Colorado headwaters-Plateau

Average air temperature looks at how warm or cool a year was overall. This is a helpful metric in comparing conditions across years. For the Forest Health Index, average air temperature is measured using a combination of air temperatures from across your watershed.

Extreme high temperatures in the summer stress forests and wildlife. These days increase water loss from transpiration and can damage trees. Additionally, extreme high temperature days increase the risk and severity of wildfires.

To measure extreme high temperature days the FHI looks at temperature measurements from a combination of on-the-ground sensors and satellite data. We count the number of days each summer that exceed 90th percentile in a normal summer about 10 days will meet this criteria.

Fire plays an important role in ecology, helping to rejuvenate disturbance-driven systems and bring diversity to the age and type of plants in the forest. In the last century, however, humans have changed when and where fires happen on the landscape—sometimes starting fires themselves, sometimes preventing fires from spreading.

For the FHI, the indicator for fire risk rates how likely to occur unplanned forest fires are by looking at a combination of factors that create fire-ready conditions, such as air temperature, rain, dryness of the air, and wind.

Total annual precipitation refers to the amount of water that fell from the sky in the last year. This includes rain and the water in snow, sleet, and hail. Precipitation plays an important role in plant survival, fire risk, insect outbreaks, and river levels.

For the Forest Health Index, we use the average amount of precipitation across the watershed. This approach gives a better sense of what is happening across the forested region as a whole, rather than looking at data from a single location.

Frost Free Days describes the number of continuous days between the last freeze in spring and the first freeze in fall. It is often associated with the growing season for many farmed or wild plants.

For the Forest Health Index, data are drawn from the Nation Climatic Data Center and the National Weather Service.

High elevation snowpack refers to of the amount of snow that piles up in the mountains during the winter. It is measured by how much water you would have if you took a column of snow and melted it—the “snow water equivalent” (SWE). In Colorado, human communities and ecosystems alike rely on snowpack to help supply the water we need to survive, and high elevation snowpack also provides critical habitat for wildlife throughout the winter.

Snowpack in the Colorado mountains is measured by the SNOw TELemetry network (SNOTEL). For this indicator, we look at the SWE for Colorado SNOTEL sites measured on April 1st of each year—the time in Colorado when snowpack is usually near its deepest for the winter.

Bears are not just an interesting animal: because they rely on healthy forests to survive, they are also an excellent indicator of forest health. Aside from the success or failure of forest forage crops (the foods bears eat, such as berries and nuts), other factors that may influence bear mortality include bear population size, new development of human homes and cities, and timing of when bears wake-up from hibernation.

In the Forest Health Index, bear mortality refers to the number of bears found dead from January through August, the season during which bears cannot legally be hunted. These deaths may be caused by natural events, roadkill, bears put down by federal or state officials, bears killed by landowners, or unknown causes.

In the Forest Health Index, Insects and Disease scores the amount of tree mortality caused by pests such as beetles and funguses. Tree-threatening diseases and insects, like bark beetles, play a natural role in the life cycle of forests. However, more intense or longer-lasting levels of infestation can disrupt forest ecosystems and change which species are most successful.

For the Forest Health Index, the insect and disease indicator uses maps generated by aerial surveys to measure the amount of dead or dying trees.

Ozone (O3) is a chemical compound found in the upper layer of our atmosphere, as well as close to the ground. In the upper layer of the atmosphere, ozone helps to protect life by protecting our planet from the sun’s ultra-violet rays, but ground-level ozone is considered a pollutant and can harm human and plant health.

The Forest Health Index looks only at ground-level ozone. Measurements are drawn from local air quality stations that measure ozone and other harmful pollutants.

Peak streamflow refers to the date in spring when water levels in the river are highest. When water comes and how much is available are important factors for forests and for the humans living downstream of them. Timing of peak streamflow is determined by warming temperatures, depth of the snowpack, and soil moisture going into winter, as well as timing of diversions (when humans move water to a location other than its natural flow).

For this indicator, we look at peak spring streamflow for the year. Peak streamflow typically happens in May or June and is closely tied to snowmelt. The data for this indicator come from US Geological Survey streamflow gauges in your watershed.

Soil moisture refers to how much water is being held in the ground at any given time. It is important in determining whether plants are able to grow, flower, and survive. It also plays a role in how much water reaches streams and rivers during rain storms or spring snow melt.

For the Forest Health Index, we use soil moisture data from GRACE, a NASA satellite that uses changes in gravity to measure water on Earth’s surface and in the ground. It operates at a broad scale, grouping together moisture from 16 mile (or more) areas. It can provide a good general sense of whether a summer is wetter or drier than the year before and reveal when soil is drying from month to month.

Humans have a dramatic impact on the landscapes we inhabit. Communities can moderate their impact by using fewer resources, conserving water and electricity, and reducing trash.

The FHI tracks resource use as the amount of energy used per person in each watershed. Communities that are reducing their per person energy use are more likely to be reducing other sources of consumption as well. Per capita energy is also influence by business and industry energy use, and changes in local businesses can alter local community energy footprints.