Investigation of Dry Spell Characteristics Over the Guinea Savanna Zone of Nigeria

Dry spells within the growing season represent a critical sub-seasonal meteorological stress that can cause crop failure even in years with adequate total seasonal rainfall. This study investigates the frequency, duration, and temporal distribution of dry spells over Nigeria's Guinea Savanna zone, covering states including Kwara, Kogi, Niger, and parts of Oyo and Osun, using daily rainfall records from nine NiMet stations for the period 2014 to 2023. A dry spell was operationally defined as a sequence of consecutive days with rainfall below 1 millimetre. Frequency distributions and trend analysis were conducted on dry spell length data stratified by the early, mid, and late growing season phases. Results reveal that dry spells of 7 to 14 days are the most common during the early growing season (April-May), while longer spells exceeding 21 days are most damaging when occurring in the critical grain-filling period of August to September. A statistically non-significant but consistent trend toward increased mean dry spell duration is observed at seven of the nine stations. Interviews with 160 farmers in Kwara and Niger states confirm that prolonged mid-season dry spells are perceived as the primary weather-related cause of sorghum and maize crop failure. Recommendations include operationalizing sub-seasonal dry spell forecast products within NiMet's advisory portfolio for the Guinea Savanna zone. Keywords: dry spell, Guinea Savanna, Nigeria, crop stress, sub-seasonal.