Presentation by John Nielson-Gammon, State Climatologist and Professor of Atmospheric Science at Texas A&M University, at the 2018 Gulf Coast Water Conservation Symposium in Houston, Texas.

1. Seeking the New Abnormal
John Nielsen-Gammon
Texas A&M University
Texas State Climatologist

2. US Multi-Day Rainfall Records
John Nielsen-Gammon, Texas A&M University 2
0
10
20
30
40
50
60
70
80Rainfall(inches)
2 days 3 days 5 days 7 days

3. 0
5
10
15
20
25
AverageRainfall(inches)
Historic analyses: Applied Weather Associates; US Army Corps of Engineers
John Nielsen-Gammon, Texas A&M University 3

4. 0
5
10
15
20
25
AverageRainfall(inches)
33.28”
Historic analyses: Applied Weather Associates; US Army Corps of Engineers
John Nielsen-Gammon, Texas A&M University 4

5. (Central/Eastern) US Depth-Area-Duration
All-Time Records Before Harvey
John Nielsen-Gammon, Texas A&M University 5
AreaDuration 2 Days 3 Days 4 Days 5 Days
1,000 sq mi
Louisiana,
August 1940
Louisiana,
August 1940
Louisiana,
August 1940
Louisiana,
August 1940
2,000 sq mi
Louisiana,
August 1940
Louisiana,
August 1940
Louisiana,
August 1940
Louisiana,
August 1940
5,000 sq mi
Louisiana,
August 1940
Texas,
June 1899
Texas,
June 1899
Texas,
June 1899
10,000 sq mi
Georges,
Florida 1998
Texas,
June 1899
Texas,
June 1899
Texas,
June 1899
20,000 sq mi
Georges,
Florida 1998
Beulah,
Texas 1967
Beulah,
Texas 1967
Beulah,
Texas 1967
50,000 sq mi
Georges,
Florida 1998
Beulah,
Texas 1967
Beulah,
Texas 1967
Beulah,
Texas 1967

6. AreaDuration 2 Days 3 Days 4 Days 5 Days
1,000 sq mi
Louisiana,
August 1940 Harvey Harvey Harvey
2,000 sq mi Harvey Harvey Harvey Harvey
5,000 sq mi Harvey Harvey Harvey Harvey
10,000 sq mi Harvey Harvey Harvey Harvey
20,000 sq mi Harvey Harvey Harvey Harvey
50,000 sq mi Harvey Harvey Harvey Harvey
(Central/Eastern) US Depth-Area-Duration
All-Time Records After Harvey
John Nielsen-Gammon, Texas A&M University 6

7. 0
5
10
15
20
25
AverageRainfall(inches)
33.28”
Historic analyses: Applied Weather Associates; US Army Corps of Engineers
John Nielsen-Gammon, Texas A&M University 7

8. 0
5
10
15
20
25
AverageRainfall(inches)
33.28”
Historic analyses: Applied Weather Associates; US Army Corps of Engineers
John Nielsen-Gammon, Texas A&M University 8
Climate change rainfall contribution? (Me, guessing)

9. 0
5
10
15
20
25
AverageRainfall(inches)
33.28”
Historic analyses: Applied Weather Associates; US Army Corps of Engineers
John Nielsen-Gammon, Texas A&M University 9
Climate change rainfall contribution? (Me, guessing)
100,000 homes?
10,000 homes?
1,000 homes?

10. 0
5
10
15
20
25
AverageRainfall(inches)
33.28”
Historic analyses: Applied Weather Associates; US Army Corps of Engineers
John Nielsen-Gammon, Texas A&M University 10
100,000 homes?
10,000 homes?
1,000 homes?
Van Oldenborgh et al. (2017)
Climate change rainfall contribution? (Me, guessing)

11. 0
5
10
15
20
25
AverageRainfall(inches)
33.28”
Historic analyses: Applied Weather Associates; US Army Corps of Engineers
John Nielsen-Gammon, Texas A&M University 11
100,000 homes?
10,000 homes?
1,000 homes?
Van Oldenborgh et al. (2017)
Risser and Wehner (2017)
Climate change rainfall contribution? (Me, guessing)

12. John Nielsen-Gammon, Texas A&M University 12

13. John Nielsen-Gammon, Texas A&M University 13
8
10
12
14
16
18
20
22
24
1946 1956 1966 1976 1986 1996 2006 2016
Yearly Maximum Observed 2-Day Rain, Long-Term
Sta ons, Harris County
Maximum Observed 2-Day Rain Number of Sta ons Repor ng

14. John Nielsen-Gammon, Texas A&M University 14

15. John Nielsen-Gammon, Texas A&M University 15

16. John Nielsen-Gammon, Texas A&M University 16
Comparison with Risser & Wehner 2017,
http://onlinelibrary.wiley.com/doi/10.1002/2017GL075888/full

17. John Nielsen-Gammon, Texas A&M University 17

18. John Nielsen-Gammon, Texas A&M University 18
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta

19. 19
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta

20. 20
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta

21. 21
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000

22. 22
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
27,0009,000

23. 23
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000 27,000

24. 24
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000 27,000
41”

25. 25
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000 27,000
41”
34”

26. 26
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000 27,000
41”
34”
1900: 500-
y

27. 27
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000 27,000
41”
34”
1900: 500-
y

28. 28
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000 27,000
41”
34”
1900: 500-
y
2017: 175-
y

29. 29
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000 27,000
41”
34”
1900: 500-
y
2017: 175-
y

