Understanding Drought

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Understanding Drought

• Gloria Forthun
• Regional Climatologist
• Southeast Regional Climate Center

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Drought Characteristics
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Drought Characteristics

• Normal part of climate variability

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Drought Characteristics

• Normal part of climate variability
• No universal definition

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Drought Characteristics

• Normal part of climate variability
• No universal definition
• Complex interdisciplinary

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Drought Characteristics

• Normal part of climate variability
• No universal definition
• Complex interdisciplinary
• Impacts can be economic, social, environmental

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Drought Characteristics

• Normal part of climate variability
• No universal definition
• Complex interdisciplinary
• Impacts can be economic, social, environmental
• Impacts can linger for years

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Drought Vs. Other Natural Disasters
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Drought Vs. Other Natural Disasters

• Onset and end of drought is difficult to
  determine

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Drought Vs. Other Natural Disasters

• Onset and end of drought is difficult to
  determine
• No precise and universally accepted definition of
  drought

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Drought Vs. Other Natural Disasters

• Onset and end of drought is difficult to
  determine
• No precise and universally accepted definition of
  drought
• Nonstructural impacts and spread over a large
  geographic area

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Types of Drought
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Types of Drought

• Common to all droughts is that they originate
  from a deficiency of precipitation that results
  in water shortage for some activity or for some
  group.

National Drought Mitigation Center
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Types of Drought

• Meteorological Drought

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Types of Drought

• Meteorological Drought
• Measured in terms of the degree of dryness
  (intensity) and the duration of the dry period

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Types of Drought

• Meteorological Drought
• Measured in terms of the degree of dryness
  (intensity) and the duration of the dry period
• Region Specific

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Types of Drought

• Agricultural Drought

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Types of Drought

• Agricultural Drought
• Meteorological drought that impacts agriculture

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Types of Drought

• Agricultural Drought
• Meteorological drought that impacts agriculture
• Usually the first economic sector to be hit

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Types of Drought

• Agricultural Drought
• Meteorological drought that impacts agriculture
• Usually the first economic sector to be hit
• Precipitation shortages, ET, soil moisture, etc

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Types of Drought

• Agricultural Drought
• Meteorological drought that impacts agriculture
• Usually the first economic sector to be hit
• Precipitation shortages, ET, soil moisture, etc
• Plant water demand versus available soil moisture
  

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Types of Drought
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Types of Drought

• Hydrologic Drought

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Types of Drought

• Hydrologic Drought
• Impacts of rainfall shortages on the hydrologic
  system (groundwater, rivers, lakes, reservoirs)

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Types of Drought

• Hydrologic Drought
• Impacts of rainfall shortages on the hydrologic
  system (groundwater, rivers, lakes, reservoirs)
• Communities vary in degree of vulnerability
  depending on their water source

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Types of Drought

• Hydrologic Drought
• Impacts of rainfall shortages on the hydrologic
  system (groundwater, rivers, lakes, reservoirs)
• Communities vary in degree of vulnerability
  depending on their water source
• Connections between basins, regions affect other
  regions

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Types of Drought

• Hydrologic Drought
• Impacts of rainfall shortages on the hydrologic
  system (groundwater, rivers, lakes, reservoirs)
• Communities vary in degree of vulnerability
  depending on their water source
• Connections between basins, regions affect other
  regions
• Out of phase or lag meteorological drought

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Source National Water and Climate Center
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Types of Drought

• Socio-economic drought

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Types of Drought

• Socio-economic drought
• Demand exceeds supply of some economic product as
  a result of weather-related low precipitation
  event(s)

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Types of Drought

• Socio-economic drought
• Demand exceeds supply of some economic product as
  a result of weather-related low precipitation
  event(s)
• Precipitation or water represents SUPPLY, which
  varies by sector, DEMAND can be for products or
  for the water itself

