Groundwater modelling: A tool for sustainable aquifer management under changing climate

Groundwater is generally considered as an invisible and silent component of hydrological cycle which is being pumped globally at an estimated rate of 750-800 billion M3/year and has become the mainstay of irrigated agriculture which underpins the food security.. The aquifer in Pakistan is a part of transboundary Indo-Gangetic aquifer which comprises almost 25% of global groundwater withdrawals and sustains agricultural productivity in Pakistan, India, Nepal and Bangladesh. Pakistan has become one of the largest groundwater-user countries - 4th largest after India, China and USA - where groundwater caters for 50% irrigation water, more than 90% drinking water and almost 100% industrial water requirements. The lack of holistic regulatory/policy framework, rapidly increasing population, industrialization, poor water productivity, week institutional framework are the major drivers for over-depletion of groundwater in the Pakistan. Management of groundwater has not been paid the appropriate attention resulting in over-exploitation of aquifer in freshwater areas, degradation of quality and increase in the cost of pumping. Pakistan is an agricultural country having an irrigation-based economy which puts it as the 8th largest food producing country where irrigated agriculture contributes more than 90% of food production. Water resources of Pakistan are under serious threats of global climatic changes. Changing patterns of rainfall, floods and droughts have led to uncertainties and deficiency in surface water flow putting tremendous pressure of groundwater reserves. Pakistan lies in the heat surplus zone on the globe and is suffering adversely from the impacts of global warming. Unprecedented floods and droughts have put the water resources of the country under stress and Pakistan has become 10th most climate-vulnerable country although it is 135th in GHG emissions.
The present paper encapsulates the findings of a project funded by the Asian Development Bank for groundwater monitoring, modelling and management in an irrigated canal commanded area of Punjab province of Pakistan where groundwater is contributing about more than 50% for crop water requirements. Groundwater system in the study area has become complex due to multiple users, undefined hydrogeology boundaries, alluvial nature of aquifer, spatial and temporal variability of surface water (river flow and rainfall). Punjab Irrigation Department (PID) has installed a network of about 800 piezometers to monitor the groundwater levels in the study area. A three-dimensional transient numerical groundwater model- MODFLOW- for Lower Bari Doab Canal (LBDC) command area has been developed and calibrated to help understand the overall groundwater potential and conditions for different hydrological and water management specific scenarios to cater for the increasing and varying water demands in future. The calibrated groundwater model was used to perform long-term simulations for predicting future groundwater conditions in the study area to determine spatial and temporal changes in groundwater levels caused by the implementation of different water resources management strategies under changing climatic conditions. Model results indicated that for next 18 years, we need to reduce the groundwater pumpage rate as well to enhance the surface water supply for aquifer sustainability. This was a unique study in Pakistan’s context where groundwater models has helped in decision making.
Key Words: Groundwater, climatic changes, livelihood, Punjab, Pakistan