Accomplishment and subjectivity of GIS-based DRASTIC groundwater vulnerability assessment method: a review.

Groundwater vulnerability assessment is an important task in water resources and land management. The most sophisticated among the vulnerability assessment techniques is the GIS-based DRASTIC model. However, despite its popularity, it is marred with excessive subjectivity glitches; little research has been conducted to address the shortcomings associated with this method. This study investigates various issues regarding the application of the GIS-based DRASTIC model through a critical review of relevant literatures. It is revealed that all the DRASTIC parameters are equally significant irrespective of their assigned weights. On the contentious quantile classifications, however, a categorical classification defined by 'very low', 'low', 'medium', 'high', and 'very high' was suggested for standardization. Based on the studied literatures, it was established that 46 % of 977 million km of land assessed globally fell within moderate to high vulnerability category-a land cover bigger than the cultivated lands obtainable in all the countries around the world except the United States, India, China, Russia, Brazil, Canada and Australia. [ABSTRACT FROM AUTHOR]