Establishment of Appropriate Time Scale Resolution for Regional Drought Characterisation in Northern Nigeria

The increasing recurrence of extreme hydrological events, such as floods and droughts, has raised serious concerns among hydrologists. A major challenge in drought analysis is the lack of precise temporal resolution, which complicates its quantification. The subjectivity in selecting appropriate indicators and timescales has led to ongoing debates in drought assessment and management. This study employed a systematic approach involving (1) the computation and evaluation of drought patterns using the Standardised Precipitation Index (SPI) across multiple timescales and thresholds, and (2) the characterisation of drought properties through temporal accumulation (TA). Findings revealed that SPI-6 and SPI-9 are the most suitable timescales for drought characterization across northern Nigeria. Additionally, the optimal timescales for specific hydrological areas (HAs) were identified: HA 1 (SPI-6), HA 2 (SPI-6), HA 3 (SPI-3), HA 4 (SPI-6), and HA 8 (SPI-1). Threshold analysis indicated that a -1.0 SPI threshold consistently recorded the highest drought frequency (61 occurrences) across all TA considerations, making it the most effective for detecting minor drought events in the study region. Consequently, this threshold is recommended for comprehensive drought assessment in northern Nigeria. To enhance future drought analysis, it is suggested that persistence studies incorporate a renewal forgetting factor. Additionally, further research should explore the relationship between meteorological droughts and external climatic drivers, such as sea surface temperature (SST). The integration of machine learning techniques is also recommended to improve temporal accumulation assessments and overall drought modelling.