Scientists know that urbanization and irrigation can influence rainfall. However, they do not fully understand how these effects vary among different types of precipitation. The researchers investigated how massive urbanization and irrigation in the United States affect the three dominant types of summer rainfall in the mid-Atlantic region. These include the mesoscale convective system (MCS), isolated deep convection (IDC), and non-convective (NC) precipitation. MCS precipitation comes from large thunderstorm systems.
IDC precipitation is from isolated thunderstorms that result from the movement of air from the lower to the upper atmosphere. Rainfall in NC is rain that is not the result of thunderstorms and is usually less intense but lasts longer and results in continuous rain. The researchers found that urbanization suppresses all three types of precipitation. In contrast, irrigation enhances NC and IDC rainfall. Irrigation has different influences on mid-Atlantic precipitation produced by MCSs. The specific influence depends on whether an MCS forms locally or remotely.
The results of the research were published in the Geophysical Research Letters.
The contrasting influences of large-scale irrigation on locally and remotely initiated MCS precipitation highlight the complexity of precipitation. The findings also show the different effects that changes in land use and land cover can have on rainfall. Finally, this study highlights the importance of understanding the various impacts of human activities on rainfall. In regions such as the mid-Atlantic, many types of precipitation contribute to summer rainfall. This means that changes in the total amount of rain and the contributions of different types of rain have important implications for water resources and their management.
The researchers, from the Pacific Northwest National Laboratory and the Indian Institute of Technology–Madras, conducted convection-permitting regional model simulations with and without urbanization or irrigation. They used simulations to investigate how massive urbanization and irrigation in the United States east of the Rocky Mountains affected summer rainfall in the heavily populated mid-Atlantic region. They applied a feature tracking algorithm to classify three types of rainfall (MCS, IDC, and NC) and analyzed the effects of large-scale urbanization and irrigation on each type of rainfall.
The team found that urbanization suppresses all three types of precipitation in the mid-Atlantic region by reducing water vapor and atmospheric instability. In contrast, irrigation enhances IDC, NC, and locally initiated MCS precipitation. Irrigation also suppresses precipitation produced by MCSs initiated in the Great Plains and Midwest, producing opposing effects on MCS precipitation. Surface cooling due to irrigation induces a high-pressure anomaly in sea level, which is compensated by a mid-level low-pressure anomaly. The mid-level pressure anomaly then weakens the prevailing mid-level winds over the western Midwest and mid-Atlantic region, preventing the MCS from moving into the mid-Atlantic.
More information:
Jianfeng Li et al, Effects of Large-Scale Urbanization and Irrigation on Summer Precipitation in the Mid-Atlantic Region of the United States, Geophysical Research Letters (2022). DOI: 10.1029/2022GL097845
Provided by the US Department of Energy
Citation: Less rain in town, more on farm: Effects of urbanization, irrigation on mid-Atlantic summer rainfall (2023, July 3) retrieved 4 July 2023 from https://phys. org/news/2023-07-town-farm-effects-urbanization-irrigation.html
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