With uncertainty currently serving as the cornerstone of the climate change topic, many water resource managers are left to wonder what the future holds for their water supply. There is no single answer that will serve all utilities, as the complexity of global warming is as vast as the globe itself. Climate models, used to predict temperature and precipitation trends, point to varying impacts of climate change from region to region, with the potential effects on water supplies ranging from minimal to extreme. Water availability can be impacted by changes in precipitation, snowpack, runoff, increased evaporation and transpiration, and changes in demand. The challenge of water resource planning, therefore, will likely be greatly impacted if the value of historic precipitation and flow data diminishes in the wake of changes and variability in weather and temperature patterns.

As the earth warms, evaporation will increase. Higher levels of atmospheric moisture are expected to result in an average net increase in global precipitation, following the old adage of “what goes up must come down.”  This simple concept is quickly complicated by the fact that the greatest unknown factor is where the precipitation will fall. Unfortunately, while global models are mostly in agreement on anticipated regional temperature changes, models predicting expected changes in regional precipitation are not. Although there is disagreement among the models as to the exact locations where the greatest precipitation change will occur, most models indicate that the mid-latitude regions of the United States and much of Europe and Asia will experience the greatest changes (Climate Change and Water Resources: A Primer for Municipal Water Providers, order # 91120, research partner: National Center for Atmospheric Research). Some experts believe there may be fewer light and moderate rainfall events and more sporadic, heavy rainfall events, even in the areas that receive greater than historic precipitation. Likewise, areas with historic droughts may experience longer, more extreme drought events, and areas that have seen few droughts may find more frequent dry spells in their future.