Meteorological flash droughts (MFDs) are sub-seasonal-to-seasonal drought phenomena characterized by rapid onset/intensification. This study assesses the changes in trends and hotspot regions of MFDs for the present and five future CMIP6 SSP forcing scenarios (SSP-FS) at global-, continental- and regional-scales. Analysis with 12 GCMs indicates that globally, frequency, duration and severity of MFDs are projected to increase ~20–50%, 20–58%, and 26–62%, respectively, with the highest occurrence probability during the summer season. The MFD hotspot regions appeared prominent in arid and semi-arid zones. MFD exposure risk is projected to exceed ~1.5 folds in most continents, with the highest risk in the Indian sub-continent. Furthermore, in Europe and South America, which are currently less impacted by MFDs, a considerable increase in hotspot regions (~122–127%) is projected under the warmest SSP-FS. The LULC-classes and elevation range most vulnerable to MFDs, and regional potential hydrometeorological drivers that trigger the development of MFDs are identified.

Accurate quantification of in situ heterogeneity and flow processes through fractured geologic media remains elusive for hydrogeologists due to the complexity in fracture characterization and its multiscale behavior. In this research, we demonstrated the efficacy of tracer-electrical resistivity tomography (ERT) experiments combined with numerical simulations to characterize heterogeneity and delineate preferential flow paths in a fractured granite aquifer. A series of natural gradient saline tracer experiments were conducted from a depth window of 18 to 22 m in an injection well (IW) located inside the Indian Institute of Technology Hyderabad campus. Tracer migration was monitored in a time-lapse mode using two cross-sectional surface ERT profiles placed in the direction of flow gradient. ERT data quality was improved by considering stacking, reciprocal measurements, resolution indicators, and geophysical logs. Dynamic changes in subsurface electrical properties inferred via resistivity anomalies were used to highlight preferential flow paths of the study area. Temporal changes in electrical resistivity and tracer concentration were monitored along the vertical in an observation well located at 48 m to the east of the IW. ERT-derived tracer breakthrough curves were in agreement with geochemical sample measurements. Fracture geometry and hydraulic properties derived from ERT and pumping tests were further used to evaluate two mathematical conceptualizations that are relevant to fractured aquifers. Results of numerical analysis conclude that dual continuum model that combines matrix and fracture systems through a flow exchange term has outperformed equivalent continuum model in reproducing tracer concentrations at the monitoring wells (evident by a decrease in RMSE from 199 to 65 mg/L). A sensitivity analysis on model simulations conclude that spatial variability in hydraulic conductivity, local-scale dispersion, and flow exchange at fracture-matrix interface have a profound effect on model simulations.

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