Spatial and Temporal Variability in Precipitation in the Upper Tennessee Valley

To properly make decisions regarding the management of regional water resources, determining the role of climate and climate change on the variability of precipitation is critical. Understanding variability is especially true for mountainous region where increases in orographic precipitation can cause potential hazards such as flooding and mudslides. The temporal variation of precipitation in the Upper Tennessee River Valley was investigated by utilizing a data set from the Tennessee Valley Authority (TVA) rain gauge network spanning the Southeast United States (US). In addition to the TVA rain gauge network, mean areal precipitation values for subbasins in the study area were also analyzed for temporal variation, and were provided by the National Weather Service (NWS). Data included 56 rain gauges as well as mean areal precipitation values for 78 subbasins, which have periods of records of 1990-2010 and 1950-2009, respectively. The Mann-Kendall trend test, Mann-Kendall-Sneyers test, Yamamoto Method, and Morlet’s wavelet were applied to reveal precipitation trends and abrupt changes in annual precipitation volumes throughout the study region. Results indicate that a. ) only 11 percent of subbasins in the study 5 area experienced statistically significant increasing or decreasing trends while no rain gauges are experiencing significant trends; b. ) seasonal precipitation trends based on monthly volumes varied with the summer and autumn series showing the largest amount of significant increasing trends for the 78 subbasins in the study area; c. ) abrupt changes in annual precipitation volumes were detected throughout the area for the 1950-2009 period of record with many subbasins having change points corresponding to strong El Nino events; and d. ) throughout the study area several subbasins displayed significant periodicities of 1, 6, 18, and 22 years in monthly volumes. The Appalachian Mountain range displayed varying trends, which are indicative of different climatic mechanisms affecting precipitation. These findings will support management policies with respect to multiple use water resources in the TVA reservoir system by providing managers critical information on historical water availability and associated variability. Introduction Global warming and the change in climate have led to increased variability of the hydrological cycle at a global scale, which has created uncertainty with predicting future climate conditions and associated variability (IPCC, 1995). Perturbations in global climate models have created the need to study subsequent changes in hydroclimatic variables (e.g. rainfall, streamflow, evapotranspiration, etc.) to understand the regional effects of climate change. According to Karl et al. (2009), the Southeast United States has experienced an increase in extreme precipitation events and moderate to severe droughts in the 20 century. For instance, since the 1970’s, moderate to severe droughts in the spring and summer months have increased by 12 and 14 percent, respectively. Ongoing modelling efforts to model and project changes in extreme weather events in the eastern United States have indicated that the Southeast region should receive up to 110.4 mm. yr. more total extreme precipitation by the end of the 2050’s (Gao et al., 2012), where extreme precipitation is defined as the 95 percentile of precipitation data for