Disaggregation of Daily Rainfall for Flood Estimation in a Monsoonal Catchment

James Ball, Phuong Cu Thi

Thursday 2 july 2015

14:35 - 14:50h at Europe 2 (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Flood risk assessment

Parallel session: 12K. Floodrisk - Assessment

Rainfall is one of the more important factors influencing flows in a river and particularly so for flood flows in a river. Hence there is a need to adequately model rainfall if flows in rivers are to be predicted with reliability. There are three components to a rainfall model, namely the rainfall depth, the spatial distribution of rainfall and the temporal distribution of rainfall. This last aspect of a rainfall model is the focus of the study that will be presented in this paper. In many Asian countries, the data for assessing the sub-daily temporal distribution of rainfall is limited by the availability of continuous records. It is far more common for the available data to comprise daily rainfall records. There is a need, therefore to disaggregate these daily rainfall records. One method that has been applied to the problem of disaggregation of daily rainfall records is the “Method of Fragments”. Presented herein will be a discussion of the application of the “Method of Fragments” to the disaggregation of daily rainfall records in a monsoonal catchment in Vietnam. The case study catchment is the Ba River where 14 daily-read gauges and 12 hourly rainfall stations across the basin were available. The similarity of statistical characteristics of these gauges was evaluated by Welch Two Sample t-test and Bartlett test of homogeneity of variances. The model is validated at 3 stations, where recorded hourly data was available. Hourly rainfall of 14 stations is then disaggregated from daily data based on the historical observed hourly data from 12 hourly stations in the basin.