Understanding Drought Gloria Forthun Regional Climatologist Southeast Regional Climate Center

Drought Characteristics

Drought Characteristics Normal part of climate variability

Drought Characteristics Normal part of climate variability No universal definition

Drought Characteristics Normal part of climate variability No universal definition Complex – interdisciplinary

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

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

Drought Vs. Other Natural Disasters

Drought Vs. Other Natural Disasters Onset and end of drought is difficult to determine

Drought Vs. Other Natural Disasters Onset and end of drought is difficult to determine No precise and universally accepted definition of drought

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

Types of Drought

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

Types of Drought Meteorological Drought

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

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

Types of Drought Agricultural Drought

Types of Drought Agricultural Drought Meteorological drought that impacts agriculture

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

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

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

Types of Drought

Types of Drought Hydrologic Drought

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

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

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

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

Source: National Water and Climate Center

Types of Drought Socio-economic drought

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

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

Types of Drought Socio-economic drought Occurs more frequently 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

Differences Between Droughts

Differences Between Droughts Intensity Degree of precipitation deficit and/or severity of impacts

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

Differences Between Droughts Duration

Differences Between Droughts Duration Seasonal Single-year Multiple-years

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.

Differences Between Droughts Spatial Extent Regions can be crop specific areas, climate divisions, water basins, coastal areas

Differences Between Droughts Spatial Extent Regional in nature Result of large scale anomalies in atmospheric circulation patterns Regions can be crop specific areas, climate divisions, water basins, coastal areas

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 Regions can be crop specific areas, climate divisions, water basins, coastal areas

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 Regions can be crop specific areas, climate divisions, water basins, coastal areas

Risk and Vulnerability

Risk and Vulnerability Hazard: Probability of occurrence, within a specified area and time, of a potentially damaging natural event (drought) Wilhite, 1997

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

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

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

Monitoring Drought Why should we monitor drought?

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

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

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

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

Monitoring Drought What is needed to monitor drought?

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

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

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

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

Monitoring Drought Importance of Drought Indices

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

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

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

Drought Indices Percent of Normal Precipitation Actual Precipitation divided by Normal Precipitation X 100%

Drought Indices Percent of Normal Precipitation Simple measurement of rainfall Actual Precipitation divided by Normal Precipitation X 100%

Drought Indices Percent of Normal Precipitation Simple measurement of rainfall Effective when used for a single region or single season Actual Precipitation divided by Normal Precipitation X 100%

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) Actual Precipitation divided by Normal Precipitation X 100%

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 Actual Precipitation divided by Normal Precipitation X 100%

Drought Indices Standardized Precipitation Index

Drought Indices Standardized Precipitation Index Based only on precipitation

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

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

Data from the Western Regional Climate Center 72 months = Nov. 1998 Data from the Western Regional Climate Center

Drought Indices Palmer Drought Severity Index Have PDSI back to 1895

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

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

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

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

Drought Indices Palmer Drought Severity Index Disadvantages Not used in other countries

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

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

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

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

Data from NOAA/CPC

Drought Indices Crop Moisture Index

Drought Indices Crop Moisture Index Derived from Palmer Drought Severity Index

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

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

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

Data from NOAA/CPC

Drought Indices Z – Index

Drought Indices Z – Index Monthly Moisture Anomaly Index

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

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

Data from NOAA/CPC

Drought Indices Surface Water Supply Index

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

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

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

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

NRCS/USDA

National Drought Monitor Blends multiple indices and outlooks No single index can be relied upon under all conditions

National Drought Monitor Blends multiple indices and outlooks Input from federal and academic scientists

Drought In New Mexico Aztec Ruins National Park Northwest Albuquerque Central Carlsbad Southeast

Understanding Drought Conclusions

Understanding Drought Conclusions Normal part of climate variability

Understanding Drought Conclusions Normal part of climate variability Onset and end of drought is difficult to determine

Understanding Drought Conclusions Normal part of climate variability Onset and end of drought is difficult to determine Nonstructural impacts

Understanding Drought Conclusions Differences Between Droughts

Understanding Drought Conclusions Differences Between Droughts Intensity

Understanding Drought Conclusions Differences Between Droughts Intensity Duration

Understanding Drought Conclusions Differences Between Droughts Intensity Duration Spatial Extent

Understanding Drought Conclusions Monitoring Drought Drought Indices

Understanding Drought Conclusions Monitoring Drought Drought Indices Quantitative assessment of climate conditions

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

Understanding Drought Conclusions Types of Drought

Understanding Drought Conclusions Types of Drought Meteorological

Understanding Drought Conclusions Types of Drought Meteorological Agricultural

Understanding Drought Conclusions Types of Drought Meteorological Agricultural Hydrologic

Understanding Drought Conclusions Types of Drought Meteorological Agricultural Hydrologic Socio-economic

Understanding Drought Conclusions Types of Drought Meteorological Agricultural Hydrologic Socio-economic Hazard X Vulnerability = Risk

U.S. Census Bureau

Thank you. Any questions?