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Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa
E. S. Gritti, C. Cassignat, O. Flores, R. Bonnefille, F. Chalié, J. Guiot,D. Jolly
Climate of the Past (CP) & Discussions (CPD) , 2010,
Abstract: Pollen data collected in Africa at high (Kuruyange, valley swamp, Burundi) and low altitude (Victoria, lake, Uganda; Ngamakala, pond, Congo) showed that after 6 ky before present (BP), pollen of deciduous trees increase their relative percentage, suggesting thus the reduction of the annual amount of precipitation and/or an increase of in the length of the dry season. Until now, pollen-climate transfer functions only investigated mean annual precipitation, due to the absence of modern pollen-assemblage analogs under diversified precipitation regimes. Hence these functions omit the potential effect of a change in precipitation seasonality modifying thus the length of the dry season. In the present study, we use an equilibrium biosphere model (i.e. BIOME3.5) to estimate the sensitivity of equatorial African vegetation, at specific sites, to such changes. Climatic scenarios, differing only in the monthly distribution of the current annual amount of precipitation, are examined at the above three locations in equatorial Africa. Soil characteristics, monthly temperatures and cloudiness are kept constant at their present-day values. Good agreement is shown between model simulations and current biomes assemblages, as inferred from pollen data. To date, the increase of the deciduous forest component in the palaeodata around 6 ky BP has been interpreted as the beginning of a drier climate period. However, our results demonstrate that a change in the seasonal distribution of precipitation could also induce the observed changes in vegetation types. This study confirms the importance of taking into account seasonal changes in the hydrological balance. Palaeoecologists can greatly benefit from the use of dynamic process based vegetation models to acccount for modification of the length of the dry season when they wish to reconstruct vegetation composition or to infer quantitative climate parameters, such as temperature and precipitation, from pollen or vegetation proxy.
Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa  [PDF]
C. Cassignat,E. S. Gritti,O. Flores,R. Bonnefille
Climate of the Past Discussions , 2009,
Abstract: Pollen data collected in Africa at high (Kuruyange, valley swamp, Burundi) and low altitude (Lake Victoria; Ngamakala, pond, Congo) showed that after 6 ky Before Present (BP), pollen of deciduous trees increase their relative percentage, thus suggesting the beginning of a drier climate and/or an increase of the dry season length. Until now, pollen-climate transfer functions only investigated mean annual precipitation, hence omitting the potential effect of a change in precipitation seasonality. In the present study, we use an equilibrium biosphere model (i.e. BIOME3.5) to estimate the sensitivity of equatorial African vegetation to such changes, at specific sites. Climatic scenarios, differing only by the monthly distribution of the current annual amount of precipitations, are tested at the above three locations in equatorial Africa. Soil nature, monthly temperatures and cloudiness are kept constant at their present day values. A good agreement is shown between model simulations and current biomes assemblages, as reconstructed from pollen data. To date, the increase of the deciduous forest component in the palaeodata around 6 ky has been interpreted as the beginning of the drier climate period. However, our results demonstrate that a seasonal change of the precipitation distribution should likely induce such reconstructed changes toward drier vegetation types. This study confirms the necessity of taking into account seasonal changes in the hydrological balance when palaeoecologists wish to reconstruct vegetation composition or to infer quantitative climate parameters, such as temperature and precipitation, from pollen or vegetation proxy.
Mixed-Forest Species Establishment in a Monodominant Forest in Central Africa: Implications for Tropical Forest Invasibility  [PDF]
Kelvin S.-H. Peh, Bonaventure Sonké, Olivier Séné, Marie-No?l K. Djuikouo, Charlemagne K. Nguembou, Hermann Taedoumg, Serge K. Begne, Simon L. Lewis
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0097585
Abstract: Background Traits of non-dominant mixed-forest tree species and their synergies for successful co-occurrence in monodominant Gilbertiodendron dewevrei forest have not yet been investigated. Here we compared the tree species diversity of the monodominant forest with its adjacent mixed forest and then determined which fitness proxies and life history traits of the mixed-forest tree species were most associated with successful co-existence in the monodominant forest. Methodology/Principal Findings We sampled all trees (diameter in breast height [dbh]≥10 cm) within 6×1 ha topographically homogenous areas of intact central African forest in SE Cameroon, three independent patches of G. dewevrei-dominated forest and three adjacent areas (450–800 m apart). Monodominant G. dewevrei forest had lower sample-controlled species richness, species density and population density than its adjacent mixed forest in terms of stems with dbh≥10 cm. Analysis of a suite of population-level characteristics, such as relative abundance and geographical distribution, and traits such as wood density, height, diameter at breast height, fruit/seed dispersal mechanism and light requirement–revealed after controlling for phylogeny, species that co-occur with G. dewevrei tend to have higher abundance in adjacent mixed forest, higher wood density and a lower light requirement. Conclusions/Significance Our results suggest that certain traits (wood density and light requirement) and population-level characteristics (relative abundance) may increase the invasibility of a tree species into a tropical closed-canopy system. Such knowledge may assist in the pre-emptive identification of invasive tree species.
