Changes in vegetation condition and surface fluxes during the North American Monsoon Experiment (NAME) 2004 Russell Scott, USDA-ARS Chris Watts, U. of Sonora

Motivation The NAM results in large changes to surface cover (i.e., It gets green!) But, few observations have ever quantified this effect in terms of changing surface energy balance, especially south of the border (where things are really happening!) September Tucson

Surface energy balance R n = SW(1-albedo) + LW n = λE + H E H G

Goals and Methodology Vertical Wind Speed Water vapor density Eddy covariance used to determine patch- or ecosystem-scale heat, water and carbon dioxide flux hour Use micrometeorological techniques to quantify changes in surface energy balance over a variety of representative biomes within the core NAM region in NAME 2004 experiment

Desert Scrub + Buffelgrass SubTropical Shrubland Santa Rita Mesquite Savanna Kendall Desert Grassland Lucky Hills Shrubland Charleston Mesquite Woodland Tropical Deciduous Forest Metflux sites (eddy fluxes, basic met, soil moisture profiles)

Observations - Results Big Picture Vegetation response Site Details: Precipitation Vegetation Albedo Surface temperature Rn/Rs Evaporation Evaporative fraction

June July August September SPOT NDVI 10-day composites Tucson Core of the veg changes

Southern sites greater and more intense precipitation But all sites still had dry periods Tropical Cyclones Mean- 350 mm, 60% in July-Sept mm mm

Enhanced Vegetation Index Much larger increases in VI observed for Sonora sites

Albedo TesopacoTDF912 RayonSTS1517 CMriparian woodland108 SRsavannah1514 KNgrassland1817 LHdesert shrub1817 Pre Post Monsoon 2-fold difference in broadband albedo But monsoon changes are very small Increased absorption in visible bands Countered by decreases in near-infrared

Daytime LST from MODIS-Aqua Sonoran sites LST drops by 25 ºC with Monsoon onset, much more than for the Arizona sites

Pre-monsoon data limited Energy partitioning Cooler, wetter surface, R n /R s

Larger changes down south, but considerable water stress still evident at the rainiest of sites Evaporation

Evaporative Fraction λE + H λEλE Water limitation still evident even at rainiest site

Summary We developed a network of sites across a gradient of NAM forcing: 1) to better understand the land surface response in terms of energy, water and CO2 exchange 2) to help improve the understanding of the land- atmosphere feedback in the NAM region