## 4 Conclusions  
The main objective of the study was to present a simplified modeling technique called VegET that blends a commonly used vegetation water balance algorithm with LSP derived from remotely sensed data for estimating landscape ETa anywhere in the world.  
A set of simplified linear equations are presented to convert NDVI-based LSPs into Kcp, which is comparable in purpose with that of the Kc described in [6]. These equations contain some threshold parameters that the user can adjust depending on the source of the LSP.  
The VegET model was run using daily weather data for two years for the conterminous United States using NDVI climatology derived from the AVHRR data set. The daily model runs were aggregated to produce two seasonal maps that reflected the general crop performance and drought incidences in 2005 and 2006. In addition, daily ETa estimates for AmeriFlux tower sites in Brookings, South Dakota, and Audubon, Arizona, tracked well the ETa estimates from flux tower measurements using the eddy covariance method. Despite concerns in the quality of the flux tower data, the day-to-day correlation coefficient between VegET ETa and raw tower latent heat flux data was greater than 0.71 on both flux tower sites. The correlation coefficient improved to greater than 0.87 using 10-day moving average data sets. Further research is required to evaluate the performance of the approach and the sensitivity of the few model parameters using more diverse data in different hydroclimatic regions of the world.  
Particularly, the VegET model brings several advantages for operational monitoring of soil water changes and ET for drought monitoring and large area water balance modeling. The blending of a hydrological model and vegetation index will allow the possibility of quantifying ET at a higher spatial scale, even when the rainfall is at a coarser spatial scale. This is possible because ET is affected by land cover while rainfall is generally a function of location, especially at longer time steps (days and season). Since global data sets tend to be coarse for rainfall and ETo while NDVI is available at higher resolutions (less than 1 km), the approach will allow the use of global data sets for localized monitoring and decision making.  
The other advantages of using the LSP in VegET is the potential for predicting ETa patterns with changing land use and land cover types. The exercise will simply involve the replacing of modeling units using predicted LSP from land use and land cover change models. For example, if a land cover is expected to convert from grassland to cropland, the VegET model will run using LSPs derived from cropland in the same region. Thus, the VegET model can be used for testing scenarios of climate change under different climate (rainfall and ETo) and land cover changes.  
Because the VegET model runs on daily or longer time steps with little effort for model setup and operation, the VegET modeling approach was demonstrated to have a promising application for drought monitoring and early warning applications at various spatial and time scales for rainfed sytems. The model can be made operational easily for any location where there is spatially explicit data on NDVI climatology, rainfall, reference ET, and soils with little or no requirement to recalibrate or develop site-specific regression equations. All required data sets are now available for different parts of the world at different resolutions.