Drought characterisation across Agro-climatic zones in Ghana

The analysis uses the CHIRPS precipitation dataset at 5 km spatial resolution to compute the Standardized Precipitation Index (SPI) across agro-climatic zones in Ghana for the period 1981–2023. CHIRPS combines satellite-based rainfall estimates with in-situ station data, providing a long-term, high-resolution gridded precipitation product well suited for drought monitoring in data-sparse regions. SPI was derived by standardizing monthly accumulated precipitation against a long-term climatological baseline. SPI was computed at multiple time scales (SPI-1, SPI-3, SPI-6, and SPI-12) to capture short-, medium-, and long-term moisture conditions relevant to agricultural systems. SPI-1 reflects immediate meteorological conditions affecting crop emergence and early growth, SPI-3 captures seasonal rainfall anomalies influencing crop development and yield formation, SPI-6 represents medium-term moisture deficits relevant to soil water availability and cropping season performance, while SPI-12 characterizes long-term hydrological drought conditions affecting groundwater, reservoir storage, and overall agricultural water security. The resulting time series captures interannual to multi-decadal rainfall variability and supports the classification of hydroclimatic conditions into seven categories, ranging from extreme dryness to extreme wetness.