Momentum and energy balance equations for compacting sediments

Coupled energy and momentum balance equations are derived for a one-dimensional sequence of compacting sediments. These transient, nonlinear partial differential equations represent the one-dimensional equations of state for an accumulating sedimentary basin. A numerical solution is presented which provides a first-order approximation for porosity, temperature, and fluid pressures in the northern Gulf of Mexico. It seems that compaction disequilibrium is the primary mechanism for development of excess fluid pressures. Furthermore, the coupling of the equations demonstrates that temperature and pressure cannot be treated independently as may have been done in diagenetic studies. Some areas for further investigations are indicated.     

1957-2014年库布齐沙漠地面风场特征

风对沙漠化过程具有重要影响,起沙风是塑造沙漠地貌格局的主要动力。根据1957-2014年库布齐沙漠周边4个基准气象站的地面风资料,从风速、风向和输沙势等方面分析库布齐沙漠的地面风场特征。结果显示：（1）库布齐沙漠的起沙风频率与平均风速有很高的相关性;（2）年平均风速为2.7 m·s^-1,全年盛行风向为WNW-NW,为中等变率锐双峰风况,合成输沙风向约为310°。4月风速最大,为中等变率环境;8月风速较小,为高变率环境;1月风速最小,为低变率环境。3-6月风速最大,风向集中度一般;11月至翌年2月风速较大,风向集中度高;7-10月风速最小,风向集中度差;（3）20世纪80年代中后期和2007年前后风速、起沙风频率和输沙势发生了较大变化,尤其是2007年前后由减小向增大发展;（4）大气环流和地表粗糙度的改变是库布齐沙漠地面风场变化的重要原因。     

Distinguishing streamflow trends caused by changes in climate,forest cover,and permafrost in a large watershed in northeastern China

Understanding how rivers respond to changes in land cover, climate, and subsurface conditions is critical for sustainably managing water resources and ecosystems. In this study, long‐term hydrologic, climate, and satellite data (1973–2012) from the Upper Tahe River watershed (2359 km²) in the Da Hinggan Mountains of northeast China were analysed to quantify the relative hydrologic effects of climate variability (system input) and the combined influences of forest cover change and permafrost thaw (system characteristics) on average annual streamflow (system response) using 2 methods: the sensitivity‐based method and the Kendall–Theil robust line method. The study period was subdivided into a forest harvesting period (1973–1987), a forest stability period (1988–2001), and a forest recovery period (2002–2012). The results indicated that the combined effects of forest harvesting and permafrost thaw on streamflow (+ 47.0 mm) from the forest harvesting period to the forest stability period was approximately twice as large as the effect associated with climate variability (+20.2 mm). Similarly, from the forest stability period to the forest recovery period, the decrease in average annual streamflow attributed to the combined effects of forest recovery and permafrost thaw (?38.0 mm) was much greater than the decrease due to climate variability (?22.2 mm). A simple method was used to separate the distinct impacts of forest cover change and permafrost thaw, but distinguishing these influences is difficult due to changes in surface and subsurface hydrologic connectivity associated with permafrost thaw. The results highlight the need to consider multiple streamflow drivers in future watershed and aquatic ecosystem management. Due to the ecological and hydrological susceptibility to disturbances in the Da Hinggan Mountains, forest harvesting will likely negatively impact ecohydrological processes in this region, and the effects of forest species transition in the forest recovery process should be further investigated.     

A timescale decomposed threshold regression downscaling approach to forecasting South China early summer rainfall

