ALBERT

Description: Karst depressions represent important sinks for sediment and such sediment can provide a valuable record of the impact of environmental change on soil erosion rates. However, the sediment dynamics of karst depressions are not well understood. This contribution reports a study of the small catchment of a karst depression in Southwest China, with a drainage area of 0.054 km 2 , aimed at using the sediment deposits in the depression to reconstruct the erosional response of the catchment to land use change and, more particularly, the deforestation which took place in 1979. 137 Cs and 210 Pb ex are used as both chronometers and as tracers. Five cores, collected from the bottom of a depression, with an area of 2652 m 2 , showed similar 137 Cs depth distributions, with a single 137 Cs peak, which was attributed to the 1979 deforestation. The 137 Cs activity associated with the peaks varied between 5.68 ± 0.64 Bq kg -1 and 9.19 ± 0.99 Bq kg -1 . The average depth of sediment deposition between 1979 and 2008 deduced from the depths of the 1979 137 Cs peak was 74.1 cm. The existence of relatively high 210 Pb ex activity of 66.33 ± 8.44 Bq kg -1 in the upper section (0-16 cm) of the core analyzed for 210 Pb ex suggests that recent sedimentation has been very limited. Net erosion rates on the hillslopes contributing runoff and sediment t to the depression were estimated to be 5258 t km -2  yr -1 from 1979 to 1990 and 256 t km -2  yr -1 from 1991 to 2008, respectively. The high sediment yield in the first period was associated with the severe soil erosion triggered by the 1979 deforestation, which resulted from the changes in land ownership immediately after the Cultural Revolution. Soil erosion has been very limited since 1990, because the thin soils had been totally removed from many parts of the karst slopes and the soils remaining on the other parts of the slopes have been protected by terracing or vegetation rehabilitation Copyright © 2012 John Wiley & Sons, Ltd.

Description: Rainfall input for hydrologic modeling is assumed uniformly distributed over the entire catchment. This can lead to significant errors. Investigations of areal rainfall in mountain areas are typically limited by a lack of adequate meteorological and hydrogeological records. This study focuses on areal rainfall in mountain areas within the Kaidu River Basin, China, with the aim of analyzing the influence of areal rainfall on the simulation accuracy of runoff prediction. We conducted a simulation using MIKE 11/NAM rainfall-runoff model over 92 days of the rain season and compared the simulation error in different methods. Based on the properties of self-similarity degree ( SSD ) in analyzing the detailed characteristics of terrain, areal rainfall was calculated to model the runoff. The results of the model simulations are generally consistent with observed data, indicating that the self-similarity topography method is able to reflect the spatial change of rainfall. This indicates that the proposed methodology is applicable for the management of water resources in mountain area. The modeling and self-similarity topography method study allowed quantification of the spatial rainfall and provided an insight into their implications in hydrological forecasting. Copyright © 2011 John Wiley & Sons, Ltd.

Description: When hydrology model parameters are determined, a traditional data assimilation method (such as Kalman filter) and a hydrology model can estimate the root zone soil water with uncertain state variables (such as initial soil water content). The simulated result can be quite good. However, when a key soil hydraulic property, such as the saturated hydraulic conductivity, is overestimated or underestimated, the traditional soil water assimilation process will produce a persistent bias in its predictions. In this paper, we present and demonstrate a new multi-scale assimilation method by combining the direct insertion assimilation method, particle swarm optimization (PSO) algorithm and Richards equation. We study the possibility of estimating root zone soil water with a multi-scale assimilation method by using observed in situ data from the Wudaogou experiment station, Huaihe river basin, China. The results indicate there is a persistent bias between simulated and observed values when the direct insertion assimilation surface soil water content is used to estimate root zone soil water contents. Using a multi-scale assimilation method (PSO algorithm and direct insertion assimilation) and an assumed bottom boundary condition, the results show some obvious improvement, but the root mean square error is still relatively large. When the bottom boundary condition is similar to the actual situation, the multi-scale assimilation method can well represent the root zone soil water content. The results indicate that the method is useful in estimating root zone soil water when available soil water data are limited to the surface layer and the initial soil water content even when the soil hydraulic conductivities are uncertain. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Rainfall–runoff processes appear to be highly nonlinear in Bayinbluk watersheds of the northwestern China. In this study, the time-scale wavelet transform has been used for the analysis of this nonstationary system. The Haar and Morlet wavelet transform were used to analyse the rainfall–runoff conversion relationship. Wavelet power spectrum and change point methods are also employed to analyse rainfall rates and runoffs measured at daily to half-hourly sampling rate. The four experimental sites (Luoto, Haer, Kuce and Shengl) are located in the Tianshan Mountains (Xinjiang province, China). Correlation analysis and wavelet transform are first applied to runoff process in different underlying surfaces. Wavelet analyses of rainfall rates and runoffs also give meaningful information on the temporal variability of the rainfall–runoff relationship. Change point and wavelet power spectrum analysis provide simple interpretation of energy distribution between different scales. The results indicate that wavelet transform is a good method for analysing the nonlinear relationship of temporal–spatial responses between rainfall and runoff. This method allowed quantification of the processes affecting runoff and provided an insight into their implications in surface water management. Copyright © 2011 John Wiley & Sons, Ltd.

