Author : Josiah Daniel Smith
Release : 2005
Genre : Drought forecasting
Kind : eBook
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Book Synopsis Data Mining and Spatiotemporal Analysis of Extreme Precipitation by : Josiah Daniel Smith

Download or read book Data Mining and Spatiotemporal Analysis of Extreme Precipitation written by Josiah Daniel Smith. This book was released on 2005. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The Prairie Pothole Region in the Northern Great Plains (PPR-NGP) of the United States frequently fluctuates from drought to deluge. The historical hydrologic record for this region reveals periods of intense, prolonged drought intermingled with rapid and destructive flooding. Drought or flooding is initiated and sustained by deficit or surplus precipitation, respectively. The weather events that accompany these disasters are characterized by large spatial and temporal variations from normal in the frequency and intensity. The unique hydrology and geology of the region makes the PPR-NGP highly sensitive to these weather perturbations. The future looks to bring more warming and thus more intense precipitation to the region. As the frequency of extreme precipitation events rises, the magnitude and occurrence of floods and droughts will be elevated. The objective of this research was to determine the factors controlling precipitation trends, drought, and flooding in the study area. Also, the weather conditions preceding the disastrous events were observed and characterized. The analysis was focused on the effects of varying precipitation intensity, frequency, and antecedent conditions as they pertain to PPR-NGP drought and Red River flooding. The results may be applied to better predict the future trends of flood and drought response to extreme precipitation. Data mining was performed on available weather station observations to extract significant information and use it to derive valuable insight into PPR-NGP drought and flooding behavior. Hydrometeorological indices calculated over various timescales were applied to assess the intensity and frequency of rainfall, the change in snow depths, and the deviation from normal precipitation. Flood discharge hydrographs were classified based on shape parameters and matched to precipitation characteristics. Spatiotemporal and statistical operations were employed to determine the controlling factors of precipitation trends, drought, summer floods, and spring floods in the PPR-NGP and Red River Basin. Current precipitation and stream flow trends indicate the potential for enhanced flood and drought activity. Precipitation intensity and frequency are ascending, but the intensity is increasing more than the frequency of monthly events. The result is that Red River discharge rates are rising six times faster than total precipitation over the basin. The rise in stream flow rates can be explained by elevated precipitation intensity and to some extent precipitation frequency during key flood months. However, the most critical flood month of April has a decreasing total precipitation trend and yet the highest rise in discharge rate. These trends come about because overall fall and winter precipitation rates are on the rise. The antecedent precipitation is stored on and in the frozen ground until released by the spring thaw, which usually takes place in April. Thus, the risk for larger April floods is affected not by a single month but by a half year's worth of increasing precipitation conditions. Large fluctuations in monthly drought conditions were determined to be equally controlled by both the frequency and intensity of precipitation events. Extreme drought took a minimum of two to three months both to develop and dissipate from a semi-arid state. Though, the biggest shifts in month-to-month conditions were observed when both precipitation intensity and frequency were well above or below normal over the same area. So the onset or end of an extreme drought took place more rapidly when the intensity and frequency changes were great and harmonized. Similarly, the spatial extent of the most intense (on average) drought cells was surprisingly little, because the overlap of large precipitation intensity and frequency shifts typically occurred over a small area. Also, the drought duration usually increased when severity reached a higher level, so that multiple months of moderate drought reduced the overall intensity for all but the most severe parts of the cells. The intensity of precipitation events was the main controlling factor in Red River summer flood occurrence and magnitude. Antecedent conditions were not essential to the development of summer floods. Conditions were often near normal prior to a flood because more of the normal rain fell in a fewer number of more intense events. Conversely, the magnitude and occurrence of spring floods was controlled by antecedent precipitation and fast snow melt rates. A significant snow pack was observed prior to both major and minor floods, while a non-flood year had little snow pack over the basin. Fall soil moisture, winter snowfall, and a fast rate of stored water release all had to be present at sufficient levels to trigger a large flood response.