Disentangling the Hierarchy of Controls and Responses in Paleoclimatic Variations: A Diagnostic Study of the Mid-Holocene Drought in the Mid-Continent of North America Using Paleohydrological Data Dyntheses and Transient Climate Simulations
Abstract
Uncertainties in the specific physical and biological processes that are reflected by paleoclimatic data sources, and uncertainties in the alignment of variable definitions in data and models are major difficulties to be addressed in data-model fusion. However, an additional complication arises from the hierarchical nature of the controls and responses that determine the sequence of climatic changes recorded by paleoclimatic data. In the case of hydrologic variations, this hierarchy includes the ultimate atmospheric circulation controls that govern large-scale moisture fluxes, support or suppress precipitation, and regulate the atmospheric moisture balance, and the proximate surface water- and energy-balance controls (and feedbacks between them). Identifying the particular hierarchy of controls and responses that determine the local water balance (and its reflection in paleoclimatic data) is not straightforward because multiple atmospheric circulation patterns can produce the same regional or local hydroclimatic conditions. Further, multiple combinations of precipitation, evaporation, soil moisture, and runoff (with the instantaneous values of the latter two terms also highly dependent on antecedent conditions) can produce the same hydrologic status. Moreover, land-surface processes, including ecological ones, have the potential for amplifying or damping hydrologic responses to larger-scale, longer-term variations. There is also considerable memory in hydrological systems. In the absence of a specific constraining hierarchy, data assimilation could easily yield the right answer for the wrong reason.
One approach toward diagnosing the specific controls of (paleo) hydroclimatic variation is to exploit the thousands of individual cases provided by transient climate simulations (e.g. TraCE-21k) using the using the standard tools of modern climate diagnostics. Tools such as the construction of composite anomalies or correlation fields to examine the large-scale controls of surface-climate anomalies is a powerful approach widely used with reanalysis datasets. We illustrate this approach using the temporal evolution and structural changes in the controls of the well-documented mid-Holocene "gigadrought" in North America.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP21B..02B
- Keywords:
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- 3335 North American Monsoon;
- ATMOSPHERIC PROCESSESDE: 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCESDE: 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4938 Interhemispheric phasing;
- PALEOCEANOGRAPHY