Description: In this study, we aimed to clarify spatial variations in xylem sap flow, and to determine the impacts of these variations on stand-scale transpiration ( E ) estimates. We examined circumferential and radial variations in sap flow velocity ( F d ) measured at several directions and depths in tree trunks of black locust ( Robinia pseudoacacia ) and native oak ( Quercus liaotungensis ), both of which have ring-porous wood anatomy, in forest stands on the Loess Plateau, China. We evaluated the impacts of circumferential variations in F d on stand-scale transpiration estimates using a simple scaling exercise. We found significant circumferential variations in F d in the outermost xylem in both species (coefficients of variation= 20–45%). For both species, F d measured at the inner xylem was smaller than that of the outermost xylem and the F d at the depth of 〉 10 mm was almost zero. The simple exercises showed that omitting circumferential variations in F d affected the E estimate by 16–21%, which was less than the effects of omitting within-tree radial and tree-to-tree variations in F d in both species. These results suggest that circumferential variations in F d can be a minor source of error for E estimates compared with within-tree radial and tree-to-tree variations in F d , regardless of the significant circumferential variations. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Quantifying of direct recharge derived from precipitation is crucial for assessing sustainability of well-irrigated agriculture. In the North China Plain, the land use is dominated by groundwater-irrigated farmland where the direct recharge derived from precipitation and irrigation. To characterizing the mean rate and historical variance of direct recharge derived from precipitation, unsaturated zone profiles of chloride and δ 18 O in the dry river bed of the Beiyishui River were employed. The results show that archival time scale of the profile covers the duration from 1980 to 2002 (corresponding to depths from 5 to 2 m) which is indicated by matching the δ 18 O peaks in the isotope profile with the aridity indexes gained by instrumental records of annual precipitation and annual potential evaporation. Using the chloride mass balance method, the mean rate of the direct recharge corresponding to the archival time scale is estimated to be 3.8 ± 0.8 mm yr -1 , which accounts for about 0.7% of the long-term average annual precipitation. Further, the direct recharge rates vary from 2.1 mm yr -1 to 6.8 mm yr -1 since 1980. In spite of the sub-humid climate, the estimate of recharge rates is in line with other findings in semiarid regions. The low rate of direct recharge is considered as a result of the relative dry climate in recent decades. In dry river bed, unsaturated zone profiles of chloride and δ 18 O combined with instrumental records could offer valuable information about the direct recharge derived from precipitation during droughts. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Stream mesoscale habitats have systematic topographic relationships to hyporheic flow patterns which may create predictable temperature variation between mesoscale habitat types. We investigated whether systematic differences in temperature metrics occurred between mesoscale habitats within reaches of small streams tributary to the upper Little Tennessee River, southern Appalachians. Surface water temperature was recorded over three or four mid-summer days in four mesoscale habitat types: riffle, main riffle, pool, and alcove in 44 stream segments (sites). Temperature metrics were calculated for each mesoscale habitat relative to the mean value of the metric over the stream: Δ maximum temperature (ΔMT), Δ average maximum temperature (ΔAMT), and Δ maximum daily variation (ΔMDV) and also for each site: standard deviation of the maximum temperature (SD MT ), and average diurnal variation (ADV). Sites were categorized as fully or partially forested. Pool tailouts had statistically significantly lower ΔMT and ΔAMT than riffle tailouts in partially forested sites, although differences were small. This was the opposite of what was expected in the presence of hyporheic exchange, indicating hyporheic exchange is not a dominant driver of mesoscale habitat temperatures at these sites. Temperature differences between mesoscale habitat units were small and unlikely to have ecological significance. We also evaluated relationships between stream temperature and riparian condition, watershed % impervious surfaces, watershed % non-forested, and elevation. ADV and SD MT were significantly higher in partially forested sites, indicating that partially forested sites have greater temperature ranges and spatial variation of maximum temperatures. ADV decreased with elevation and increased with % impervious surfaces. Copyright © 2013 John Wiley & Sons, Ltd.

