Sensitivity and feedbacks associated with vegetation-related land surface parameters in a general circulation model

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:7234758

Lofgren, B M

A series of general circulation model (GCM) experiments were run to investigate the effects on climate of surface albedo, surface roughness, and field capacity. When decreased surface albedo is prescribed, at low latitudes, precipitation and soil moisture are increased, because of the increased upward motion resulting from additional atmospheric heating. At mid-latitudes, the precipitation is insensitive to decreased surface albedo, but soil moisture is decreased. A prescribed decrease in land surface roughness causes a general decrease in evaporation from land and water vapor flux convergence over land, and consequently also in precipitation. Land surface albedo was interactive with the GCM climate, using the climate to determine the vegetative cover. When compared to a control case with constant surface albedo over all land, tropical rainforests have increased precipitation and soil moisture. This promotes more growth of vegetation, causing positive feedback within the system. Subtropical deserts have decreased precipitation and soil moisture, and there is evidence of a southward shift in the Sahara. Midlatitudes have little response in precipitation, but have soil moisture responses which imply negative feedback. When surface roughness is interactively predicted, low-latitude forests have increased precipitation, primarily along coasts where there are shoreward winds. This leads to increased vegetation and greater surface roughness, making it a positive feedback. At midlatitudes the roughness of the forests causes enhanced Ekman convergence, resulting in increased precipitation. Neither the pattern changes in precipitation nor of changes in soil moisture as a fraction of field capacity is clearly correlated to the distribution of initially predicted field capacity. When all three parameters are made interactive simultaneously, the precipitation and soil moisture responses are approximately the sum of the responses to individual parameters.

• Research Organization: Princeton Univ., NJ (United States)
• OSTI ID: 7234758
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
540220 -- Environment
Terrestrial-- Chemicals Monitoring & Transport-- (1990-)
AIR-BIOSPHERE INTERACTIONS
ALBEDO
ATMOSPHERIC PRECIPITATIONS
CLIMATES
EARTH ATMOSPHERE
FEEDBACK
GENERAL CIRCULATION MODELS
MATHEMATICAL MODELS
METEOROLOGY
PLANTS
SENSITIVITY ANALYSIS