Using Satellite Imagery to detect changes in Vegetation in Arid Environments Kelley Keese GIS in Water Resources

87% Shrubland2.5% Grassland 10% Bare 0.5% other Land UseElevation Study Site Nevada Southern Nevada Mojave Desert 130 km NW Las Vegas 22 km x 28 km Vegetation Production Data (Ron Green, pers com)

AVHRR AVHRR Advanced Very High Resolution Radiometer Provides 4 – 6 band multipectral data NOAA polar-orbiting satellite series Data from the University of Arizona Bi weekly composites of maximum NDVI; Tiff format : data presented 0 – 255 bit scale ftp://aria.arizona.edu/pub/usndvi_vc/GeoTIFFS/

Normalized Difference Vegetation Index from AVHRR (C 2 – C 3) / (C 2 + C 3) Channel 1 - chlorophyll causes considerable absorption Channel 2 - spongy mesophyll leaf structure leads to considerable reflectance (Tucker1979, Jackson et al.1983, Tucker et al. 1991).

Methods Crop the dataCrop the data Convert to NDVI scale of –1 to 1Convert to NDVI scale of –1 to 1 Compute an average for months of Feb-JulyCompute an average for months of Feb-July Compute the “departure from average”Compute the “departure from average” Generate tables of NDVI values to compute the aerial average for each monthGenerate tables of NDVI values to compute the aerial average for each month Did this 90 times!!!! … and generated tables for 6 yearsDid this 90 times!!!! … and generated tables for 6 years More Raster calculations to compute the average for each monthMore Raster calculations to compute the average for each month 36 more Raster calculations to compute the DA (monthly – mean)36 more Raster calculations to compute the DA (monthly – mean)

Departure from Average February 1995 Avg = 0.160

Departure from Average March 1995 Avg = 0.193

Departure from Average April 1995 Avg = 0.203

Departure from Average May 1995 Avg = 0.216

Departure from Average June 1995 Avg = 0.211

Departure from Average July 1995 Avg = 0.189

Departure from Average February 1998 Avg = 0.190

Departure from Average March 1998 Avg = 0.210

Departure from Average April 1998 Avg = 0.200

Departure from Average May 1998 Avg = 0.280

Departure from Average June 1998 Avg = 0.235

Departure from Average July 1998 Avg = 0.248

Conclusions Study shows that vegetation in desert systems is very responsive to water availability 1 km resolution satellite data does indeed detect changes in vegetation in arid environments Implications:

Implications Water Resources  Evapotranspiration (ET) plays a critical role in controlling groundwater recharge  Understanding response of vegetation to climate forcing should help us better determine system response to climate change  Need to understand climate/vegetation dynamics to estimate potential impact of land use change on water resources (e.g. brush control) Contaminant Transport and Remediation  Phytoremediation: use of plants to clean up toxic waste sites  Some engineered barrier designs for waste containment depend primarily on ET to minimize water movement into underlying waste