Politics of scale and community-based forest management in southern Malawi

This article uses insights from theory on the social production of scale and multiple social and natural science methods to interrogate village-scale community-based forest management (CBFM) in southern Malawi, focusing on boundary demarcation, rule formulation and scaling, and dynamics of external facilitation. Examination of political agendas of those who pursued, gained from, or protested particular scalar CBFM arrangements uncovered otherwise hidden scalar politics, whose outcomes impeded more than they advanced CBFM goals. I argue that clarifying the scalar politics and configuration of forest governance arrangements can lead to a more nuanced understanding of CBFM challenges and create new opportunities for addressing them. Containerized, single-level CBFM institutions mismatched interacting social, ecological and institutional scalar configurations and relations, and confounded CBFM. Unequal international-donor/national and national/community scalar relations were as important as intra-community dynamics in explaining performance of CBFM. They constructed CBFM on a shaky foundation that put institutional and personal agendas and short-term goals over long-term socioecological sustainability. The politics of rescaling forest rules from village to (broader) Traditional Authority level alienated them from communities and undermined enforcement. Diverse motivations behind a scale-related strategy that separated usufruct from territorial rights in allocating forests mostly undermined socioecological CBFM goals. While scale is not the key or only explanation of CBFM performance, negotiated scaling offered a proactive way to anticipate scale-related conflicts in particular settings, and for communities to create institutional forms that minimize such conflicts at local or intermediate scale levels. Findings support strong, well-resourced states and caution against donor-driven quick fixes.     

Experimental observation of strong mixing due to internal wave focusing over sloping terrain

This paper reports on experimental observation of internal waves that are focused due to a sloping topography. A remarkable mixing of the density field was observed. This result is of importance for the deep ocean, where internal waves are believed to play a role in mixing. The experiments were performed on the rotating platform at the Coriolis Laboratory, Grenoble. The rotation, its modulation and density stratification were set to be in the internal wave regime. After applying various data processing techniques we observe internal wave rays, which converge to a limiting state: the wave attractor. At longer time scales we observe a remarkably efficient mixing of the density field, possibly responsible for driving observed sheared mean flows and topographic Rossby waves. We offer the hypothesis that focusing of internal waves to the wave attractor leads to the mixing.     

Mapping Cropping Practices Using MODIS Time Series: Harnessing the Data Explosion

The MODIS (Moderate Resolution Imaging Spectroradiometer) 250m EVI dataset provides a valuable ongoing means of characterising and monitoring changes in land use and resource condition. However the multiple factors that influence a time series of greenness data make the data difficult to analyse and interpret. Without prior knowledge, underlying models for time series in a given remote sensing image are often heterogeneous. So while conventional time series analysis methods such as wavelet transform and Fourier analysis may work well for part of the image, these models are either invalid or must be substantially re-parameterised for other parts of the image. To overcome these challenges we propose a new approach to distil information from earth observation time series data. The characteristics of a remote sensing time series are represented by a set of statistics (which we call coefficients) selected to correspond to the dynamics of a natural system. To ensure the coefficients are robust and generic, statistics are calculated independently by applying statistical models with less complexity on shorter segments within the time series. An International Standards Organization (ISO) Land Cover classification (Jansen 2000) was generated for cropping regions in the Gwydir and Namoi catchments, in Australia. Areas identified in the classification as irrigated and rain fed cropping were analysed using a tailored time series analysis tool. The crop analysis tool identifies time series features such as the number and duration of fallow periods, crop timing, presence/absence of a crop during a year for a specific growing season. This information is combined with paddock boundaries derived from Landsat imagery to provide detailed year-by-year insight into cropping practices in the Gwydir and Namoi catchments.     

