Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Hydrol. Earth Syst. Sci. Discuss., 8, 7237–7259, 2011 Hydrology and www.hydrol-earth-syst-sci-discuss.net/8/7237/2011/ Earth System HESSD doi:10.5194/hessd-8-7237-2011 Sciences 8, 7237–7259, 2011 © Author(s) 2011. CC Attribution 3.0 License. Discussions Predicted and This discussion paper is/has been under review for the journal Hydrology and Earth observed System Sciences (HESS). Please refer to the corresponding final paper in HESS precipitation if available. M. Curi´ c´ and D. Janc Analysis of predicted and observed Title Page accumulated convective precipitation in Abstract Introduction the area with frequent split storms Conclusions References Tables Figures M. Curi´ c´ and D. Janc J I Institute of Meteorology, University of Belgrade, 11000 Belgrade, Serbia J I Received: 26 May 2011 – Accepted: 6 July 2011 – Published: 22 July 2011 Back Close Correspondence to: M. Curi´ c´ (curic@ff.bg.ac.rs) Published by Copernicus Publications on behalf of the European Geosciences Union. Full Screen / Esc Printer-friendly Version Interactive Discussion 7237 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract HESSD Convective clouds generate extreme rainfall events and flash floods in small areas with both large spatial and temporal variability. For this reason, the monitoring of the 8, 7237–7259, 2011 total accumulated precipitation fields at the surface with rain gauges and meteorolog- 5 ical radars has both strengths and weakness. Alternatively, a numerical cloud model Predicted and may be a useful tool to simulate convective precipitation for various analyses and pre- observed dictions. The main objective of this paper is to show that the cloud-resolving model precipitation reproduces well the accumulated convective precipitation obtained from the rain gauge network data in the area with frequent split storms. We perform comparisons between M. Curi´ c´ and D. Janc 10 observations and model samples of the areal accumulated convective precipitation for a 15-yr period over treated area. Twenty-seven convective events have been selected. Statistical analyses reveal that the model areal accumulated convective precipitation Title Page closely match their observed values with a correlation coefficient of 0.80. Abstract Introduction 1 Introduction Conclusions References Tables Figures 15 Flash floods in small areas leading to huge material damage and loss of life are mainly caused by convective precipitation. The correct reproduction of both its spatial and temporal distribution contributes to the improvements on hydrological analysis and pre- J I dictions. Meteorologists have two main tools to estimate convective precipitation at the J I ground: rain gauge and meteorological radar data. Although rain gauges measure 20 accumulated precipitation accurately, the spatial pattern of convective precipitation is Back Close poorly represented due to the limited resolution and spot-like coverage of the observa- Full Screen / Esc tional network (Barnolas et al., 2010). Meteorological radars may be a better option in little basins or in regions where convection is important. However, radar data have im- portant disadvantages because they are an indirect measure of rainfall and with worse Printer-friendly Version 25 results of rainfall depth in a given location compared to rain gauge data (Hunter, 1996; Interactive Discussion Young et al., 1999). Many studies, therefore, have been realized to minimize radar errors (Chumchean et al., 2006). 7238 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Various rainfall models are developed depending on the availability of radar data and the rain gauge network spatial resolution (Willems, 2001; Sayed et al., 2003). Despite HESSD that, the best approach is to use various numerical cloud models that are capable of 8, 7237–7259, 2011 simulating the accumulated convective precipitation with a higher spatial and temporal 5 resolution independently of availability of radar data and rain gauge network density. This is important to predict and reconstruct the accumulated convective precipitation Predicted and fields as inputs to the hydrological models (Droegemeier et al., 2000; Gilmore et al., observed 2004b). The improvement of model microphysics is essential because convective pre- precipitation cipitation is very sensitive to the uncertainties in cloud microphysics (Gilmore et al., M. Curi´ c´ and D. Janc 10 2004a, b). The choice of a hydrometeor size distribution is critical for the cloud model outputs (Curi´ c´ et al., 1998; Cohen and McCaul, 2006). There are studies that use the meteorological models to simulate the convective precipitation over a large area as Title Page well as to compare