Evaluation of the wave transformation in an open bay with two spectral models

An evaluation of two state of the art phase averaged wave models for the transformation scale, SWAN and STWAVE, is carried out in the present work. The target area is the Obidos Bay located in the central part of the Portuguese continental nearshore. The wave input for the two models is provided by an offshore buoy. In order to compare the nearshore outputs of the wave models against in-situ measurements, a directional buoy and an ADCP, operating in intermediate water depth, are used. The wave parameters considered for comparisons are significant wave height, peak period and wave direction. Sensitivity analyses studies and evaluations in the spectral and geographical spaces concerning the results of the two models are also carried out in both intermediate and shallow water. The present study provides some information on the performances of the two wave models in different forcing conditions as well as on their sensitivity in relationship with various input parameters and some physical processes. STWAVE appears to be faster and more robust than SWAN, which on the other hand has more options and flexibility. In statistical terms the results are comparable.     

Regime shifts: Can ecological theory illuminate the mechanisms?

“Regime shifts” are considered here to be low-frequency, high-amplitude changes in oceanic conditions that may be especially pronounced in biological variables and propagate through several trophic levels. Three different types of regime shift (smooth, abrupt and discontinuous) are identified on the basis of different patterns in the relationship between the response of an ecosystem variable (usually biotic) and some external forcing or condition (control variable). The smooth regime shift is represented by a quasi-linear relationship between the response and control variables. The abrupt regime shift exhibits a nonlinear relationship between the response and control variables, and the discontinuous regime shift is characterized by the trajectory of the response variable differing when the forcing variable increases compared to when it decreases (i.e., the occurrence of alternative “stable” states). Most often, oceanic regime shifts are identified from time series of biotic variables (often commercial fish), but this approach does not allow the identification of discontinuous regime shifts. Recognizing discontinuous regime shifts is, however, particularly important as evidence from terrestrial and freshwater ecosystems suggests that such regime shifts may not be immediately reversible. Based on a review of various generic classes of mathematical models, we conclude that regime shifts arise from the interaction between population processes and external forcing variables. The shift between ecosystem states can be caused by gradual, cumulative changes in the forcing variable(s) or it can be triggered by acute disturbances, either anthropogenic or natural. A protocol for diagnosing the type of regime shift encountered is described and applied to a data set on Georges Bank haddock, from which it is concluded that a discontinuous regime shift in the abundance of haddock may have occurred. It is acknowledged that few, if any, marine data are available to confirm the occurrence of discontinuous regime shifts in the ocean. Nevertheless, we argue that there is good theoretical evidence for their occurrence as well as some anecdotal evidence from data collection campaigns and that the possibility of their occurrence should be recognized in the development of natural resource management strategies.     

Comparison of the performance of flow‐routing algorithms used in GIS‐based hydrologic analysis

Flow direction and specific catchment area were calculated for different flow‐routing algorithms using TAPES‐G and TauDEM. A fuzzy classification was used along with eight topo–climatic attributes to delineate six landscape classes from a 10‐m USGS DEM. A series of maps and tabular outputs were produced to compare flow‐routing predictions in different parts of the study area in the Santa Monica Mountains of southern California. The matched pair t‐test was used to compare the performance of pairs of specific catchment area grids across six user‐defined fuzzy landscape classes. The results show that (1) the ‘source’ cells predicted with the D∞, DEMON, and FD8 algorithms were confined to hilltops; (2) two single flow‐routing algorithms (Rho8, D8) produced poor results; and (3) the choice of flow‐routing algorithm has potentially important consequences for the calculation of upslope contributing areas, sediment transport capacity, topographic wetness, and several other topographic indices. Copyright © 2007 John Wiley & Sons, Ltd.     

浙江省山区综合开发的探讨

山区综合开发必须调整偏农型产业结构,实行合理利用自然资源和旨在使山区人口向山下流动的积极的社会经济政策,摆脱与分散性密切相关的自给自足观念。由于山区物质、信息流动阻力大,城镇发展宜取多核分散型,要注意交通等基础设施的超前建设,改善山区环境。     

Spatial and temporal predictions of soil moisture dynamics,runoff, variable source areas and evapotranspiration for plynlimon,mid-wales

For many years hydrologists have tried to build physically realistic models which are still simple enough to be fitted to a range of observations made in the field. This is an ongoing process which will become even more difficult as the quality and variety of field and remotely sensed data improves. Hence models must be able to predict soil moisture patterns in time and in space as well as the outflow hydrograph. The model presented here (TOPMODEL) aims to predict the nature of variable source areas in a way that reflects their dynamics over space and time. All component processes are described and shown in operation. As TOPMODEL and similar models have a growing popularity, this paper can be seen as a demonstration of the model's predictive capabilities. The model is applied to the catchments of Plynlimon, mid-Wales for 1984, 1985 and 1986 data sets. The model has been thoroughly tested and cross-validated against independent data sets for different time periods, for a separate catchment, for internal gauges and for wet and dry periods. The resulting predicted soil moisture patterns show a small, semi-permanent variable source area that has the ability during large storms to expand dynamically over short time periods. Spatial predictions of evapotranspiration are also shown which reflect the influence of soil moisture patterns on this process. The weakest component of the model is the representation of root zone evaporation and how this pre-sets the antecedent condition of the catchment during long dry periods.     

TECHNIQUES OF CONSTRUCTING REGIONAL INPUT-OUTPUT TABLES: ACHIEVEMENTS

The development of any analytical method should have to experience at least four stages: its initial status, growth, mature and declining. However, although the regional input-output analysis has been widely applied for more than forty years, it is still one of the most important approach in regional economic analysis and forecast at present in the world. This is due to the never ended modifications and its great potentials. In this paper, we review the historical development of the regional input-output analysis.     

Classification problems of samples of finite mixtures of compositions

A discriminant technique based on mixture models is presented to be applied when observations are a sample of a mixture of compositions with each component following an additive logistic normal distribution on the d-dimensional simplex. The efficiency of this discriminant technique is compared empirically with the efficiency of the standard discriminant technique based on logcontrast. Simulated compositional data and a real dataset are used to carry out these comparisons.     

Stream nitrate levels in a small catchment in south west England over a period of 35 years (1970–2005)

This study considers a 35‐year record of streamwater nitrate concentration in a small agricultural catchment in south west England (Slapton Wood). The study revisits earlier work to assess whether upward trends have been maintained and how the controls upon streamwater concentration have been altered. The study has shown that (1) the catchment has reached a new position of equilibrium and increases in nitrate concentration have lessened; (2) the occurrence of severe drought in the record means that records of less than a decade are misleading and only long‐term records can illustrate changes of state; (3) the change of state observed in the catchment is illustrated in the switching of long‐term memory effects from a negative to a positive annual memory and (4) several significant long‐term impulsivity relationships with rainfall that become insignificant over the course of the study period. The study shows the importance of long‐term records in understanding changes in state in catchments and understanding the time constants of a range of driving processes. Copyright © 2009 John Wiley & Sons, Ltd.     

Formulation and application of the unsaturated/saturated catchment models SUSCAT and WEC‐C

This paper describes the formulation and application of a coupled unsaturated/saturated model framework developed to investigate the impact of mining on catchment water yield and groundwater dynamics. The model conceptualization was implemented in both a finite‐element (SUSCAT) and finite‐difference (WEC‐C) solution scheme and found to give similar results. The model framework simulates a coupled surface‐water and groundwater system in which a physically based solution scheme was used to simulate one‐dimensional movement through the unsaturated zone, and a distributed model was used to simulate two‐dimensional saturated groundwater flow. Each soil column comprises a series of layers, each layer being connected to adjacent cells. Subsurface lateral flow is considered when any cell within a layer develops a saturated thickness. Simulation results presented are based on a catchment in the Darling Range, Western Australia that was progressively mined and subsequently rehabilitated. The results predicted the groundwater system beneath the mine areas to have a peak rise owing to mining of between 2 and 4 m. Six years after mining, and following vegetation rehabilitation, the groundwater rise had reduced to 1 m above simulated unmined levels. The corresponding streamflow increase as a result of mining was estimated to peak at 21 mm/year and declined to 7·4 mm/year eight years after revegetation of the mined areas. The simulated groundwater response and streamflow results derived from both models were found to be consistent with observed data. Copyright © 2002 John Wiley & Sons, Ltd.