Land cover effects on soil water and thermal dynamics in arid environments: a comparative study of oasis and desert areas

In this study, wavelet cross-spectrum analysis was used to investigate the influence of meteorological factors on soil water and thermal dynamics in arid environments. The study used data from five observation sites in four land cover categories, including cropland mosaic (CM), urban and built-up (UBU), deciduous broadleaf (DB) over the oasis, and bare soil (BS), collected during June–September 2012. The results indicate that precipitation, irrigation, and evaporation primarily affect the mean and deviation of soil moisture in CM, resulting in the highest values. In contrast, precipitation and evaporation have the greatest impact on BS, leading to the lowest values. Besides, aside from the soil moisture at the 40 cm depth in the desert where the silt soil demonstrates optimal water storage conditions, soil moisture levels generally decrease with depth, with precipitation and irrigation helping to maintain soil moisture saturation levels between 40 and 60 cm in CM. Precipitation events have an immediate effect on soil moisture and temperature, while evaporation has a lag effect of 1–2 days. The soil temperature over all layers shows a 1-day cycle, which is easily disrupted by precipitation and irrigation. Correlation coefficients between soil moisture and precipitation/evaporation decrease with depth over all land covers. The vertical flow of soil moisture in the shallower layers over CM lasts for 10 days, while that over BS lasts up to 2 days, and deeper layers over CM can last up to 20 days. The study findings indicate that maintaining soil water stability at the 20–60 cm layer by irrigation in cropland is more effective for water retention, which provides valuable insights for water management strategies and agriculture in arid regions.