the modeled and observed datasets (e.g. Amengual et al., 2007). Recently, comparison of the long-term samples of observed and model areal accumu- Abstract Introduction 15 lated convective precipitation from isolated storms show the capability of the cloud- resolving model to match observations in mountainous and flat land areas (Curi´ c´ and Conclusions References Janc, 2011). Tables Figures The complex feature of the accumulated convective precipitation in a small area is affected by the storm cell structure. Some convective storms contain essentially only J I 20 one kind of cell. Others contain a mixture of ordinary cells and supercells either si- multaneously or at different times. However, convective storm splitting and subsequent J I split motion affect the most complex spatial convective precipitation pattern. Split right- Back Close and left-moving storms are cyclonic and anticyclonic, respectively (Adlerman et al., 1999). Each split storm also contains one or more cells and may split again (Curi´ c´ et Full Screen / Esc 25 al., 2009). Split storms are not mirror images of each other. Observational evidence shows that the right-moving storms are favored in the environment characterized by Printer-friendly Version clockwise-turning hodographs. There are, however, the long-lived left-moving con- vective storms within environments with the same wind shear conditions (Grasso and Interactive Discussion Hilgendorf, 2001). The importance of the storm splitting process is also recognized 7239 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | in urban areas (Niyogy et al., 2011). The knowledge of the spatial pattern of convec- tive precipitation herein is necessary due to the drainage requirements. We must also HESSD emphasize that radar data give a weak estimation of convective precipitation inten- 8, 7237–7259, 2011 sity associated with the splitting processes. For this reason, hydrometeorologists must 5 find another effective tool to estimate the convective precipitation in such a complex scenario. Predicted and Bearing the above considerations in mind, the main objective of this paper is to observed show whether the cloud-resolving model can simulate well convective precipitation in precipitation an area with frequent storm splitting episodes. We use a cloud-resolving mesoscale M. Curi´ c´ and D. Janc 10 model with substantially improved microphysics and initial conditions (Curi´ c´ and Janc, 2011) to reproduce well the observed accumulated convective precipitation in this area. We compared the modeled and observed amounts of areal accumulated convective Title Page precipitation by using a statistical analysis. Correct description of the convective pre- cipitation in space and time in this complex case would be essential with regard to Abstract Introduction 15 various meteorological and hydrological predictions and analyses. Conclusions References 2 Study area and data Tables Figures For the purpose of this study we select the area in the west part of Serbia in which split J I storms occur frequently and may cause flash floods. This area is situated at a northern latitude between 43◦300 N and 44◦160 N and eastern longitude between 20◦ and 21◦ E J I 20 (Fig. 1). The most prominent region of this mountainous area is the centrally located Back Close West Morava river valley which is roughly oriented from northwest to southeast. The valley floor is flat and very narrow, especially in the middle. The southern valley side Full Screen / Esc has higher mountains with peak values over 1.5 km above the valley floor. This valley is affected by convective events with flash floods that are often produced by the NW Printer-friendly Version 25 air mass convective storms. These storms were initialized frequently over the Zlatibor Interactive Discussion plateau (west from the treated area) with a mean height of approximatively 1 km MSL in agreement with Curi´ c´ (1982) and Curi´ c´ and Janc (1992). 7240 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | The convective precipitation data were collected from the rain gauge network pre- sented in Fig. 1. The geographical coordinates of 54 rain gauges with their altitudes HESSD are also presented in Table 1. For our analysis, we use the daily-accumulated precip- 8, 7237–7259, 2011 itation. We select samples from 27 convective precipitation events over a 15-yr period 2 5 (1981–1995) in the treated area of approximately 6870 km . The analysis performed is based on the following criteria: the convective precipitation has an intensity in excess Predicted and of 2.5 mm h−1 and a duration of less than 2 h, which only contributes to the daily accu- observed mulated precipitation. The event is observed by at least half of the rain gauge