2010 oil spill: trajectory projections based on ensemble drifter analyses

An accurate method for long-term (weeks to months) projections of oil spill trajectories based on multi-year ensemble analyses of simulated surface and subsurface (z = −800 m) drifters released at the northern Gulf of Mexico spill site is demonstrated during the 2010 oil spill. The simulation compares well with satellite images of the actual oil spill which show that the surface spread of oil was mainly confined to the northern shelf and slope of the Gulf of Mexico, with some (more limited) spreading over the north/northeastern face of the Loop Current, as well as northwestward toward the Louisiana–Texas shelf. At subsurface, the ensemble projection shows drifters spreading south/southwestward, and this tendency agrees well with ADCP current measurements near the spill site during the months of May–July, which also show southward mean currents. An additional model analysis during the spill period (Apr–Jul/2010) confirms the above ensemble projection. The 2010 analysis confirms that the reason for the surface oil spread to be predominantly confined to the northern Gulf shelf and slope is because the 2010 wind was more southerly compared to climatology and also because a cyclone existed north of the Loop Current which moreover was positioned to the south of the spilled site.     

Analytical and numerical analysis of tides and salinities in estuaries; part II: salinity distributions in prismatic and convergent tidal channels

Estuaries, commonly, are densely populated areas serving the needs of the inhabitants in multiple ways. Often the interests are conflicting and decisions need to be made by the local managers. Intake of fresh water for consumption, agricultural purposes or use by industries may take place within a region not far landward of the limit of salt intrusion. Human interventions (e.g. deepening of the navigation channels) or climate changes (sea level rise, reduction of the river discharge) can bring these intake locations within the reach of saline or brackish water and consequently endanger their function. To support policy and managerial decisions, a profound knowledge of processes associated with the salinity structure in estuaries is required. Although nowadays advanced numerical three-dimensional models are available that are able to cope with the complexity of the physics there is still a need for relatively simple tools for quick-scan actions in a pre-phase of a project or for instructive purposes. The analytical model described in this paper may serve these needs. It computes the maximum salinity distribution using the dispersion coefficient in the mouth as the only model parameter. The model has been calibrated using observational data in a large number of estuaries and experimental data in a tidal flume. The dispersion coefficient was successfully related to geometric and hydrodynamic parameters resulting in an expression that can be used for convergent estuaries as well as prismatic channels, see Eqs. 25a and 25b. Application of the model in a predictive mode showed its promising capabilities. Comparison with three-dimensional numerical models indicates that the channel geometry in the estuary mouth largely influences dispersive processes. The analytical model for salt intrusion may be used in combination with the analytical model for tidal propagation in convergent estuaries and tidal channels by Van Rijn (part I). In this way, input is obtained on the tidal velocity amplitude and the Chézy roughness following calibration of this model on tidal amplitudes along the estuary.     

Designing a long-term flood risk management plan for the Scheldt estuary using a risk-based approach

The Scheldt is a tidal river that originates in France and flows through Belgium and the Netherlands. The tides create significant flood risks in both the Flemish region in Belgium and the Netherlands. Due to sea level rise and economic development, flood risks will increase during this century. This is the main reason for the Flemish government to update its flood risk management plan. For this purpose, the Flemish government requested a cost-benefit analysis of flood protection measures, considering long-term developments. Measures evaluated include a storm surge barrier, dyke heightening and additional floodplains with or without the development of wetlands. Some of these measures affect the flood risk in both countries. As policies concerning the limitation of flood risk differ significantly between the Netherlands and Flanders, distinctive methodologies were used to estimate the impacts of measures on flood risk. A risk-based approach was applied for Flanders by calculating the impacts of flood damage at different levels of recurrence, for the base year (2000) and in case of a sea level rise of 60 cm by 2100. Policy within the Netherlands stipulates a required minimal protection level along the Scheldt against storms with a recurrence period of 1 in 4,000 years. It was estimated how flood protection measures would delay further dyke heightening, which is foreseen as protection levels are presently decreasing due to rising sea levels. Impacts of measures (safety benefits) consist of delays in further dyke heightening. The results illustrate the importance of sea level rise. Flood risks increased fivefolds when a sea level rise of 60 cm was applied. Although more drastic measures such as a storm surge barrier near Antwerp offer more protection for very extreme storms, a combination of dykes and floodplains can offer higher benefits at lower costs.     

