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Öğe The Challenge of Unprecedented Floods and Droughts in Risk Management(NATURE PORTFOLIO, 2022) Çavuş, Yonca; vd.Risk management has reduced vulnerability to foods and droughts globally1,2, yet their impacts are still increasing3. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data4,5. On the basis of a global dataset of 45?pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of foods and droughts but faces difculties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the frst, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difculty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change3. .Öğe Critical Drought Intensity-Duration-Frequency Curves Based On Total Probability Theorem-Coupled Frequency Analysis(International Association of Hydrological Sciences [Associate Organisation], 2021) Çavuş, Yonca; Aksoy, Hafzullah; Çetin, Mahmut; Eriş, Ebru; Burgan, Halil İbrahim; Yıldırım, Işılsu; Sivapalan, MurugesuA methodology using the standardised precipitation index is proposed to develop critical drought intensity-duration-frequency (IDF) curves. We define dry periods within which we recognise droughts of different durations. The most severe drought for each drought duration in each year is called the critical drought. The total probability theorem-coupled frequency analysis is used to determine the bestfit probability distribution function of drought severity, which is then converted to intensity. The generalised extreme value probability distribution function is found to best fit the critical drought severity. The methodology is implemented using monthly precipitation data for a meteorological station in Turkey. The critical drought intensity decreases linearly with increasing drought duration, whereas the return period increases exponentially when the drought becomes more severe. The site-specific IDF curves furnished with an empirical relationship between the intensity and return period allow one to characterise the drought not by an index-based intensity but by its return period. This kind of presentation is physically easier to nderstand, in particular for stakeholders and decision makers in practice.Öğe Revisiting Major Dry Periods by Rolling Time Series Analysis for Human-Water Relevance in Drought(SPRINGER, 2022) Çavuş, Yonca; Stahl, Kerstin; Aksoy, HafzullahDrought is increasingly gaining importance for society, humans, and the environment. It is analyzed commonly by the use of available hydroclimatic or hydrologic data with little in depth consideration of specifc major dry periods experienced over a region. Also, it is not a common practice to assess the probability of drought categories with a rolling time series and hence the changing knowledge for operational drought monitoring. A combination of such quantitative analysis with a comprehensive qualitative assessment of drought as a human-water relation aimed to fll this gap performing a case study in the Seyhan River Basin, Turkey. Six major dry periods were identifed from the precipitation time series of 19 meteorological stations. Major dry periods were analyzed by rolling time series and full time series, and they were also analyzed individually. A major dry period could be impor tant in terms of its duration while another in terms of its severity or intensity, and each with its own impact on the human-water relations that can be infuential on the drought mitigation, management and governance. Signifcantly higher probabilities were calculated for extreme droughts with the use of individual major dry periods. An important outcome from the study is that drought is underestimated in practice with the sole use of the whole data record.Öğe Spatiotemporal Analysis of Drought by CHIRPS Precipitation Estimates(SPRINGER WIEN, 2022) Çavuş, Yonca; vd.Drought is one of the most devastating natural hazards causing considerable losses in all climatic zones of the world. It is one of the most complex and the least understood hazards at the same time because of its spatially heterogeneous and temporally variable character. Spatially dense and uniformly distributed ground-based meteorological data are needed for proper spatial and temporal drought analysis. In practice, such data are lacking in general due either to the nonexistence of ground stations or their uneven and scarce distribution over a region. This creates a great potential in the use of satellite precipitation estimates (SPEs) such as the long-period high-resolution Climate Hazards Group Infrared Precipitation with Station (CHIRPS) data in drought analysis. In this study, we aim to analyze drought over the Kucuk Menderes River Basin in the western part of Turkey by using the CHIRPS data, which were found highly correlated with precipitation in the local ground stations. The analysis was performed by considering the spatial variability and temporal change in the drought characterization based on the Standardized Precipitation Index (SPI) calculated at the 3-month (seasonal) timescale. Drought in the river basin was found to have a within-year variability from month to month, and a spatial variability over the basin in any given month. Also, an over-year variability with a decreasing trend exists, which could be considered a signal for more strengthened droughts in the future. The study eventually demonstrates how the CHIRPS SPEs could be useful in the spatial and temporal drought analysis for regions with limited ground-based meteorological data.