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Types of Drought

• Socio-economic drought
• Demand exceeds supply of some economic product as
  a result of weather-related low precipitation
  event(s)
• Precipitation or water represents SUPPLY, which
  varies by sector, DEMAND can be for products or
  for the water itself
• Occurs more frequently
• change in how often or long a drought occurs
• in the vulnerability within society
• or both

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Differences Between Droughts
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Differences Between Droughts

• Intensity
• Degree of precipitation deficit and/or severity
  of impacts

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Differences Between Droughts

• Intensity
• Degree of precipitation deficit and/or severity
  of impacts
• Departure of a climate index from normal linked
  to duration to determine impacts

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Differences Between Droughts

• Duration

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Differences Between Droughts

• Duration
• Seasonal
• Single-year
• Multiple-years

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Differences Between Droughts

• Duration
• Seasonal
• Single-year
• Multiple-years
• Multiple timescales
• Example
• Year One below normal
• Year Two -- near normal timing off for crop
  demand
• Year Three near normal not enough to recover
  from hydrologic drought.

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Differences Between Droughts

• Spatial Extent

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Differences Between Droughts

• Spatial Extent
• Regional in nature
• Result of large scale anomalies in atmospheric
  circulation patterns

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Differences Between Droughts

• Spatial Extent
• Regional in nature
• Result of large scale anomalies in atmospheric
  circulation patterns
• One or more regions, one or more states

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Differences Between Droughts

• Spatial Extent
• Regional in nature
• Result of large scale anomalies in atmospheric
  circulation patterns
• One or more regions, one or more states
• Can shift from season to season

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Risk and Vulnerability
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Risk and Vulnerability

• Hazard Probability of occurrence, within a
  specified area and time, of a potentially
  damaging natural event (drought)

Wilhite, 1997
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Risk and Vulnerability

• Hazard
• Vulnerability Characteristics of people,
  activities, or the environment that makes them
  susceptible to the impacts of drought measure of
  the ability to anticipate, cope with, resist, and
  recover from the impacts of drought

Wilhite, 1997
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Risk and Vulnerability

• Hazard
• Vulnerability
• Risk Result of exposure to hazard and
  vulnerability

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Drought
Reduction in rainfall over an extended period of
time
Social Component Demand exceeds Supply
Intensity
Duration
Spatial Extent
Natural Hazard
Vulnerability
RISK
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Monitoring Drought

• Why should we monitor drought?

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Monitoring Drought

• Why should we monitor drought?
• Determine the current status of specific
  resources

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Monitoring Drought

• Why should we monitor drought?
• Determine the current status of specific
  resources
• Detect changes and long-term trends

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Monitoring Drought

• Why should we monitor drought?
• Determine the current status of specific
  resources
• Detect changes and long-term trends
• Obtain knowledge of fundamental linkages and
  processes at work

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Monitoring Drought

• Why should we monitor drought?
• Determine the current status of specific
  resources
• Detect changes and long-term trends
• Obtain knowledge of fundamental linkages and
  processes at work
• Enable development and implementation of early
  warning indicators

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Monitoring Drought

• What is needed to monitor drought?

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Monitoring Drought

• What is needed to monitor drought?
• Combination of climate, soil, and water data

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Monitoring Drought

• What is needed to monitor drought?
• Combination of climate, soil, and water data
• Local and regional coverage

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Monitoring Drought

• What is needed to monitor drought?
• Combination of climate, soil, and water data
• Local and regional coverage
• Impact assessments

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Monitoring Drought

• What is needed to monitor drought?
• Combination of climate, soil, and water data
• Local and regional coverage
• Impact assessments
• Drought Indices

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Monitoring Drought

• Importance of Drought Indices

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Monitoring Drought

• Importance of Drought Indices
• Simplify complex interrelationships and provide a
  good communication tool for many audiences

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Monitoring Drought

• Importance of Drought Indices
• Simplify complex interrelationships and provide a
  good communication tool for many audiences
• Quantitative assessment of climate conditions

