Thermodynamic and Dynamic Responses to Deforestation in the Maritime Continent: A Modeling Study

Min-Hui Lo,Chu-Chun Chen,Jin-Yi Yu,Yu-Chiao Liang,Eun-Soon Im,Iping Tang,Chia-Wei Lan,Rong-You Chien,Wei-Ting Chen,Ren-Jie Wu

doi:10.1175/jcli-d-18-0310.1

Abstract

Abstract Tropical deforestation can result in substantial changes in local surface energy and water budgets, and thus in atmospheric stability. These effects may in turn yield changes in precipitation. The Maritime Continent (MC) has undergone severe deforestation during the past few decades but it has received less attention than the deforestation in the Amazon and Congo rain forests. In this study, numerical deforestation experiments are conducted with global (i.e., Community Earth System Model) and regional climate models (i.e., Regional Climate Model version 4.6) to investigate precipitation responses to MC deforestation. The results show that the deforestation in the MC region leads to increases in both surface temperature and local precipitation. Atmospheric moisture budget analysis reveals that the enhanced precipitation is associated more with the dynamic component than with the thermodynamic component of the vertical moisture advection term. Further analyses on the vertical profile of moist static energy indicate that the atmospheric instability over the deforested areas is increased as a result of anomalous moistening at approximately 800–850 hPa and anomalous warming extending from the surface to 750 hPa. This instability favors ascending air motions, which enhance low-level moisture convergence. Moreover, the vertical motion increases associated with the MC deforestation are comparable to those generated by La Niña events. These findings offer not only mechanisms to explain the local climatic responses to MC deforestation but also insights into the possible reasons for disagreements among climate models in simulating the precipitation responses.

Highlights

Anthropogenic land use and land cover changes, especially deforestation, can have substantial effects on the local and remote climate
To understand the mechanism that induces the precipitation changes, we examine the changes in the vertical profile of the dynamic component of the moisture advection term over the land area of the Maritime Continent (MC) between the control run and the deforestation run (Fig. 7a for Community Earth System Model version 1.0.3 (CESM) and Fig. 7b for Regional Climate Model version 4.6 (RegCM4))
By comparing the experimental runs that replace forest with grassland with control runs, we find that deforestation tends to increase surface temperatures and precipitation over the land regions in the MC

Summary

Introduction

Anthropogenic land use and land cover changes, especially deforestation, can have substantial effects on the local and remote climate. Converting rain forest into bare ground or grassland has three major effects on land surface conditions: 1) a reduction in evapotranspiration, 2) an increase in surface albedo, and 3) a decrease in surface roughness. The enhanced wind speed might mitigate this effect, the net effect is a decrease in evapotranspiration (Maloney 1998). These two nonradiative processes contribute to changes in the water and energy budgets, resulting in a positive temperature response. Radiative processes reduce the net incoming radiation (through the increase in surface albedo) to produce a cooling effect. As a result, warming is the net response to tropical deforestation. This differs from the temperate and boreal zones, where radiative processes are more important and the overall result of deforestation is a net cooling (Davin and de NobletDucoudré 2010; Malyshev et al 2015)

Methods

Discussion

Conclusion