Diagnostic study of errors in the simulation of tropical continental precipitation in general circulation models  [PDF]
J. Srinivasan
Annales Geophysicae (ANGEO) , 2003,
Abstract: A simple diagnostic model has been used to identify the parameters that induce large errors in the simulation of tropical precipitation in atmospheric General Circulation models (GCM). The GCM that have been considered are those developed by the National Center for Environmental Prediction (NCEP), the National Center for Atmospheric Research (NCAR) and the Japanese Meteorological Agency (JMA). These models participated in the phase II of the Atmospheric Model Inter-comparison Project (AMIP II) and simulated the climate for the period 1979 to 1995. The root mean-square error in the simulation of precipitation in tropical continents was larger in NCEP and NCAR simulations than in the JMA simulation. The large error in the simulation of precipitation in NCEP was due to errors in the vertical profile of water vapour. The large error in precipitation in NCAR in North Africa was due to an error in net radiation (at the top of the atmosphere). The simple diagnostic model predicts that the moisture converge is a nonlinear function of integrated water vapour. The large error in the interannual variance of rainfall in NCEP over India has been shown to be due to this nonlinearity. Key words. Meteorology and atmospheric dynamics (precipitation; tropical meteorology; convective processes)
Development of IDF-curves for tropical india by random cascade modeling
A. Rana,L. Bengtsson,J. Olsson,V. Jothiprakash
Hydrology and Earth System Sciences Discussions , 2013, DOI: 10.5194/hessd-10-4709-2013
Abstract: Efficient design of urban drainage systems is based on statistical analysis of past rainfall events at fine time scales. However, fine time scale rainfall data are usually lacking in many parts of the world. A possible way forward is to develop methods to derive fine time scale rain intensities from daily observations. This paper applied cascade-based disaggregation modeling for generation of fine time scale rainfall data for Mumbai, India from daily rainfall data. These data were disaggregated to 10-min values. The model was used to disaggregate daily data for the period 1951–2004 and develop intensity-duration-frequency (IDF) relationships. This disaggregation technique is commonly used assuming scale-invariance using constant parameters. For the Mumbai rains it was found better to use parameters dependent on time scale and rain volume. Very good agreement between modeled and observed disaggregation series was found for the time scales larger than 1/2 h for the 1/2-yr period when short term data were available. Although the parameters were allowed to change with time scale, the rain intensities of duration shorter than 1/2 h were overestimated. When IDF-curves had been established, they showed that the current design standard for Mumbai city, 25 mm h 1, has a return period of less than one year. Thus, annual recurring flooding problems in Mumbai appear evident.
