Increase in near-surface atmospheric moisture content due to land use changes: Evidence from the observed dewpoint temperature data

Land use change can significantly affect root zone soil moisture, surface energy balance, and near-surface atmospheric temperature and moisture content. During the second half of the twentieth century, portions of the North American Great Plains have experienced extensive introduction of irrigated agriculture. It is expected that land use change from natural grass to irrigated land use would significantly increase near-surface atmospheric moisture content. Modeling studies have already shown an enhanced rate of evapo-transpiration from the irrigated areas. The present study analyzes observed dewpoint temperature (T_d) to assess the affect of irrigated land use on near-surface atmospheric moisture content. This investigation provides a unique opportunity to use long-term (1982-2003) mesoscale T_d data from the Automated Weather Data Network of the high plains. Long-term daily T_d data from 6 nonirrigated and 11 irrigated locations have been analyzed. Daily time series were developed from the hourly data. The length of time series was the primary factor in selection of these stations. Results suggest increase in growing-season T_d over irrigated areas. For example, average growing-season T_d due to irrigation can be up to 1.56°C higher relative to nonirrigated land uses. It is also found that T_d for individual growing-season month at irrigated locations can be increased up to 2.17°C by irrigation. Based on the results, it is concluded that the land use change in the Great Plains has modified near-surface moistness.