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Abstract As a natural disaster, drought has inverse effects on the agricultural and environmental sectors. Comprehensive drought evaluation is critical for integrated water resources management and drought monitoring. Drought is generally evaluated temporally and spatially without considering its trend, but in recent years, the study of drought trends has become common. However, in drought trend analyses, it is necessary to identify the frequency change of drought classification, along with the sub-trends and their magnitudes, which have been identified in this research with the combined frequency analysis and innovative trend analysis methodologies (F-ITA). Three different drought indices, the standardized precipitation index (SPI), Standardized precipitation evapotranspiration index (SPEI), and streamflow drought index (SDI), were calculated at different time scales at Florya Station, Istanbul, Türkiye, Durham Station in the United Kingdom, and Vargonas (Vargönäs) KRV Station in Sweden. The results showed that F-ITA improved the drought evaluation with a more detailed investigation of meteorological and hydrological drought trends on a microscale rather than stating a decrease or increase trend. There was no trend for SPI-3 and -6 F-ITA; for SPI-12 F-ITA, all drought classifications showed a monotonic increase trend. For example, for SPI-1 and SPEI-1 F-ITA, the abnormally dry classification showed minimal change with frequencies of 35%. The SPEI-12 F-ITA graph showed an increasing trend in all drought classifications. For SPEI-12, the frequency of exceptional drought (extremely dry) events increased from 0.11% (0.66%) to 1.21% (2.3%), while severe and moderate drought frequencies rose significantly from 3.73% to 4.61% and 7.46% to 11.4%, respectively. Finally, monotonic trend increases were noticed in the SDI at all time scales for all classifications. Graphical abstract
Arra et al. (Mon,) studied this question.