Effects of human population and forestry trees on the hydrologic cycle: A modeling-based study

The hydrologic cycle is increasingly disrupted due to the rising human population and the associated decline in forest trees. The rationale of this work was to address the disruption in the hydrologic cycle, which is caused by the dual adverse effects of human population growth: reducing forestry trees and diminishing clouds' formation. The proposed model assumes that the density of forestry trees decreases due to harvesting activities to fulfill the resource demands of human population. Additionally, it posits that the transpiration from forestry trees contributes to an increased density of vapor clouds' formation, while population growth adversely impacts the natural formation rate of vapor clouds. The model was analyzed by employing qualitative analysis, demonstrating the feasibility and stability of equilibrium solutions. Furthermore, to capture the consequences of environmental fluctuations on the model's dynamics, the proposed deterministic model was extended to a stochastic framework. The analytical and numerical work sought to provide the directives for understanding and mitigating the adverse effects of human activities on the hydrologic cycle, promoting sustainable practices to restore ecological equilibrium. Results of the model analysis reveal that an increase in human population leads to a decline in both rainfall and forestry trees. However, reforestation with high-transpiration tree species can mitigate rainfall decline and restore balance to the hydrologic cycle. Moreover, the maximum density of forest trees is achieved when the utility of rain by the forest trees and the natural formation of vapor clouds are maximal. Also, the minimal anthropogenic hindrance in reducing the natural formation of vapor clouds, combined with the maximal efficiency of vapor clouds to naturally convert into raindrops, facilitates maximum rainfall.