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Drought & Flood Planning

There are approximately five common definitions of drought. Keep in mind that "flooding" is simply the extremes. Many of the things we can do to mitigate drought can also help mitigate floods. Drought and floods are two sides of the same coin. 


Definitions 2-5 stem from meteorological drought (precipitation deficit) and describe impacts to different natural and human systems.

  1. Meteorological drought – Below normal precipitation for an extended time - ranging from a season to several years. Different than aridity, which is a permanent feature of a region’s climate characterizing low average precipitation.

  2. Hydrological drought – A lack of water in the hydrological system (both surface and groundwater) due to precipitation shortfalls. Often, hydrological drought and its impacts lag behind meteorological drought.

  3. Agricultural/Soil moisture drought – Impacts to dryland and/or irrigated agriculture due to precipitation shortfalls, reduced groundwater or surface water supplies and soil water deficits. This can be exacerbated by high air temperature, low humidity and wind.

  4. Socioeconomic drought – Impacts of drought conditions on supply and demand of economic goods (e.g. Lost income from crops in 2017 in eastern Montana and the Yellowstone River closure in 2016 resulting in a loss of tourism revenue in Park County). *Note, FWP did not consider the river closure in 2016 an official “drought” closure.   

  5. Ecological drought – “An episodic deficit in water availability that drives ecosystems beyond thresholds of vulnerability, impacts ecosystem services and triggers feedbacks in natural and/or human systems.” (Crausbay & Ramirez, 2017)

​Assessing Drought


Assessing drought is complex and relies on a combination of precipitation, snowpack, streamflow, groundwater, air temperature, soil moisture and other data that are often used to create a single-value “index” of drought. Drought indices have changed over time as monitoring capabilities and understanding of drought have improved. Drought indices are often used to establish a “level” of drought severity that links to financial response programs (e.g. USDA’s Livestock Forage Program that provides compensation for grazing losses due to drought).

Common Drought Indices:


Palmer Drought Severity Index (PDSI): First drought index. Still widely used. Based on precipitation, air temperature and soil moisture.

Palmer Hydrologic Drought Index (PHDI): Derived from the PDSI to understand long-term impacts of meteorological drought on water. It is a measure of long-term hydrologic drought that accounts for the timelag in hydrologic systems after a meteorological drought.

Surface Water Supply Index (SWSI):  Used for snowpack-dependent watersheds. SWSI values range from “extremely wet” to “extremely dry” and account for snowpack, mountain precipitation, streamflow, reservoir storage and soil moisture conditions.

Standardized Precipitation Evapotranspiration Index (SPEI): Incorporates precipitation and accounts for impacts of air temperatures on water demand (potential evapotranspiration).

Vegetation Drought Response Index (VegDRI): Generated weekly, depicting fine spatial resolution of vegetation stress using satellite imagery, climate data, PDSI and SPI, land cover, and soil characteristics.

Evaporative Demand Drought Index (EDDI): An experimental drought monitoring and early warning tool. Accounts for atmospheric evaporative demand, or “atmospheric thirst,” for a given location across a range of time from one week to one year. EDDI can provide early warning of agricultural drought and flash drought.

Monitoring Drought

The U.S. Drought Monitor began in 1999 as a combined effort of the National Drought Mitigation Center (NDMC) at the University of Nebraska-Lincoln, the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Department of Agriculture. The NDMC produces weekly maps of drought conditions across the United States. Figure 2 depicts Montana’s drought status as of Thursday, October 25, 2018.


The State of Montana’s Drought Monitoring Subcommittee provides Montana’s drought data to the U.S. Drought Monitor on a weekly basis. The Drought Monitoring Subcommittee includes Montana-based representatives from the following organizations:

  • Montana Department of Natural Resources and Conservation (DNRC)

  • Montana Department of Fish Wildlife & Parks (FWP)

  • Montana Bureau of Mines and Geology (MBMG)

  • Montana Department of Agriculture (DOA)

  • Montana Disaster and Emergency Services (DES)

  • Montana State Library

  • Montana Association of Counties (MACO)

  • Montana Climate Office,

  • U.S. Geological Survey (USGS)

  • National Oceanic and Atmospheric Administration (NOAA)

  • Farm Services Agency (FSA)

  • USDA National Agricultural Statistics Service (NASS)

  • National Weather Service (NWS)

  • Fort Belknap Tribe 

Watershed groups, conservation districts and municipalities across Montana use drought indices, U.S. Drought Monitor maps and water supply data to assess and communicate about water supply in their areas. Photos 1 and 2 demonstrate water supply communication tools used by Broadwater County Conservation District and the City of Bozeman.  

