Showing papers by "Lu Zhang published in 2008"

Responses of streamflow to changes in climate and land use/cover in the Loess Plateau, China

Abstract: [1] To control the severe soil erosion in the Loess Plateau, China, a great number of soil conservation measures including terracing, afforestation, and construction of sediment-trapping dams have been implemented since the 1950s. These measures have resulted in large-scale land use and land cover change. It is important to evaluate the impacts of these soil conservation measures on streamflow as streamflow is an important determinant on catchment sediment yield and obviously is related to water security in the region. In this study, data from 11 catchments in the Loess Plateau were analyzed to investigate the responses of streamflow to the land use/cover changes. The nonparametric Mann-Kendall test and the Pettitt test were used to identify trends and change points in the streamflow records. All 11 catchments had significant negative trend in annual streamflow of −0.13 to −1.58 mm a−1. Change points in streamflow occurred between 1971 and 1985. A method was employed to evaluate the impacts of climate variability and land use/cover changes on mean annual streamflow on the basis of precipitation and potential evaporation. It was estimated that the land use/cover changes accounted for over 50% of the reduction in mean annual streamflow in 8 out of the 11 catchments. However, climate (i.e., precipitation and potential evaporation) played a more important role in reducing the streamflow in the three remaining catchments. Among the soil conservation measures, construction of sediment-trapping dams and reservoirs, with associated irrigation water extractions from the latter, appeared to be the main cause of the reduced streamflow.

Modelling hydrological response to different land‐use and climate change scenarios in the Zamu River basin of northwest China

Abstract: Changes in climate and land use can significantly influence the hydrological cycle and hence affect water resources. Understanding the impacts of climate and land-use changes on streamflow can facilitate development of sustainable water resources strategies. This study investigates the flow variation of the Zamu River, an inland river in the arid area of northwest China, using the Soil and Water Assessment Tool distributed hydrological model. Three different land-use and climate-change scenarios were considered on the basis of measured climate data and land-use cover, and then these data were input into the hydrological model. Based on the sensitivity analysis, model calibration and verification, the hydrological response to different land-use and climate-change scenarios was simulated. The results indicate that the runoff varied with different land-use type, and the runoff of the mountain reaches of the catchment increased when grassland area increased and forestland decreased. The simulated runoff increased with increased precipitation, but the mean temperature increase decreased the runoff under the same precipitation condition. Application of grey correlation analysis showed that precipitation and temperature play a critical role in the runoff of the Zamu River basin. Sensitivity analysis of runoff to precipitation and temperature by considering the 1990s land use and climate conditions was also undertaken. Copyright © 2007 John Wiley & Sons, Ltd.

Estimating catchment evaporation and runoff using MODIS leaf area index and the Penman-Monteith equation

Abstract: [1] This paper shows the feasibility of using steady state water balances of gauged catchments to calibrate a spatially explicit evaporation model and then applying this to estimate mean annual runoff for 120 gauged catchments in the Murray-Darling Basin (MDB) of Australia from 2001 to 2005. We used remotely sensed leaf area indices from the Moderate Resolution Imaging Spectrometer (MODIS) mounted on the polar-orbiting Terra satellite with the Penman-Monteith equation, gridded meteorology, and a two-parameter biophysical model for surface conductance (G s ) to estimate 8-day average evaporation at 1-km resolution. Parameters for the G s model were optimized using steady state water balance estimates (precipitation minus runoff) in the gauged catchments in three precipitation zones of the MDB, and the calibrated evaporation model was then used to estimate evaporation (E RS ) and runoff from gauged and ungauged catchments in the MDB. Mean annual calibrated estimates of E RS compared well with water balance estimates, indicated by a root-mean-square error (RMSE) of 78.6 mm/a and the Nash-Sutcliffe coefficient of efficiency (CE) of 0.68. Reasonable agreement was obtained between the estimated mean annual runoff (R RS ) (rainfall minus E RS ), and the measured runoff (RMSE = 71.0 mm/a and CE = 0.75). Cross validation showed that estimated E RS and R RS were almost as good as the calibrated ones. Furthermore, R RS has an accuracy similar to that of a seven-parameter conceptual rainfall-runoff model in the gauged catchments. The results show that the evaporation model can be easily applied to estimate steady state evaporation and runoff and that E RS can be used with rainfall-runoff models to improve accuracy of estimated runoff in ungauged catchments.

River sediment load and concentration responses to changes in hydrology and catchment management in the Loess Plateau region of China

Abstract: [1] To reduce the sediment load of China's Yellow River, soil conservation measures have been progressively implemented across the Loess Plateau region since the 1950s The effectiveness of these soil conservation measures (which were also coincident with reduced rainfall and streamflow) in controlling sediment movement remains to be ascertained Here the association between sediment movement, hydrological variability, and the implementation of soil conservation measures is examined for the Coarse Sandy Hilly Catchments region of the Yellow River basin The hypothesis that the soil conservation measures have reduced suspended sediment yields beyond that associated with rainfall reductions alone, principally by reducing sediment concentration, is examined Annual sediment yield decreased significantly over time in all subcatchments, and the timing of the change (between 1971 and 1985) was consistent with the timing of change in streamflow Annual mean sediment concentration in 7 of the 11 catchments exhibited a statistically significant decreasing trend over time, indicating that soil conservation practices reduced the mobilization of sediment in most areas, typically accounting for ∼75% of the observed reductions in annual sediment yield Lesser reductions in area-specific sediment yield at larger catchment areas after the soil conservation measures were emplaced suggests that larger rivers may be reeroding stored sediment As these sediment stores are likely to be relatively large given the high historic yields, relatively high area-specific sediment yields may persist at larger catchment areas even with improvements to sediment management in smaller tributaries

