Extreme rainfall indices in Distrito Federal, Brazil: Trends and links with El Nino southern oscillation and Madden-Julian oscillation

摘要

This study investigates trends and the effects of the interannual and intraseasonal climate variability on the extreme weather of Brazil's capital city Distrito Federal (DF). This area is highly vulnerable to climate variability, having suffered from droughts and floods that affected the drinking water supply and agriculture. We perform trend analysis of 12 rainfall-related indices from 13 ground observation stations and assess the influence of El Nino southern oscillation (ENSO) and Madden-Julian oscillation (MJO) on rainfall totals and extreme indices. The trend analysis confirms: (a) the increase of the dry spells length and (b) the anticipation of the onset of dry periods at regional level. That is also true when considering dry spells in the rainy season, a hazard known in the agriculture sector as veranico. On the other hand, extreme wet conditions became less severe in the last decades. Supressed monthly rainfall conditions, and some wet indices, are associated with La Nina episodes. The MJO's intraseasonal variability seems to play a substantial role in DF's climate. MJO phases 3, 7 and 8 are associated to enhanced rainfall conditions; whereas rainfall is supressed during phase 5. Moreover, dry spells during the rainy season, or veranico, often coincide with MJO phase 5. When combined with ENSO, the basic response of rainfall to MJO activity changes substantially showing statistically significant influence of El Nino on phases 2 and 8; while La Nina on phases 4, 6 and 7. The findings contribute to a better understanding of the ongoing changes in extreme climate as well as the influence of natural climate variability on local's climate, information that can be used in the management of water resources and land use of DF.