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

2025 Wildland Fire EMS Awards

Date:  June 12, 2026
Questions? 
Please contact: Emergency Medical Committee

The NWCG Emergency Medical Committee (EMC) announces the recipients of the 2025 Wildland Fire Emergency Medical Service (EMS) Awards. EMC annually recognizes individuals and groups who have demonstrated outstanding actions or accomplishments that are above and beyond the expectation of one’s normal mission or job duties.

Congratulations to all the awardees and nominees. Through leadership and initiative, they have made significant contributions to the safety of the wildland fire community. These awards are well deserved.

References:

2025 Wildland Fire EMS Awards

Emergency Medical Committee

Incident Position Standards and the Next Generation Position Task Book Now Available for RAMP

Date:  June 12, 2026
Questions? 
Please contact: Airtanker Base Operations Unit

NWCG is excited to announce that Incident Position Standards and the Next Generation Position Task Book are now available for Ramp Manager (RAMP).

The Performance Support Package for this position was developed as part of the Incident Performance and Training Modernization effort. These resources support trainees, qualified personnel, and evaluators in their respective roles.

Any changes to qualification pathways will take effect with the next update of the NWCG Standards for Wildland Fire Position Qualifications, PMS 310-1, scheduled for release in January 2027.

References:

NWCG Ramp Manager Position Page

National Interagency Aviation Committee

Make an Impact: Serve the Wildland Fire Community as an IPTM SME!

Date:  June 11, 2026
Questions? 
Please contact: NWCG SME Specialist

Note: Positions with an * will last approximately 6 months.
Positions with ** will last 12 - 18 months.

NWCG is seeking experienced wildland firefighters and support personnel to serve as Subject Matter Experts (SMEs) for the Incident Performance and Training Modernization (IPTM) initiative. IPTM aims to transition NWCG’s training and qualification system to a performance-based model by updating position descriptions, Incident Position Standards, Next Generation Position Task Books (Next Gen PTBs), and training where needed.

NWCG is currently recruiting SMEs for the Fall 2026 positions listed below:

  • Equipment Manager (EQPM)*
  • Fixed Wing Parking Tender (FWPT)**
  • Mixmaster (MXMS)*
  • Public Information Officer Complex (PIOC)*
  • Retardant Crewmember (RTCM)*
  • Strike Team Leader Crew (STCR)*
  • Strike Team Leader Engine (STEN)*
  • Strike Team Leader Heavy Equipment (STEQ)*
  • Task Force Leader (TFLD)**
  • Wildland Fire Investigator (INVF)** 

Projects begin October 2026. Sign up by July 10, 2026, at the link below and review the attached document for additional details. 

References:

NWCG SME Interest Sign-up

IPTM Subject Matter Expert Duties and Expectations Document

Incident Performance and Training Modernization (IPTM)

RMC Safety Bulletin 26-001: Rhabdomyolysis in Wildland Firefighters

Date:  May 28, 2026
Questions? 
Please contact: Risk Management Committee

The Risk Management Committee (RMC) has issued Safety Bulletin 26-001: Rhabdomyolysis in Wildland Firefighters. Research from 2016 to 2025 shows that 88 cases of rhabdomyolysis (rhabdo) were reported. Analysis of reports from eSafety, the Safety Management Information System (SMIS), and the Wildland Fire Lessons Learned Center (LLC) indicates that rhabdo is common during this time of year due to Work Capacity Tests and contributing factors such as weather, hydration, nutrition, and medication or supplement use.

RMC issued this safety bulletin to raise awareness in the Wildland Fire Community, and to provide research findings and educational resources that support reducing future cases of rhabdo.

References:

NWCG Alerts

RMC Safety Bulletin 26-001: Rhabdomyolysis in Wildland Firefighters