Downscaling service - short term rainfall

SUDPLAN Newsletter 1 (December 2010): In SUDPLAN, an automated downscaling service has been developed which allows a user to upload a historical short-term rainfall time series and have it modified in line with the expected future changes in that particular location.

Design and evaluation of sewer system components and urban flood protective structures are critically dependent on the properties of short-term rainfall. As these components have an expected life time of up to 100 years, it is crucial to take climate change into account.

In SUDPLAN, an automated downscaling service has been developed which allows a user to upload a historical short-term rainfall time series and have it modified in line with the expected future changes in that particular location. This data may be used in hydrologic and hydraulic models to assess performance of existing or planned structures also in a changed climate.

Time series downscaling

The time series downscaling is performed by Delta Change, which generally means that future changes of the rainfall pattern, as estimated from climate model data, are transferred to observed data.

In the SUDPLAN rainfall downscaling service, future changes of the frequency distribution of 30-min rainfall intensities may be transferred to local short-term rainfall observations, by an approach recently developed at SMHI (Olsson et al., 2009).

The main output is a time series which differs from the user-uploaded one in two ways (see Figure 1). (1) In each time stamp, the observation year has been replaced by a future target year. (2) Each rainfall registration has been re-scaled to account for future changes in the probability distribution of short-term rainfall intensities. A tailor-made visualisation tool will be developed for easy graphical inspection and evaluation.

Downscaled rain
Figure 1 Example of original and downscaled rainfall time series from the SUDPLAN rainfall downscaling service.

In addition to the downscaled time series, the user will be provided with a table of percentage changes in different key rainfall properties (mean, maximum and frequency), separated into seasons (Table 1).

downscaled rain2
Table 1 Example of general rainfall changes from the SUDPLAN rainfall downscaling service.

The data, information and tools provided are intended to give the user a solid basis for urban hydrological climate change impact assessment.