The impact of deforestation on orographic cloud formation in a complex tropical environment

Ecological changes observed in cloud forests in the Monteverde area, northern Costa Rica, including disappearance of anuran populations and expansion of bird and bat ranges to higher elevations, have been linked to an increasing trend in dry-season mist-free days. Prior studies suggest that this trend may be influenced by both large-scale processes of climate change and regional-scale changes in land cover. Preliminary investigations exploring the impact of land use on cloud formation indicated that drying and warming of boundary layer air in response to lowland deforestation leads to increased cloud base heights. In the present study, numerical model experiments utilizing realistic land-use scenarios and atmospheric conditions are used to further explore the impact of land-use change on orographic cloud formation. The Regional Atmospheric Modeling System (RAMS) was used to simulate orographic cloud formation during the time period of 1–14 March 2003 in the Monteverde region for pristine, current, and future land-use scenarios. The simulations were initiated from the same atmospheric conditions and subject to similar lateral boundary conditions. Comparisons against observations showed that RAMS was capable of realistically simulating the nature of orographic cloud formation and boundary-layer thermodynamics. Numerical simulations indicated that deforestation in the lowlands and adjacent pre-montane areas results in an increase in average cloud base height and a consequent decrease in the areal extent of montane forests immersed in clouds. In the current and future land-use scenarios, warmer and drier air is found over the lowlands and pre-montane areas. […].