A timescale decomposed threshold regression(TSDTR) downscaling approach to forecasting South China early summer rainfall(SCESR) is described by using long-term observed station rainfall data and NOAA ERSST data. It makes use of two distinct regression downscaling models corresponding to the interannual and interdecadal rainfall variability of SCESR.The two models are developed based on the partial least squares(PLS) regression technique, linking SCESR to SST modes in preceding months on both interannual and interdecadal timescales. Specifically, using the datasets in the calibration period 1915–84, the variability of SCESR and SST are decomposed into interannual and interdecadal components. On the interannual timescale, a threshold PLS regression model is fitted to interannual components of SCESR and March SST patterns by taking account of the modulation of negative and positive phases of the Pacific Decadal Oscillation(PDO). On the interdecadal timescale, a standard PLS regression model is fitted to the relationship between SCESR and preceding November SST patterns. The total rainfall prediction is obtained by the sum of the outputs from both the interannual and interdecadal models. Results show that the TSDTR downscaling approach achieves reasonable skill in predicting the observed rainfall in the validation period 1985–2006, compared to other simpler approaches. This study suggests that the TSDTR approach,considering different interannual SCESR-SST relationships under the modulation of PDO phases, as well as the interdecadal variability of SCESR associated with SST patterns, may provide a new perspective to improve climate predictions.     

海岛礁光学和雷达影像基于改进非子采样小波变换的自动配准

Homologous feature point extraction is a key problem in the optical and synthetic aperture radar （SAR） image registration for islands. A new feature point extraction method using a threshold shrink operator and non-subsampled wavelet transform （TSO-NSWT） for optical and SAR image registration was proposed. Moreover, the matching for this proposed feature was different from the traditional feature matching strategies and was performed using a similarity measure computed from neighborhood circles in low-frequency bands. Then, a number of reliably matched couples with even distributions were obtained, which assured the accuracy of the registration. Application of the proposed algorithm to SPOT-5 （multi-spectral） and YG-1 （SAR） images showed that a large number of accurately matched couples could be identified. Additionally, both of the root mean square error （RMSE） patterns of the registration parameters computed based on the TSO-NSWT algorithm and traditional NSWT algorithm were analyzed and compared, which further demonstrated the effectiveness of the proposed algorithm. The algorithm can supply the crucial step for island image registration and island recognition.     

From Grain to Floodplain: Evaluating heterogeneity of floodplain hydrostatigraphy using sedimentology,geophysics, and remote sensing

Stratigraphy is a fundamental component of floodplain heterogeneity and hydraulic conductivity and connectivity of alluvial aquifers, which affect hydrologic processes such as groundwater flow and hyporheic exchange. Watershed-scale hydrological models commonly simplify the sedimentology and stratigraphy of floodplains, neglecting natural floodplain heterogeneity and anisotropy. This study, conducted in the upper reach of the East River in the East River Basin, Colorado, USA, combines point-, meander-, and floodplain-scale data to determine key features of alluvial aquifers important for estimating hydrologic processes. We compare stratigraphy of two meanders with disparate geometries to explore floodplain heterogeneity and connectivity controls on flow and transport. Meander shape, orientation, and internal stratigraphy affected residence time estimates of laterally exchanged hyporheic water. Although the two meanders share a sediment source, vegetation, and climate, their divergent river migration histories resulted in contrasting meander hydrofacies. In turn, the extent and orientation of these elements controlled the effective hydraulic conductivity and, ultimately, estimates of groundwater transport and hyporheic residence times. Additionally, the meanders’ orientation relative to the valley gradient impacted the hydraulic gradient across the meanders—a key control of groundwater velocity. Lastly, we combine our field data with remotely sensed data and introduce a potential approach to estimate key hydrostratigraphic packages across floodplains. Prospective applications include contaminant transport studies, hyporheic models, and watershed models. © 2019 John Wiley & Sons, Ltd.     

Theoretical constraints to gully erosion research: time for a re‐evaluation of concepts and assumptions?

Gullies are conceptualized in the literature as essentially fluvial forms with dimensional boundaries arbitrarily defined between rills and river channels. This notion is incompatible with the existing variability of form and process, as mass movements frequently exert a fundamental control on gully initiation and expansion, to the point of features outgrowing their original contributing area. The inability of a conceptual framework to incorporate existing observations inevitably constrains methodologies and research results. In this commentary, several examples of published results are contrasted with the prevailing assumption of an essentially fluvial nature, with the purpose of encouraging discussion on the need for a revised conceptual framework in gully erosion research. Copyright © 2011 John Wiley & Sons, Ltd.     

