|Even Longer Records....
Data from a variety of paleoclimate sources document drought conditions across North America over the last 10,000 years. These records, with decade to century resolution, document extended periods of extremely dry conditions in different regions of North America. These periods of drought were severe enough and of long enough duration to impact vegetation composition, fire frequency, and to mobilize sand dunes in the Great Plains.
Evidence for these dry periods comes from paleoclimatic proxy data such as pollen, charcoal, minerals and other materials within lake sediments, and sand dune sediments. Fossil pollen data provide information about changes in vegetation composition, used to reconstruct past changes in precipitation and temperature. Relative changes in charcoal abundance, indicative of fire, are interpreted in terms of climatic conditions favorable to fire. Changes in the composition and the chemistry of sediments of lakes provide information on regional aridity and drought. Lake level records are a direct measurement of moisture balance providing information on long term hydrologic variability. The interpretation and dating of ancient soils and wild-blown sand/silt deposits constrain the timing and magnitude of sand dune mobilization associated with large-scale droughts.