Exploration of an adaptive merging scheme for optimal precipitation estimation over ungauged urban catchment

Sherien Fadhel, Miguel Angel Rico-Ramirez, Dawei Han
2016 Journal of Hydroinformatics  
General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: ABSTRACT Merging raingauge-radar data improves the accuracy of precipitation estimation for urban areas. Since the rain gauge network around the ungauged urban catchment is fixed, the relevant research question is about the optimal merging area that produces the best rainfall estimation inside the catchment. To
more » ... swer this, an incremental radar-gauge merging performed by gradually increasing: the distance from the centre of the study area, the number of merging gauges around it and the radar domain. The proposed adaptive merging scheme is applied to a small urban catchment in west Yorkshire, Northern England for 118 extreme events from 2007 to 2009. The performance of the scheme is assessed using four experimental raingauges installed inside the study area. The result shows that there is indeed an optimum radar-gauge merging area and consequently there is an optimum number of rain gauges that produce the best merged rainfall data inside the study area. Different merging methods produce different results for both classified and unclassified rainfall types. Although the scheme was applied on daily data, it's applicable to other temporal resolutions. This study is of important value for other studies such as urban flooding analysis, since it provides improved rainfall estimation for ungauged urban catchment. The density of the rain gauge network has a great impact on the performance of the rainfall merging method (Jewell and Gaussiat 2013; Jewell and Gaussiat 2015). A denser rain gauge network produces a more precise estimation of the observed rainfall field (Ballester and More 2007). Recent studies related to rain gauge network density have investigated the sensitivity of the network density based on different rainfall merging methods (Villarini et al.2008; Goudenhoofdt and Delobbe 2009; Nanding et al. 2015) . The analyses show that the sensitivity of the more complex merging methods (e.g., geostatistical interpolations) is higher than that for simpler merging methods (e.g., the mean field bias corrections). Moreover, the performance of geostatistical merging improves with the increase of the network density. Jewell and Norman (2014) developed a more refined procedure for gauge quality control to improve the gauge density used for merging by maximizing the number of gauges used for merging and at the same time reducing the error resulted from gauge measurements. It was found that the quality of the merged rainfall over a 15 minute time scale was improved. Berndt et al. (2014) showed that the conditional merging method outperformed both Kriging with External Drift (KED) and indicator KED. The authors checked the performance of merged rainfall for seven cases ranged from 10 minutes to 6 hours and also included 5 different scenarios of rain gauge network densities, from low to high network densities. In contrary Jewell and Gaussiat (2015) showed that the KED method overwhelmed other geostatistical merging methods, which is the reason that KED may be adopted by the Met Office as its favoured method for real time radar-gauge merging in England and Wales. Published studies mainly addressed the issue of merging radar and gauge data over a large domain. However, in many cases urban areas lack of a rain gauge network, and there is a lack of studies assessing the performance of the rainfall merged product inside ungauged catchments. The challenge is how to select relevant rain gauges around the study area for the merging. By conventional thinking, the more gauges within a fixed area, the better the results due to the increased gauge density; but in this case, the situation is not so straightforward because the gauges will be outside the study area. The only way to increase the number of gauges is to increase the merging area (i.e. more gauges are included).
doi:10.2166/hydro.2016.022 fatcat:pikpgxhionbpbbdl5br7oqdhgu