Estimation of the domestic water demand‒supply scenario and its key driving factors in the Islamabad-Rawalpindi Metropolitan Area, Pakistan.

Domestic water availability is intricately linked with a growing population, urbanization, and associated land use/land cover change (LULCC). Precise and periodic assessments of water supply and demand are imperative for the sustainability of urban ecosystems. The present study provides a situational analysis of the domestic water supply and demand and LULC to quantify their impacts on water resources in the rapidly growing water scarce metropolitan area of Islamabad-Rawalpindi. Data regarding demography, water demand and supply were collected from concerned government departments, and the water demand-supply balance was projected for the years 2021-2050 through simple equations. Two remotely sensed satellite imageries (Landsat 8 OLI and Landsat 5 TM) were retrieved and supervised classification was performed for land use land cover (LULC) analysis during last two decades 1999 and 2019.The results revealed that the current domestic water supply is 65 million gallons per day (MGD) and 54.074 MGD in Islamabad and Rawalpindi, respectively. The per capita water availability is estimated as 60 GPCD (gallons per capita per day) in Islamabad, whereas it is 76.40 GPCD in Rawalpindi. Water demand has outstripped conventional supplies, leading to deficits of 52 MGD and 18.50 MGD in Islamabad and Rawalpindi, respectively. The groundwater depth has decreased from 22.8 m to 56 m in Islamabad and from 37.8 m to 59 m in Rawalpindi. This decline is positively correlated with the density of installed tube wells, borehole wells, demographic factors and LULCC. LULC analysis depicts rapid decline in open land which has been replaced by settlements. Moreover, the area of open land decreased significantly from 68.46% to 18.92%whereas the area under the built environment increased significantly from 7.77% to 36.51% from 1999-2019. However, increase in the forest cover and water was insignificant. This land transformation contributed to a reduction in the water table depth and recharge to aquifers and escalating water demand. The study concluded that the groundwater resources of twin cities are under stress. In addition, forecasted water demand will also increase in the future with increasing population, economic growth and lifestyle changes while increasing groundwater abstraction, and diminished water infiltration rates due to urban expansion will compromise water availability for future generations. The findings provide valuable information to concerned agencies, policy makers and stakeholders to take appropriate long-term measures to address repercussions of unplanned urbanization and LULC to ensure a sustainable water supply to the urban populace.