The aim of this study is two folds. The primary aim of the study is to apply a detailed watershed model for the quantification of climate and land use change impacts on the hydrology and NPS pollution in the case study watershed in a developing country. Secondly, it aims to develop a pathway for researchers in developing countries that takes into account the data availability, cost of data collection and model performance to design a watershed modelling project tailor made to the specific modelling objectives based on a threshold level of data requirement, model results and cost, optimized for maximum benefit. In this study Better Assessment Science Integrating point and Non-point Sources (BASINS), and Hydrological Simulation Program-FORTRAN (HSPF), are used for the characterization of watershed hydrology and diffuse pollution and quantification of the effects of land use and climate change on the hydrologic regime and NPS pollutant loads in the Koycegiz watershed, Turkey. Based on the Weight of Evidence (WoE) analysis; Best Professional Judgment (BPJ) in modeling experience and literature review are used to define the relationships between Data, Cost and Model Performance Index and objective evidences are put forth to develop a hypothesis incorporating an application scenario for BASINS/HSPF application in a developing country identifying the minimum data requirement, corresponding relative cost and acceptability of model results, respectively.

The Hydrological Simulation Program-FORTRAN (HSPF) is an analytical tool designed to simulate hydrology and water quality in natural and man-made systems. HSPF is used to apply mathematical models to simulate the movement of water, sediment, and other constituents through watersheds. This analysis helps predict possible environmental problems in the watershed. With the growing need to care for and monitor the effects of man on the environment, it became apparent that a method for rapid analysis of those effects was needed. The Watershed Modeling System (WMS) interface creates a way for the user to input a multitude of parameters into the input file and then to run HSPF. The input parameters are linked to all the tools within WMS including automated basin delineation and parameter definition using a graphical user interface. As mentioned above, the purpose of including an interface to HSPF in WMS is to provide a way for engineers to delineate a water-shed and set up an HSPF model quickly. The watershed delineation tools, as well as the Geological Information System tools, in WMS allow automated development of much of the input necessary for HSPF. However, several new tools and dialogs have been added to complete the HSPF input data. To begin an HSPF simulation in WMS, the HSPF data must be initialized for the watershed model. This is a simple procedure that involves the click of a button within the HSPF Global Options dialog box. Once the data are initialized, the user may access the various dialog boxes within the HSPF interface. The following sections will describe the input dialogs involved in the interface and will explain the expected input parameters. It is recommended that the user consult the HSPF documentation to receive a complete description of how HSPF uses the parameters.