HR: 0800h
AN: GC41A-0108    [Abstracts]
TI: Observing Seasonal and Diurnal Hydrometeorological Variability Within a Tropical Alpine Valley: Implications for Evapotranspiration
AU: * Hellstrom, R A
EM: rhellstrom@bridgew.edu
AF: Bridgewater State College, Geography, Conant Science Building, Bridgewater, MA 02325, United States
AU: Mark, B G
EM: mark.9@osu.edu
AF: The Ohio State University, Geography, 154 N Oval Mall, Columubs, OH 43210, United States
AB: Conditions of glacier recession in the seasonally dry tropical Peruvian Andes motivate research to better constrain the hydrological balance in alpine valleys. There is an outstanding need to better understand the impact of the pronounced tropical hygric seasonality on energy and water budgets within pro-glacial valleys that channel glacier runoff to stream flow. This paper presents a novel embedded network installed in the glacierized Llanganuco valley of the Cordillera Blanca (9°S) comprising eight low-cost, discrete temperature and humidity microloggers ranging from 3470 to 4740 masl and an automatic weather station at 3850 masl. Data are aggregated into distinct dry and wet periods sampled from two full annual cycles (2004-2006) to explore patterns of diurnal and seasonal variability. The magnitude of diurnal solar radiation varies little within the valley between the dry and wet periods, while wet season near-surface air temperatures are cooler. Seasonally characteristic diurnal fluctuations in lapse rate partially regulate convection and humidity. Steep lapse rates during the wet season afternoon promote up-slope convection of warm, moist air and nocturnal rainfall events. Standardized grass reference evapotranspiration (ET0) was estimated using the FAO-56 algorithm of the United Nations Food and Agriculture Organization and compared with estimates of actual ET from the process-based BROOK90 model that incorporates more realistic vegetation parameters. Comparisons of composite diurnal cycles of ET for the wet and dry periods suggest about twice the daily ET0 during the dry period, attributed primarily to the 500% higher vapor pressure deficit and 20% higher daily total solar irradiance. Conversely, the near absence of rainfall during the dry season diminishes actual ET below that of the wet season by two orders of magnitude. Nearly cloud-free daylight conditions are critical for ET during the wet season. We found significant variability of ET with elevation up through the valley. Humidity and temperature measurements were analyzed to show significant effects of elevation and proximity to melt-water lakes on vapor pressure deficit.
DE: 1630 Impacts of global change (1225)
DE: 1637 Regional climate change
DE: 1700 HISTORY OF GEOPHYSICS
DE: 3344 Paleoclimatology (0473, 4900)
DE: 6334 Regional planning (1880)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting