Global Precipitation Observations and CMIP/AMIP Calculations: Means, Trends and Intensity Changes
Abstract
Monthly analyses of observed global precipitation from Global Precipitation Climatology Project are used to compare with both AMIP and CMIP results for the period of 1979-2014. Global mean precipitation during the period from GPCP is 2.7 +/- 0.2 mm/d compared to ensemble means from both AMIP and CMIP of about 3.0 mm/d, placing the models overall just outside of one s from the observational analysis. Most of the model excess precipitation is in the tropics along the ITCZ and the SPCZ..
The trend in mean global precipitation is slightly positive, as expected in the models, and this is roughly confirmed from the observations. However, there are distinct spatial patterns in precipitation trends over the 1979-2014 period in the observations (GPCP). In the tropics, the AMIP models, driven by observed SSTs, capture the positive trends near the Equator in the western Pacific, Indian Ocean and Atlantic and the northeast and southwest extensions from western Pacific maximum into the subtropics. The observations, however, have a narrow positive trend extending across most of the Pacific in the ITCZ that is not fully captured by the AMIP results. The CMIP ensemble results do not have the very large positive trend in the western Pacific/Maritime Continent region, but have the central/eastern Pacific maximum along the ITCZ, but much broader than the observations. When examining the trends in a zonal mean sense (over both land and ocean), the AMIP results are much closer to the observations in latitude distribution and magnitude than the CMIP results. Trends in intensity change in terms of precipitation percentile are also examined at the monthly scale as a function of latitude. At the ITCZ latitude all percentiles increase for both the observations and both types of models, although the CMIP results have a much broader (latitude-wise) and weaker feature. In the subtropics, the high percentiles (> 70th, more intense rainfall) increase and lower percentiles (< 50th, light monthly rainfall) decrease in the observations. Again, the models show similar results, though with detailed discrepancies, with the AMIP showing a closer pattern to the observations. In terms of the magnitude of the percentile changes, the models show much weaker trends than the observations, with the AMIP results much stronger than CMIP, but still about half the observed trend.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC42E..05A
- Keywords:
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- 1616 Climate variability;
- GLOBAL CHANGE;
- 1626 Global climate models;
- GLOBAL CHANGE;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE;
- 1866 Soil moisture;
- HYDROLOGY