Layer: Multidecadal Repeat-Dryness Exposure Index (2000-2022, May-Sept) (ID: 2)

Name: Multidecadal Repeat-Dryness Exposure Index (2000-2022, May-Sept)

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Description: Multidecadal Repeat-Dryness Exposure Index (MDAEI). This dataset depicts spatial locations that are prone to reoccurrence of atmospheric precipitation levels below the long-term average from 1948-2021 during the warm season (May-September). Arid climatic conditions during the warm season have been identified to predispose forested ecosystems to disturbance with impacts to wildfire area burned and enhance forest vulnerability to bark beetle infestations (Holden et al. 2018 https://www.pnas.org/doi/10.1073/pnas.1802316115; Egan et al. 2023, in press). The MRDEI is a climate-based indicator that represents locations that have experienced repeat-dryness during warm season throughout the long-term dry cycle that has impacted western U.S. from 2000-2021. This dataset was derived from the standardized precipitation index (SPI; Guttman 1999: https://drought.unl.edu/archive/Documents/NDMC/Workshops/136/Ref/SPI_Guttman.pdf; McKee et al. 1993 https://www.droughtmanagement.info/literature/AMS_Relationship_Drought_Frequency_Duration_Time_Scales_1993.pdf) that was calculated at 16 km2 resolution, respectively for each of 481k grid cells across the conterminous U.S., using the Parameter-elevation with independent slope model dataset (PRISM, Daly et al. 1994) and normalized across 1948-2021 period by fitting Gamma distribution, using observations to compute Cumulative Distribution Function (CDF), then evaluating CDF with inverse Gaussian function to derive final SPI anomaly values (Holden and Hoylman 2023 https://doi.org/10.5281/zenodo.7921890, https://zenodo.org/record/7921890). Then, the temporal frequency of dry anomalies for each site-specific grid cell was calculated from 2000-2021, scaled by severity of dry anomaly with <= -3 SPI severe dry as a baseline, and divided by the baseline to represent cumulative percent (%) of years with severe dry equivalence (Egan et al. 2023, in press) Egan et al. 2023. Association of Multidecadal Repeat-Dryness with Bark Beetle and Wildfire Forest Disturbances from 2000-2022 across conterminous United States. In press: Forest Health Monitoring: National Status, Trends, and Analysis. 2023 National Report. Map and Data Disclaimer: The USDA Forest Service makes no warranty, expressed or implied, including the warranties of Merchant ability and fitness for a particular purpose, and assumes no legal liability or responsibility for the accuracy, reliability, completeness, or utility of these geospatial data, or for the improper or incorrect use of these geospatial data. These geospatial data and related maps or graphics are not legal documents and are not intended to be used as such. The data and maps may not be used to determine title, ownership, legal descriptions or boundaries, legal jurisdiction, or restrictions that may be in place on either public or private land. Natural hazards may or may not be depicted on the data and maps, and land users should exercise due caution. The data are dynamic and may change over time. The user is responsible to verify the limitations of the geospatial data and to use the data accordingly.

Copyright Text: USDA Forest Service

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