1. WAFB Chief Meteorologist LSU AgCenter Climatologist
Flooding in the Amite Basin:
Increased Threat in the Coming Months?
Jay Grymes
WAFB Chief Meteorologist
LSU AgCenter Climatologist
Strengthening El Niño?

2. Flooding in the Amite Basin: Increased Threat in the Coming Months?
-- reviewed daily mean stage for ‘Amite nr Denham Springs’
for the period Oct 1974 – present
data courtesy of USGS, Louisiana
-- “flood events” defined as at least one day with
daily mean stage ≥ 29.0 ft
-- “moderate flood” defined as at least one day with
daily mean stage ≥ 35.0 ft
-- “major flood” defined as instantaneous stage ≥ 39.0 ft

3. Nov-to-Mar Rainfall: Departure from Normal
El Nino Winter/Springs:
Rainfall Below Normal
Rainfall Above Normal

4. El Niño ‘Signature’ along the Gulf Coast: ‘Active’ Sub-Tropical Jet
More Frequent
Gulf Lows
“Warm” SSTs

5. December-thru-May Rainfall: Louisiana EC Climate Division
El Niño
El Niño/Southern Oscillation
(ENSO) Ranking
La Nada
“Neutral”
La Niña
Series Median
6-mo. Rainfall (in.)
Seasonal rainfall
tends to be greater
during El Niño events
Rainfall Data: NOAA/National Climatic Data Center
ENSO Ranks: NOAA/NWS Climate Prediction Center

6. Amite River near Denham Springs Flood Events: Oct 1974 – Present
by Month
51 Events
-- 4 as ‘tropical’
-- 3 in summer/fall
‘Babe’
(1977)
‘Gustav’
(2008)
‘Juan’
(1985)
‘Allison’
(2001)
River Stage Data: USGS, Louisiana

7. Amite River near Denham Springs Flood Events: Oct 1974 – Present
by Month
51 Events
Apr & Apr 1983
. . . ‘major’ floods
both during El Niños
‘Major’ Floods: > 39 ft
1983
1977
1990
River Stage Data: USGS, Louisiana

8. Amite River near Denham Springs Flood Events by Year: 1974 – Present
(All Months)
River Stage Data: USGS, Louisiana

9. Amite River near Denham Springs Flood Events by Year: 1974 – Present
(December thru May)
‘Major’ Floods:
> 39 ft
River Stage Data: USGS, Louisiana

10. NWS/CPC ENSO ONI Index: Jan-Feb-Mar Index Score
35 Seasons: 9 El Niños & 9 La Niñas
El Niño
La Niña
ONI Index: NWS Climate Prediction Center

11. NWS/CPC ENSO ONI Index: Jan-Feb-Mar Index Score
& Occurrences of Winter/Spring Floods 5 1
El Niños:
16 floods
in 9 seasons
El Niño 1 2 3 1 1 2
La Niñas:
5 floods
in 9 seasons 1 1 1 2
La Niña
No ‘moderate’ to ‘major’ floods
La Nadas:
23 floods in 17 seasons
ONI Index: NWS Climate Prediction Center

12. Climatic
Regime
Ratio
Floods : Seasons
El Niño
1.8 : 1
La Nada
1.4 : 1
La Niña
0.6 : 1
Tropical
0.1 : 1

13. Flooding in the Amite Basin: Increased Threat in the Coming Months?
Climatic
Regime
Ratio
Floods : Seasons
El Niño
1.8 : 1
La Nada
1.4 : 1
La Niña
0.6 : 1
Tropical
0.1 : 1
While flooding in the coming months is not a certainty, climatic signals
(El Niño) point to an elevated threat of ‘high water’ along the Amite
near Denham Springs and therefore much of the greater Amite Basin.