1. Understanding Drought
Gloria Forthun
Regional Climatologist
Southeast Regional Climate Center

2. Drought Characteristics

3. Drought Characteristics
Normal part of climate variability

4. Drought Characteristics
Normal part of climate variability
No universal definition

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

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

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

8. Drought Vs. Other Natural Disasters

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

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

11. 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

12. Types of Drought

13. 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

14. Types of Drought
Meteorological Drought

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

16. 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

18. Types of Drought
Agricultural Drought

19. Types of Drought Agricultural Drought
Meteorological drought that impacts agriculture

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

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

22. 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

23. Types of Drought

24. Types of Drought
Hydrologic Drought

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

26. 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

27. 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

28. 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

29. Source: National Water and Climate Center

31. Types of Drought
Socio-economic drought

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

33. 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

34. 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

35. Differences Between Droughts

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

37. 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

38. Differences Between Droughts
Duration

39. Differences Between Droughts
Duration
Seasonal
Single-year
Multiple-years

40. 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.

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

42. 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

43. 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

44. 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

45. Risk and Vulnerability

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

47. 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

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

49. 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

50. Monitoring Drought
Why should we monitor drought?

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

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

53. 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

54. 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

55. Monitoring Drought
What is needed to monitor drought?

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

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

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

59. 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

60. Monitoring Drought
Importance of Drought Indices

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

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

63. 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

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

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

66. 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%

67. 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%

68. 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%

70. Drought Indices
Standardized Precipitation Index

71. Drought Indices Standardized Precipitation Index
Based only on precipitation

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

73. 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

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

75. Drought Indices
Palmer Drought Severity Index
Have PDSI back to 1895

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

77. 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

78. 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

79. 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

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

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

82. 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

83. 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

84. 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

85. Data from NOAA/CPC

86. Drought Indices
Crop Moisture Index

87. Drought Indices Crop Moisture Index
Derived from Palmer Drought Severity Index

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

89. 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

90. 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

91. Data from NOAA/CPC

92. Drought Indices
Z – Index

93. Drought Indices
Z – Index
Monthly Moisture Anomaly Index

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

95. 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

96. Data from NOAA/CPC

97. Drought Indices
Surface Water Supply Index

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

99. 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

100. 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

101. 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

102. NRCS/USDA

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

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

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

116. Understanding Drought Conclusions

117. Understanding Drought Conclusions
Normal part of climate variability

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

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

120. Understanding Drought Conclusions
Differences Between Droughts

121. Understanding Drought Conclusions
Differences Between Droughts
Intensity

122. Understanding Drought Conclusions
Differences Between Droughts
Intensity
Duration

123. Understanding Drought Conclusions
Differences Between Droughts
Intensity
Duration
Spatial Extent

124. Understanding Drought Conclusions
Monitoring Drought
Drought Indices

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

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

127. Understanding Drought Conclusions
Types of Drought

128. Understanding Drought Conclusions
Types of Drought
Meteorological

129. Understanding Drought Conclusions
Types of Drought
Meteorological
Agricultural

130. Understanding Drought Conclusions
Types of Drought
Meteorological
Agricultural
Hydrologic

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

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

134. U.S. Census Bureau

135. Thank you.
Any questions?