Cloud modeling
\cite{Weaver_2001}
Deforestation caused changes
\cite{Lawton2001}
- Because grasses and crops usu- ally have shallower roots than do forest trees, the volume of water available for transpiration and latent heat transfer is greater for forests than for agricultural land developed from them (15, 16).
- Deforestation and conversion ofland to pasture or cropland generally increase surface al- bedo (12), reduce aerodynamic roughness length and mechanically turbulent mixing in the boundary layer (13), reduce evapotranspiration, and increase the ratio of convective sensible heat transfers to latent heat transfers from the surface to the atmosphere (13).
- Late morning dry season cumulus was much less abundant over the long-deforested parts of Costa Rica’s Rio San Juan basin than over the nearby forested region in Nicaragua. The less thoroughly deforested areas of Costa Rica near the river showed intermediate degrees ofcumu- lus development. Landsat images of dry season days with cumulus cloud field development in the region also showed that cumulus clouds were commonly absent or poorly developed over deforested areas (Fig. 1B).
- Our simulations suggest that conversion of
forest to pasture has a significant impact on cloud formation. The differences between sim- ulated forest and pasture surface air tempera- tures and sensible and latent heat transfers (Fig. 2, A through C) were similar to those observed between Amazonian forest and adjacent pasture. The greater evaporative flux over forest lowered the lifting condensation level in comparison to that over pasture and increased the convective available potential energy in air parcels. The dry season atmosphere measured by the soundings we used was such that mixing in the boundary layer became vigorous enough to initiate cloud formation in both forested and pasture scenarios by mid-morning.
- Reduced evapotranspiration after deforesta-
tion in tropical lowlands decreases the moisture content of the air mass flowing up the slopes of adjacent mountains. This increases the lifting condensation level and thus the elevation ofthe base of the cloud deck. The model results thus suggest that deforestation in the lowland tropics of the trade wind zone tends to shift the cloud forest environment upward in adjacent down- wind mountains.