Modelling the impact of afforestation on average annual streamflow in the Loess Plateau, China

Abstract: To prevent severe soil erosion and to ensure sustainable development, the Chinese Central Government mandated in 1999 that forest cover would be significantly increased in the Loess Plateau, China. It is important to assess the subsequent impact on streamflow and its spatial distribution in the region. The water balance model of et al. (2001)Zhang et al. (2001) was used in this study, and the results showed that the model was able to accurately simulate average annual evapotranspiration (ET), but not average annual streamflow when compared with streamflow measurements from 38 hydrologic stations in the coarse sandy hilly catchments (CSHC) in the Loess Plateau. The model was then calibrated using the measured streamflow, and the index of agreement increased from 0·21 to 0·63, the relative error and root mean square error decreased from 42·7 and 17·2 to 18·0% and 7·9 mm, respectively. Hierarchical cluster analysis and stepwise regression were employed to regionalize the optimized model parameter and relate it to the dryness index and forest cover. Once calibrated, the water balance model was used to assess the impacts of two plantation scenarios on streamflow. The two plantation scenarios assume nearly 5·8 and 10·1% of the study area can be planted with trees. It was predicted that streamflow from the region will decrease by 5·5 and 9·2% under the two plantation scenarios. The rate of streamflow reduction decreased from southeast to northwest mainly due to decreasing precipitation. Copyright © 2007 John Wiley & Sons, Ltd.

A warning from an ancient oasis: intensive human activities are leading to potential ecological and social catastrophe

Abstract: The Shiyang River Basin is an inland river basin in the Hexi Corridor, Gansu Province, northwest China. Shiyang is the largest basin in terms of human population density and has the highest exploit...

A comparison of three methods for determining vineyard evapotranspiration in the arid desert regions of northwest China

Abstract: Accurate measurement and estimation of crop evapotranspiration (ET) plays an important role in understanding field soil water cycle and managing water-saving irrigation in the arid regions. This study compares three methods for estimating ET: field Water Balance (WB), Eddy Covariance (EC) and Bowen Ratio-Energy Balance (BREB). The experiment was conducted in a vineyard in the arid desert regions of northwest China. Results indicate that the three methods provided similar estimate of total ET. Compared to total ET measured by WB (ETWB) during the whole growing stage, total ET estimated by EC (ETEC) was 1.57% lower, and total ET estimated by BREB (ETBREB) was 5.19% higher. Variations of ETEC and ETBREB are similar at hourly or daily timescale, but the values are slightly different. At sunrise or sunset, ETBREB increases or decreases more rapidly than ETEC. The difference between ETBREB and ETEC is linearly related to the residual of the energy balance for EC and the two methods yielded close estimates when the residual was small. This study showed that the three methods provided accurate estimates of ET at daily and seasonal timescales and the methods can be used to estimate ET from vineyards in arid environments. Copyright © 2008 John Wiley & Sons, Ltd.

Development of Hydro-Informatic Modelling System and its application

Abstract: The understanding of hydrological cycle is the core of hydrology and the scientific base of water resources management. Meanwhile, simulation of hydrological cycle has long been regarded as an important tool for the assessment, utilization and protection of water resources. In this paper, a new tool named Hydro-Informatic Modelling System (HIMS) has been developed and introduced with case studies in the Yellow River Basin in China and 331 catchments in Australia. The case studies showed that HIMS can be employed as an integrated platform for hydrological simulation in different regions. HIMS is a modular based framework of hydrological model designed for different utilization such as flood forecasting, water resources planning and evaluating hydrological impacts of climate change and human activities. The unique of HIMS is its flexibility in providing alternative modules in the simulation of hydrological cycle, which successfully overcome the difficulties in the availability of input data, the uncertainty of parameters, and the difference of rainfall-runoff processes. The modular based structure of HIMS makes it possible for developing new hydrological models by the users.

Evaluation of Methods for Estimating the Effects of Vegetation Change and Climate Variability on Streamflow

Abstract: [1] Changes in vegetation cover can significantly affect streamflow. Two common methods for estimating vegetation effects on streamflow are the paired catchment method and the time trend analysis technique. In this study, the performance of these methods is evaluated using data from paired catchments in Australia, New Zealand, and South Africa. Results show that these methods generally yield consistent estimates of the vegetation effect, and most of the observed streamflow changes are attributable to vegetation change. These estimates are realistic and are supported by the vegetation history. The accuracy of the estimates, however, largely depends on the length of calibration periods or pretreatment periods. For catchments with short or no pretreatment periods, we find that statistically identified prechange periods can be used as calibration periods. Because streamflow also responds to climate variability, in assessing streamflow changes it is necessary to consider the effect of climate in addition to the effect of vegetation. Here, the climate effect on streamflow was estimated using a sensitivity-based method that calculates changes in rainfall and potential evaporation. A unifying conceptual framework, based on the assumption that climate and vegetation are the only drivers for streamflow changes, enables comparison of all three methods. It is shown that these methods provide consistent estimates of vegetation and climate effects on streamflow for the catchments considered. An advantage of the time trend analysis and sensitivity-based methods is that they are applicable to nonpaired catchments, making them potentially useful in large catchments undergoing vegetation change.