Exploring the Effectiveness of Modified Z Score for Drought Monitoring: A Comparative Study using Innovative Comparison Analysis

Abstract

Monitoring meteorological drought requires reliable methods to determine when, how long, and how severe drought events are. Although several drought indices exist, questions persist regarding their suitability, comparability, and effectiveness across different climatic contexts. This study aimed to evaluate the effectiveness of modified Z-Score (mZS) with respect to Rainfall Anomaly Index (RAI), and Z-Score Index (ZSI) using rainfall data (1977 – 2020) of Dadin-Kowa Town in Gombe State Nigeria. This study suggested Innovative Comparison Analysis (ICA), to evaluate the performance of mZS with the other indices under review. Sen’s Slope of Innovative Trend (Slope of IT), Mann–Kendall Test, and Sen’s Slope were used for further evaluation of the trend reported by the indices under review. The result revealed that mZS, RAI, and ZSI consistently identified an increasing trend in rainfall across annual, growing seasonal, and monthly scales except for May, which showed a decreasing trend in Dadin-Kowa from 1977 to 2020. The ICA demonstrated a strong agreement between mZS and ZSI, and a relatively moderate agreement between mZS and RAI. The study concludes that mZS proved effective and statistically comparable to the established indices. Its consistent alignment with other indices highlights its potential for broader application in localized drought monitoring. It is recommended that Future drought monitoring frameworks in any given ecological setting should consider integrating mZS.