Stable isotope and mineralogical investigation of the genesis of amethyst geodes in the Los Catalanes gemological district,Uruguay, southernmost Paraná volcanic province

Stable isotopes (C, O, S) and mineralogical studies of the world-class amethyst-geode deposits of the Los Catalanes gemological district, Uruguay, constrain processes operative during mineral deposition. The mineralized basaltic andesites from the Cretaceous Paraná volcanic province are intensely altered to zeolites (clinoptilolite) and clay minerals. Variations in the δ¹⁸O values of silica minerals in geodes (chalcedony, quartz, and amethyst) are much larger and the values generally somewhat lower (21.2–31.5‰) in the Uruguayan deposits than in the Ametista do Sul area of southern Brazil. The range of δ³⁴S values (−15.0 to −0.3‰) of altered basaltic rocks requires (in addition to sulfur of magmatic origin) the involvement of ³⁴S-depleted sedimentary sulfur from bacterial sulfate reduction. The results delimit the mineralizing processes to a post-eruption environment characterized by low temperature and strong interaction of the lava flows with meteoric water.     

Numerical simulation of idealized granular assemblies with plane elliptical particles

The paper presents the development of algorithms that have been implemented in a computer program used to simulate the performance of idealized granular systems composed of elliptical-shaped particles. The work is an extension of numerical simulation methods which have been successfully used in micromechanics research on disk-shaped or polygon-shaped particles by the authors and others. The simulation of elliptical-shaped particles offers the possibility to explore the influence of particle shape on the micromechanical behaviour of plane assemblies of particles and the stress-strain behaviour of these systems at the macro scale. Typical results of simulation runs are presented to illustrate the importance of particle shape on the macroscopic stress-strain response of plane systems.     

Searching for evidence of changes in extreme rainfall indices in the Central Rift Valley of Ethiopia

Extreme rainfall events have serious implications for economic sectors with a close link to climate such as agriculture and food security. This holds true in the Central Rift Valley (CRV) of Ethiopia where communities rely on highly climate-sensitive rainfed subsistence farming for livelihoods. This study investigates changes in ten extreme rainfall indices over a period of 40 years (1970–2009) using 14 meteorological stations located in the CRV. The CRV consists of three landscape units: the valley floor, the escarpments, and the highlands all of which are considered in our data analysis. The Belg (March–May) and Kiremt (June–September) seasons are also considered in the analysis. The Mann-Kendall test was used to detect trends of the rainfall indices. The results indicated that at the annual time scale, more than half (57 %) of the stations showed significant trends in total wet-day precipitation (PRCPTOT) and heavy precipitation days (R10mm). Only 7–35 % of stations showed significant trends, for the other rainfall indices. Spatially, the valley floor received increasing annual rainfall while the escarpments and the highlands received decreasing annual rainfall over the last 40 years. During Belg, 50 % of the stations showed significant increases in the maximum number of consecutive dry days (CDD) in all parts of the CRV. However, most other rainfall indices during Belg showed no significant changes. During Kiremt, considering both significant and non-significant trends, almost all rainfall indices showed an increasing trend in the valley floor and a decreasing trend in the escarpment and highlands. During Belg and Kiremt, the CDD generally showed increasing tendency in the CRV.

     

A Thermodynamics-Based Model on the Internal Erosion of Earth Structures

The present paper describes a model of internal erosion of earth structures, based on rigorous thermodynamic principles and the theory of porous media. A particular focus of this paper is concerned with the initial stage of internal erosion, when the pore volume forms a continuous network, without the formation of macroscopic cavities or channels. The continuum approach is applicable in this case. The soil skeleton saturated by a pore fluid is treated as the superposition of three continua in interaction, with independent velocity fields. The pore fluid itself consists of a mixture of water and eroded particles. The erosion kinetics is based on the shear stress developed at the solid–fluid interface. The applicability of the model is illustrated by numerical simulations based on the finite element method. These simulations show how the phenomenon of piping can progressively arise, and preferentially in regions where hydraulic gradients are critical. Effects of mechanical degradations due to internal erosion are at the same time demonstrated.