|Scott, Russell - Russ|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2009
Publication Date: 5/1/2010
Citation: Lizarraga-Celaya, C., Watt, C., Rodriguez, J., Garatiza-Payan, J., Scott, R.L., Saiz-Hernandez, J. 2010. Spatio-temporal variations in surface characteristics over the North American Monsoon region. Journal of Arid Environments. 74:540-548. Interpretive Summary: The North American Monsoon (NAM) dominates summer climate and is responsible for providing the majority of rainfall over a large portion western North America. Knowing how ecosystems respond to this input of rainfall is critical to understanding how surface vegetation response may affect monsoon intensity. In this study, we use satellite observations to quantify the surface temperature and vegetation response of ecosystems to the monsoon rains along a latitude gradient that varies in monsoon intensity. The onset of the NAM rainy season in early summer is one of the main precursors for vegetation growth across the entire NAM region. At all the sites, it is observed that the mean daytime land surface temperature cools several degrees as the NAM fully develops. We also found that desert shrub and subtropical shrub regions in northern latitudes show large temperature and smaller vegetation variations, while the tropical deciduous forests in lower latitudes show much larger vegetation and smaller temperature changes. Satellite data proves to be a valuable tool for assessing the dynamics of seasonal and interannual surface characteristics helpful in determining climate responses.
Technical Abstract: In this paper we summarize the surface characteristics for six locations in western Mexico and southwestern USA (from a subhumid climate in Jalisco, Mexico to the Sonoran Desert climate in Arizona, USA),that lie along a meridional transect within the North American Monsoon (NAM) core region using available MODerate Resolution Imaging Radiometer (MODIS) satellite data and supplementary surface instrumental data for two of these sites in Sonora, Mexico. The climate analysis for each site is carried out for the period 2000–2008, that includes all available MODIS data. A comparison of seasonal and annual variability in surface conditions for the enhanced vegetation index (EVI), albedo and land surface temperature (LST) at each site is presented. With the help of available surface data from field observations, a more detailed analysis of Rayon and Rosario de Tesopaco sites is presented. The qualitative behavior and climate response of three types of vegetation: desert shrub, subtropical shrub, and tropical deciduous forest ecosystems are analyzed under the influence of the NAM summer wet season. The onset of the NAM warm wet season in early summer, is one of the main precursors of generalized EVI growth in all the NAM region. At all the sites, it is observed that the mean daytime LST cools several degrees as the NAM fully develops. During the warm wet season, in the case of open and sparse vegetation regions such as desert shrub and subtropical shrub, albedo values fall slightly during the NAM season, while in closed and dense tropical deciduous forest regions albedo shows a slight increase. Differences in soil reflectivity at these sites are probably responsible for this rather unexpected behavior. Additionally it is found that, desert shrub and subtropical shrub regions in northern latitudes show large LST and small EVI/albedo seasonal variability, whilst tropical deciduous forests in lower latitudes show much larger EVI/albedo and smaller LST seasonal variability. Thus MODIS data proves to be a valuable tool for assessing the dynamics of seasonal and interannual surface characteristics helpful in determining climate patterns.