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Monitoring Drought

• Importance of Drought Indices
• Simplify complex interrelationships and provide a
  good communication tool for many audiences
• Quantitative assessment of climate conditions
• Provide a historical perspective that can be used
  in planning and design applications

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Drought Indices

• Percent of Normal Precipitation

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Drought Indices

• Percent of Normal Precipitation
• Simple measurement of rainfall

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Drought Indices

• Percent of Normal Precipitation
• Simple measurement of rainfall
• Effective when used for a single region or single
  season

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Drought Indices

• Percent of Normal Precipitation
• Simple measurement of rainfall
• Effective when used for a single region or single
  season
• Disadvantage Mean (average) is not the same as
  the median (value exceeded by 50 of
  precipitation events)

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Drought Indices

• Percent of Normal Precipitation
• Simple measurement of rainfall
• Effective when used for a single region or single
  season
• Disadvantage Mean (average) is not the same as
  the median (value exceeded by 50 of
  precipitation events)
• Example Mean precipitation 1.26, Median
  .77, half the years are above .77 and half are
  below .77. Using the mean, .77 would be 61 of
  normal

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Drought Indices

• Standardized Precipitation Index

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Drought Indices

• Standardized Precipitation Index
• Based only on precipitation

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Drought Indices

• Standardized Precipitation Index
• Based only on precipitation
• Normalized distribution so values are standard
  deviations from the median

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Drought Indices

• Standardized Precipitation Index
• Based only on precipitation
• Normalized distribution so values are standard
  deviations from the median
• Developed for multiple time scales to show
  impacts on different water resources

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Data from the Western Regional Climate Center
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Drought Indices

• Palmer Drought Severity Index

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Drought Indices

• Palmer Drought Severity Index
• Advantages
• Based on precipitation, temperature, and local
  available water content of the soil

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Drought Indices

• Palmer Drought Severity Index
• Advantages
• Based on precipitation, temperature, and local
  available water content of the soil
• Most effective for impacts sensitive to soil
  moisture conditions

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Drought Indices

• Palmer Drought Severity Index
• Advantages
• Based on precipitation, temperature, and local
  available water content of the soil
• Most effective for impacts sensitive to soil
  moisture conditions
• Provides a measurement of the abnormality of
  recent weather

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Drought Indices

• Palmer Drought Severity Index
• Advantages
• Based on precipitation, temperature, and local
  available water content of the soil
• Most effective for impacts sensitive to soil
  moisture conditions
• Provides a measurement of the abnormality of
  recent weather
• Places current conditions in a historical
  perspective

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Drought Indices

• Palmer Drought Severity Index
• Disadvantages

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Drought Indices

• Palmer Drought Severity Index
• Disadvantages
• Values for intensity, beginning of drought, and
  ending of drought are arbitrary and the same
  across US

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Drought Indices

• Palmer Drought Severity Index
• Disadvantages
• Values for intensity, beginning of drought, and
  ending of drought are arbitrary and the same
  across US
• Assumes no runoff until soil is saturated

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Drought Indices

• Palmer Drought Severity Index
• Disadvantages
• Values for intensity, beginning of drought, and
  ending of drought are arbitrary and the same
  across US
• Assumes no runoff until soil is saturated
• Assumes no frozen precipitation or frozen ground

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Drought Indices

• Palmer Drought Severity Index
• Disadvantages
• Values for intensity, beginning of drought, and
  ending of drought are arbitrary and the same
  across US
• Assumes no runoff until soil is saturated
• Assumes no frozen precipitation or frozen ground
• Percent of time an area is in severe or extreme
  drought is greater than probability can account
  for

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Data from NOAA/CPC
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Drought Indices

• Crop Moisture Index

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Drought Indices

• Crop Moisture Index
• Derived from Palmer Drought Severity Index

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Drought Indices

• Crop Moisture Index
• Derived from Palmer Drought Severity Index
• Short term moisture conditions
• responds rapidly to changing conditions