Spatial and temporal variability of pore‐water pressures in residual soil slopes in a tropical climate

It is critical to understand and quantify the temporal and spatial variability in hillslope hydrological data in order to advance hillslope hydrological studies, evaluate distributed parameter hydrological models, analyse variability in hydrological response of slopes and design efficient field data sampling networks. The spatial and temporal variability of field‐measured pore‐water pressures in three residual soil slopes in Singapore was investigated using geostatistical methods. Parameters of the semivariograms, namely the range, sill and nugget effect, revealed interesting insights into the spatial structure of the temporal situation of pore‐water pressures in the slopes. While informative, mean estimates have been shown to be inadequate for modelling purposes, indicator semivariograms together with mean prediction by kriging provide a better form of model input. Results also indicate that significant temporal and spatial variability in pore‐water pressures exists in the slope profile and thereby induces variability in hydrological response of the slope. Spatial and temporal variability in pore‐water pressure decreases with increasing soil depth. The variability decreases during wet conditions as the slope approaches near saturation and the variability increases with high matric suction development following rainfall periods. Variability in pore‐water pressures is greatest at shallow depths and near the slope crest and is strongly influenced by the combined action of microclimate, vegetation and soil properties. Copyright © 2002 John Wiley & Sons, Ltd.     

Evaluation of sensitivity of land surface hydrology representations with and without land–atmosphere feedback

This paper compares various ways of quantifying the importance of land–atmosphere feedback. A widely used land surface hydrology model is used in coupled (to a planetary boundary layer model) and uncoupled modes to compare the adequacy of different feedback indices. It is found that existing feedback indices are primarily based on ‘one factor at a time’ sensitivity analysis and cannot adequately capture the interaction between land and atmosphere. A new index is used which combines factorial design concepts and traditional sensitivity analysis. This index is shown to capture and quantify the strength of interaction between land surface parameters and atmosphere. To assess the effects of forcing characteristics on the stand alone model sensitivity, several ways to specify near-surface atmospheric conditions are evaluated. It is found that commonly used forcing conditions (e.g. model generated or observed time-series of near-surface atmospheric variables) may not be adequate to mimic the coupled model environment for evaluating the land surface representations. The partially coupled model sensitivity is shown to capture a major feedback loop related to water holding capacity, surface fluxes and near-surface atmospheric processes. These results suggest that sensitivity from the stand alone model should be interpreted with caution and future evaluations should strive to incorporate land–atmosphere feedback, at least within a partially coupled model. © 1997 John Wiley & Sons, Ltd.     

Late quaternary paleoclimatic reconstructions for interior Alaska based on paleolake-level data and hydrologic models

Hydrologic models are developed for two lakes in interior Alaska to determine quantitative estimates of precipitation over the past 12,500 yrs. Lake levels were reconstructed from core transects for these basins, which probably formed prior to the late Wisconsin. Lake sediment cores indicate that these lakes were shallow prior to 12,500 yr B.P. and increased in level with some fluctuation until they reached their modern levels 4,000-8,000 yr B.P. Evaporation (E), evapotranspiration (ET), and precipitation (P) were adjusted in a water-balance model to determine solutions that would maintain the lakes at reconstructed levels at key times in the past (12,500, 9,000 and 6,000 yr B.P.). Similar paleoclimatic solutions can be obtained for both basins for these times. Results indicate that P was 35-75% less than modern at 12,500 yr B.P., 25-45% less than modern at 9,000 yr B.P. and 10-20% less than modern at 6,000 yr B.P. Estimates for E and ET in the past were based on modern studies of vegetation types indicated by fossil pollen assemblages. Although interior Alaska is predominantly forested at the present, pollen analyses indicate tundra vegetation prior to about 12,000 yr B.P. The lakes show differing sensitivities to changing hydrologic parameters; sensitivity depends on the ratio of lake area (AL) to drainage basin (DA) size. This ratio also changed over time as lake level and lake area increased. Smaller AL to DA ratios make a lake more sensitive to ET, if all other factors are constant.