Water vapour variability induced by urban/rural surface heterogeneities during convective conditions

Abstract

Scientific interest in urban meteorology has increased because highly populated areas experience high vulnerability to pollution or heavy rain. However, compared to urban air quality or urban heat island (UHI) processes, the urban water vapour cycle is poorly understood because it has been investigated less due to the lack of upper-air measurements and the high sensitivity of surface measurements to local heterogeneities. In this paper, surface measurements of wind, temperature, pressure and humidity, as well as integrated water vapour (IWV) from GPS and MODIS and numerical simulations, have been used to investigate the urban cycle of water vapour in May and June 2004 during the VAPIC field experiment in the Paris area.The surface data show the typical characteristics of an urban area with the absence of water vapour sources and a UHI of about 6 • C at night. The urban IWV distribution differs completely, with an urban IWV excess on average between 1600 and 0600 UTC (with a maximum of about 1.5 kg m −2 at 0600 and 1700 UTC). No IWV difference between the urban and rural areas is found in the middle of the day. The numerical simulations reproduce accurately the urban IWV anomaly.Shallow surface wind convergence associated with the UHI during nighttime provides moisture from the rural areas. Urban areas are therefore under wind convergence for most of the time. The rural water vapour sources and the depth of the convergence control the amplitude of the urban IWV excess. At about 1200 UTC, entrainment at the top of the urban boundary layer is the key process that inhibits the urban IWV excess observed at night.

The effect of indiscriminate nudging time on large and small scales in regional climate modelling: Application to the Mediterranean basin

“…This behaviour is systematic whatever the simulation day and is In addition to these limits, our scale truncation into large and small scales leads to an estimation of q r ls / q ref ls on a small number of points in the spectral domain, and probably a significant increase of the domain size (which however leads to a significant increase of the numerical cost) would have made more accurate the estimation of q r ls / q ref ls (Seth and Giorgi, 1998 (13), we obtain τ opt 3.4 h, which is close to the value obtained from the direct estimation (∼ 6 h) and to the value chosen in many numerical studies which generally justify this choice by the time interval between consecutive analyzes or reanalyses used to drive the RCM (e.g. Salameh et al, 2007;Champollion et al, 2009).…”

A coupled energy transport and hydrological model for urban canopies evaluated using a wireless sensor network

“…Understanding of urban land surface processes, such as transport of energy, water, trace gases and pollutants, is key to solving many urban environmental problems. In addition, accurate parametrizations of urban surface exchange schemes can substantially improve the performance of mesoscale numerical models (Cuenca et al, 1996;Masson, 2006;Champollion et al, 2009;Hamdi et al, 2010;Flagg and Taylor, 2011).…”

Linear breeze scaling: from large‐scale land/sea breezes to mesoscale inland breezes

“…At smaller scales, many studies have shown that landuse practices such as deforestation or changes due to agricultural management as well as urbanization may affect regional climate, ecosystems and water resources (Segal et al, 1988;Stohlgren et al, 1998;Pielke and Avissar, 1990;Lemonsu and Masson, 2002;Lemonsu et al, 2006; LINEAR BREEZE SCALING 1767 Champollion et al, 2009) and, on a global scale, spatially heterogeneous land-use effects may be at least as important in altering the weather as changes in climate patterns associated with greenhouse gases (Pielke et al, 2002;Pielke, 2005). Surface heterogeneities over the continent induce spatial variability in surface heat fluxes that can create inland breezes similar to sea/land breeze systems (Mahfouf et al, 1987;Mahrt et al, 1994;Patton et al, 2005;Courault et al, 2007).…”