Simulating the connections of ENSO and the hydrology of the Blue Nile using a climate model of the tropics

Abstract. We simulate the observed statistical relationship between ENSO and the hydrology of the Blue Nile using the tropical-band version of the regional climate model RegCM4 (or Reg-TB) for the 28 yr period 1982–2009. An ensemble of 9 simulations is completed to investigate the role of ENSO in the hydrology of the Blue Nile catchment. Re-TB shows a good skill in simulating the climatology of temperature, outgoing long-wave radiation patterns as well as related atmospheric circulation features during the summer season (i.e. the rainy season over the Blue Nile catchment). The model also succeeds in reproducing the observed negative correlation between Pacific SST and rainfall anomalies over the Blue Nile catchment, and in particular the association of droughts over the Blue Nile with El Niño events that start during the April–June period. We thus propose that observations as well as model forecasts of Pacific SST during this season should be used in seasonal forecasting of the Blue Nile flow.