this paper, the distributed hydrological modeling technique was adopted to simulate flood discharge with consideration of spatial variability using DEMs and remotely sensed data. In our approach, the grid based digital elevation data was used for the presentation of watershed discretization and deriving flow path system and parameters. The infiltration and rainfall excess on each hillslope grid cell were calculated using the Green-Ampt infiltration equation. Soil lateral flow was estimated based on Darcys law and continuity equation, overland and channel flows were calculated by using one-dimensional kinematic wave equations on hillslope and channel grid cells respectively. The land use and land cover data derived from remotely sensed images was used for the determination of Mannings roughness coefficients. The soil type data was used for deriving soil hydraulic parameters needed for calculation. The approach was applied in Jiaokou Watershed with area of 259 km2, a sub-basin of Yongjiang River in Zhejiang Province, China. The data collected for this study included land cover processed from Landsat TM images, soil type distribution from the soil maps, and 100-m spatial resolution DEMs produced from digital topographic maps. Spatial distribution of rainfall for each flood event was calculated by using distance inverse interpolation methods. Nine flood events were simulated, two of which were used for calibration, and the others for validation. The simulated hydrographs at basin outlet showed good agreement with observed ones for both calibrated and validated flood events, and average coefficients of efficiency were 94% for calibrated flood events and 92% for validated flood events.

Scale-dependence effects of landscape on seasonal water quality in Xitiaoxi catchment of Taihu Basin, China.

Further understanding the mechanisms of landscape-water interactions is of great importance to water quality management in the Xitiaoxi catchment. Pearsons correlation analysis, stepwise multiple regression and redundancy analysis were adopted in this study to investigate the relation between water quality and landscape at the sub-catchment and 200 m riparian zone scales during dry and wet seasons. Landscape was characterized by natural environmental factors, land use patterns and four selected landscape configuration metrics. The obtained results indicated that land use categories of urban and forest were dominant landscape attributes, which influenced water quality. Natural environment and landscape configuration were overwhelmed due to land management activities and hydrologic conditions. In general, the landscape of the 200 m riparian zone appeared to have slightly greater influence on water than did the sub-catchment, and water quality was slightly better explained by all landscape attributes in the wet season than in the dry season. The results suggested that management efforts aimed at maintaining and restoring river water quality should currently focus on the protection of riparian zones and the development of an updated long-term continuous data set and higher resolution digital maps to discuss the minimum width of the riparian zone necessary to protect water quality.

Regularized Back-Propagation Neural Network for Rainfall-Runoff Modeling

In this study, we applied regularized back-propagation neural network (BPNN), which made use of a performance function different from normal BPNN, to predict daily flow. On the other hand, Broyden-Fletcher-Goldfarb-Shanno (BFGS) -algorithm-based BPNN was also used to compare its prediction performance with that of regularized BPNN. From 1979 to 1998, precipitation and stream flow data in Xitiaoxi watershed for 20 years were collected. All these data were divided into 2 sets: one was the training set (1979-1988), and the other was the testing set (1989-1998). The mean absolute error (MAE), mean square error (MSE) and coefficient of efficiency (CE) were used to evaluate the performance of these two algorithms. The results indicated that regularized BPNN could enhance generalization ability and avoid over fitting effectively, and it outperformed BFGS-algorithm-based BPNN during training and testing stages. From this study, it could be found that regularized BPN is appropriate for rainfall-runoff modeling due to its simple structure and high accuracy.