Changes in the regional hydroclimate of the Midwest United States between the 6-kBP and current climate

Otieno, Francis
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This study used the NCAR Mesoscale Model version 5 release 3 (MM5v3) to simulate the climate of North America at 6000 years before present (6-kBP), and also tested the ability of the model in simulating the paleo-climate, which is significantly different from the present and partially verifiable. It also compared the paleo-climate simulations with the present and investigated the impact of changes in insolation, CO2 concentration, and vegetation on climate. To limit the influence of GCM bias on the simulations, the study used NCEP-DOE reanalysis II data for both 6-kBP and current climates. The present study differs from previous paleo-climate simulation, because it used a regional model instead of GCM, and also included differences in vegetation between the climates, which were ignored in the previous studies. The simulation results are compared with proxy records and paleo-climate simulation from General Circulation Models (GCM).;Results from the study show that MM5v3 is capable of simulating the paleo-climate. The simulated changes between the present and the 6-kBP climates are consistent with the proxy records and lake level data. The regional land-atmosphere interaction and the feedbacks better represented in MM5v3 than in GCM; hence the study obtained improved simulations for the Midwest, US. This study suggests that given realistic initial and lateral boundary conditions, MM5v3 is capable of simulating details of climates (past or future) that differ from present.;The simulated 6-kBP precipitation over Midwest is less than the present, but the evaporation is higher, resulting in negative precipitation minus evaporation (P-E). This is consistent with observed low lake level at 6-kBP over the region, but was not captured by previous GCM studies. However, analysis of the results reveals that less transport of moisture to the Midwest at 6-kBP caused the lower precipitation. Sensitivity tests show that a change in insolation influences both temperature and precipitation; a change in vegetation affects precipitation; but changes in CO2 produce less significant changes in temperature and precipitation.

Geological and atmospheric sciences, Meteorology