Effects of large-scale deforestation on precipitation in the monsoon regions: Remote versus local effects

Abstract

In this paper, using idealized climate model simulations, we investigate the biogeophysical effects of large-scale deforestation on monsoon regions. We find that the remote forcing from largescale deforestation in the northern middle and high latitudes shifts the Intertropical Convergence Zone southward. This results in a significant decrease in precipitation in the Northern Hemisphere monsoon regions (East Asia, North America, North Africa, and South Asia) and moderate precipitation increases in the Southern Hemisphere monsoon regions (South Africa, South America, and Australia). The magnitude of the monsoonal precipitation changes depends on the location of deforestation, with remote effects showing a larger influence than local effects. The South Asian Monsoon region is affected the most, with 18% decline in precipitation over India. Our results indicate that any comprehensive assessment of afforestation/ reforestation as climate change mitigation strategies should carefully evaluate the remote effects on monsoonal precipitation alongside the large local impacts on temperatures.deforestation | biogeophysical effects | Hadley Cell movement | ITCZ shift | monsoon regions H istorical land cover change has been one of the major drivers of climate change. By the 1750s, ∼6-7% of the global land surface area had been deforested for agriculture. Today, croplands and pasture lands make up approximately one third of the global land surface (1-4). In terms of area, croplands and pasture lands increased globally from 620 million ha in 1700 to 4,960 million ha by 2000 (1). This large-scale conversion of forests to croplands or grasslands can impact climate through biogeochemical (changes in atmospheric composition) and biogeophysical (changes in physical land surface characteristics such as albedo, evapotranspiration, and roughness length) processes.The impacts of past, present, and future biogeochemical and biogeophysical effects from land use change have been investigated by numerous studies (5-10). These studies find that the biogeochemical process primarily causes global effects while biogeophysical processes cause strong local effects. The combined biogeochemical and biogeophysical effects from land cover change in the Holocene before 1850 were modeled as a global mean warming of 0.73 K (9).During the historical period (1750 to present day), deforestationassociated CO 2 emissions have contributed ∼180 ± 80 PgC to the cumulative anthropogenic CO 2 emissions (11) and a warming of ∼0.16-0.30 K (biogeochemical effect) to anthropogenic climate change (5, 6). This warming is probably partly offset by the biogeophysical effect of albedo increase, which may have caused a global mean cooling by ∼0.03-0.27 K (5, 7, 8). However, other major biogeophysical processes, such as reduction in evapotranspiration and roughness length due to deforestation, could result in warming (12).Several studies have investigated the link between land cover change and local climate change (13-16). For example, deforestation (16) in the tropics (18....

Effects of Arctic geoengineering on precipitation in the tropical monsoon regions

“…Similar to past studies McGee et al 2013;Devaraju et al 2015) we investigate the Fig. 7 Latitudinal profile of annual mean northward atmospheric heat transport anomalies relative to the CTL case for the 2XCO2, ARCTIC, POLAR and GLOBAL cases.…”

“…ITCZ position is located using a metric called precipitation centroid (P cent ) defined as the median latitude of zonal mean area-weighted precipitation between 20°S and 20°N, interpolated to a 0.01° grid as used in many previous studies (Devaraju et al 2015;Donohoe et al 2013;Frierson and Hwang 2012). The mechanisms leading to the shifting of ITCZ are discussed in the next subsection.…”

“…The changes in cross-equatorial atmospheric heat transport have been investigated in many previous studies which relate the shifts in ITCZ due to various phenomena and forcings to changes in heat transports (Frierson and Hwang 2012;Donohoe et al 2013;Devaraju et al 2015). The annual mean northward heat transport (AHT) is calculated under steady state assumptions as:…”

“…The shifting of ITCZ has been discussed in not only Arctic geoengineering studies, but also in various other studies that investigate the effects of extra-tropical forcing such as high latitude sea ice cover changes (Chiang and Bitz 2005), high latitude volcanic eruptions (Oman et al 2005;Robock et al 2008;Haywood et al 2013), boreal deforestation (Devaraju et al 2015), high latitude ice sheets corresponding to the glacial periods (Broccoli et al 2006) and hemispherical asymmetries in clear-sky albedo (Voigt et al 2014). One of the effects associated with ITCZ shift is the change in cross-equatorial heat transport Frierson and Hwang 2012).…”

Simulated Impact of Desertification and Deforestation on Indian Monsoon Rainfall and Surface Fluxes: RegCM4.0 Simulations

“…Devaraju et al [1] investigated the impacts of deforestation and found significant reduction of precipitation in each local area in the Northern Hemisphere monsoon regions of East Asia, North America, and North Africa. Displacement of the Inter-Tropical convergence zone more southwards due to high-latitude deforestation indicated in study by Devaraju et al [1]. Also they suggest that remote effects on rainfall are stronger than local effects.…”