Unraveling East Africa’s

Climate Paradox

Bradfield Lyon

Alessandra Giannini, Nicolas Vigaud

Our Common Future under

Climate Change

7-10 July 2015

Paris, France

“Long Rains”

“Short Rains”

The Region

1

“Long Rains”

“Short Rains”

The Region The Paradox

March-May “Long Rains” Season

Observed 1999-2014 Projected 2020-2050

1

Some Hypotheses

•Climate models are missing, or misrepresenting, key aspects of

the ACC signal Models are wrong, the future will be drier, not wetter.

•What paradox? The recent drying is associated with “natural” processes

that are masking climate change It’s a mismatch of timescales, the

future will become wetter (in both the short- and long-term).

•The jury is still out. The recent drying is largely due to natural variability,

but the models are not capturing the climate change signal correctly

In the short-term it will likely become wetter. After that…???

East Africa: A Climate Paradox?

2

Evidence for a Recent and Abrupt Climate Shift

East Africa Rainfall Index (GPCC)

East Africa OLR Index (NOAA)

1999

1999

Leading EOF, Mar-May Rainfall

1999

3

Lyon and DeWitt (2012, GRL)

Evidence for a Recent and Abrupt Climate Shift

East Africa Rainfall Index (GPCC)

East Africa OLR Index (NOAA)

1999

1999

Leading EOF, Mar-May Rainfall

1999

3

Lyon and DeWitt (2012, GRL)

Evidence for a Recent and Abrupt Climate Shift

West Pacific SST Gradient Anomaly

Std. MAM SST Anomaly 1999-2014

Obs. Pac. Warm Pool PRCP Anomaly

AMIP (7 models) Warm Pool PRCP Anom.

1999

1999

1999

cold warm

4

Lyon (2015, AGU Book Chapter)

Evidence for a Recent and Abrupt Climate Shift

EOF1 Pac. SST (remove ENSO, Trend)

5 Lyon (2014, J. Climate)

r = 0.72

p < 0.05

PRCP Anomaly Cold PDO Phases

EOF1 Pac. SST (remove ENSO, Trend)

Evidence for a Recent and Abrupt Climate Shift

5 Lyon (2014, J. Climate)

r = 0.72

p < 0.05

Evidence for a Recent and Abrupt Climate Shift

ECHAM Model MAM Rainfall Anomaly 1999-2013

Observed, global SST

Observed, Tropical Pac. SST

MODEL FORCING

De-trended, global SST, GHG = 1880

Thanks to Marty Hoerling, NOAA/ESRL for 1880 runs…

6 Lyon (2015, AGU Book Chapter)

CMIP5 Model Simulations of the Current Climate

Observed CMIP5

Climatological “Short” and “Long”

rainy seasons are reversed in

CMIP5 models rel. to observations.

Monthly Rainfall Climatology, Current Climate

Obs. show less warming than

CMIP5 in the eq. East Pacific

in the current climate

CMIP5 generate too much

warming in the western Indian

Ocean relative to obs.

7 Yang et al. (2014, J. Climate)

CMIP5 models

amplify current SST

biases in projections

CMIP5 Model Projections: SST

west east

8 Yang et al. (2014, J. Climate), Lyon (2015, AGU Book Chapter)

Conclusions

References ------------------------------------------------------------------------------------------------------------------------------------------------------

This work was supported by funding from the NSF

and NASA, which is gratefully acknowledged.

• Lyon, B., 2014: Seasonal Drought in the Greater Horn of Africa and its Recent Increase

during the March-May Long Rains. Journal of Climate, 27, 7953-7975.

• Yang, W., R. Seager, M.A. Cane, and B. Lyon, 2014: The East African Long Rains in

Observations and Models. Journal of Climate, 27, 7185-7202.

• Lyon, B., and D.G. DeWitt, 2012: A Recent and abrupt decline in the East African long

rains. Geophysical Research Letters, DOI: 10.1029/2011GL050337. --------------------------------------------------------------------------------------------

• Recent drying during the long rains primarily due to decadal variability

of Tropical Pacific SSTs.

• Its possible ACC may have acted to enhance the severity of recent

droughts, but it cannot account for the abrupt nature of the recent

decline or past decadal periods of drought, such as 1914-1925.

• CMIP5 models exhibit major errors in simulating the obs. East African

climate and large scale SST patterns. These errors are amplified in

projections Little confidence in current projections of EA climate.