The tenth IMSC, Beijing, China, 2007 - International Meetings on ...

<strong>The</strong> prevailing climate on our country is due to its location in dry and semi-dry district,
as a result, drought is the commonest phenomenon in this country. One of the drought and
climatologic drought's definitions is as follow. If the precipitation is less than average during
long-term period, it is called drought. <strong>The</strong> drought of northwestern of Iran which is due to the
shortage of precipitation has caused starvation and poverty.First, the research framework,
theoretical principle, and study of precipitation fluctuations, trend, temperature, humidity, wind,
evapotranspiration of stations are under study. <strong>The</strong>n the precipitation correlation between
stations and precipitation and temperature correlation with respect to altitudes have been
studied. In order to determine the reasons of drought in the region which is under study,
primarily, the fluctuations of time, frequency and degree of drought as per Z score have been
examined which prove in statistical and synoptic network that due to simultaneous drought in
region in terms of severity, weakness frequency, time, location at different stations are different.
And later on study of reasons of drought with regard to the pattern movement of general
circulation of climate with Tel connection which results in changing in pattern pressure in
region and movement of circumpolar western line and blocking systems by benefiting from
normal distribution probability the return period 2,5,20,100,1000 were determined and the
occurrence of probability in distribution %20 & 80% was calculated and return period with
5-year drought range and 5-year humid period range.
Quantifying Uncertanties Associated With Climate Variaiblity and Climate Change Studies: the
Cox´S Semiparametric Approach
Aline de Holanda Nunes Maia
e-mail:ahmaia@cnpma.embrapa.br
Embrapa Meio Ambiente
Holger Meinke
e-mail:holger.meinke@wur.nl
Wageningen University, Department of Plant Sciences
A wide range of probabilistic approaches have been used for assessing climatic risks and
associated uncertainties: multiple linear regression (Martis et al, 2002), logistic regression
(Nichols, 1984; Lo et al, <strong>2007</strong>), nonparametric approaches based on empirical cumulative
distribution functions (Maia & Meinke, 1998; Maia et al, 2004), among others.
In this paper, we quantify risks by using probability of exeedance curves (PECs) and
propose the use of the proportional hazards model (also referred to as Cox model - Cox, 1972;
CPH model) to investigate the influence of continuous (e.g. oceanic/atmospheric indexes) or
categorical predictors (e.g. classes derived from El Niño/Southern Oscillation) on these risks.
CPH model is widely used in medical analyses of survival data that examine the effect of
explanatory variables on survival times. This allows the ranking of risk factors and quantitative
assessments of their impacts. <strong>The</strong>se methods are well established in medical research and
used routinely for risk assessment in medical studies (e.g. Finkelstein et al, 1993; De Lorgeril,
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