HR: 17:45h
AN: H24C-08    [Abstracts]
TI: On the seasonal predictability of daily rainfall characteristics over Indonesia
AU: * Robertson, A W
EM: awr@iri.columbia.edu
AF: International Research Institute for Climate and Society (IRI), Columbia University Lamont Campus, Palisades, NY 10964, United States
AU: Moron, V
EM: moron@cerege.fr
AF: University of Aix-Marseilles (CEREGE), Europôle de l'Arbois, Aix en Provence, NY 13545, France
AU: Swarinoto, Y
EM: yunus@bmg.go.id
AF: Bureau of Meteorology and Geophysics (BMG), Indonesia, Jl. Angkasa I No. 2, Kemayoran, Jakarta, NY 10720, Indonesia
AB: Using Indonesia as a case study, we investigate the seasonal predictability of monsoonal rainfall in terms of its daily characteristics, including rainfall frequency, mean daily intensity, mean length of dry spells, as well as the onset date of the rainy season. Our methodology consists of retrospective seasonal forecasts made with the ECHAM4.5 atmospheric GCM driven by SST predictions made with the constructed analog method (1979-2002). The seasonal forecast is then "downscaled" to the station scale using a non-homogeneous hidden Markov model, to produce large ensembles of stochastic daily rainfall sequences from which the statistic of interest is calculated and compared against station data. Particular attention is paid to probabilistic measures of skill, including conditional exceedance probabilities. Our key findings are that rainfall frequency and mean dry-spell length are more skillfully hindcast than the seasonal total of rainfall for the September–December season. The date of monsoon onset is also found to be highly predictable in these experiments. Supporting evidence will be presented from analyses of the spatial coherence properties of these various daily rainfall characteristics computed from station data. We argue that these findings may have important potential uses in agricultural and water resource management.
DE: 1816 Estimation and forecasting
DE: 1847 Modeling
DE: 1854 Precipitation (3354)
DE: 1869 Stochastic hydrology
DE: 1873 Uncertainty assessment (3275)
SC: Hydrology [H]
MN: 2007 Fall Meeting