Global simulation of lakes and river transport in climate models, and investigations of lake/climate...

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منو

" Global simulation of lakes and river transport in climate models, and investigations of lake/climate feedbacks during the middle Holocene "
M. T. Coe J. E. Kutzbach

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112972
Doc. No	:	TLpq304380260
Main Entry	:	J. E. Kutzbach
	:	M. T. Coe
Title & Author	:	Global simulation of lakes and river transport in climate models, and investigations of lake/climate feedbacks during the middle Holocene\ M. T. CoeJ. E. Kutzbach
College	:	The University of Wisconsin - Madison
Date	:	1997
student score	:	1997
Degree	:	Ph.D.
Page No	:	133
Abstract	:	The goal of this study is to investigate the sensitivity of climate to changes in the area and location of surface waters (lakes and wetlands). A model (SWAM) is developed to predict surface water area and river transport globally. SWAM is based on a linear reservoir hydrologic model and requires, as input, climatic estimates of runoff, precipitation, and evaporation from either observations or climate simulations, and estimates of topography from digital terrain models. SWAM is first applied on a usd2\sp\circusd x usd2\sp\circusd resolution to modern and middle Holocene climates of northern Africa. The middle Holocene simulation (6000 years before present), using climate input from the GENESIS climate model experiment, illustrates the potential sensitivity of surface water area to climatic change. SWAM simulates an increase in surface water area of northern Africa from about 1% coverage (modern) to about 3% (6000 yr BP). The increase is primarily a result of a greatly expanded Lake Chad and increased waters to the north of the Niger bend. The second part of this study examined whether expanded middle Holocene surface waters may have had an impact on the strength of the summer monsoon of northern Africa. Three experiments with the National Center for Atmospheric Research Community Climate Model version 3 are analyzed: (1) a modern simulation, (2) a middle Holocene simulation with 6000 yr BP orbital forcing, and (3) a middle Holocene simulation with 6000 yr BP orbital forcing and prescribed expanded surface water. The expanded surface waters in northern Africa result in significant changes in the simulated climate especially in northern summer. Net surface radiation and evaporation increase due to expanded surface waters by amounts which are comparable to changes due to orbital forcing alone. Precipitation increases regionally, but decreases to the south of the lakes. The geographic distribution of precipitation in the experiment with increased surface water area is in better agreement with observations than the simulation without surface water changes. This result demonstrates the need for including interactive lake models within climate models. In the third part of the study, SWAM is applied on a higher resolution usd(5\sp\primeusd x usd5\sp\primeusd) to simulate present-day lakes and river transport for all continents (except Antarctica and Greenland). The model develops its own river transport directions based on elevation. Subjective and objective techniques are developed to reduce the digital terrain model bias of overestimating surface water. The model simulates the large scale modern surface water features and river transport in fair agreement with observations. The simulated modern lake area (about 3% of the land area) is somewhat larger than the observed area (about 2%). Wetlands are poorly simulated by the model due to the coarse resolution of the digital terrain models. The results obtained from SWAM indicate that present-day terrain models are adequate for including interactive lakes and rivers in climate simulations. (Abstract shortened by UMI.)
Subject	:	Atmosphere
	:	climate
	:	Earth sciences
	:	Hydrology
	:	Pure sciences