Impact of land use on Costa Rican tropical montane cloud forests: Sensitivity of orographic cloud formation to deforestation in the plains

Abstract

[1] The current study provides new insights into the coupling of land use in lowland and premontane regions (i.e., regions below 1000 m) and orographic cloud formation over the Monteverde cloud forests. Rawinsondes launched during the Land Use Cloud Interaction Experiment (LUCIE) together with those from the National Centers for Environmental Prediction (NCEP) provided profiles that were used to drive the Colorado State University Regional Atmospheric Modeling System (CSU RAMS) model, which simulated three realistic land use scenarios (pristine forests, current conditions and future deforestation). For current conditions, the model-simulated clouds were compared against those observed at hourly intervals by the Geostationary Environmental Observational Satellite-East (GOES E) satellite. The model performed best on 6 different days. The model-simulated profiles of dew point and air temperatures were compared with the observed profiles from rawinsondes for these days. There was generally very good agreement below 700 mb, the region of the atmosphere most crucial to the cloud forests. The average model simulations for the 6 days show that when the lowland and premontane regions were completely forested, the orographic cloud bank intersected the mountains at the lowest elevations, covered the largest land surface area and remained longest on the surface in the montane regions. Deforestation has decreased the cloud forest area covered with fog in the montane regions by around 5-13% and raised the orographic cloud bases by about 25-75 m in the afternoon. The model results show that further deforestation in the lowland and premontane regions would lead to around 15% decrease in the cloud forest area covered with fog and also raise the orographic cloud base heights by up to 125 m in the afternoon. The simulations show that deforestation in the lowland and premontane regions raises surface sensible heat fluxes and decreases latent heat fluxes. This warms the air temperature and results in a lower dew point temperature of air masses that blow over the lowland and premontane regions. These air masses when lifted form the orographic cloud bank at higher elevations.

Regional long-term climate change (1950-2000) in the midtropical Atlantic and its impacts on the hydrological cycle of Puerto Rico

“…These results are in agreement with the increases in cloud base heights observed over the Monteverde region of Costa Rica due to localized deforestation [Lawton et al, 2001;Nair et al, 2003;Ray et al, 2006], although these previous studies did not include the effects of global climate change in the configuration of their modeling experiments and conclusions.…”

“…The liquid water mixing ratio (g kg −1 ) contains the amount, in total mass, of cloud droplets and raindrops per kilogram of dry air, and therefore accounts for the two completely nonfrozen cloud microphysics hydrometeors in the atmospheric regional model cloud module that indicate the cloud formation and rain development process in the tropics. It has been reported that changes in wind patterns and vertical wind motions should also produce changes in cloud base heights, an important parameter in tropical montane cloud forests [Hamilton et al, 1993;Bruijnzeel and Proctor, 1993;Still et al, 1999;Nair et al, 2003;Ray et al, 2006;Lawton et al, 2011]. A montane cloud forest is defined as a tropical or subtropical moist forest in elevated terrain in which the cloud base is persistently or seasonally at or below the vegetation canopy level.…”

“…et al., 2001;Nair et al, 2003;Ray et al, 2006], which is resulting in increased severity of regional droughts. Regional model simulations of pasture and forested scenarios show that lowland and premontane deforestation increases air temperatures and sensible heat fluxes and decreases dew point temperatures and latent heat fluxes of air masses that when lifted eventually lead to the formation of orographic cloud banks at higher elevations.…”

Dramatic declines in neotropical salamander populations are an important part of the global amphibian crisis

“…Cloud water provides an important source of moisture in tropical montane cloud forests during the dry season (18,19), when salamanders would be expected to be under the highest physiological stress; most cloud forest habitats contain little or no standing water, and plethodontid salamanders depend on adequate moisture for surface activity because of their permeable skins (20). Lawton et al (21) and Nair et al (22) showed that deforestation in lowland and premontane regions leads to an elevational increase of the cloud base, and Ray et al (23) used a modeling approach to demonstrate that deforestation in the lowlands of Costa Rica has led to an increase in mist-free conditions in the cloud forest at Monteverde. The Pacific lowlands and premontane areas of Guatemala have been extensively deforested; although the Pacific plain deforestation occurred before the salamander sampling in the 1970s, much of the premontane forest disappeared during and after this time (24).…”

Managing water services in tropical regions: From land cover proxies to hydrologic fluxes

“…In Costa Rica, for example, complete deforestation of lowland and premontane regions (\1000-1400 m.a.s.l.) was hypothesized to generate an upward 50-100 m shift in cloudbank elevation (Ray et al 2006). Such an effect would impart considerable influence on any project designed to increase cloudwater interception at lower elevations.…”