Food Security in Vietnam during the 1990s: The Empirical Evidence

food security, calorie consumption, Vietnam

Wavelet correlations to reveal multiscale coupling in geophysical systems

The interactions between climate and the environment are highly complex. Due to this complexity, process-based models are often preferred to estimate the net magnitude and directionality of interactions in the Earth System. However, these models are based on simplifications of our understanding of nature, thus are unavoidably imperfect. Conversely, observation-based data of climatic and environmental variables are becoming increasingly accessible over large scales due to the progress of space-borne sensing technologies and data-assimilation techniques. Albeit uncertain, these data enable the possibility to start unraveling complex multivariable, multiscale relationships if the appropriate statistical methods are applied. Here, we investigate the potential of the wavelet cross-correlation method as a tool for identifying multiscale interactions, feedback and regime shifts in geophysical systems. The ability of wavelet cross-correlation to resolve the fast and slow components of coupled systems is tested on synthetic data of known directionality, and then applied to observations to study one of the most critical interactions between land and atmosphere: the coupling between soil moisture and near-ground air temperature. Results show that our method is not only able to capture the dynamics of the soil moisture-temperature coupling over a wide range of temporal scales (from days to several months) and climatic regimes (from wet to dry), but also to consistently identify the magnitude and directionality of the coupling. Consequently, wavelet cross-correlations are presented as a promising tool for the study of multiscale interactions, with the potential of being extended to the analysis of causal relationships in the Earth system.Comment: Submitted to Journal of Geophysical Research - Atmospher

Analysis of the convective timescale during the major floods in the NE Iberian Peninsula since 1871

Floods are the most severe natural hazard in the western Mediterranean basin. They cause most of the damages and most of the victims. Some of the selected floods caused more than one hundred casualties each and a large quantity of damages in infrastructures. In a previous work (Balasch, et al., 2015), using the PREDIFLOOD database (Barriendos et al., 2014) we studied the atmospheric conditions that occurred during some of the most important floods occurred in the north-east of the Iberian Peninsula in the last centuries: 1874, 1875, 1894, 1897, 1898, 1901, 1907, 1913, 1919, 1932, 1937, 1940, 1962, 1963, 1977, 1994, 1996, and 2000. We analyzed the atmospheric synoptic situations at the time of each flood from the data provided by NOAA 20th Century Reanalysis and we compared it to the rainfall spatial distributions obtained with the hydrological modeling. In this work we enlarge the previous investigation by analyzing the evolution of a convective index proposed by Done et al. (2006) and modified by Molini et al. (2011). This index, called convective time scale, is obtained from the evolution of CAPE and is used to separate equilibrium and non-equilibrium convection. In the former, CAPE generated by large-scale processes is balanced by the consumption due to convection. In the second case, CAPE is created by large-scale processes over a long time and is rapidly consumed during outbreaks of convection. Both situations produced a totally different evolution of CAPE with low and approximately constant values in the first case and large and variable values in the second. Additionally, from this index it can be estimated the rainfall rate. We use data provided by NOAA 20th Century Reanalysis, to calculate the convective time scale and to analyze its evolution and horizontal distribution. We study the correspondence between the convective timescale, the season when the flood occurred, duration of the rainfall, and the specific peak flow rate of the flood. Finally, for the most recent episodes rainfall rate estimation from the convective timescale is compared with the observations. Balasch, J. C., Ruiz-Bellet, J. L., Tuset, J., Barriendos, M., Mazón, J., Pino, D. and Castelltort, X.: Transdisciplinary and multiscale reconstruction of the major flash floods in NE Iberian Peninsula. EGU General Assembly, 2015. Barriendos, M., Ruiz–Bellet, J. L., Tuset, J., Mazon, J., Balasch, J. C., Pino, D., Ayala, J. L.: ThePeer ReviewedPostprint (published version

Telosentis exiguus (von Linstow, 1901) (Palaeacanthocephala: Illiosentidae), a generalist parasite of fishes in the Mediterranean basin

The morphology of material of the acanthocephalan genus Telosentis van Cleave, 1923 from different parts of the Mediterranean basin is examined in order to assess the validity of T. molini van Cleave, 1923. A redescription of T. exiguus, a generalist species of fishes in the Mediterranean basin, is presented especially in relation to the number of proboscis hooks. The main characteristic of T. exiguus is a cylindrical or club-shaped proboscis, which is covered with 12 longitudinal rows of 14–19 hooks in males and 16–20 in females. Males and females differ in both body size and the number of proboscis hooks. T. molini is considered a junior synonym of T. exiguus. A key to the species of Telosentis is presented

DOES HETEROGENEITY MATTER IN THE CONTEXT OF THE GRAVITY MODEL?

