The influence of vegetation on the ITCZ and South Asian monsoon in HadCM3 (original) (raw)
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Journal of Geophysical Research: Atmospheres, 2015
Land use and land cover change (LULCC) is primarily characterized as forest conversion to cropland for the development of agriculture. Previous climate modeling studies have demonstrated the LULCC impacts on mean climate and its long-term trends. This study investigates the diurnal and seasonal climatic response to LULCC in monsoon Asia through two numerical experiments with potential and current vegetation cover using the fully coupled Community Earth System Model. Results show that LULCC leads to a reduced diurnal temperature range due to the enhanced (reduced) diurnal cycle of the ground heat flux (sensible heat flux). Daily minimum surface air temperature (T min) exhibits a clear seasonality over India as it increases most in the premonsoon season and least during the summer monsoon season. Similarly, a strong anticyclonic anomaly is present at 850 hPa over India in spring and over eastern China in autumn, but weak changes in circulation appear in winter and summer. In addition, the LULCC results in significant changes in the variability of the 2 m air temperature, as characterized by an enhanced variability in India and a reduced variability in northern China to eastern Mongolia in autumn and winter. Possible land-atmosphere feedback loops involving surface albedo, soil moisture, evapotranspiration, atmospheric circulation, and precipitation are offered as biogeophysical mechanisms that are responsible for the region-specific LULCC-induced diurnal and seasonal response. Lawrence and Chase, 2010]. Model simulations show that the impacts of LULCC on temperature and precipitation are less important than those of large-scale sea surface temperature (SST) anomalies at the global scale. However, in regions with significant LULCC, their impacts can be equal to or more than those caused by SST forcing [Findell et al., 2009]. In addition to the mean climate, LULCC also strongly impacts temperature and rainfall extremes, which can amplify or mask the effect of increasing CO 2 [Pitman et al., 2012; Avila et al., 2012]. Monsoon Asia, which comprises South, Southeast, and East Asia, is a typical monsoon region with intense human activities. Approximately half of the world's population lives in monsoon Asia, where the land cover has been dramatically changed by human activities over the past centuries [Ramankutty and Foley, 1999; Goldewijk, 2001; United Nations, 2013]. Because of this reason, the potential impacts of LULCC on monsoon Asian climate have drawn more and more attention. Numerous studies have been performed using climate models in various subregions of monsoon Asia, such as the Tibetan Plateau [e.g.,
Journal of Earth System Science, 2009
The change in the type of vegetation fraction can induce major changes in the local effects such as local evaporation, surface radiation, etc., that in turn induces changes in the model simulated outputs. The present study deals with the effects of vegetation in climate modeling over the Indian region using the MM5 mesoscale model. The main objective of the present study is to investigate the impact of vegetation dataset derived from SPOT satellite by ISRO (Indian Space Research Organization) versus that of USGS (United States Geological Survey) vegetation dataset on the simulation of the Indian summer monsoon. The present study has been conducted for five monsoon seasons (1998)(1999)(2000)(2001)(2002), giving emphasis over the two contrasting southwest monsoon seasons of 1998 (normal) and 2002 (deficient).
Contrasting regional and global climate simulations over South Asia
Climate Dynamics, 2020
Two ensembles of climate simulations, one global and one regional, are used to investigate model errors and projected climate change in seasonal mean temperature and precipitation over South Asia. The global ensemble includes ten global climate models (GCMs). In the regional ensemble all ten GCMs are downscaled by a regional climate model—RCA4 over South Asia at 50 km resolution. Our focus is on the Indian Summer Monsoon season (June–August) and we show that RCA4 can reproduce, reduce or amplify large-scale GCM biases depending on regions and GCMs. However, the RCA4 bias pattern in precipitation is similar across the simulations, regardless of forcing GCM, indicating a strong RCA4 imprint on the simulated precipitation. For climate change, the results indicate, that RCA4 can change the signal projected by the GCM ensemble and its individual members. There are a few RCA4 simulations with a substantial reduction of projected warming by RCA4 compared to the driving GCMs and with a larg...
