Multiscale Meteorological Drought Dynamics Using Penman-Monteith SPEI in a Humid Tropical Environment, Owerri, Nigeria
Iheukwumere P. Onyemachi *
Department of Civil Engineering, School of Engineering and Engineering Technology, Federal University of Technology, Owerri, Imo State-460114, Nigeria.
Benedicta U. Dike
Department of Civil Engineering, School of Engineering and Engineering Technology, Federal University of Technology, Owerri, Imo State-460114, Nigeria.
Herbert U. Nwoke
Department of Civil Engineering, School of Engineering and Engineering Technology, Federal University of Technology, Owerri, Imo State-460114, Nigeria.
Ify L. Nwaogazie
Department of Civil and Environmental Engineering, University of Port Harcourt, Choba, Port Harcourt, 500004, Nigeria.
Chiedozie F. Ikebude
Department of Civil and Environmental Engineering, University of Port Harcourt, Choba, Port Harcourt, 500004, Nigeria.
*Author to whom correspondence should be addressed.
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.
Keywords: Meteorological drought, standardized precipitation evapotranspiration index (SPEI), penman-monteith evapotranspiration, atmospheric evaporative demand, multiscale drought, humid tropical climate, climatic water balance, drought monitoring