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Modeling Present and Future River Runoff Using Global Atmospheric Models

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Master's thesis

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A global atmospheric model is used to calculate the monthly river runoff for 30 of the worlds major rivers for the present climate and for a doubled CO2 climate. The model has a horizontal resolution of 4 deg X 5 deg, but the runoff from each model box is quartered and added to the appropriate river drainage basin on a 2 deg X 2.5 deg resolution. A new routing scheme is used to allow runoff calculated for a particular grid box to flow to an adjacent downstream grid box and ultimately to the mouth of the river. The total instantaneous runoff leads runoff at the mouth by one to two months. The model generated runoff at the mouth is compared to observations for several different simulations. The runoff peaks of high-latitude rivers are due to spring snow melt and there is a time lag between when the snow melts and when the melt water reaches the mouth. The new routing scheme allows the calculation of runoff at any location in the river basin. Model-generated river runoff and precipitation for the Mississippi River and its tributaries are analyzed for the present climate, where annual precipitation is within 5 of the observed precipitation. However, model-generated monthly precipitation is too high in the spring and too low in the summer and fall. In a model simulation with doubled CO2, river runoff increases for 27 of the 30 rivers and in most cases coincides with increased precipitation. All high-latitude rivers show an increase in precipitation and runoff with a shift in the runoff maximum, approximately one month earlier, due to an earlier snow melt season. In a doubled CO2 climate, snow mass decreases for mid and high-latitude rivers in North America and northwestern Asia, but increases for rivers in northeastern Asia, where observed winter temperatures average -30 deg to -50 deg C

Subject Categories:

  • Meteorology
  • Hydrology, Limnology and Potamology

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