Decadal Patterns of Climate Factors and Their Influence on Vegetation Condition Across Five Tillamook County (OR) Watersheds

The purpose of this report is monitoring, which is an essential element in natural resources management. Conservation of natural resources, for example, requires a well-established plan that includes a monitoring program to determine outcomes, and verify and validate these outcomes. These analyses can provide researchers and environmental decision-makers with early warning signals for widespread general trends as well as a means to identify specific areas where land conditions are degrading or improving. In this report we describe long term changes in greenness and climatic factors for the Tillamook basin from 1989 to 2019. Changes in greenness across terrestrial landscapes can result from human activities or natural processes. The rate of losing or gaining greenness may occur over short or long periods of time depending on the individual activity or combined activities. Long-term data sets of greenness typically cover large landscapes, and when paired with weather and land-use data, provide an opportunity to quantify spatial and temporal changes in vegetation, and their rates. This analysis of temporal trends of greenness is conducted to quantify changes, and the direction of these changes, in the Tillamook basin using statistical models. Rapid changes in greenness were found to indicate the presence of local factors such as fire, agriculture, and removal of greenspace, whereas gradual changes in greenness can be related to changes in climatic factors directly, or indirectly such as tree mortality from disease. The report describes the temporal trend in selected climatic factors and greenness and their correlation using time series analyses. Results summarize changes in greenness as related to local or climatic factor changes. Within the Tillamook basin, several areas were examined via Google Earth and leveraging local expert knowledge to validate the cause of change in greenness. Section 3 describes and characterizes climatic factors (minimum, maximum, mean, and dewpoint temperatures, and minimum and maximum vapor pressure deficit, and derived climatic factors (potential evapotranspiration, moisture index and apparent temperature)) over 31 years. This section also describes seasonal precipitation (wet and dry seasons) and seasonal anomalies (seasonal total precipitation > seasonal average) that were analyzed to characterize trends and other statistics. The statistical analyses were applied in each pixel and results were mapped to visualize changes in the Tillamook basin. 

Impact/Purpose

EPA developed a comprehensive conservation and management plan (CCMP) for Tillamook Bay following designation of the bay as “an estuary of national significance” and was included in National Estuary program (NEP) in 1999 (www.oregon.gov/deq/FilterDocs/NCtilloverview.pdf).  Tillamook Bay provides many goods and services, and source of economy to locals and many others. ORD’s Pacific Ecological Systems Division (PESD) of the Center for Public Health and Environment Assessment (CPHEA) has prepared a report that: (1) assembles a case study to monitor and quantify changes in vegetation cover over the Tillamook Basin using remote sensing, the Normalized Difference Vegetation Index (NDVI), an indicator of greenness; and (2) describes long term changes in greenness and climatic factors for the Tillamook basin from 1989 to 2019. Changes in greenness across terrestrial landscapes can result from human activities or natural processes. The rate of losing or gaining greenness may occur over short or long periods of time depending on type of an individual activity or combined activities. Long-term data sets of greenness typically cover large landscapes, and when paired with weather and land-use data, provide an opportunity to quantify spatial and temporal changes in vegetation, and their rates. The analyses of temporal trends of greenness are done to quantify changes, and direction of changes, in Tillamook basin using statistical models. Rapid changes in greenness indicate the presence of local factors such as fire, agriculture, removal of greenspace, whereas gradual changes in greenness can be related to changes in climatic factors directly, or indirectly such as tree mortality from disease.  Long-term monitoring is an essential element in natural resources management. Conservations of natural resource, for example, requires a well-established plan that includes a monitoring program to determine outcomes, and verify and validate these outcomes.

Citation

Nash, M., Matt Harwell, M. Van Fossen, D. Rosenbaum, AND T. Dewitt. Decadal Patterns of Climate Factors and Their Influence on Vegetation Condition Across Five Tillamook County (OR) Watersheds. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-25/337, 2025.

• NASH_ETAL-TILLAMOOK_NDVI-REPORT FINAL-508 COMPLIANT.PDF (PDF)  (NA  pp, 7.8 MB, about PDF)