Mapping potential groundwater accumulation zones for Karachi city using GIS and AHP techniques.

Karachi is the largest industrial metropolitan of Pakistan facing an acute water shortage which is leading to an overdraft of groundwater resources in the city. Groundwater is an important freshwater resource for the city as millions of people depend for sustenance. However, over-exploitation of groundwater has led to decreased groundwater levels within the city leading to environmental issues of depleting aquifers, deteriorating groundwater quality, land subsidence, and harm to groundwater-dependent ecosystems. The objective of the study was to assess the potential groundwater accumulation zones by integrating hydrogeological aspects of the city through nine thematic layers using the Geographic Information System (GIS) based multi-criteria decision analysis (MCDA) technique. The potential groundwater accumulation map reveals that 20% of the area has a low potential, 70% has moderate potential, and around 10% of the area in the city is composed of a high potential accumulation zone. The upstream regions of the city have the highest recharge potential because of sandy soil and barren land use, which promote high infiltration rates. The urbanized downstream areas have the lowest recharge potential due to impervious fabric. The findings reveal that the MCDA technique can be used with confidence in data-scarce regions for groundwater resource assessment and management. The recharge potential map can help better manage groundwater resources in the city by helping explore groundwater extraction opportunities and could hint at areas suitable for artificial recharge wells/ponds.