Impact of Vegetation on the Indian Summer Monsoon: Model Sensitivity Experiments
2010
This study examines response of vegetation on the simulation of July rainfall in 1998 and 2002 using meso-scale model MM5. The model was integrated with two nested domains at 90 and 30 km resolution. The outer domain covers from 30 • S-50 • N, 30 • E-120 • E and inner domain from 5 • N-40 • N, 65 • E-105 • E over the Indian region. Two experiments are performed, each consisting of the model integration from middle of June to end of July for both 1998 excess and 2002 deficient monsoon years. In the first run (Expt1), the model was integrated with United States Geological Survey (USGS) vegetation. In the second run (Expt2), the model was integrated with Indian Space Research Organization (ISRO) satellite derived vegetation. Results indicate that Expt1 (USGS) has greater tendency of overestimation of rainfall. It is seen that RMSE (Root Mean Square Error) in the month of July for all India rainfall is lower for Expt2 (ISRO). Model bias of July is also closer to unity for ISRO derived vegetation (Expt2). Tibetan anticyclone is better simulated by ISRO vegetation (Expt2). 321 May 3, 2010 11:41 AOGS -AS 9in x 6in b951-v16-ch28 322 T. Pattanaik et al. The success of ISRO derived vegetation can be attributed to greater spatial coverage over Indian region. Still it is difficult to conclude the superiority of vegetation fraction between USGS and ISRO. Intensive study is required for exploring the detailed impact of vegetation on Indian region.
Geographical Reports of Tokyo Metropolitan University, 2020
This study investigates land-atmosphere coupling over South Asia during the pre-monsoon and monsoon seasons. We conducted three ensemble simulations using the Weather Research and Forecasting (WRF) model (version 3.8.1) as a regional climate model (RCM) coupled with the Noah land surface model (LSM). The default WRF configuration overestimates the roughness length for heat over short vegetation and underestimates the same metric over tall vegetation, leading to a larger sensible heat flux over all South Asia in both aforementioned seasons. This overestimated (underestimated) the strength of the land-atmosphere coupling over larger (smaller) sensible heat flux regions. Dynamically updating the roughness length for heat as a function of canopy height in the LSM results in an error reduction for this variable for different vegetation types. This leads to weaker land-atmosphere coupling for certain regions, resulting in a lower sensible heat flux, in both the pre-monsoon and monsoon seasons. This reduction of sensible heating affects the formation of convection over those regions.
We assessed the present and future climatologies of mean summer monsoon over South Asia using a high resolution regional climate model (RegCM4) with a 25 km horizontal resolution. In order to evaluate the performance of the RegCM4 for the reference period and for the far future (2070-2099), climate change projections under two greenhouse gas representative concentration pathways (RCP4.5 and RCP8.5) were made, the lateral boundary conditions being provided by the geophysical fluid dynamic laboratory global model (GFDL-ESM2M). The regional climate model (RCM) improves the simulation of seasonal mean temperature and precipitation patterns compared to driving global climate model (GCM) during present-day climate conditions. The regional characteristic features of South Asian summer monsoon (SASM), like the low level jet stream and westerly flow over the northern the Arabian Sea, are well captured by the
Examining Indian Monsoon Variability in Coupled Climate Model Simulations and Projections
2010
South Asian summer monsoon (June through September) rainfall simulation and its potential future changes are evaluated in a multi-model ensemble of global coupled climate models outputs under World Climate Research Program Coupled Model Intercomparison Project (WCRP CMIP3) data set. The response of South Asian summer monsoon to a transient increase in future anthropogenic radiative forcing is investigated for two time slices , middle (2031-2050) and end of the 21 st century (2081-2100) in the non-mitigated Special Report on Emission Scenarios (SRES) B1, A1B and A2 .There is large inter-model variability in simulation of spatial characteristics of seasonal monsoon precipitation. Ten out of 25 models are able to simulate space-time characteristics of South Asian monsoon precipitation reasonably well for the twentieth century.
