Semi-arid Zone
The semi-arid zone (depicted in yellow at right) is generally characterized by annual precipitation of 10 to 20 inches (30-year average). In semi-arid regions, drought can be severe enough to impact herbage production for multiple years. The combination of grazing stress and drought stress results in declines in ecological condition in this region.
Transition Zone
A transition zone occurs between the semiarid and sub-humid climate zones to the east.
Sub-humid Zone
The sub-humid climate zone is characterized by relatively high humidity and cloud cover which diminishes the rate at which summer evening temperatures decline compared to the semiarid zone. In this zone (where average annual precipitation is more than 28 to 30 inches), drought effects on plant communities are often short lived. However, season-long continuous grazing during the growing season will still result in serious declines in range condition.