Effects of Land Surface Type on Sea-Breeze Convection in the Houston Area

Convective storms are an important and common phenomenon in many regions of the world. These storms can generate heavy rain, strong winds, and lightning, among other hazards. However, despite their importance to local weather, infrastructure, transportation, and daily life, convective storms remain difficult to forecast. Operational numerical weather prediction models often fail to accurately predict the timing, location, and intensity of these storms. These forecast inaccuracies are affected, in part, by model representations of land surface characteristics, including surface roughness, soil moisture, and vegetation type, which impact heat and momentum fluxes between the surface and the atmosphere. The goal of this work is to quantify the impact of land surface properties on case studies of convective storms, to improve operational model representations of these impacts, and understand how changes in land surface resulting from climate change may impact future convective behavior in coastal regions.
This study focuses on case-study simulations of deep convection observed around Houston, TX during the Experiment of Sea-breeze Convection, Aerosols, Precipitation, and Environment (ESCAPE) in late May and June 2022. Two days with widespread deep convection near Houston (02 June and 21 June) were simulated with the Regional Atmospheric Modeling System (RAMS), a compressible, non-hydrostatic, cloud-resolving model. To examine the effects of land surface on convective characteristics, several sensitivity simulations were conducted. In addition to a control simulation using land surface type data from the North American Land Change Monitoring System (NALCMS), experiments were conducted with different land surface types, including: 1) uniform pasture land; 2) uniform forest; 3) replacing Houston with a mixture of pasture land and forest; 4) expanding the size of Houston (simulating population growth); and 5) replacing wetlands with open water (mimicking expected effects of sea level rise). Each day was also simulated with the control (NALCMS) land surface and a 1K higher dewpoint, to assess the relative impact of background meteorological conditions versus land surface changes.
Preliminary results indicate that changes to land surface type significantly impact the timing and location of convective updrafts, but have only modest effects on domain-wide precipitation. By contrast, increasing the dewpoint without changing surface type more than doubles domain-wide precipitation and greatly increases the strength and coverage of convective updrafts relative to the control simulation. This poster will describe the details of the case studies, as well as the sensitivity to land surface characteristics. The impacts of land surface type on location and timing of convective initiation, storm strength and duration, and storm microphysical and dynamical characteristics, as well as the processes driving these impacts, will be presented.