Construction of climate change scenarios for a tropical monsoon region
Climate Research, 2005
Composite seasonal scenarios (per °C change in global equilibrium mean) were developed for the Indian subcontinent for the period 2010-2039 using 5 General Circulation Models (GCMs), namely, HadCM2, CSIRO-MK2b, CGCM1, GFDL-R15 and ECHAM4/OPYC3. These scenarios indicate a general warming over the entire region by about 0.3 to 0.6°C (± 0.2°C) with more warming in the northern part and less in the southern part of the country. The study shows pockets of negative and positive changes in rainfall over the study area. Large variations in the estimation of rainfall changes from different models also set the upper and lower limits to more extreme values. Further, scenarios indicate a warming of about 0.4 ± 0.2°C over Gangetic West Bengal (GWB) and surrounding regions in the eastern part of the country. The maximum change in rainfall over this part of the country, according to the scenarios developed, would be 4%. Sub-grid scale seasonal scenarios have been developed over GWB and surrounding regions through statistical downscaling. HadCM2 and ECHAM4/OPYC3 are considered for this purpose, as they more effectively represent spatial and temporal variations in rainfall and temperature over the area. Results reveal more warming (0.3 to 0.9°C) and more rainfall changes (-5 to + 9%) than the projections developed without downscaling the GCM output. Further, scenarios developed for the winter and pre-monsoon seasons show unusual changes in rainfall and temperature, which may be due to mesoscale activities present in the study area.
Journal of Climate, 2010
A global and seasonal assessment of regions of the earth with strong climate-vegetation biophysical process (VBP) interactions is provided. The presence of VBP and degree of VBP effects on climate were assessed based on the skill of simulations of observed global precipitation by two general circulation models of the atmosphere coupled to three land models with varying degrees of complexity in VBP representation. The simulated VBP effects on precipitation were estimated to be about 10% of observed precipitation globally and 40% over land; the strongest impacts were in the monsoon regions. Among these, VBP impacts were highest on the West African, South Asian, East Asian, and South American monsoons. The specific characteristics of vegetationprecipitation interactions in northern high latitudes were identified. Different regions had different primary impact season(s) depending on regional climate characteristics and geographical features. The characteristics of VBP effects on surface energy and water balance as well as their interactions were also analyzed. The VBPinduced change in evaporation was the dominant factor in modulating the surface energy and water balance. The land-cloud interaction had substantial effects in the feedback. Meanwhile, the monsoon regions, midlatitudes lands, and high-latitude lands each exhibited quite different characteristics in circulation response to surface heating changes. This study is the first to compare simulations with observations to identify and assess global seasonal mean VBP feedback effects. It is concluded that VBPs are a major component of the global water cycle.
Journal of the Meteorological Society of Japan, 2011
This study investigated the impacts of historical land use/cover changes (LUCC), from forest to cultivated land, on the seasonal cycle of the hydroclimate over the Indian subcontinent and southern China. The mechanism of these impacts was studied by conducting numerical experiments using an atmospheric general circulation model MIROC3.2 coupled with the land surface scheme MATSIRO and historical global land use/cover changes between 1700 and 1850. A previous study found a decrease in summer (JJA) precipitation over the Indian subcontinent and southern China induced by extended cultivation between 1700 and 1850. We further found that evapotranspiration in the Indian subcontinent notably decreased, particularly in the spring, while that in southern China discernibly decreased throughout the year. The di¤erence in the changes in evapotranspiration in the spring over both regions could be explained by the amount of precipitation during the dry season. In the Indian subcontinent, the marked decrease in evapotranspiration in May due to LUCC caused the decrease in precipitation during the same season. However, in southern China, the decrease of precipitation from March to April was contributed rather by the decrease of water vapor flux convergence due to atmospheric circulation changes than by the decrease of evapotranspiration.