Effects of RegCM3 parameterizations on simulated rainy season over South America

Abstract

The impacts of change in the Grell convective scheme and biosphere−atmosphere transfer scheme (BATS) in RegCM3 are described. Three numerical experiments (RegZhang, RegClaris and RegArain) are conducted to reduce the RegCM3-Grell rainfall underestimation over tropical South America. The simulation referred to as RegZhang follows modifications made by Zhang et al. (2008) in the BATS. The RegClaris combines the RegZhang BATS parameters with a reduction of water drainage at the bottom of the subsoil layer in the regions covered by the tropical rain forest and a shorter convective time period for the Grell scheme. The RegArain considers this same modification in the Grell scheme, but uses a deeper total soil column and a deeper root system in the BATS. After the first year of simulation, the soil water content in RegZhang is progressively drained out of the soil column resulting in a deficit of rainfall in the Amazon. The RegClaris and RegArain, on the other hand, simulate a similar rainfall annual cycle in the Amazon, showing substantial improvement not only in phase but also in intensity. This improvement is partially related to an increase in evapotranspiration due to a larger availability of water in the soil column. A remote effect is also noted over the La Plata Basin region, where the larger summer rainfall rate may be related to the increase in moisture transport from the Amazon. Wind-and rainfall-based indices are applied to identify South American monsoon (SAM) timing. The RegClaris rainfall rates are adequate to identify the onset and the demise of SAM according to the observed data, whereas the rainfall deficit in RegZhang is associated with a delay in the onset and an early demise of the SAM.

Surrogate Climate Change Scenario and Projections with a Regional Climate Model: Impact on the Aridity in South America

“…More details about the model are given in [16]. In the present study modified parameters of BATS land-surface model for vegetation type 6 (tropical rain forest) are used to reduce the rainfall dry bias over tropical South America, as reported in earlier RegCM versions [21].…”

Greenhouse Gas Induced Changes in the Seasonal Cycle of the Amazon Basin in Coupled Climate-Vegetation Regional Model

“…Currently, there is evidence that human emission of greenhouse gases are associated with an increase in temperature, which in turn may lead to substantial modifications of the hydrological cycle on both regional and global scales [5,6]. Several studies have explored the potential impact of human-induced global warming on the tropical environment and climate of South America (e.g., [6][7][8][9][10][11]).…”

“…As discussed by [5,6,[10][11][12][13][14][15][16], assessing the seasonal and spatial variation of thermodynamic fluxes is mandatory for a reasonable understanding of processes governing the exchange between the biosphere and the lower troposphere. For instance, Hutyra et al [17] argued that drought frequency is an excellent predictor of the forest-savanna boundary, indicating the key role of extreme climatic events for inducing vegetation change.…”

An Assessment of the South Asian Summer Monsoon Variability for Present and Future Climatologies Using a High Resolution Regional Climate Model (RegCM4.3) under the AR5 Scenarios

“…The dynamic and physics of the RCMs are adequate for integrating the climate data at a high resolution and can improve the simulation results from comparatively coarse resolution GCMs [24]. At present, the regional climate models (RCMs) are used to dynamically downscale the output of the GCMs and reanalysis data for seasonal climate variability, climate change impact and regional climate processes studies [25]. The performance of different RCMs have been investigated over South Asia with the emphasis on the SASM [6,8,[26][27][28][29][30][31][32][33][34][35].…”