Geoscience Reference
In-Depth Information
Tropical (30
o
S − 30
o
N)
15
(a)
GPCP v2.2
Historical
RCP 4.5
RCP 8.5
10
5
0
−5
10
5
0
−5
−10
−15
(b)
−20
1950
1960
1970
1980
1990
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100
Year
Fig. 6 Changes in tropical (30S-30N) mean precipitation (%) in a the wet regions (above the 70th
percentile of monthly precipitation) and in b the dry regions (below the 70th percentile) relative to the
1988-2005 period for the historical, RCP4.5 and RCP8.5 scenario simulations (thick lines denote 10-model
ensemble means, models 1-10 in Table
2
) and the GPCP observations. A 24-month running mean is applied
precipitation responses, as a function of precipitation intensity (P
i
), for the present day and
also the simulated climate change responses.
The 5-day P averages are constructed, and a deseasonalized intensity (i) distribution
constructed each month; 5-day averages are chosen to avoid structural inconsistencies
between data sets that occur at higher time resolutions (Liu and Allan
2012
). The linear
regression of P
i
is computed with respect to tropical mean T (deseasonalized anomalies)
and normalized by mean P
i
to give units of %/K. Figure
7
a illustrates the intensification of
P at the 99th percentile in both AMIP5 simulations and GPCP 1 Degree Daily (DD) V1.1
daily observations (Huffman et al.
2009
) of around 15 %/K, larger than expected from
Clausius-Clapeyron scaling. At the lowest percentiles, P
i
decreases with tropic-wide
warming, consistent with the monthly mean responses shown in Fig.
6
.
The GPCP 1DD observations generally show a similar but more positive response than
the AMIP5 simulations (Fig.
7
a), explained primarily by ocean regions, for P
i\99 %
(Fig.
7
b). The SSM/I observations display a more positive sensitivity still for these per-
centiles and do not capture the decline in P
i\60 %
with warming. This may be explained by
the limited sampling of low rain rates by the instantaneous overpasses (e.g., Liu and Allan
2012
). GPCP gauge-based observations and AMIP5 simulations display remarkable
agreement over the land (Fig.
7
c), consistent with monthly mean variability (Liu et al.
2012
); for P
i\99 %
the response is negative and explained by ENSO variability: during
warmer El Ni ˜o years, there is less rainfall on average over land (e.g., Gu et al.
2007
).
