The Economics of Climate Change Adaptation and Water Resources: An Application to Dams

Dam construction has increased rapidly since the 1950’s, especially in developing countries. Climate change is likely to impact the demand for new dams as well as future water and sediment inflow in rivers, thereby influencing the utility, management, and lifetime of dams. Proper construction of dams and sediment management can also help reduce the cost and mitigate the risks dams might be facing as a result of changing climate patterns, which will allow communities to utilize water resources more efficiently and sustainably. This dissertation develops a series of dynamic optimization models to determine how the size of different type of dams and their management strategies can help achieve the above goals. First, a single purpose dam’s optimization problem is explored to arrive at desirable results for maximization of net economics benefits with respect to initial reservoir capacity, sediment removal amount, and decommissioning time. Application of this model to Sambor dam in the lower Mekong River basin shows that allowing for optimal reservoir capacity and sediment removal choice has a significant impact on dam life and total net present value, in the absence of climate change considerations. However, both the desirable reservoir capacity and total net present value vary considerably with climate change. Second, management of multi purpose dams under climate change is discussed with respect to determination of optimal reservoir capacity and sediment removal. These two factors generally increase in magnitude as the functions of a dam and its potential benefits increase. Third, optimal reservoir design and systematic management of cascading dams under climate change are studied for coordinated and non-coordinated cases to arrive at the best policy solution. In the application considered, a coordinated strategy between two dams (Luang Prabang Dam and Xayaburi Dam) is beneficial for the entire system, though the difference between the total net present values from the two types of strategies is relatively small. Generally, coordination resulted in the upstream dam requiring a larger reservoir capacity and accumulating more of incoming sediment in order to ease the negative externality to the downstream dam. Finally, the possibility of dam failure is also incorporated in the model of a single dam based on expected annual peak flood flow trends. An innovation in this regard is the determination of an optimally sized spillway to protect against flood overtopping. Three categories of peak flood flow trends are considered to reflect alternate climate change scenarios. With the risk of dam failure involved, the optimal choice of reservoir capacity and spillway capacity are significantly impacted by water availability and the amount of incoming sediment as influenced by climate factors

Dynamics of a diffusive predator-prey system with fear effect in advective environments

We explore a diffusive predator-prey system that incorporates the fear effect in advective environments. Firstly, we analyze the eigenvalue problem and the adjoint operator, considering Constant-Flux and Dirichlet (CF/D) boundary conditions, as well as Free-Flow (FF) boundary conditions. Our investigation focuses on determining the direction and stability of spatial Hopf bifurcation, with the generation delay $\tau$ serving as the bifurcation parameter. Additionally, we examine the influence of both linear and Holling-II functional responses on the dynamics of the model. Through these analyses, we aim to gain a better understanding of the intricate relationship between advection, predation, and prey response in this system

Should I Stay or Should I Go: Two Features to Help People Stop An Exploratory Search Wisely

poster abstractAs information becomes more ubiquitously available, many information users tend to experience a sense of anxiety due to the “information overload”. Few studies have systematically examined searchers’ stopping behavior, i.e., how users recognize how much information is enough to terminate a search. Bad decisions on a stopping point will lead to either insufficient information or unnecessary waste of time and effort without much additional information gain. Understanding searchers’ stopping behavior is extremely important to assist in thorough search result evaluation and to prevent a premature or a too-late search stopping. In this study, we present the design and implementation of two search techniques: Result Preview (RP) and History Review (HR), to help people make right decisions about when to terminate a search and how to consume information efficiently when facing an overwhelming amount of information. The basic idea of RP is to visualize the distribution of newly retrieved and re-retrieved documents to users, and that of HR is to display the previous search activities for searchers to review what has been done to help define the next steps. Both features are aiming at guiding searchers through the process of problem solving and decision making about whether to stay or leave during the search process. To implement the two techniques, we developed the search system on Bing Search API. The Bing search results were brought back to the search interface using AJAX and PHP. A formal user experiment with 24 participants is also proposed to evaluate the benefits and limitations, and also inform the future RP and HR design

The Effect of Task Type and Information Format on Web Searching Performance

Web search engines have become a useful tool helping Web users seek required information. Such Web sites typically present searched results as a textual list that may include thousands of Web pages. Because of the unstructured content and format of information that searchers receive, they often feel the pressure of information overload, which will inevitably compromise the quality of decision-making. Although researchers as well as practitioners have developed various information visualization approaches to enhance information presentation on Web search engines, the benefits of using such technology are unknown. This study will investigate whether and under what circumstances visualization of search results enhances users’ search performance. Cognitive fit theory will be used as the theoretical foundation of this paper. The objectives of the paper are 1) to extent cognitive fit theory in the emergent domain of Web searching, 2) to understand the effects of the user interface on search performance, and 3) to guide search engine designers on how to best present results to support different search tasks

Multivariable Scaling for the Anomalous Hall Effect

We derive a general scaling relation for the anomalous Hall effect in ferromagnetic metals involving multiple competing scattering mechanisms, described by a quadratic hypersurface in the space spanned by the partial resistivities. We also present experimental findings, which show strong deviation from previously found scaling forms when different scattering mechanism compete in strength but can be nicely explained by our theory