Spatial models for flood risk assessment

The problem of computing risk measures associated to flood events is extremely important not only from the point of view of civil protection systems but also because of the necessity for the municipalities of insuring against the damages. In this work we propose, in the framework of an integrated strategy, an operating solution which merges in a conditional approach the information usually available in this setup. First we use a Logistic Auto-Logistic (LAM) model for the estimation of the univariate conditional probabilities of flood events. This approach has two fundamental advantages: it allows to incorporate auxiliary information and does not require the target variables to be independent. Then we simulate the joint distribution of floodings by means of the Gibbs Sampler. Finally we propose an algorithm to increase ex post the spatial autocorrelation of the simulated events. The methodology is shown to be effective by means of an application to the estimation of the flood probability of Italian hydrographic regions

A note on maximum likelihood estimation of a Pareto mixture

In this paper we study Maximum Likelihood Estimation of the parameters of a Pareto mixture. Application of standard techniques to a mixture of Pareto is problematic. For this reason we develop two alternative algorithms. The first one is the Simulated Annealing and the second one is based on Cross-Entropy minimization. The Pareto distribution is a commonly used model for heavy-tailed data. It is a two-parameter distribution whose shape parameter determines the degree of heaviness of the tail, so that it can be adapted to data with different features. This work is motivated by an application in the operational risk measurement field: we fit a Pareto mixture to operational losses recorded by a bank in two different business lines. Losses below an unknown threshold are discarded, so that the observed data are truncated. The thresholds used in the two business lines are unknown. Thus, under the assumption that each population follows a Pareto distribution, the appropriate model is a mixture of Pareto where all the parameters have to be estimated.

A framework for cut-off sampling in business survey design

In sampling theory the large concentration of the population with respect to most surveyed variables constitutes a problem which is difficult to tackle by means of classical tools. One possible solution is given by cut-off sampling, which explicitly prescribes to discard part of the population; in particular, if the population is composed by firms or establishments, the method results in the exclusion of the “smallest” firms. Whereas this sampling scheme is common among practitioners, its theoretical foundations tend to be considered weak, because the inclusion probability of some units is equal to zero. In this paper we propose a framework to justify cut-off sampling and to determine the census and cut-off thresholds. We use an estimation model which assumes as known the weight of the discarded units with respect to each variable; we compute the variance of the estimator and its bias, which is caused by violations of the aforementioned hypothesis. We develop an algorithm which minimizes the MSE as a function of multivariate auxiliary information at the population level. Considering the combinatorial optimization nature of the model, we resort to the theory of stochastic relaxation: in particular, we use the simulated annealing algorithm.Cut-off sampling, skewed populations, model-based estimation, optimal stratification, simulated annealing

Spatial models for flood risk assessment

The problem of computing risk measures associated to flood events is extremely important not only from the point of view of civil protection systems but also because of the necessity for the municipalities of insuring against the damages. In this work we propose, in the framework of an integrated strategy, an operating solution which merges in a conditional approach the information usually available in this setup. First we use a Logistic Auto-Logistic (LAM) model for the estimation of the univariate conditional probabilities of flood events. This approach has two fundamental advantages: it allows to incorporate auxiliary information and does not require the target variables to be indepen- dent. Then we simulate the joint distribution of floodings by means of the Gibbs Sampler. Finally we propose an algorithm to increase ex post the spatial autocorrelation of the simulated events. The methodology is shown to be effective by means of an application to the estimation of the flood probability of Italian hydrographic regions.Flood Risk, Conditional Approach, LAM Model, Pseudo-Maximum Likelihood Estimation, Spatial Autocorrelation, Gibbs Sampler.

Interpreting in the European Commission

(No abstract available

Searching for Non-monotonic Effects of Fiscal Policy: New Evidence

Data revisions and the availability of a longer sample offer the opportunity to reconsider empirical findings that suggest that in the OECD countries national saving responds non-monotonically to fiscal policy. The paper confirms that the circumstance most likely to give rise to a non-monotonic response of national saving to a fiscal impulse is a "large and persistent impulse," defined as one in which the full employment surplus, as a percentage of potential output, changes by at least 1.5 percentage points per year over a two-year period. This particular circumstance remains the only statistically significant one even when we allow for non-monotonic responses to arise when public debt is growing rapidly or interest rate spreads are widening. We find that non-monotonic responses are similar for fiscal contractions and expansions. In particular, an increase in net taxes has no effect on national saving during large fiscal contractions or expansions. For government consumption there is a large, albeit in some specifications less than complete, offset during expansions or contractions.

Searching for Non-Monotonic Effects of Fiscal Policy: New Evidence

Data revisions and the availability of a longer sample offer the opportunity to reconsider the empirical findings that suggest that in the OECD countries national saving responds non-monotonically to fiscal policy. The paper confirms that the circumstance most likely to give rise to a non-monotonic response of national saving to a fiscal impulse is a “large and persistent impulse”, defined as one in which the full employment surplus, as a percent of potential output, changes by at least 1.5 percentage points per year over a two-year period. This particular circumstance remains the only statistically significant one even when we allow for non-monotonic responses to arise when public debt is growing rapidly or interest rate spreads are widening. We find that non-monotonic responses are similar for fiscal contractions and expansions. In particular, an increase in net taxes has no effect on national saving during large fiscal contractions or expansions. For government consumption there is a large, albeit in some specifications less then complete, offset during expansions or contractions.Fiscal policy, national saving

Searching for Non-Monotonic Effects of Fiscal Policy: New Evidence

Data revisions and the availability of a longer sample offer the opportunity to reconsider the empirical findings that suggest that in the OECD countries national saving responds non-monotonically to fiscal policy. The paper confirms that the circumstance most likely to give rise to a non-monotonic response of national saving to a fiscal impulse is a "large and persistent impulse", defined as one in which the full employment surplus, as a percent of potential output, changes by at least 1.5 percentage points per year over a two-year period. This particular circumstance remains the only statistically significant one even when we allow for non-monotonic responses to arise when public debt is growing rapidly or interest rate spreads are widening. We find that non-monotonic responses are similar for fiscal contractions and expansions. In particular, an increase in net taxes has no effect on national saving during large fiscal contractions or expansions. For government consumption there is a large, albeit in some specifications less then complete, offset during expansions or contractions.

Use of natural resins in repairing damaged timber beams – An experimental investigation

Different techniques including the application of steel elements, composite materials and polymeric resins have been used in the past to repair damaged timber beams. However, there is a growing need to replace these materials with those with minimal environmental impact. In addition, stringent requirements of conservation authorities on the compatibility between repair and parent materials have also necessitated search for innovative repair materials for timber beams. Therefore, an increasing shift of focus towards the use of materials derived from natural sources in repairing and reinforcing timber structures is currently experienced. This paper presents the results of an exploratory study on the use of natural resins (rosin and bone glue) in repairing oak timber beams. 15 oak timber beams with cross section dimensions of 67 x 67 mm and 1100 mm in length were tested in four-point bending to failure. Undamaged, damaged (unrepaired) and damaged but repaired timber beams (with rosin and bone glue) were tested. The effectiveness of the repair material and technique was analysed based on the bending capacity and mid span deflection at failure. The initial results show negligible effectiveness of rosin in repairing timber beams. In fact, about 16% reduction (average) in load carrying capacity with a corresponding 5% decrease (average) in maximum displacement was recorded. Relatively higher level of effectiveness was recorded with the use of bone glue (about 10 % average increase in load carrying capacity). However, over 30% corresponding average increase in the maximum displacement was also recorded. Further work investigating different repair techniques and other natural resins is presently underway