New Study “Land Use Change Impacts On Regional Climate Over Kilimanjaro” By Fairman Jr. Et Al 2011

There is a new paper which addresses an interesting question on the role of land use/land cover change in the vicinity of Mount Kilimanjaro on the climate in this region. The paper is

Fairman, J. G., Jr., U. S. Nair, S. A. Christopher, and T. Mölg (2011), Land use change impacts on regional climate over Kilimanjaro, J. Geophys. Res., 116, D03110, doi:10.1029/2010JD014712

and the abstract reads

“Glacier recession on Kilimanjaro has been linked to reduction in precipitation and cloudiness largely because of large‐scale changes in tropical climate. Prior studies show that local changes in land cover can also impact orographic cloudiness, precipitation, and terrain‐generated circulation patterns. This study uses the Regional Atmospheric Modeling System to simulate dry season orographic cloudiness, rainfall, and orographic flow patterns over Kilimanjaro for current deforested and reforested land cover scenarios. The simulations for current land cover show satisfactory performance compared to surface meteorology and satellite‐observed cloudiness. Clouds occur less frequently in response to deforestation, with the magnitude of decrease increasing with deforestation. On the windward side, cloud liquid water path (LWP) and precipitation both show decreases at lower elevations (∼1000–2000 m) and increases at higher elevations (2000–4000 m) in response to deforestation. This pattern is caused by decreased aerodynamic resistance, leading to enhanced wind speeds and convergence at higher elevations. On the lee regions, LWP deficits found in deforested simulations coincide with regions of reduced moisture while precipitation increased slightly at lower elevations (1000–1800 m) and decreased at higher elevations (1800–4000 m). Kilimanjaro offers less obstruction to background airflow, and reduced moisture transport to the lee side is found for deforested conditions, causing reduced LWP and rainfall. However, land use change has little effect on cloudiness and rainfall at elevations in excess of 4000 m and is not expected to impact glaciers in the summit zone of Kilimanjaro during the dry season. The effect in other seasons requires further investigation.”

The conclusions read

This study utilized numerical model simulations to investigate the impact of land cover changes at lower elevations of Kilimanjaro on the regional climate of the area. RAMS was used to simulate atmospheric conditions for July 2007, assuming current, deforested, and forested land cover scenarios. The findings from the comparison of these simulations can be summarized as follows.

1. Comparison of RAMS simulations for current land use conditions against surface meteorological observations and satellite observations of cloudiness show satisfactory performance of RAMS over the study region.

 2. The RAMS simulations show that deforestation at lower elevations of Kilimanjaro lead to a decrease in the frequency of cloud occurrence at all elevations. The cloud liquid water path decreases in response to deforestation except at higher elevations on the windward side where it increases. Reforestation has the opposite effect, increasing frequency of occurrence of clouds at all elevations, increases in cloud liquid water path except at higher elevation on the windward side where it decreases.

 3. Precipitation decreases at low elevations and increases at midelevations on the windward side in response to deforestation. On the leeward side, precipitation decreases at midelevations, while there is a very small increase at lower elevations. The magnitude of differences increases with the extent of deforestation.

 4. Flow diversion values computed for the different scenarios also show that obstruction caused by Kilimanjaro is enhanced when the lower elevations areas are reforested.

5. Surface moisture patterns are also altered because of changes in terrain flow, with reforestation increasing moisture transport to the lee side of the mountain compared to current vegetation and deforestation.

6. While differences in surface moisture contributes to decrease in frequency of occurrence in cloudiness, changes in flow pattern caused by reduced aerodynamic roughness play an important role. When the lower‐elevation regions are deforested, Kilimanjaro offer less obstruction to background flow, and the resulting increase in flow around the mountain causes reduced moisture transport to the lee side, causing reduced cloud liquid water path and precipitation. On the windward side, the increase in wind speed directed parallel to the topographic gradient at higher elevations, caused by reduced aerodynamic roughness in upwind areas, leads to enhanced surface convergence, cloud liquid water path, and precipitation.

7. Lack of precipitation at the peak during the period of study prevents making conclusions about potential impacts on precipitation at that level. Further study is required to investigate the possibility of such effects occurring during other seasons.

This study addresses only the impact of deforestation on one dry season month. There are no compelling reasons for expecting the physical processes that cause the changes in clouds and precipitation to be substantially different if the analysis is extended to include the dry season month of July from other years. However, further study that extends the analysis to other seasons is required to establish the overall impact of land use change on the higher‐elevation climate of Kilimanjaro.

This is yet another important study which documents the significant role of human alterations of the  landscape on the climate.

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