A group of earlier investigations has identified some specific regions over the world in which hydrometeorological surface parameters (i.e. precipitation and streamflow) appear to have consistent relationships with the extreme phases of the Southern Oscillation (SO). This paper examines a climatic link between the monthly streamflows in Turkey and the tropical El Niñ o and La Niñ a events using a large data set and comprehensive empirical methodology. Coherent and significant streamflow responses were detected in two core regions, namely the northwestern Anatolia (NWA) and the eastern Anatolia (EA). The areal extent of both regions with a defined seasonal signal for the case of each tropical event was determined. Some subregions whose indications are considered to be better than those for the whole core region were also isolated within the core region. In the Susurluk subregion identified in the NWA, the April-October seasonal positive streamflow anomalies were found to have a highly significant relation with the El Niñ o events. Although there is a possibility that the NWA region is influenced by the El Niñ o events, this was not confirmed by the hypergeometric test used to assign a significance level for the relationship. A similar analysis has shown that the La Niñ a events have no noticeable influences on streamflows in the NWA. For the EA region, above normal conditions have been observed during the April(0) -November(0) period and the May(0) -February(+ ) period for the El Niñ o and La Niñ a events, respectively. Moreover, the annual cycle analysis somewhat implies a modulation of regional streamflow in the core regions during the signal period. In some parts of the core regions, correlation results confirm these signals. The results of this study are discussed and are said to be in agreement with the most relevant previous studies concerning precipitation to understand complex global circulation dynamics. In conclusion, mid-latitude streamflow responses to the extreme phases of SO are detectable over Turkey. Copyright

Abstract:In this study, Turkish climatic variables (precipitation, stream flow and maximum and minimum temperatures) were first analysed in association with both the Southern Oscillation (SO) and the North Atlantic Oscillation (NAO). The relationships between Turkish maximum and minimum monthly temperatures and the extreme phases of the SO (El Niño and La Niña events) were examined. The results of this analysis showed that relationships between Turkish monthly maximum temperatures and El Niño and La Niña contain some complexity still to be identified, because both events produce a signal indicating a correspondence with cold anomalies in the aggregate composites. A relationship between turkish minimum temperatures and El Niño was detected in western Anatolia, whereas there was no significant and consistent signal associated with La Niña. Moreover a series of cross-correlation analyses was carried out to demonstrate the teleconnections between the climatic variables and both the NAO and SO. The NAO during winter was found to influence precipitation and stream-flow patterns. In contrast temperature patterns appeared to be less sensitive to the NAO. Furthermore, lag-correlation results indicated a prediction potential for both precipitation and stream-flow variables in connection with the NAO. Simultaneous and time-lag correlations between the climatic variables and the SO index, in general, indicated weaker relationships in comparison with those for the NAO. These analyses also showed that the influences of the SO on Turkish temperature data are negligible. The outcomes were presented in conjunction with an explanation regarding physical mechanisms behind the implied teleconnections.

Abstract:The homogeneity of newly compiled 212 precipitation records in Turkey for the period 1973-2002 was checked by the Standard Normal Homogeneity Test (SNHT) and Pettitt Test. Stations were considered inhomogeneous if at least one of the tests rejects the homogeneity. As a result, 43 out of 212 stations were found to be inhomogeneous. In addition, the previously detected Southern Oscillation (SO)-related precipitation anomalies by the authors were quantified at each station using the gamma distribution. The observed SO-related shifts in the median precipitation amounts expressed as gamma percentiles may be considered as a typical SO response of that station. The results of this study confirm the wet responses of Turkish precipitations to El Nino events, whereas those for La Nina events seem to be masked by sampling variations within the study period.

Some previous global and regional studies have indicated teleconnection between the extreme phases of the Southern Oscillation (SO) and Turkish climate and hydrologic variables; however, they failed to suggest a strong correlation structure. In this study, categorised Southern Oscillation index (SOI) and Multivariate ENSO (El Nino Southern Oscillation) index (MEI) series were used to examine the far-reaching effects of the SO on temperature, precipitation and streamflow patterns in Turkey. These SO indicators were categorised into five subgroups according to their empirical distributions. Correlations between the categorised SO indicators and three analysis variables were computed using the Spearman's rho from lag-0 to lag-4. Significance of calculated correlations was tested at the 0Ð01 level for station-based analysis and at the 0Ð05 level for regional analysis. Temperature records demonstrated significant correlations with the categorised SOI and MEI in nearly half of the entire stations. For some categories, precipitation and streamflow were found to be correlated with the SO indicators in some stations mainly in western Turkey. Regional analyses of temperature and precipitation revealed a clear and strong correlation structure with the categorised SO indicators on a large portion of Turkey. This was not concluded by the earlier pertinent studies. Besides, this study showed that significant correlations were obtained not only for the SO extreme phases (namely, El Nino and La Nina) but also for neutral and moderate phases of the SO. Plausible explanations for the observed teleconnection are presented.

Trends in annual and seasonal drought patterns in Turkey were investigated on the basis of regionally averaged surface humidity index (SHI) series. For this purpose, two nonparametric approaches, Mann-Kendall test and Sen's T test, were used. For some regions, significant upward trends in fall SHI series were detected due to the increasing precipitation for the period 1951-1998. The North Atlantic Oscillation influences on the SHI series were also investigated and significant negative correlations were found for some regions. Résumé :Les tendances dans les sécheresses annuelles et saisonnières en Turquie ont été étudiées en se basant sur l'indice d'humidité de surface (SHI) moyen dans la région. À cette fin, deux approches non paramétriques, le test de Mann-Kendall et le test de Sens, ont été utilisées. Dans certaines régions, des tendances importantes à la hausse dans le SHI d'automne ont été détectées en raison d'une augmentation des précipitations pour la période entre 1951 et 1998. Les influences des oscillations de l'Atlantique Nord sur le SHI ont également été examinées; des corrélations négatives importantes ont été trouvées pour certaines régions.