Cezar Ionescu

Coastal flood damage and adaptation costs under 21st century sea-level rise.

Significance Coastal flood damages are expected to increase significantly during the 21st century as sea levels rise and socioeconomic development increases the number of people and value of assets in the coastal floodplain. Estimates of future damages and adaptation costs are essential for supporting efforts to reduce emissions driving sea-level rise as well as for designing strategies to adapt to increasing coastal flood risk. This paper presents such estimates derived by taking into account a wide range of uncertainties in socioeconomic development, sea-level rise, continental topography data, population data, and adaptation strategies. Coastal flood damage and adaptation costs under 21st century sea-level rise are assessed on a global scale taking into account a wide range of uncertainties in continental topography data, population data, protection strategies, socioeconomic development and sea-level rise. Uncertainty in global mean and regional sea level was derived from four different climate models from the Coupled Model Intercomparison Project Phase 5, each combined with three land-ice scenarios based on the published range of contributions from ice sheets and glaciers. Without adaptation, 0.2–4.6% of global population is expected to be flooded annually in 2100 under 25–123 cm of global mean sea-level rise, with expected annual losses of 0.3–9.3% of global gross domestic product. Damages of this magnitude are very unlikely to be tolerated by society and adaptation will be widespread. The global costs of protecting the coast with dikes are significant with annual investment and maintenance costs of US

Clarifying vulnerability definitions and assessments using formalisation

12–71 billion in 2100, but much smaller than the global cost of avoided damages even without accounting for indirect costs of damage to regional production supply. Flood damages by the end of this century are much more sensitive to the applied protection strategy than to variations in climate and socioeconomic scenarios as well as in physical data sources (topography and climate model). Our results emphasize the central role of long-term coastal adaptation strategies. These should also take into account that protecting large parts of the developed coast increases the risk of catastrophic consequences in the case of defense failure.

Relation-based computations in a monadic BSP model

The purpose of this paper is to present a formal framework of vulnerability to climate change, to address the conceptual confusion around vulnerability and related concepts. The framework was developed using the method of formalisation – making structure explicit. While mathematics as a precise and general language revealed common structures in a large number of vulnerability definitions and assessments, the framework is here presented by diagrams for a non‐mathematical audience. Vulnerability, in ordinary language, is a measure of possible future harm. Scientific vulnerability definitions from the fields of climate change, poverty, and natural hazards share and refine this structure. While theoretical definitions remain vague, operational definitions, that is, methodologies for assessing vulnerability, occur in three distinct types: evaluate harm for projected future evolutions, evaluate the current capacity to reduce harm, or combine the two. The framework identifies a lack of systematic relationship between theoretical and operational definitions. While much conceptual literature tries to clarify vulnerability, formalisation is a new method in this interdisciplinary field. The resulting framework is an analytical tool which supports clear communication: it helps when making assumptions explicit. The mismatch between theoretical and operational definitions is not made explicit in previous work.

Generic Libraries in C++ with Concepts from High-Level Domain Descriptions in Haskell

Abstract We propose a Haskell monadic model of bulk synchronous parallel programs and apply it to the analysis of relation-based computations. Relation-based computations are simple but general patterns found in scientific computing applications. They are easy to implement sequentially, but difficult to parallelize. We use the model to give high-level specifications of distributed relation-based algorithms and outline how to obtain testable parallel implementations from these specifications via equational reasoning. We sketch the architecture of a C++ library of components for distributed relation-based computations. We argue that the model can be used to provide a concise and consistent library documentation.