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Drought Indices

• Crop Moisture Index
• Derived from Palmer Drought Severity Index
• Short term moisture conditions
• responds rapidly to changing conditions
• Useful for identifying potential agricultural
  drought

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Drought Indices

• Crop Moisture Index
• Derived from Palmer Drought Severity Index
• Short term moisture conditions
• responds rapidly to changing conditions
• Useful for identifying potential agricultural
  drought
• Misleading for long-term conditions

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Data from NOAA/CPC
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Drought Indices

• Z Index

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Drought Indices

• Z Index
• Monthly Moisture Anomaly Index

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Drought Indices

• Z Index
• Monthly Moisture Anomaly Index
• Moisture departure for the past 4 weeks and a
  climate weighting factor

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Drought Indices

• Z Index
• Monthly Moisture Anomaly Index
• Moisture departure for the past 4 weeks and a
  climate weighting factor
• Indicator of potential forest fire ignition

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Data from NOAA/CPC
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Drought Indices

• Surface Water Supply Index

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Drought Indices

• Surface Water Supply Index
• Indicator of surface water conditions where
  mountain snowpack is a major component

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Drought Indices

• Surface Water Supply Index
• Indicator of surface water conditions where
  mountain snowpack is a major component
• Calculated by river basin

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Drought Indices

• Surface Water Supply Index
• Indicator of surface water conditions where
  mountain snowpack is a major component
• Calculated by river basin
• Based on snowpack, streamflow, precipitation, and
  reservoir storage

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Drought Indices

• Surface Water Supply Index
• Indicator of surface water conditions where
  mountain snowpack is a major component
• Calculated by river basin
• Based on snowpack, streamflow, precipitation, and
  reservoir storage
• Needs to be re-evaluated if there are changes in
  water management within the basin

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NRCS/USDA
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National Drought Monitor

• Blends multiple indices and outlooks

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National Drought Monitor

• Blends multiple indices and outlooks
• Input from federal and academic scientists

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Drought In New Mexico

• Aztec Ruins National Park Northwest
• Albuquerque Central
• Carlsbad
• Southeast

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Understanding DroughtConclusions
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Understanding DroughtConclusions

• Normal part of climate variability

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Understanding DroughtConclusions

• Normal part of climate variability
• Onset and end of drought is difficult to
  determine

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Understanding DroughtConclusions

• Normal part of climate variability
• Onset and end of drought is difficult to
  determine
• Nonstructural impacts

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Understanding DroughtConclusions

• Differences Between Droughts

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Understanding DroughtConclusions

• Differences Between Droughts
• Intensity

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Understanding DroughtConclusions

• Differences Between Droughts
• Intensity
• Duration

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Understanding DroughtConclusions

• Differences Between Droughts
• Intensity
• Duration
• Spatial Extent

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Understanding DroughtConclusions

• Monitoring Drought
• Drought Indices

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Understanding DroughtConclusions

• Monitoring Drought
• Drought Indices
• Quantitative assessment of climate conditions

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Understanding DroughtConclusions

• Monitoring Drought
• Drought Indices
• Quantitative assessment of climate conditions
• Combination of drought indices to give overall
  picture of what is occurring

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Understanding DroughtConclusions

• Types of Drought

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Understanding DroughtConclusions

• Types of Drought
• Meteorological

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Understanding DroughtConclusions

• Types of Drought
• Meteorological
• Agricultural

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Understanding DroughtConclusions

• Types of Drought
• Meteorological
• Agricultural
• Hydrologic

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Understanding DroughtConclusions

• Types of Drought
• Meteorological
• Agricultural
• Hydrologic
• Socio-economic

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Understanding DroughtConclusions

• Types of Drought
• Meteorological
• Agricultural
• Hydrologic
• Socio-economic
• Hazard X Vulnerability Risk

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U.S. Census Bureau
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Thank you.

• Any questions?

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