Landscape Evaporative Response Index (LERI)

The Landscape Evaporative Response Index (LERI) is an experimental drought-monitoring and early warning guidance tool that measures the anomaly in the actual evapotranspiration (ETa) from the land surface. This webpage provides LERI plots based on accumulated 8-day, monthly, seasonal, growing season, and annual ETa for the contiguous United States and northern Mexico at a 1-km spatial resolution. LERI data are available from January 2000 to the present — a period that corresponds to the availability of MODIS satellite data on which it depends.

ETa is the sum of transpiration from vegetation and evaporation from soil (and water bodies), and is accumulated over a given time period for a given location. The ETa data on which LERI is based are produced by the U. S. Geological Survey using the operational Simplified Surface Energy Balance (SSEBop) model (Senay et al., 2013). SSEBop combines evapotranspiration fraction (i.e., the ability of the land surface to meet the atmospheric demand for water vapor, expressed as a proportion of that demand) generated from remotely sensed MODIS thermal imagery, acquired every 8 days, with climatological atmospheric evaporative demand as represented by reference evapotranspiration derived using the Penman-Montieth formulation and driven by from University of Idaho's Gridded Surface Meteorological Data for that period.

LERI uses a rank-based, non-parametric (Tukey) method to estimate percentiles of the SSEBop ETa data compared to the available period of record (January 2000 to present). LERI percentiles are binned into four drought categories (LD0 - LD3) analogous to the US Drought Monitor (USDM) categories (i.e., D0 - D3) and using the same percentile breaks that USDM considers for soil moisture. LERI does not have an LD4 category (i.e., the 2nd -percentile break) because of the short period of the record.