Date of Award
Doctor of Philosophy (PhD)
Sundar A. Christopher
James H. Crawford
Land use--Environmental aspects., Land cover--Environmental aspects., Deforestation., Climatic changes.
Due to increasing urbanization, deforestation, and agriculture, land use and land cover (LULC) cover change over Southeast Asia has risen during the last three decades. The Center for Remote Imaging, Sensing and Processing (CRISP) Moderate Resolution Imaging Spectroradiometer (MODIS) derived land cover classification datasets show that 19.7% of peat swamp forests over the Southeast Asian maritime continent region (10°S~20°N and 90°E~135°E) have been cleared for agricultural purposes between 2000 and 2010. The influences of land-use changes have been suggested as important reasons for climate change over SE Asia. However, the role and rationale of their effects on alteration of regional climate variables are poorly understood. Therefore quantification efforts on the impacts of land-use changes on regional climate must be conducted. In this study, nested grid simulations based on Weather Research Forecasting Version 3.7.1 modeling system (WRFV3.7.1) over the central region of the Sarawak coast are used to investigate the climatic impacts of land use change over the maritime continent. The uncertainties of model simulations are first qualified based on a set of experiments with different combinations of physical parameterization packages including cumulus (CU), planetary boundary Layer (PBL), and land surface (LSM) schemes along with updating accurate land use characterization from satellite datasets. The designed simulated surface conditions, vertical profiles of temperatures and moisture, precipitation and cloud fields are further compared with both ground meteorological networks and satellite observations. Numerical simulations initialized with CRISP MODIS derived land cover scenarios for years 2000 and 2010 were then conducted for the month of August 2009, which is one of the strongest El Niño years closest to the available land dataset. The decreased evapotranspiration and increased land surface temperature from the large deforested areas have increased the surface Bowen ratio by 0.11 along with other changes of surface properties including decrease in roughness length and leaf area index. These biogeophysical impacts due to LULC changes have caused an increase of 1.2 Wm-2 in sensible heat flux and 11.7 Wm-2 decrease in latent heat flux which accompanied by a decrease in total cloud water path around 16.1 gm-2 and a reduction in accumulated precipitation of about 27.77mm during the selected wet month of the year. Our results suggest tropical deforestation over SE Asian maritime continent results in a reduction in cloud frequency, humidity, and convective precipitation. These shifts in the regional weather pattern can be attributed to enhanced land-sea breeze circulations and a reduction in available surface moisture from evaporation over the transitioned LULC region. Sensitivity studies further highlight the importance of accurate characterization of land surface in the model, and also emphasize that this regional climate transition can be increasingly strong as the deforestation increase. Our study illustrates the importance of this work for policy makers in control of making decisions regarding LULC change in the future.
Feng, Nan, "Understanding the climatic impacts of land use and land cover change over southeast Asia maritime continent using numerical model and satellite observations" (2016). Dissertations. 88.