Browsing by Subject "Water balance (Hydrology)"
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Item Climate change, hydrology, and ecological models: intercomparison and validation(2003) Gordon, Wendy Silverman; Fowler, Norma L.; Famiglietti, James StephenThis dissertation consisted of three related studies. The first study used historical streamflow records from the Hydro-Climatic Data Network (HCDN) representing 13 unimpaired watersheds to validate runoff simulated by six terrestrial ecosystem models (Biome-BGC, Century, GTEC, LPJ, MC1, and TEM) comprising VEMAP. The validation exercise tracked the historical period of VEMAP from 1895-1993. This study demonstrated that the models performed better in wet watersheds, where runoff was generally underestimated, than dry ones, where runoff was overestimated. The static vegetation models outperformed the dynamic vegetation models. TEM, an independently calibrated model, was the best performer. GTEC, a model missing a snow routine and an evaporation function, was the lowest performer. This study suggested that improvements to these types of models may come from more realistic descriptions of hydrologic processes in arid environments. The second study examined water balance parameters of four of these models (Biome-BGC, Century, LPJ, and MC1) from the inception of the VEMAP climatological data base in 1895 through 2100. The 21st century simulations were based on the Hadley Centre and Canadian Centre for Climate Modeling general circulation models (GCM). Runoff and actual evapotranspiration trends were positive in the majority of cases. Percentage changes in runoff exceeded underlying changes in precipitation and this amplification increased over time. Results varied by model and GCM. The third study sought to address an underlying assumption of the validation work. Streamflow gauging stations included in the HCDN have been carefully screened to filter out factors that could confound their use in the assessment of long-term climate signals. One criterion for station inclusion was that land uses in the watershed had not changed over the period of record so as to significantly alter natural streamflow. This assumption was explicitly tested in a watershed selected for the validation study by interpreting remotely-sensed imagery from the North American Landscape Characterization (NALC) project, and land cover was found to be relatively unchanged over the period examined, 1972-1992. Runoff modeling of land-cover changes was accomplished using the Long-Term Hydrologic Impacts Assessment model and runoff changes were less than 5% over the twenty year period.Item Effects of water storage on the earth's wobble(1985-12) Hinnov, Linda Alide; Wilson, Clark R.An evaluation of the global water storage contribution to the Chandler wobble has never been undertaken because: (1) the hydrological data necessary for the reconstruction of an extended monthly time series have not been available; and (2) the water storage contribution has traditionally been regarded as relatively unimportant because of its minor role in the excitation of the annual wobble. However, a crude approximation of the global water storage series is possible using worldwide records of monthly precipitation and temperature, accumulating precipitation at individual locations whenever temperatures are at 0° Celsius or below. Comparison of this modeled series with a previous estimate of the annual component of the global water balance, and with the observed monthly polar motion series, indicates good agreement with the former, and a significant correlation with the latter near the Chandler frequency.Item Water storage contributions to the excitation of polar motion(1989-05) Kuehne, John William, 1960-; Wilson, Clark R.The goal of this research was to investigate further the role of air redistribution and continental water storage changes in the excitation of both the annual and Chandler wobbles for the period 1900-85. The annual and Chandler excitations from air redistribution have been studied by Wilson and Haubrich (1976), Wahr (1982), and Hinnov and Wilson (1985). Annual excitation from water storage was estimated by Van Hylckama (1970), Hinnov and Wilson (1985), and Chao and O'Connor (1988). Chandler wobble excitation from water storage changes has been addressed only by Hinnov and Wilson (1985). This study was undertaken as a refinement to their encouraging but preliminary results.