Contributions to a computational theory of policy advice and avoidability

A class of closely related problems, a problem domain, can often be described by a domain-specific language, which consists of algorithms and combinators useful for solving that particular class of problems. Such a language can be of two kinds: it can form a new language or it can be embedded as a sublanguage in an existing one. We describe an embedded DSL in the form of a library which extends a general purpose language. Our domain is that of vulnerability assessment in the context of climate change, formally described at the Potsdam Institute for Climate Impact Research. The domain is described using Haskell, yielding a domain specific sublanguage of Haskell that can be used for prototyping of implementations. In this paper we present a generic C++ library that implements a domain-specific language for vulnerability assessment, based on the formal Haskell description. The library rests upon and implements only a few notions, most importantly, that of a monadic system, a crucial part in the vulnerability assessment formalisation. We describe the Haskell description of monadic systems and we show our mapping of the description to generic C++ components. Our library heavily relies on concepts , a C++ feature supporting generic programming: a conceptual framework forms the domain-specific type system of our library. By using functions, parametrised types and concepts from our conceptual framework, we represent the combinators and algorithms of the domain. Furthermore, we discuss what makes our library a domain specific language and how our domain-specific library scheme can be used for other domains (concerning language design, software design, and implementation techniques).

Sequential decision problems, dependent types and generic solutions

We present the starting elements of a mathematical theory of policy advice and avoidability. More specifically, we formalize a cluster of notions related to policy advice, such as policy, viability, reachability, and propose a novel approach for assisting decision making, based on the concept of avoidability. We formalize avoidability as a relation between current and future states, investigate under which conditions this relation is decidable and propose a generic procedure for assessing avoidability. The formalization is constructive and makes extensive use of the correspondence between dependent types and logical propositions, decidable judgments are obtained through computations. Thus, we aim for a computational theory, and emphasize the role that computer science can play in global system science.

Vulnerability Modelling with Functional Programming and Dependent Types

We present a computer-checked generic implementation for solving finite-horizon sequential decision problems. This is a wide class of problems, including inter-temporal optimizations, knapsack, optimal bracketing, scheduling, etc. The implementation can handle time-step dependent control and state spaces, and monadic representations of uncertainty (such as stochastic, non-deterministic, fuzzy, or combinations thereof). This level of genericity is achievable in a programming language with dependent types (we have used both Idris and Agda). Dependent types are also the means that allow us to obtain a formalization and computer-checked proof of the central component of our implementation: Bellmans principle of optimality and the associated backwards induction algorithm. The formalization clarifies certain aspects of backwards induction and, by making explicit notions such as viability and reachability, can serve as a starting point for a theory of controllability of monadic dynamical systems, commonly encountered in, e.g., climate impact research.

Dependently-Typed Programming in Scientific Computing

We present an interdisciplinary effort in the field of global environmental change, related to the understanding of the concept of ‘vulnerability’. We have used functional programming to capture the generic aspects of the myriad of definitions of vulnerability, and have used the resulting formalization to learn something new about vulnerability and to write some better software for vulnerability assessment. In the process, we have also found out something about formalization in general, about the advantages and disadvantages of dependent types, and about the role of computing science in the larger intellectual landscape.

Functional prototypes for generic C++ libraries: a transformational approach based on higher-order, typed signatures

Computer simulations are essential in virtually every scientific discipline, even more so in those such as economics or climate change where the ability to make laboratory experiments is limited. Therefore, it is important to ensure that the models are implemented correctly, that they can be re-implemented and that the results can be reproduced. Typically, though, the models are described by a mixture of prose and mathematics which is insufficient for these purposes. We argue that using dependent types allows us to gradually reduce the gap between the mathematical description and the implementation, and we give examples from economic modelling. We discuss the consequences that our incremental approach has on programming style and the requirements it imposes on the dependently-typed programming languages used.

Towards a Formal Framework of Vulnerability to Climate Change

This paper presents a method for developing generic C++ software libraries from functional prototypes, based on program transformation. More precisely, the type signatures of generic functions, i.e., functions parameterized on types, are transformed. This transformation maps type-level expressions from functional higher-order, typed languages to type-level expressions in C++. In particular, type-level functional constructs such as higher-order functions and type constructors, are mapped to type parameters of generics that are constrained with appropriate concepts. The core of the transformation is a novel form of “defunctionalization” at the level of types. To make the transformation retargetable, we based it on two kernel languages that can be bound to different functional and object-oriented languages. For this paper, we use bindings to Haskell as front end and C++ with concepts as back end. Our transformational approach presents an alternative to a language extension and is useful particularly for functional prototyping where functional features are employed at specification time. We illustrate our approach by a case study: we show how we developed a generic C++ library for vulnerability modeling in the context of global change from a functional prototype in Haskell.