Spatial and temporal characteristics of meteorological drought and wetness incidences: a comparative analysis in Ghana, West Africa, and mainland Portugal, Southwestern Europe

The frequency and duration of drought and wetness incidences have increased in various land regions as the global climate warms. These incidences threaten various sectors, including agriculture and food security, water resources, and people’s health and livelihoods, needing regular monitoring for improved adaptation. This study analysed the spatial and temporal characteristics of meteorological drought and wetness incidences in Ghana and mainland Portugal between 1981 and 2019. The Standardised Precipitation Evapotranspiration Index (SPEI) and Standardised Precipitation Index (SPI) were utilised to assess drought and wetness event characteristics parameters based on frequency and duration over 3- and 12-month time scales. The results revealed increased drought events in the northern parts of Ghana compared to the southern parts, while in Portugal, the southern areas exhibited greater drought events than the northern regions based on the SPEI and SPI. Between 1981 and 2019, Ghana experienced more extreme drought events than Portugal, which experienced moderate drought events. In Ghana, severe drought events occurred in 1983, followed by moderate wetness in 2008 and 2019, while in Portugal, severe drought events ensued in 2005 and severe wetness events in 2010. Both countries have experienced increased frequencies and durations of drought and wetness events, coupled with increased spatial variability. Most parts of Ghana, except for the southwestern areas, experienced more frequent and longer durations of drought events. The southern parts of Portugal had more frequent and longer durations of drought events than the northern parts on both the SPEI and SPI, while the wetness events showed the reverse. The drought and wetness event incidences revealed increasing and decreasing spatial trends in both countries. Regular monitoring of drought and wetness events, especially those of a meteorological nature, is important in both countries as their occurrence can lead to other types of drought.