Drivers of future changes in East African precipitation

Precipitation amounts over East Africa have been declining over the last decades. These changes and future climate change over the region are highly debated. This study analyzes drivers of future precipitation changes over East Africa by applying a classification of circulation patterns on 15 historical and future members of the COordinated Regional climate Downscaling EXperiment. Typical circulation types (CTs) are obtained. Under a high emission scenario, changes in the frequency of occurrence of these CTs attribute for 23% of the total change in precipitation over East Africa by the end of the century. The remaining part (77%) is not related to East African synoptics, e.g. changes in moisture content, local/mesoscale feedbacks, and changes in moisture influx. These other effects comprise increases in precipitation close to the equator and the Somali region, while decreases are found over northwestern Ethiopia, the Sudan region and the lake areas.ISSN:1748-9326ISSN:1748-931

What is the surface mass balance of Antarctica? An intercomparison of regional climate model estimates

International audienceAbstract. We compare the performance of five different regional climate models (RCMs) (COSMO-CLM2, HIRHAM5, MAR3.10, MetUM, and RACMO2.3p2), forced by ERA-Interim reanalysis, in simulating the near-surface climate and surface mass balance (SMB) of Antarctica. All models simulate Antarctic climate well when compared with daily observed temperature and pressure, with nudged models matching daily observations slightly better than free-running models. The ensemble mean annual SMB over the Antarctic ice sheet (AIS) including ice shelves is 2329±94 Gt yr−1 over the common 1987–2015 period covered by all models. There is large interannual variability, consistent between models due to variability in the driving ERA-Interim reanalysis. Mean annual SMB is sensitive to the chosen period; over our 30-year climatological mean period (1980 to 2010), the ensemble mean is 2483 Gt yr−1. However, individual model estimates vary from 1961±70 to 2519±118 Gt yr−1. The largest spatial differences between model SMB estimates are in West Antarctica, the Antarctic Peninsula, and around the Transantarctic Mountains. We find no significant trend in Antarctic SMB over either period. Antarctic ice sheet (AIS) mass loss is currently equivalent to around 0.5 mm yr−1 of global mean sea level rise (Shepherd et al., 2020), but our results indicate some uncertainty in the SMB contribution based on RCMs. We compare modelled SMB with a large dataset of observations, which, though biased by undersampling, indicates that many of the biases in SMB are common between models. A drifting-snow scheme improves modelled SMB on ice sheet surface slopes with an elevation between 1000 and 2000 m, where strong katabatic winds form. Different ice masks have a substantial impact on the integrated total SMB and along with model resolution are factored into our analysis. Targeting undersampled regions with high precipitation for observational campaigns will be key to improving future estimates of SMB in Antarctica