This paper argues that there is a differential behaviour between the richest and the poorest economies in the gravity model framework. Results show that geographical and cultural factors are more important for developing than for developed economies, and a good economic policy in developing countries is to invest in technological innovation and in transport infrastructure.developed and developing countries

Optimal rainfall insurance contracts for maize producers in Ghana’s Northern Region

The risk of food insecurity due to climate change in developing countries has encouraged development partners to seek new approaches to improve the resilience of subsistence agriculture to covariate shocks. Such innovative approaches include investment in safety nets such as rainfall insurance. However, a policy question remains: How does one determine the practicality of rainfall insurance for a particular district? This paper attempts to fill this gap by assessing the viability of rainfall insurance contracts for agricultural production in Ghana’s Northern Region. Using a stop-loss framework, an optimal contract is determined by choosing its parameters by maximizing the objective function in the form of covariance between crop loss and indemnity payment, the objective function given a predetermined fair premium rate. The theoretical contract is implemented using monthly rainfall and annual maize crop yield data from 1998 to 2004 from 12 districts in the Northern Region under varying premium rates. We conclude that rainfall insurance may not be viable for all districts in the Northern Region; however, the contracts are likely to be viable in districts that exhibit a positive Pearson correlation coefficient between maize yield loss and indemnity payments.Climate change, maize yield, rainfall insurance,

First passage time statistics of Brownian motion with purely time dependent drift and diffusion

Systems where resource availability approaches a critical threshold are common to many engineering and scientific applications and often necessitate the estimation of first passage time statistics of a Brownian motion (Bm) driven by time-dependent drift and diffusion coefficients. Modeling such systems requires solving the associated Fokker-Planck equation subject to an absorbing barrier. Transitional probabilities are derived via the method of images, whose applicability to time dependent problems is shown to be limited to state-independent drift and diffusion coefficients that only depend on time and are proportional to each other. First passage time statistics, such as the survival probabilities and first passage time densities are obtained analytically. The analysis includes the study of different functional forms of the time dependent drift and diffusion, including power-law time dependence and different periodic drivers. As a case study of these theoretical results, a stochastic model for water availability from surface runoff in snowmelt dominated regions is presented, where both temperature effects and snow-precipitation input are incorporated

First passage time statistics of Brownian motion with purely time dependent drift and diffusion

Systems where resource availability approaches a critical threshold are common to many engineering and scientific applications and often necessitate the estimation of first passage time statistics of a Brownian motion (Bm) driven by time-dependent drift and diffusion coefficients. Modeling such systems requires solving the associated Fokker-Planck equation subject to an absorbing barrier. Transitional probabilities are derived via the method of images, whose applicability to time dependent problems is shown to be limited to state-independent drift and diffusion coefficients that only depend on time and are proportional to each other. First passage time statistics, such as the survival probabilities and first passage time densities are obtained analytically. The analysis includes the study of different functional forms of the time dependent drift and diffusion, including power-law time dependence and different periodic drivers. As a case study of these theoretical results, a stochastic model for water availability from surface runoff in snowmelt dominated regions is presented, where both temperature effects and snow-precipitation input are incorporated

An experimental study of interceptors for drag reduction on high-performance sailing yachts

Interceptors have been widely used in recent years in fast ferries and small high-speed leisure and commercial craft for ride and trim control, and steering. In the context of high-performance sailing yachts, they first appeared in 2008 on the yacht Ecover 3 which was dismasted while leading the Vendee Globe Challenge race. However, in spite of their popularity in power craft, few studies have been published investigating the impact of interceptors on vessel performance, and apparently none in the case of sailing yachts. In the current study, interceptors are compared with an aerodynamic device known as a Gurney flap. It is shown that interceptors are generally substantially smaller than Gurney flaps. A comprehensive experiment programme is presented exploring the impact of interceptors on the performance of an Open 60 yacht hull. Results show a marked reduction in calm-water resistance over a wide speed range, with benefits of 10–18% in the speed range between 8 and 20 knots, accompanied by reduced sinkage and trim. The gains observed are much larger than those observed in powercraft, and also substantially greater than those achievable through trim changes by moving ballast longitudinally. The benefits appear to be largely sustained in small waves