Constraining regional water and carbon fluxes by combining a mobile measurement platform with satellite remote sensing
Regional estimates of evapotranspiration (ET) are needed for environmental analysis and management purposes, however current methods for determining regional ET have major limitations that limit their usefulness. I developed a surface mobile measurement technique, the Regional Evaporative Fraction Energy Balance platform (REFEB), which measures Evaporative Fraction (EF) and Water Use Efficiency (WUE). First I validate the REFEB against Eddy Covariance measurements in the Imperial Valley, California. I use satellite observations of vegetation greenness to extrapolate field-scale measurements to regional EF maps and combine these maps with satellite observations of net radiation to derive monthly and annual calculations of ET. I compared REFEB's regional estimates to a surface water budget based on irrigation and drainage measurements, which showed good annual and seasonal agreement.
Second, I applied REFEB to assess ET across a montane, Mediterranean climate gradient in the San Jacinto and Santa Rosa Mountains of Southern California (Study Area). Monthly, stratified Evaporative Fraction (EF) measurements were made across an elevational gradient We used these measurements to map monthly patterns of EF. Monthly EF maps were converted to ET using net radiation observations. I compared the REFEB ET estimates to a modified Priestly-Taylor (PT) formula as well as spatially interpolated estimates of precipitation and stream flow gauge runoff and Eddy Covariance (EC) tower estimates of ET. Unlike previous approaches, REFEB did not overestimate ET. Finally, I compared Study Area measurements to climate data and satellite observations of vegetation indices to assess the seasonal and interannual controls of precipitation and vegetation on energy partition. Precipitation amount and timing had the largest effect on energy partitioning in the Study Area with vegetation having a larger control at higher elevations. Multi-year vegetation data shows that vegetation increases in a stepwise pattern with precipitation while temperature has less control on vegetation. Collectively, these results show that REFEB is a viable method for assessing regional carbon and water fluxes.
0768: Environmental science