A critical comparison of using a probabilistic weather generator versus a change factor approach: irrigation reservoir planning under climate change

In the UK, there is a growing interest in constructing on-farm irrigation reservoirs, however deciding the optimum reservoir capacity is not simple. There are two distinct approaches to generating the future daily weather datasets needed to calculate future irrigation need. The change factor approach perturbs the observed record using monthly change factors derived from downscaled climate models. This assumes that whilst the climate changes, the day-to-day climate variability itself is stationary. Problems may arise where the instrumental record is insufficient or particularly suspect. Alternatively, probabilistic weather generators can be used to identify options which are considered more robust to climate change uncertainty because they consider non-stationary climate variability. This paper explores the difference between using the change factor approach and a probabilistic weather generator for informing farm reservoir design at three sites in the UK. Decision outcomes obtained using the current normal practice of 80% probability of non-exceedance rule and simple economic optimisations are also compared. Decision outcomes obtained using the change factor approach and probabilistic weather generators are significantly different; whether these differences translate to real-world differences is discussed. This study also found that using the 80% probability of non-exceedance rule could potentially result in maladaptation

Irrigation demand modelling using the UKCP09 weather generator: lessons learned

The determination of irrigation demand is typically based on crop modelling using a long historic record of local daily weather data. However, there are rarely adequate weather station records near to given sites; often any local records cover a limited number of years, are incomplete, costly or are of poor quality. This paper examines whether version 1 of the UKCP09 weather generator can provide a simpler and effective method of calculating irrigation demand with sufficient accuracy for regulatory and design purposes. The irrigation demands at seven sites distributed around England were modelled using the UKCP09 baseline climatology and compared with results modelled using daily observed weather records. For the design dry year used for irrigation planning, the weather generator replicated the observed conditions with reasonable accuracy. The weather generator was however less successful at replicating extreme dry years. These results are encouraging but also provide a note of caution for the use of these generated datasets for studying current irrigation demand and by implication for modelling future needs under climate change. The study also demonstrated a simple sub-sampling approach for reducing the processing demands if using the dataset in more complex models, though this would not remove any underlying error

The control of Corynebacterium pseudotuberculosis infection in sheep flocks : a mathematical model of the impact of vaccination, serological testing, clinical examination and lancing of abscesses

A mathematical model of Corynebacterium pseudotuberculosis infection in sheep flocks was used to evaluate strategies for control and elimination of caseous lymphadenitis (CIA). Control strategies tested were vaccination, serological testing and removal of seropositives, clinical examination and removal of sheep with abscesses, lancing abscesses, and appropriate combinations. Three different infection rates with and without replacement of culled ewes were used to evaluate the control options. Controls were either implemented immediately after infection was detected in a flock or once CIA was at endemic equilibrium, and with different frequencies of examination or testing. Elimination of infection was defined as 99% confidence that no sheep were infected with C. pseudo tuberculosis. The control strategies were evaluated by estimating the reduction in infection or probability of elimination and the number of ewes culled from the flock. Lancing abscesses reduced the prevalence of infection when the initial prevalence was 0.90, but vaccination combined with clinical examination reduced infection rapidly with little impact on lamb productivity. Further research is required to develop a diagnostic test with at least 0.90 specificity and sensitivity under field conditions before any methods of control can be recommended with confidence

Dispersion Relations in String Theory

We analyze the analytic continuation of the formally divergent one-loop amplitude for scattering of the graviton multiplet in the Type II Superstring. In particular we obtain explicit double and single dispersion relations, formulas for all the successive branch cuts extending out to plus infinity, as well as for the decay rate of a massive string state of arbitrary mass 2N into two string states of lower mass. We compare our results with the box diagram in a superposition of $\phi^3$-like field theories. The stringy effects are traced to a convergence problem in this superposition.Comment: 17 pages, COLUMBIA-YITP-UCLA/93/TEP/45 (figures fixed up

The Formation of Thin Continuous Films from Isolated Nuclei

Formation of thin continuous films from isolated nuclei and effect of electron beam, residual gases, and surface conditions on film growt

Continental-scale patterns of pathogen prevalence: a case study on the corncrake

Pathogen infections can represent a substantial threat to wild populations, especially those already limited in size. To determine how much variation in the pathogens observed among fragmented populations is caused by ecological factors, one needs to examine systems where host genetic diversity is consistent among the populations, thus controlling for any potentially confounding genetic effects. Here, we report geographic variation in haemosporidian infection among European populations of corncrake. This species now occurs in fragmented populations, but there is little genetic structure and equally high levels of genetic diversity among these populations. We observed a longitudinal gradient of prevalence from western to Eastern Europe negatively correlated with national agricultural yield, but positively correlated with corncrake census population sizes when only the most widespread lineage is considered. This likely reveals a possible impact of local agriculture intensity, which reduced host population densities in Western Europe and, potentially, insect vector abundance, thus reducing the transmission of pathogens. We conclude that in the corncrake system, where metapopulation dynamics resulted in variations in local census population sizes, but not in the genetic impoverishment of these populations, anthropogenic activity has led to a reduction in host populations and pathogen prevalence

Connection between the Loop Variable Formalism and the Old Covariant Formalsm for the Open Bosonic String

The gauge invariant loop variable formalism and old covariant formalism for bosonic open string theory are compared in this paper. It is expected that for the free theory, after gauge fixing, the loop variable fields can be mapped to those of the old covariant formalism in bosonic string theory, level by level. This is verified explicitly for the first two massive levels. It is shown that (in the critical dimension) the fields, constraints and gauge transformations can all be mapped from one to the other. Assuming this continues at all levels one can give general arguments that the tree S-matrix (integrated correlation functions for on-shell physical fields) is the same in both formalisms and therefore they describe the same physical theory (at tree level).Comment: Latex file, 24 page