{ "snippet": "Characterize moisture deficit and surplus for the most recent 3-year period relative to long-term average.", "summary": "Characterize moisture deficit and surplus for the most recent 3-year period relative to long-term average.", "accessInformation": "USDA - GEO; USDA - USFS \u2013 GO", "thumbnail": "thumbnail/thumbnail.png", "maxScale": 1155581.108577, "typeKeywords": [ "ArcGIS Server", "Data", "Image Service", "Service" ], "description": "
Direct Download (Raster Data Gateway)<\/span><\/span><\/a><\/p> Objective:<\/span><\/span> Characterize current moisture deficit and surplus relative to the long-term average.<\/span><\/span><\/p> Data:<\/span><\/span> <\/span><\/span>The indicator represents areas of moisture deficit as a z-score. A z-score is a statistical method for assessing how different a value (i.e., most recent 3 years) is from the mean (historical average). The source climate data is from PRISM. Mean moisture values were derived from historical data on precipitation and Thornthwaite potential evapotranspiration, from 1900 to <\/span><\/span>t<\/span><\/span>-minus 4 (<\/span><\/span>t<\/span><\/span> = current TCA Assessment year). The greater the negative z-value, the larger the departure from average conditions, indicating larger moisture deficits.<\/span><\/span><\/p> These data highlight regions of moisture deficit as a z-score calculated from the reference time period and current conditions. There is a lag between the assessment year and the most recent drought data, for example, the 2024 TCA Assessment used 2021-2023 to represent current conditions and 1900-2020 for the reference time period. Data were summarized at the Subsection scale of the USFS National Hierarchy of Ecological Units and applied to the corresponding landscape (LTA).<\/span><\/span><\/p> Data Format:<\/span><\/span> Raster data are continuous<\/span><\/span><\/p> Units: <\/span><\/span>Mean difference in z-score<\/span><\/span><\/p> Spatial Resolution:<\/span><\/span> 4000m (4km)<\/span><\/span><\/p> Source data:<\/span><\/span> <\/span><\/span>PRISM<\/span><\/span><\/a>; <\/span><\/span>z-score calculations provided by the USFS Office of Sustainability and Climate based on the methods found here: <\/span><\/span>https://www.fs.usda.gov/research/treesearch/43361<\/span><\/span><\/a><\/p> Additional Resources:<\/span><\/span><\/p> Details on <\/span><\/span>Method Changes and Source Data Versions<\/span><\/span><\/a><\/p> Overview of the Terrestrial Condition Assessment: <\/span><\/span>TCA Hubsite<\/span><\/span><\/a> or <\/span><\/span>Landfire Office Hour Presentation<\/span><\/span><\/a><\/p> Explore the results of the most recent assessment: <\/span><\/span>TCA Interactive Data Viewer<\/span><\/span><\/a><\/p> Learn more about the TCA KPI: <\/span><\/span>TCA Dashboard<\/span><\/span><\/a><\/p>