CHARACTERIZING LANDSCAPE EVAPOTRANSPIRATION DYNAMICS USING REMOTE SENSING AND GLOBAL WEATHER DATASETS

Characterizing Landscape Evapotranspiration Dynamics using Remote Sensing and Global Weather Datasets

Senay¹, G.B., S. Bohms², D.S. Morgan³, M. Moreo⁴, S. Qi⁵ and S. Christenson⁶

1:U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center; 2: SGT, contractor to USGS EROS; 3: USGS Oregon Water Science Center; 4: USGS Nevada Water Science Center; 5: USGS Colorado Water Science Center, 6: USGS New Mexico Water Science Center

For presentation at the 3^rd USGS Modeling Conference

Denver, Colorado; June 7-11, 2010

Special Session: Remote Sensing Based Models of Water Availability and Water Use (ET) in the Dry Ecosystems of Southwestern USA

Landscape evapotranspiration (ET) is a key component of the hydrologic water balance of a watershed. The increasing availability of global datasets for weather variables and remotely sensed data for land surface temperature allows us to make estimates of landscape ET. Spatial distribution of landscape ET can be used as an indicator of vegetation performance in terms of biomass accumulation which is directly associated with water use. Furthermore, ET can be used to estimate the spatio-temporal dynamics of the rates and total amounts of groundwater recharge and withdrawal from aquifer systems in irrigated areas. We have applied the Simplified Surface Energy Balance (SSEB) modeling approach to characterize landscape ET for the Columbia Plateau, Nevada Transect and High Plains Aquifer using 10 years (2000-2009) of available satellite data. We used weather data from the Global Data Assimilation System (GDAS) to calculate reference ET. Land Surface Temperature (LST) was derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. The comparison between model generated actual ET and independent estimates of irrigation application depth showed good correspondence (r² > 0.90) in the Yakima Valley with about a third of estimated irrigation application being converted into ET. Potential groundwater recharge and withdrawal sites were identified. The spatial and temporal patterns of monthly and seasonal actual ET corresponded well with common knowledge in regard to irrigated areas and differences in land cover types in the case of Nevada Transect and High Plains Aquifer. More validation of the ET estimates will need to be conduced using independent flux measurements and basin water balance modeling. The method is promising for large scale operational monitoring of landscape ET across varied landscapes for drought monitoring and water balance studies.

ET: Evapotranspiration

LST: Land Surface Temperature

SSEB: Simplified Surface Energy Balance

MODIS: Moderate Resolution Imaging Spectroradiometer

GDAS: Global Data Assimilation System

USGS: U.S. Geological Survey