Frequency, Spatial Distribution, and Influence of Consecutive Dry Days on Rainfed Agriculture

Given the climate variability of semi-arid regions, this study analysed rainfall regimes and their influence on consecutive dry days (CDDs) and cowpea (Vigna unguiculata) productivity in Ceará, Brazil. Rainfall data from 184 municipalities (1990–2019) and productivity records were used across eight homogeneous rainfall regions. Water scenarios (very dry, dry, normal, rainy, and very rainy) were defined using quantiles, and three CDD classes were considered: CDD1 (5–10 days), CDD2 (11–15 days), and CDD3 (>15 days). Statistical analyses were performed with the Kruskal–Wallis test and Spearman’s correlation, and spatial patterns were mapped with ordinary kriging. Ceará’s climate normal was 837 mm, with the Central Sertão and Inhamuns and Jaguaribana showing the lowest rainfall. A total of 39,382 CDD events were identified, with 67% as CDD1, 16% as CDD2, and 17% as CDD3. Cariri had the highest CDD1 occurrences, while Central Sertão and Inhamuns recorded the highest CDD3. Cowpea yield averaged 286 ± 85 kg ha−1, with the lowest productivity in Central Sertão and Inhamuns due to reduced rainfall and frequent CDD3. Productivity correlated positively with CDD1 in one very dry scenario and negatively with CDD3 in very dry, dry, and normal conditions. The findings highlight regional vulnerabilities and the strong link between CDD and crop yield.