Spatiotemporal variability and trends of droughts in the Mediterranean coastal region of Türkiye

Abstract

Drought, defined as the period when water availability considerably remains below normal levels for a certain time period, has devastating social, economic and environmental impacts. It is significant to closely monitor the temporal and spatial variability of drought in order to implement policies to mitigate the drought risk and ensure the sustainable management of water resources. In this study, three different drought indices, standard precipitation index (SPI), standardized precipitation-evapotranspiration index (SPEI) and reconnaissance drought index (RDI), are calculated for 3-, 6- and 12-month time scales from the precipitation and temperature data measured in 11 meteorological observation stations within the Mediterranean coastal region of Turkiye during 1972-2020. Initially, two absolute homogeneity tests were applied, namely the standard normal homogeneity test (SNHT) and the Pettitt test, to detect abrupt changes in drought index time series. Then, trend analysis was carried out with the innovative trend analysis (ITA) and improved visualization of ITA (IV-ITA) methods to determine the temporal variation of the drought in the region. A graphical representation is developed for the drought classifications based on IV-ITA. As a result of the SNHT and Pettitt test, significant change points were found at a 5% significance level in 91.92% and 85.86% of all indices, respectively. In both tests, breaks were detected at similar times (between 1972 and 1974) at Marmaris station, while at Alanya station, changes were found between 1972 and 1973 for the SNHT and in 2008 for the Pettitt test. The trend differences between extreme conditions (extremely dry and wet) decreased with an increase in time scale, distinctively. The ITA trends were almost identical for 3-month time scales, and they started to differ with time scale increases. Particularly, the presence of negative differences in data points contributes to the augmentation of drought periods, despite a few instances of extreme cases and minor fluctuations that can also be observed in IV-ITA. The findings obtained from the study are expected to provide valuable information about the recent shifts in drought in the Mediterranean basin. SPI, RDI and SPEI are applied monthly for 3-, 6- and 12-month time scales in 11 meteorological observation stations that are in the interior (IS) and coastal (CS) stations along the Mediterranean coastal region of Turkiye from 1972 to 2020. Change point detection and trend analysis are carried out with different methods to determine the spatiotemporal variation of the drought in the region.image