Effects of vegetation on soil temperature and water content: Field monitoring and numerical modelling

Presence of vegetation in urban landscape influences soil temperature and soil moisture. Some studies in literature have focused on development of correlations between the above two parameters for agricultural fields and forest regions. These correlations could be dissimilar due to the differences in soil conditions (density and type), vegetation species and temperature between agricultural and urban landscape. This paper investigates the effects of vegetation on soil temperature and soil moisture by an integrated approach of field monitoring and numerical modelling. A simple hydrological model is developed to capture seasonal variations of surface soil temperature and its effect on root water uptake. Hypothesis of effects of soil temperature on root water uptake was investigated using field measurements of soil water content. Field site in urban landscape containing bare, grass and tree species were selected for investigation. There existed a contrasting trend in water content response between summer and autumn for both bare and vegetated soils. Due to higher evapotranspiration in summer, water content in vegetated soils were lower by up to 50%. However, water content in vegetated soil was found to be up to 70% higher than in a bare soil during autumn. It could be due to the lower soil temperature that inhibits root water uptake ability. This was verified using a series of numerical simulations that consider effects of soil temperature on root water uptake. Without considering soil temperature effects on root water uptake, there was an overestimation of reduction of soil water content by up to 50% in autumn period.