Space-time variations of hydrological drought severities and trends in the semi-arid Euphrates Basin, Turkey

The main purpose of this study is to map the spatio-temporal variation of hydrological drought severities in the Euphrates Basin by using Kriging, Radial Based Function (RBF), Inverse Distance Weighting (IDW), Local Polynomial Interpolation (LPI), and Global Polynomial Interpolation (GPI) methods and to determine the distribution of hydrological drought trends. For this purpose, 18 streamflow observation stations and grid-based ERA5 reanalysis data were employed in and around the Euphrates Basin. The standardized runoff index (SRI) was calculated on monthly, 3-month, and 12-month time scales to determine hydrological droughts. Hydrological drought trends were determined by Mann Kendall (MK) and Modified Mann Kendall (MMK) tests. According to SRI, spatial-temporal distributions of droughts were mapped by Kriging, RBF, IDW, GPI, and LPI methods in the Geographical Information Systems environment. The LPI and Kriging method was selected as the most effective methods to predict hydrological droughts based on the cross-validation error. As a result of the trend analysis, the predominance of decreasing SRI trends in May (61.1%), June (72.2%), July (55.6%), August (61.1%) indicates that the basin is at risk of hydrological drought, especially in summer. According to the maps of spatial droughts, the widespread distribution of droughts in the basin indicated that the basin was greatly affected by hydrological droughts. For this reason, it has been emphasized that transboundary water effective management between riparian countries, planning of water structures, and effective implementation of the drought management plan is of great importance.