Drought has become a recurrent phenomenon in Turkey in the last few decades. Significant drought conditions were observed during years of late 1980s and the trend continued in the late 1990s. The country's agricultural sector and water resources have been under severe constraints from the recurrent droughts. In this study, spatial and temporal dimensions of meteorological droughts in Turkey have been investigated from vulnerability concept. The Standardized Precipitation Index (SPI) method was used to detail geographical variations in the drought vulnerability based on frequency and severity of drought events at multiple time steps. Critical (threshold) rainfall values were derived for each station at multiple-time steps in varying drought categories to determine least amount of rainfall required to avoid from drought initiation. The study found that drought vulnerability portrays a very diverse but consistent picture with varying time steps. At regional scale, south-eastern and eastern Anatolia are characterized with moderate droughts at shorter time steps, while the occurrence of severe droughts at shorter time steps is observed at non-coastal parts of the country. A similar picture was observed with very severe droughts. The critical (threshold) values exhibited rising numbers during the growing season at 3-month step in the South-eastern Anatolia, which might have significant consequences considering presence of large irrigation projects underdevelopment in the region. In general, rainfall amounts required for non-drought conditions decrease from the coastal parts toward the interiors with increasing time steps.
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.
Abstract:The Gulf region, including the United Arab Emirates (UAE), has been experiencing warming trends since late 1980s. This study investigates non-stationary behaviour of the long-term mean monthly temperature series of the UAE by time series analysis. The last three decades are distinctly characterised with definite rising trends in the temperatures in majority of the stations, with exception of the Al Ain station which indicated cooling temperature trends. Cumulative warming varied between 0.3 and 2.8°C, with more warming observed in the coastal stations. Marked shifts in the mean temperatures were observed especially in the Abu Dhabi, Al Ain, Sharjah, Dubai, and Ras'al Khaima stations at 6-10 year time periods. The time series analysis of the temperature series, in general, indicated non-randomness, implying periodicity with sinusoidal component. The periodograms were characterised 12-month periodicity (varying seasonally) with the monthly series and 4-16 years of periodicity with the annual series. The peak frequencies of the monthly series corresponded to a seasonal periodical component. The 16-year cycles are more pronounced in the stations with short duration data while the smaller cycles are peculiar to the longer durations.
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