Drought Predictions


10 day weather forecasts have exponentially improved from the 1960's today. As scientific models get better, the hope is that longer-term predictions of drought can help communities better prepare for the future. Montana State University and other researchers published a report that attempts to provide multiple scenarios that we are facing in the Greater Yellowstone area. The full study can be found here. A summary of the possible trends we are facing is below. And many of the details behind this study can be found in the Upper Yellowstone Watershed summit presentations which you can read here.

GY Climate Assessment.png
Drought Response


Drought response involves actions taken during or after a drought. Drought response plans may involve triggers that initiate some action when indicators such as water supply or water temperature reach or exceed certain thresholds. The UYWG is working on our own drought response plan with community buy-in from all stakeholders.

Example of a Drought Plan: The Big Hole River Watershed Committee has had a voluntary drought response plan in place since 1997. The plan relies on cooperation from several entities including landowners, anglers, agencies and others to keep enough water in the Big Hole River during summer months to prevent impacts to fluvial Arctic Grayling.

Drought Impacts and Community Responses


The core of a drought planning effort revolves around being able to identify a community’s vulnerabilities to drought across its major water use sectors (agriculture, stock, municipal, domestic, industrial, recreation, tourism, fish and wildlife).

Identifying drought impacts (historical and present) greatly relies on input from various stakeholders, especially long-time residents of an area. Once stakeholders identify how their community is impacted by drought, they can begin to identify direct actions that will reduce drought vulnerability.  

Drought Adaptation

Drought adaptation encompasses a range of multi-sector actions taken before a drought occurs to minimize drought impacts. The U.S. Bureau of Reclamation structures drought adaptation planning guidelines around the following questions (posed to a community):

  • How will we recognize the next drought in the early stages? (assessment and monitoring)

  • How will drought affect us? (impacts and vulnerabilities)

  • How can we protect ourselves from the next drought? (adaptation and resilience)

Drought adaptation = sound water supply management.


(General) examples of multi-sector drought adaptation:

  1. Reduce water demand.

  2. Increase irrigation headworks, conveyance and on-farm efficiencies.

  3. Improve floodplain connectivity to enhance natural groundwater storage and boost late-season streamflow.

  4. Improve soil health (porosity) and water-holding capacity. 

  5. Enhance riparian area health through grazing management.

  6. Restore side channel and tributary connectivity in large river systems to enhance cold water refugia for fish.

  7. Plant drought-tolerant crops and forage.

  8. Shift timing of fishing to early morning and late evening.

(Specific) Voluntary Actions taken by some UYWG Alfalfa Producers:

  1. Allow the crop to be mature and dry at the time of the last cutting so that the plants will go into dormancy. However, if irrigation water is reduced but available all of the growing season, deferring irrigation until the temperatures cool in late August and September may be a good strategy.

  2. Use moderate irrigation rates on fewer acres rather than lightly irrigating all acres. Spreading water on more acres results in lower average tons of hay per inch of water efficiency because a larger percentage of water is evaporated from the soil as compared to what is transpired through the plant. Thus more total alfalfa yield is produced on fewer acres with deficit irrigation.

  3. Apply water to the best soils and dry up shallow or marginal irrigation sets.

  4. Severe drought and plant death are more likely in sandy soils. Plants will resume growth if the roots and crowns have not dried out. Avoid irrigating drought-induced dormant alfalfa until late in the fall, when lower temperatures will maintain dormancy. This will preserve stored root reserves for winter maintenance and spring growth (Fransen 2001).

  5. Replace worn nozzles which can apply up to 50% excess water. Repair leaks which can result in unproductive water losses of up to 30% of system capacity, and shut off inefficient equipment, such as end guns.

Specific Volunteer Actions taken by some UYWG Tourism Businesses:


Soil health improvement through use of cover crops, no-till farming and other methods can improve water retention capacity and bolster resilience during drought.

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