Effect of explicit urban land surface representation on the simulation of the 26 July 2005 heavy rain event over Mumbai, India

Abstract

Abstract. We investigate whether explicit representation of the urban land surface improves the simulation of the recordbreaking 24-h heavy rain event that occurred over Mumbai, India on 26 July 2005 as the event has been poorly simulated by operational weather forecasting models. We conducted experiments using the Regional Atmosphere modeling system (RAMS 4.3), coupled with and without explicit urban energy balance model-town energy budget (TEB) to study the role of urban land -atmosphere interactions in modulating the heavy rain event over the Indian monsoon region. The impact of including an explicit urban energy balance on surface thermodynamic, boundary layer, and circulation changes are analyzed. The results indicate that even for this synoptically active rainfall event, the vertical wind and precipitation are significantly influenced by heterogeneity in surface temperatures due to urbanization, and the effect is more significant during the storm initiation. Interestingly, precipitation in the upwind region of Mumbai city is increased in the simulation, possibly as a feedback from the sea breeze -urban landscape convergence. We find that even with the active monsoon, the representation of urbanization contributes to local heavy precipitation and mesoscale precipitation distribution over the Indian monsoon region. Additional experiments within a statistical dynamical framework show that an urban model by itself is not the dominant factor for the enhanced rainfall for a Mumbai heavy rain event; the combination of updated SST fields using Tropical Rainfall Measurement Mission (TRMM) data with the detailed representation of urban effects simulated by the TEB model created realistic gradients that successfully maintained the Correspondence to: D. Niyogi (climate@purdue.edu) convergence zone over Mumbai. Further research will require more detailed morphology data for simulating weather events in such urban regions. The results suggest that urbanization can significantly contribute to extremes in monsoonal rain events that have been reported to be on the rise.

Urbanization signature in the observed heavy rainfall climatology over India

“…Lei et al (2008)'s analysis of a record heavy rain event over Mumbai revealed that localized convection and heavy rainfall in and around Mumbai may be enhanced by convergence associated with the urban circulation. Similar results were reported by Niyogi et al (2006), Shem and Shepherd (2008), and Shepherd et al (2009) for warm season convection and rainfall over Oklahoma City, Oklahoma; Atlanta, Georgia and Houston Texas, respectively.…”

“…While a number of studies provide a detailed analysis of the impact of urbanization on the local precipitation climatology for urban areas of developed countries such as Atlanta , Houston (Shepherd and Burian, 2003;Shepherd et al, 2009), Tokyo (Kusaka et al, 2000), Sydney (Gero and Pitman, 2006), Oklahoma City (Niyogi et al, 2006), Indianapolis Beijing (Zhou et al, 2004), and Mumbai (Lei et al, 2008), the impact of urbanization on continental-scale rainfall changes and large-scale systems such as Indian summer monsoon system has not been analyzed in adequate detail, and is the focus of this paper.…”

“…Results from METROMEX suggest that the urban effects lead to 5-25% increased precipitation, particularly 50-75 km downwind of the urban center during the summer months (Changnon et al, 1991). There is increasing evidence that urbanization and changes in urban-rural boundaries can have a significant feedback on the spatiotemporal patterns of precipitation (Shepherd et al, 2002;Shepherd and Burian, 2003;Niyogi et al, 2006;Mote et al, 2007;Lei et al, 2008). Cotton and Pielke (2007, Chapter 5;Pielke et al, 2007, Section 7) summarize numerous studies as to how urbanization alters rainfall patterns as a result of mesoscale circulations and through changes in convective available potential energy (CAPE).…”

Sensitivity of high-temperature weather to initial soil moisture: a case study using the WRF model

“…Xue et al, 2001;Holt et al, 2006;Lei et al, 2008;Sun et al, 2012). Many of these studies highlighted the importance of land surface processes on heavy rainfall events.…”

Visualization-Based Decision Tool for Urban Meteorological Modeling

“…Grid 1 had 64 x 48 horizontal grid points covering the entire continental United States (US) w ith a prognostic tim e step of 90 second s. The second grid had 82 x 74 horizontal grid points covering m ost of the Eastern part of the US w ith a tim e step of 30 second s. The third grid com prised of 94 x 94 horizontal grid points w ith a tim e step of 10 second s, and covers all of Ind iana. The m od el w as configured based on success w ith previous cases d ocum ented in Lei et al (2008) and Lei and N iyogi (2011) and w ith terrain following the pressure/ sigm a-coord inate system w ith 36 vertical layers w ith a finer vertical spacing from 0.05 km to 1.27 km and a fixed spacing thereafter until 8. …”