Evidence based decision making reduce risks, helps to save costs and facilitates damage mitigation. IWRM impact assessment is a process where the needed evidence is being created.

Decision makers, whether in the government or private sectors, have to make decisions on water resources. The decisions may be related with infrastructure, hydropower, flood protection, irrigation, water allocation etc. More and more often it’s question of sharing diminishing supplies between ever-increasing demands or get backing for cost optimization in infrastructure planning. Drivers such as demographic and climatic changes further increase the stress on water resources and constitute risks for infrastructure.

The information provision is based on mathematical modelling techniques. The model is approximating real world physical processes and can predict the state of nature into the future more or less reliably depending on available input information. The outputs from the model are presented graphically, spatially, statistically and as time series and are applied to an application at hand.

An IWRM modelling based project follows a procedure:

Source data is being collected which follows by rapid model setup and calibration, in close co-operation with the client. One of the main objectives in every project is capacity building and ensuring post project continuity so stakeholders should participate as much as is possible in these initial phases. The application and relevant scenario options are discussed – the application may be, e.g. to assess hydro power plant construction options on fish production and food safety; or assess effects on climate change and floods on flood protection or bridge construction. After 25 years of continuous IWRM-model development and application for practical purposes, we can state that there are very few constraints in the IWRM-model capacity to support any application at hand.

The three last steps are iterative and easily repeatable. Typical outputs are

- indicator maps and animations which can be overlayed and compared with alternative scenarios
- charts for visualizing tabular data and indicator trends

The actual design and impact assessment with conclusions and recommendations need human involvement. Based on the documented evidence, methods and outputs provided by the process, the IWRM planning options can be evaluated, prioritized and communicated.