30. 30
3-DayRainfallTotal(inches)
0
6
12
18
24
30
36
42
48
http://iopscience.iop.org/article/10.1088/1748-9326/aa9ef2/meta
9,000 27,000
41”
34”
1900: 500-
y
2017: 175-
y
2055: 70-y

31. John Nielsen-Gammon, Texas A&M University 31
National Academy of Sciences, 2016

32. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 32
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
Increase

33. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 33
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
X
Increase

34. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 34
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
X
Increase
/

35. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 35
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
X
Increase
/

36. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 36
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
X
Increase
/

37. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 37
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
X
Increase
/

38. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 38
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
X
Increase
/

39. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 39
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
X
Increase
/
Historical

40. Drought: Consider the Possibilities
John Nielsen-Gammon, Texas A&M University 40
HeavyRainIntensity
Steady
Total Rainfall Amount
Increase Steady Decrease
X
Increase
/
Historical
Model
Projections

41. Messages
• Harvey was exceptional
• Odds of extreme rainfall have increased
– And will continue to increase
– Odds change ballpark estimate: Factor of 3 (2-8)
per °C global warming
– Amount change ballpark estimate: 15% (10-30%)
per °C global warming
John Nielsen-Gammon, Texas A&M University 41

42. More Messages
• Annual rainfall amounts have increased
– But may decrease in future
• Future drought intensity depends on:
– Intensity of heavy rain
– Overall rainfall amounts
– Increasing temperatures (a given)
• Houston has been unlucky
John Nielsen-Gammon, Texas A&M University 42

43. Comprehensive Rainfall Survey
(NSF-funded project)
• Data being collected
– Weather & climate (COOP, WBAN)
– Hydrological (HCFCD, LCRA)
– Popular networks (CoCoRaHS, WU)
– Independent “backyard” observers
• Analysts: Texas A&M, AWA, MetStat
• Please share your data!
– http://climatexas.tamu.edu/harvey/survey/
– n-g@tamu.edu
John Nielsen-Gammon, Texas A&M University 43

44. Bonus Slides
John Nielsen-Gammon, Texas A&M University 44

45. Measure of Stalling: Corral Size
• Contains all storm locations over three days

46. Image: New York Times 2017, with data from NWS, NASA GEOS, and IBTRACS
Harvey’s corral radius: 123 km centered at 12 UTC Aug 27
Average maximum sustained wind while stalled: 50 kt (26 m/s)

47. How Slow Can Tropical Cyclones Go?
0
5
10
15
20
25
30
35
0 200 400 600 800 1000 1200 1400 1600 1800
NumberofStorms
Smallest Corral Radius (km) for Each Storm
“Stalling”: 1 in 7.4

48. Stalled Tropical Cyclones:
Month, Intensity

49. 50
75
100
125
150
175
200
0 20 40 60 80 100 120
CorralRadius(km)
Average Wind Speed (kt)
200-400 inland 100-200 inland 0-100 inland 0-50 offshore
50-100 offshore 100-150 offshore 150-200 offshore
Coastal Stalls At Least As Slow and
Intense As Harvey
Flora
1963
5 Days
1910
Mitch
1998
Harvey
2017
One of 2 costliest
Atlantic storms ever
One of 5 deadliest
known Atlantic storms
One of 5 deadliest
known Atlantic storms

50. 50
75
100
125
150
175
200
0 20 40 60 80 100 120
CorralRadius(km)
Average Wind Speed (kt)
200-400 inland 100-200 inland 0-100 inland 0-50 offshore
50-100 offshore 100-150 offshore 150-200 offshore
Record Totals (mm)
2550
1300
760
236 1538
452
482
959
1148
308
676
830
541
707
1033
652
250
702
470
372
579 FL
US
GA
AL
CUBA
1576
MEXICO

51. Juan (1985)
John Nielsen-Gammon, Texas A&M University 51

52. Number of Coastal Stalls:
100 km inland to 50 km offshore
0
2
4
6
8
Other
Cuba
Mex/CentAm
USA

53. Probability of Harvey Rain
• Probability of strong stall
• Conditional probability of moisture channel
John Nielsen-Gammon, Texas A&M University 53

54. Stalled Tropical Cyclones:
Month, Intensity

55. Probability (per century) of Strong Stall
in 1°x1° Box
• 1917-2017: 0.08
• 1967-2017: 0.13
• Superstall (<100 km): 0.02
John Nielsen-Gammon, Texas A&M University 55

56. 0
5
10
15
20
25
30
35
40
45
50
1000 10000 100000
PrecipitationDepth(In)
Storm Area (Sq. Mile)
Comparison Between Harvey and
Probable Maximum Precipitation
Harvey 48-hr
PMP 48-hr
Harvey 72-hr
PMP 72-hr
Lines being below the square boxes means that Harvey did not exceed
the previously estimated Probable Maximum Precipitation for the Gulf region
Graphic by David Maidment, University of Texas at Austin
John Nielsen-Gammon, Texas A&M University 56

57. 0
5
10
15
20
25
30
AverageRainfall(inches)
Historic analyses: Applied Weather Associates
John Nielsen-Gammon, Texas A&M University 57

58. 0
5
10
15
20
25
30
AverageRainfall(inches)
Historic analyses: Applied Weather Associates
John Nielsen-Gammon, Texas A&M University 58

59. Contact Information
• John Nielsen-Gammon
• n-g@tamu.edu
• http://climatexas.tamu.edu
John Nielsen-Gammon, Texas A&M University 59