Integration of Three Standardized Drought Indices utilizing Modified Triple Collocation and Scaled Triple Collocation relative to Triple Collocation

Droughts have a detrimental effect on plenty of social and economic endeavors along with surface and groundwater resources. Therefore, drought must be adequately considered when planning and regulating the water supply. This study will look at the latest developments in merging techniques to lessen the inconsistent drought monitoring and characterization attributed to the global standard shortage. The current research considers the framework of three distinct standardized indicators, SPI, SPTI, and SPEI, of six metrological stations in Pakistan from 1971 to 2017, intending to analyze drought using integrating techniques. Two merging techniques, Modified Triple Collocation (MTC) and proposed Scaled Triple Collocation (STC), are examined relative to Triple Collocation (TC). Correlation, Sen’s Slope, Taylor diagram, Kling Gupta Efficiency (KGE), and error variance analyses were used to evaluate their performance. The correlation study reveals that individual series have a comparable relationship with Merged Drought Index (MDI) model from MTC, STC, and TC. However, individual indices SPI and SPTI are strongly associated with MTC and STC-based MDI compared to SPEI. Sen's slope shows the same trend across all approaches with minimal amplitude divergence. KGE was assessed using an average of one hundred thousand simulated values, and STC and TC demonstrated higher efficiency than MTC. But MTC has a lower error variance in contrast to STC and TC. Overall, the current study's findings validate that Merged Drought Index (MDI) based on MTC and proposed STC provides a better quantitative way to merge three separate drought indices into a single index. So, MDI successfully captured recorded drought episodes throughout the research locations, indicating that the merging method can be a workable option to identify drought accurately.