Science and Communication Issues Associated with Precipitation in the NCA

The Third United States National Climate Assessment (NCA3) included several key messages about precipitation. Extreme rainfall has been increasing and is expected to continue to increase in the future. Droughts have been increasing in some regions and are projected to become more intense in most areas due to increases in evaporation. On certain aspects of precipitation, strong statements were not made because of uncertainties in the science and the geographic location of the U.S. with respect to global change patterns. The U.S. straddles the transition zone between drier subtropics and wetter high latitudes. Projections of flooding are uncertain because of the complexities of seasonal timing of extreme rainfall increases, counteracting influence of decreased soil moisture, and the interactions of climate changes with watershed characteristics. While droughts may increase in intensity in most areas, there are uncertainties in northern areas where both precipitation and evaporation may increase. Communication of these complex science issues to the primary non-scientist audience of the NCA3 was a challenge. Both the science and communication challenges will be discussed in this talk.