Assessment of Water Quality Indices in the Iraqi Tigris River Using Remote Sensing Technique: A Comprehensive Study

Abstract This study objects to evaluate the Water Quality Indices (WQIs) of the Tigris River in Wasit, Iraq, using the Arithmetic Weighted Water Quality Index (AW-WQI), Canadian Water Quality Index (CCME-WQI), Heavy Metal Pollution Index (HPI-WQI), National Sanitation Foundation Index (NSF-WQI), and Overall Index of Pollution (OIP-WQI). Twelve water samples were collected at different locations in the study area during the winter and spring of 2024. Each index evaluates the water quality in the study area based on specific criteria. In separate periods (winter and spring seasons of 2024), we categorized the water quality in the research region according to each indication: AW-WQI (70.517-102.611), CCME-WQI (39.763-47.1404), HPI-WQI (82.526-118.846), NSF-WQI (54.66-60.12), and OIP-WQI (1.9769-2.4686). We have created twenty-six combinations of spectral reflectance bands, reflectance values of seven bands, band ratios for the first five bands, and nine spectral indices. This study showed a significant correlation between the spectral reflectance data of Landsat-9 OLI-2 bands and the WQIs using Pearson correlation and multiple linear regression (MLR) model equations. We evaluated the performance of the MLR model for the WQIs across different seasons. The AW-WQI model showed a coefficient of determination R 2 of 84% in winter and 98% in spring. At the same time, the CCME-WQI recorded R 2 of 97% in winter and 75% in spring. The HPI-WQI received R 2 of 93% and 98% in spring. The NSF-WQIs received R 2 of 62% and 98% in spring. Finally, the OIP-WQI received R 2 of 92% and 99% in spring. These results highlight the seasonal variation in the predictive accuracy of the WQI models, with some minor differences between the experimental results and those obtained through remote sensing techniques. The WQIs showed that the water needed to be more suitable for consumption due to elevated levels beyond the permissible limit in most study area locations. Multiple sources of pollution in the region discharge hazardous waste into the river, causing WQIs to exceed permissible limits in most study areas.