* Metric Name: Risk of Tree Dieoff During Drought  

* Tier: 1  

* Data Vintage: 2021  

* Unit Of Measure: This is a dimensionless index that ranges from 0 to ~20000. Low values indicate minimal or no risk of tree dieoff during drought, either or both because there are few trees in the pixel and/or there is ample local moisture even during periods of extreme precipitation shortfall. High values indicate significant risk of tree dieoff during drought, as a result of both a high density of trees at the site and likelihood of extreme local moisture shortfall.

A quantitative continuous variable that reflects the risk of tree dieoff
during a significant drought period (SPI48 drought = -2).

* Creation Method: Calculated by combining information on the local moisture balance and tree density. Local moisture balance was calculated as the ratio of Annual Evapotranspiration with the canopy observed in 2021 to Precipitation during a SPI 48 drought = -2 based on local P observations during 1991-2020. This ratio quantifies the local moisture deficit/surplus that would be expected during a 48-month period with precipitation that is 2 standard deviations below the local 30 year Normal. Tree cover was determined from Landsat. **** See https://doi.org/10.1038/s41561-019-0388-5 for further information.  

* Credits: CECS;