Multiscale Meteorological Drought Dynamics Using Penman-Monteith SPEI in a Humid Tropical Environment, Owerri, Nigeria

Abstract

This study investigated multiscale (1-, 3-, 6-, and 12-month) meteorological drought dynamics in Owerri, southeastern Nigeria, using the Standardized Precipitation Evapotranspiration Index (SPEI) derived from FAO-56 Penman-Monteith reference evapotranspiration (PET). Monthly hydroclimatic records (1992-2022) retrieved from the Nigerian Meteorological Agency (NiMet) were analysed to evaluate climatic water balance, drought variability, temporal trends, and the influence of evapotranspiration using non-parametric and comparative statistical techniques. The three-parameter log-logistic distribution did not provide an adequate representation of the climatic water balance series for Owerri; therefore, alternative probability models were evaluated to identify the most appropriate distribution for each accumulation scale. Mean PET and climatic water balance were 109.38 mm and 85.34 mm, respectively. PET exhibited a significant decreasing trend (MK-Z = −2.525, p = 0.0116) with a change point in March 2007; climatic water balance showed no significant long-term trend. Agreement between SPEI and SPI increased with accumulation timescale, while significant differences were confined to the 1- and 3-month timescales. These findings demonstrate that atmospheric evaporative demand primarily influences short-term drought characterisation, whereas precipitation dominates longer-term drought variability. One significance of the study was to provide a station-based multiscale drought assessment for Owerri, Nigeria, in the literature. However, the major constraint of this study is its reliance on data from a single NiMet station to represent the entire Imo State.