Skip to main content

 

NFDRS

Home

Goals & Objectives

Document Templates

Library

Curriculum

Incident Action Plans

Data Introduction

Fire Occurrence

Weather

GIS & NIFC AGOL

Calendar Events

FireFamilyPlus

WIMS

Links

Fuel Models

Nelson Model

Models Introduction

Growing Season Index

WFAS

Policy Docs & Agency Guidelines

Growing Season Index (GSI)

NFDRS header graphic. Decorative.

 

The Growing Season Index (GSI) In NFDRS 2016, controls live fuel moistures, replacing the 1000-hour and X1000 controls in the 1978/88 versions. The moisture bounds  (30-250 for herbaceous and 50-200 for woody shrubs) and behavior of annuals versus perennials are maintained.

 The Growing Season Index is a simple metric of plant physiological limits to photosynthesis. It is highly correlated to the seasonal changes in both the amount and activity of plant canopies. It predicts the green-up and senescence of live fuels and the influence of water stress events on vegetation. Increasing values of GSI indicate periods of improving conditions for live fuels and decreasing values indicate periods of detrimental weather conditions. GSI is calculated as a function of the three indicators of important weather factors that regulate plant functions. These indicators are combined into a single indicator that integrates the limiting effects of temperature, water and light deficiencies. The importance of each of the three indicators is explained below and a summary of the Growing Season is given at the conclusion.

Minimum Temperature

Many of the biochemical processes of plants are sensitive to low temperatures. Although ambient air temperatures certainly influence growth, constraints on phenology appear to be more closely related to restrictions on water uptake by roots when soil temperatures are sub optimal and many field studies show variable ecosystem responses over a range of minimum temperatures.

Vapor Pressure Deficit (VPD)

Water stress causes partial to complete stomatal closure, reduces leaf development rate, induces the shedding of leaves, and slows or halts cell division. Although models are available to calculate a soil water balance, they require knowledge of rooting depth, soil texture, latent heat losses, and precipitation. As a surrogate, we selected an index of the evaporative demand, the vapor pressure deficit (VPD) of the atmosphere.

Photoperiod or Daylength

Photoperiod provides a plant with a reliable annual climatic cue because it does not vary from year to year at a given location. We assume that photoperiod provides the outer envelope within which other climatic controls may dictate foliar development. Studies have shown that photoperiod is important to both leaf flush and leaf senescence throughout the world.

Upper and lower limits of the indicator functions used to calculate the Growing Season

Input VariableUnconstrained (1)Completely Limiting (0)
Minimum Temperature5ºC /41º F-2ºC /28º F
Vapor Pressure Deficit (Pascals)900 Pascals4100 Pascals
Photoperiod (Daylength)11 hours10 hours

Learn more about the Growing Season Index (GSI)

 

NWCG Latest Announcements

NEW! S-231, Engine Boss Course Available Now

Date:  March 6, 2026
Questions? 
Please contact: Incident Operations Subcommittee

NWCG is pleased to announce the new S-231, Engine Boss (Single Resource) course is now available on the Wildland Fire Learning Portal (WFLP). Developed through the Incident Performance and Training Modernization (IPTM) effort, this training supports individuals working towards Engine Boss, Single Resource (ENGB) incident qualifications. 

This is a performance-based instructor-led training (ILT) that focuses on the application of ENGB responsibilities during wildland fire operations, emphasizing readiness, information gathering, risk management, engine tactics, and Wildland Urban Interface (WUI) operations. Trainees apply these skills through scenario-based group work and an optional field day that reinforces hands-on engine operation tasks. 

References:

S-231, Engine Boss (Single Resource) (Instructor-led)

NWCG Engine Boss, Single Resource (ENGB) Position Page

Wildland Fire Learning Portal

NWCG Celebrates 50 Years!

Date:  March 6, 2026
Questions? 
Please contact: NWCG Executive Secretary

NWCG is proud to celebrate 50 years of service to the wildland fire community. Beginning in 1976 with an interagency agreement between the Department of Interior and Department of Agriculture, NWCG has grown to include additional member agencies and is recognized as the standard-setting leader in wildland fire operations.

To honor where we’ve been and highlight where we are going, the NWCG team has created a video showcasing our history and accomplishments. The video is now available on the NWCG website.

References:

NWCG 50 Year Anniversary Video

NEW! S-131, Firefighter Type 1 Course Available Now

Date:  March 6, 2026
Questions? 
Please contact: Incident Operations Subcommittee

NWCG is pleased to announce the new S-131, Firefighter Type 1 course is now available on the Wildland Fire Learning Portal (WFLP). Developed through the Incident Performance and Training Modernization (IPTM) effort, this course is a performance-based instructor-led training (ILT) that focuses on the application of situational awareness and decision making, building on the knowledge and concepts introduced in previous required courses. Using a threaded fictitious fire, each unit focuses on a performance-based activity in which students practice applying their decision-making and problem-solving skills.

The S-131, Firefighter Type 1 course is required for individuals seeking qualifications to be a Firefighter Type 1 (Squad Boss) (FFT1) or an Incident Commander Type 5 (ICT5).

References:

S-131, Firefighter Type 1 (Instructor-led)

NWCG Firefighter Type 1 (Squad Boss) Position Page

NWCG Incident Commander Type 5 Position Page

Wildland Fire Learning Portal

2026 Professional Reading List

Date: March 4, 2026
Questions? 
Please contact: WFLDP Curriculum Management

The Wildland Fire Leadership Development Program (WFLDP) is announcing the 2026 Professional Reading List.  The goal of the annual reading list is to promote the reading and discussion of the selected books throughout the year. 

The six books chosen for this year are: How to Win Friends and Influence People by Dale Carnegie; Leadership Strategy and Tactics by Jocko Willink; Meditations by Marcus Aurelious; Quiet by Susan Cain; The Little Book of Stoic Quotes by Phil Van Treuren; and The Confident Mind by Nate Zinsser.

References:

Professional Reading Program

Wildland Fire Leadership Development Program