Description: Root zone soil water content impacts plant water availability, land energy and water balances. Because of unknown hydrological model error, observation errors and the statistical characteristics of the errors, the widely used Kalman filter (KF) and its extensions are challenged to retrieve the root zone soil water content using the surface soil water content. If the soil hydraulic parameters are poorly estimated, the KF and its extensions fail to accurately estimate the root zone soil water. The H-infinity filter (HF) represents a robust version of the KF. The HF is widely used in data assimilation and is superior to the KF, especially when the performance of the model is not well understood. The objective of this study is to study the impact of uncertain soil hydraulic parameters, initial soil moisture content and observation period on the ability of HF assimilation to predict in situ soil water content. In this article, we study seven cases. The results show that the soil hydraulic parameters hold a critical role in the course of assimilation. When the soil hydraulic parameters are poorly estimated, an accurate estimation of root soil water content cannot be retrieved by the HF assimilation approach. When the estimated soil hydraulic parameters are similar to actual values, the soil water content at various depths can be accurately retrieved by the HF assimilation. The HF assimilation is not very sensitive to the initial soil water content, and the impact of the initial soil water content on the assimilation scheme can be eliminated after about 5-7 days. The observation interval is important for soil water profile distribution retrieval with the HF, and the shorter the observation interval, the shorter the time required to achieve actual soil water content. However, the retrieval results are not very accurate at a depth of 100 cm. Also it is complex to determine the weighting coefficient and the error attenuation parameter in the HF assimilation. In this article, the trial-and-error method was used to determine the weighting coefficient and the error attenuation parameter. After the first establishment of limited range of the parameters, 'the best parameter set' was selected from the range of values. For the soil conditions investigated, the HF assimilation results are better than the open-loop results. © 2010 John Wiley & Sons, Ltd..

Description: Quantifying of direct recharge derived from precipitation is crucial for assessing sustainability of well-irrigated agriculture. In the North China Plain, the land use is dominated by groundwater-irrigated farmland where the direct recharge derived from precipitation and irrigation. To characterize the mean rate and historical variance of direct recharge derived from precipitation, unsaturated zone profiles of chloride and δ 18O in the dry river bed of the Beiyishui River were employed. The results show that archival time scale of the profile covers the duration from 1980 to 2002 (corresponding to depths from 5 to 2 m) which is indicated by matching the δ 18O peaks in the isotope profile with the aridity indexes gained by instrumental records of annual precipitation and annual potential evaporation. Using the chloride mass balance method, the mean rate of the direct recharge corresponding to the archival time scale is estimated to be 3·8 ± 0·8 mm year -1, which accounts for about 0·7% of the long-term average annual precipitation. Further, the direct recharge rates vary from 2·1 to 6·8 mm year -1 since 1980. Despite the subhumid climate, the estimate of recharge rates is in line with other findings in semiarid regions. The low rate of direct recharge is considered as a result of the relative dry climate in recent decades. In dry river bed, unsaturated zone profiles of chloride and δ 18O combined with instrumental records could offer valuable information about the direct recharge derived from precipitation during droughts. © 2011 John Wiley & Sons, Ltd..

Description: Rainfall-runoff processes appear to be highly nonlinear in Bayinbluk watersheds of the northwestern China. In this study, the time-scale wavelet transform has been used for the analysis of this nonstationary system. The Haar and Morlet wavelet transform were used to analyse the rainfall-runoff conversion relationship. Wavelet power spectrum and change point methods are also employed to analyse rainfall rates and runoffs measured at daily to half-hourly sampling rate. The four experimental sites (Luoto, Haer, Kuce and Shengl) are located in the Tianshan Mountains (Xinjiang province, China). Correlation analysis and wavelet transform are first applied to runoff process in different underlying surfaces. Wavelet analyses of rainfall rates and runoffs also give meaningful information on the temporal variability of the rainfall-runoff relationship. Change point and wavelet power spectrum analysis provide simple interpretation of energy distribution between different scales. The results indicate that wavelet transform is a good method for analysing the nonlinear relationship of temporal-spatial responses between rainfall and runoff. This method allowed quantification of the processes affecting runoff and provided an insight into their implications in surface water management. © 2011 John Wiley & Sons, Ltd.