**1. Introduction**

The growing trend in global warming has resulted in the occurrence of extreme climate events (drought/floods) that impact the hydrological system of the Himalayan region in South Asia. The response of groundwater behavior to environmental changes has been studied world‐ wide by numerous researchers, for example, see references [1–4]. The changing pattern of precipitation affects the recharge of the groundwater, which controls the behavior of water table

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in the system [5,6]. The Indus groundwater system is also facing the temporal as well as spatial impacts of changing environment. A detailed appraisal of the subsurface aquifer system is thus vital in the context of prevailing conditions of drought/flood and the growing demand of water for sustainable development in the region. In recent years, groundwater numerical simula‐ tion models have been widely applied to groundwater dynamic simulation and as a manage‐ ment tool. The development and application of a groundwater model is a common practice for themanagementofgroundwaterresources[7].Manyscientificeffortshavebeenmadetodevelop more comprehensive and computationally efficient models involving complex hydrogeologic processes [8,9]. In many numerical models of a groundwater aquifer, for example, Feflow and MODFLOW, the continuous domain of groundwater system is replaced by a discretized grid network and the governing groundwater flow equation is solved at the network nodes. The inverse modeling (also called parameter optimization) is capable of assigning approximate values to the hydrological parameters by employing approximate methods to solve the partial differential equation (PDE), which describes the flow in a porous medium.

Pakistan is in the grip of a water crisis. This involves a hydroelectric power shortfall, per capita water availability less than 1100 m3 , falling levels of groundwater, and limited water supplies in metropolitan areas, including the twin cities of Rawalpindi and Islamabad. Because pumping exceeds recharge, groundwater reserves are becoming significantly depleted. Groundwater overdraft has caused the groundwater table to decline remarkably and resulted in a series of ecological issues such as deterioration of water quality, soil aridity, deterioration of vegetation, and land desertification [10,11].

In the present study, a three-dimensional numerical groundwater flow modeling using finitedifference Visual MODFLOW coupled with decision support tools of geoinformatics was applied to analyze the spatial and temporal behavior of groundwater in the valley plain of the sub-Himalayan watershed in Pakistan. The multilayered aquifer system of the watershed is recharged mainly by the surrounding dissected land and rocky mountainous terrain. The behavior of the groundwater system was predicted in response to probable hydrogeological stresses.
