Seasonal (March–May) Drought Analysis of Kitui County, Kenya, Using the Standardised Precipitation Index and the Vegetation Health Index, 2011–2026

Romana Jacky, Rashid Ongoma or Romana zion

Kitui County, Kenya, was assessed for drought conditions during the March–April–May (MAM) long rains season from 2011 to 2026 using the Standardised Precipitation Index (SPI) and the Vegetation Health Index (VHI). SPI was computed in Google Earth Engine using daily precipitation data from CHIRPS, as the standardised anomaly of MAM precipitation relative to a 1981–2010 baseline on a 0.05° grid, averaged across the county. VHI was taken from the FAO MAM seasonal VHI product, clipped to the county, rescaled to 0–100 and summarised by zonal statistics. The seasons were classified using the McKee SPI scale and an FAO-based VHI scale. Mean SPI ranged from −1.06 (2019) to 3.67 (2018), and mean VHI from 24.0 (2017) to 68.5 (2018). SPI was near normal in nine seasons and indicated dry conditions only in 2019 (moderately dry). VHI indicated drought in seven seasons (two extreme, four severe and one moderate: 2011, 2012, 2015, 2016, 2017, 2019 and 2022) and mild drought in two more. The two indices were significantly and strongly correlated (Pearson r = 0.91, 95% CI 0.76–0.97, p < 0.001), and the result held under Spearman’s rank test (ρ = 0.89) and when the extreme 2018 season was excluded (r = 0.89). Vegetation stress was therefore experienced in several seasons, including two extreme ones, in which rainfall anomalies did not indicate drought. This supports using the two approaches together in seasonal monitoring. The findings are for the MAM season only and are not an annual drought assessment.