29,811 research outputs found
Modeling structural change in spatial system dynamics: A Daisyworld example
System dynamics (SD) is an effective approach for helping reveal the temporal
behavior of complex systems. Although there have been recent developments in
expanding SD to include systems' spatial dependencies, most applications have
been restricted to the simulation of diffusion processes; this is especially
true for models on structural change (e.g. LULC modeling). To address this
shortcoming, a Python program is proposed to tightly couple SD software to a
Geographic Information System (GIS). The approach provides the required
capacities for handling bidirectional and synchronized interactions of
operations between SD and GIS. In order to illustrate the concept and the
techniques proposed for simulating structural changes, a fictitious environment
called Daisyworld has been recreated in a spatial system dynamics (SSD)
environment. The comparison of spatial and non-spatial simulations emphasizes
the importance of considering spatio-temporal feedbacks. Finally, practical
applications of structural change models in agriculture and disaster management
are proposed
Modeling water resources management at the basin level: review and future directions
Water quality / Water resources development / Agricultural production / River basin development / Mathematical models / Simulation models / Water allocation / Policy / Economic aspects / Hydrology / Reservoir operation / Groundwater management / Drainage / Conjunctive use / Surface water / GIS / Decision support systems / Optimization methods / Water supply
AGRICULTURE AS A MANAGED ECOSYSTEM: POLICY IMPLICATIONS
One of the greatest challenges facing agriculture for the foreseeable future is to resolve conflicts caused by a growing competition for the services of the soil, water, and other natural resources on which agriculture depends-driven by growing demands for food, fiber, and for nonagricultural services these resources provide. To meet this challenge, research is needed which is integrated across the relevant sciences to better understand and predict the properties of agricultural production systems in all of the dimensions that have come to be represented by the concept of sustainability. If we were to achieve this capability to analyze agriculture as a managed ecosystem, it would be possible to move beyond the current regime of agricultural policies, driven largely by interest-group politics, toward science-based policies that recognize the tradeoffs associated with competing uses of natural resources.Environmental Economics and Policy,
A Detailed Hydro-Economic Model for Assessing the Effects of Surface Water and Groundwater Policies: A Demonstration Model from Brazil
Policymakers, managers of water use associations, and many others in developing countries are considering policy actions that will directly or indirectly change the costs and availability of groundwater and surface water for agricultural users. While in many cases such actions may bring about welcomed increases in water use efficiency, little is known about the likely effects of changes in irrigation costs or water access on farmer behavior, or on farmer incomes in the short or long runs, and virtually nothing is known about the detailed immediate or knock-on effects on water resources that such policy actions might cause. This paper reports the preliminary results of research aiming to fill these large scientific gaps by developing a detailed hydrologic model and a detailed economic model of agriculture in the context of the Buriti Vermelho (BV) sub-catchment area of the São Francisco River Basin in Brazil. A spatially explicit, farm-level, positive mathematical programming model capable of accommodating a broad array of farm sizes and farm/farmer characteristics is being developed to predict the effects of alternative water policies and neighbors water use patterns on agricultural production. Special attention is given to precisely defining and estimating the distinct variable costs (including labor and electrical energy costs) and capital costs of surface water and groundwater, which are considered perfect substitutes for irrigation. Shadow values for non-marketed inputs (land, family labor, and water) are estimated in the first step of the modeling process. A high-resolution, spatially distributed hydrologic model (MOD-HMS) is being developed to simulate three-dimensional, variably-saturated subsurface flow and solute transport. Subsurface flow is simulated using the three-dimensional Richards equation while accounting for a) application of water at the surface, b) precipitation, c) soil evaporation and crop transpiration, and d) agricultural pumping. Demonstration versions of both models are presented and tested: the economic model assesses the effects of increasing water scarcity on cultivated area, crop mix, input mix and farm profits; the hydrologic model uses two irrigation water use scenarios to demonstrate the effects of each on surface water flows and storage, and on groundwater storage and well depth. The models are not currently linked, but a detailed plan to do so is presented and discussed. The paper concludes by discussing next steps in research and policy simulations.Resource /Energy Economics and Policy,
Tolerable versus actual soil erosion rates in Europe
Erosion is a major threat to soil resources in Europe, and may impair their ability to deliver a range of ecosystem goods and services. This is reflected by the European Commission's Thematic Strategy for Soil Protection, which recommends an indicator-based approach for monitoring soil erosion. Defined baseline and threshold values are essential for the evaluation of soil monitoring data. Therefore, accurate spatial data on both soil loss and soil genesis are required, especially in the light of predicted changes in climate patterns, notably frequency, seasonal distribution and intensity of precipitation. Rates of soil loss are reported that have been measured, modelled or inferred for most types of soil erosion in a variety of landscapes, by studies across the spectrum of the Earth sciences. Natural rates of soil formation can be used as a basis for setting tolerable soil erosion rates, with soil formation consisting of mineral weathering as well as dust deposition. This paper reviews the concept of tolerable soil erosion and summarises current knowledge on rates of soil formation, which are then compared to rates of soil erosion by known erosion types, for assessment of soil erosion monitoring at the European scale
Identifying Advantages and Disadvantages of Variable Rate Irrigation – An Updated Review
Variable rate irrigation (VRI) sprinklers on mechanical move irrigation systems (center pivot or lateral move) have been commercially available since 2004. Although the number of VRI, zone or individual sprinkler, systems adopted to date is lower than expected there is a continued interest to harness this technology, especially when climate variability, regulatory nutrient management, water conservation policies, and declining water for agriculture compound the challenges involved for irrigated crop production. This article reviews the potential advantages and potential disadvantages of VRI technology for moving sprinklers, provides updated examples on such aspects, suggests a protocol for designing and implementing VRI technology and reports on the recent advancements. The advantages of VRI technology are demonstrated in the areas of agronomic improvement, greater economic returns, environmental protection and risk management, while the main drawbacks to VRI technology include the complexity to successfully implement the technology and the lack of evidence that it assures better performance in net profit or water savings. Although advances have been made in VRI technologies, its penetration into the market will continue to depend on tangible and perceived benefits by producers
Basic research planning in mathematical pattern recognition and image analysis
Fundamental problems encountered while attempting to develop automated techniques for applications of remote sensing are discussed under the following categories: (1) geometric and radiometric preprocessing; (2) spatial, spectral, temporal, syntactic, and ancillary digital image representation; (3) image partitioning, proportion estimation, and error models in object scene interference; (4) parallel processing and image data structures; and (5) continuing studies in polarization; computer architectures and parallel processing; and the applicability of "expert systems" to interactive analysis
Aerospace medicine and biology: A continuing bibliography with indexes (supplement 323)
This bibliography lists 125 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during April, 1989. Subject coverage includes; aerospace medicine and psychology, life support systems and controlled environments, safety equipment exobiology and extraterrestrial life, and flight crew behavior and performance
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