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Plants respond to conditions in their immediate vicinity. Thus, to understand the vegetative moisture stress during drought, it is important to measure the local moisture balance. The actual evapotranspiration fraction (AETF) provides such a measure. Specifically, it indicates whether a location is expected to experience local drying during a drought, or whether the location receives sufficient precipitation that it will remain moist even during an extended drought. An extended drought is defined by a 48-month period where the Standardized Precipitation Index (SPI, NCAR 2022) is two standard deviations below the long-term mean (SPI-48 = -2). Such a drought is expected approximately once every 50 years in the Sierra Nevada. The southern Sierra 2012-2015 drought was a SPI-48 drought = -2.0, which resulted in severe vegetation die-off and a marked reduction in water deliveries.--------The AETF ranges from 0 to > 100%; a low value indicates a wetter location during drought and a high value indicates a drier location. Locations <100% would be expected to generate runoff, even during a SPI-48 drought = -2.0, and would be expected to continue generating runoff. Locations >100% would be expected to desiccate the soil during drought, with negligible runoff, and increasing vegetation drought stress.----------------This raster has been modified from the base 30m version in the following ways:-------- - It has been aggregated from a 30m to a 300m scale by averaging across the 30m values----------------- Unit Of Measure: Percent |