Strzepek et al. identified potentially stressed agricultural regions by focusing on specific geopolitical regions and estimating likely water demands based on trends of increasing or decreasing industrial water need. The increase of both urban populations as well as the increase of a nation’s GDP correlate with dramatically increased water usage per capita, so countries which are developing larger cities and industrial economies are likely to require more water in the future. Subsurface water, the most common source for agricultural irrigation, will be placed under increasingly heavy demand as non-agricultural needs grow, thus decreased supply was considered in modeling future availability.
     In order to incorporate the effects of a changing climate on already threatened agricultural water sources, the modeling methodology used three distinct climate scenarios to predict future supply; a stable unchanging climate, a generally wetter climate and a generally drier climate. In any of the scenarios, threatened areas are identified, however which areas are most challenged depends on the scenario. For instance, in Europe under the drier scenario agriculture water supply is threatened whereas in the wetter scenario it is not. Some areas, like Brazil and the U.K. are not likely to face climate change-based agricultural water shortage under either scenario.
    The researchers identified a region’s likelihood for water shortage by considering how much water is currently available for agriculture, and then factored the likely increased demands from industry and urban use. Many ‘developing’ countries face a specifically difficult water management challenge. Industrial development requires increasingly large water inputs, especially as a coolant for power plants. The intensive water use of these processes diverts water away from agricultural availability. Urban residents use significantly more water. This is the result, in many developing countries, of  a change from limited central sources such as a town pump, well or water truck to plumbing directly into the house. This allows for the potential of overuse in a local area as individuals use more than what is sustainable for the region as a whole. This trend also appears on a larger scale, as transnational borders dissect rivers and watersheds. In these stations certain administrative regions can overuse, creating scarcity downstream. Here, the researchers identified a shortage of appropriate agricultural water management, globally, as a cause of consistent local misuse and constructed need.
    The other demand for water are Environmental Flow Requirements. These are the calculated need for flowing water in an ecosystem which is institutionally maintained in order to secure ecosystem services. The EFR of a given areas varies greatly depending on the type of ecosystem. For example Oceanian water ways require 54 percent of water, while those in the Nile river basin require 23 percent. These values are calculated to satisfy only minimum ecological requirements.