Rainfall Comparison from Different Precipitation Estimates over West Africa  [PDF]
I. A. Balogun, R. A. Balogun, T. Ademola
Atmospheric and Climate Sciences (ACS) , 2018, DOI: 10.4236/acs.2018.81002
Abstract: Comparison of different instantaneous precipitation estimates over three climatic zones in West Africa was carried out using Tropical Rainfall Measurement Mission (TRMM), 3A12 and 3A25 algorithms, the 3B43 rainfall product, and rain gauge product from the Global Precipitation Climatology Center (GPCC) as ground truth. The 3A12 rainfall product is observed to over-estimate rainfall intensity during MAM and JJAS periods, in all the zones, except in Guinea where it is observed to under-estimate rainfall intensity during the JJAS season. It was also observed that Savannah and Sahel had substantial frequency (occurrences) of zero (0 mm/hr) rainfall intensities during MAM, but only the Sahel zone indicated high frequencies of 0 mm/hr rainfall intensities during JJAS. The mean 3A12 rainfall indicated substantial disparity with that of the gauge (GPCC) rainfall especially in Guinea and Savannah. During peak rainfall season (JJAS) all the rainfall products under-estimate rainfall in Guinea and Sahel region of West Africa, but over-estimates rainfall in the Savannah region, whereas during low rainfall episodes (MAM), all the rainfall products over estimate rainfall when compared with the gauge (GPCC) rainfall product. The Gauge (GPCC)-3B43 had the best relationship (highest correlation) in all the three zones during MAM. All the rainfall products showed very strong correlation with Gauge (GPCC) in all the zones in West Africa during the March-May (MAM) period. The Gauge (GPCC)-3B43 correlation maintained the best relationship with Gauge (GPCC) among the rainfall products, during JJAS.
Estimating Tropical Cyclone Precipitation from Station Observations
REN Fumin,WANG Yongmei,WANG Xiaoling,LI Weijing,
REN Fumin
,WANG Yongmei,WANG Xiaoling,LI Weijing

大气科学进展 , 2007,
Abstract: In this paper, an objective technique for estimating the tropical cyclone (TC) precipitation from station observations is proposed. Based on a comparison between the Original Objective Method (OOM) and the Expert Subjective Method (ESM), the Objective Synoptic Analysis Technique (OSAT) for partitioning TC precipitation was developed by analyzing the western North Pacific (WNP) TC historical track and the daily precipitation datasets. Being an objective way of the ESM, OSAT overcomes the main problems in OOM,by changing two fixed parameters in OOM, the thresholds for the distance of the absolute TC precipitation (D0) and the TC size (D1), into variable parameters.Case verification for OSAT was also carried out by applying CMORPH (Climate Prediction Center MORPHing technique) daily precipitation measurements, which is NOAA's combined satellite precipitation measurement system. This indicates that OSAT is capable of distinguishing simultaneous TC precipitation rain-belts from those associated with different TCs or with middle-latitude weather systems.
The sensitivity of tropical convective precipitation to the direct radiative forcings of black carbon aerosols emitted from major regions
C. Wang
Annales Geophysicae (ANGEO) , 2009,
Abstract: Previous works have suggested that the direct radiative forcing (DRF) of black carbon (BC) aerosols are able to force a significant change in tropical convective precipitation ranging from the Pacific and Indian Ocean to the Atlantic Ocean. In this in-depth analysis, the sensitivity of this modeled effect of BC on tropical convective precipitation to the emissions of BC from 5 major regions of the world has been examined. In a zonal mean base, the effect of BC on tropical convective precipitation is a result of a displacement of ITCZ toward the forcing (warming) hemisphere. However, a substantial difference exists in this effect associated with BC over different continents. The BC effect on convective precipitation over the tropical Pacific Ocean is found to be most sensitive to the emissions from Central and North America due to a persistent presence of BC aerosols from these two regions in the lowermost troposphere over the Eastern Pacific. The BC effect over the tropical Indian and Atlantic Ocean is most sensitive to the emissions from South as well as East Asia and Africa, respectively. Interestingly, the summation of these individual effects associated with emissions from various regions mostly exceeds their actual combined effect as shown in the model run driven by the global BC emissions, so that they must offset each other in certain locations and a nonlinearity of this type of effect is thus defined. It is known that anthropogenic aerosols contain many scattering-dominant constituents that might exert an effect opposite to that of absorbing BC. The combined aerosol forcing is thus likely differing from the BC-only one. Nevertheless, this study along with others of its kind that isolates the DRF of BC from other forcings provides an insight of the potentially important climate response to anthropogenic forcings particularly related to the unique particulate solar absorption.
Impact of Global Warming on Intensity-Duration-Frequency (IDF) Relationship of Precipitation: A Case Study of Toronto, Canada  [PDF]
Erick Carlier, Jamal El Khattabi
Open Journal of Modern Hydrology (OJMH) , 2016, DOI: 10.4236/ojmh.2016.61001
Abstract: Annual maximum rainfall intensity for several duration and return periods has been analyzed according to the Gumbel distribution. The Intensity-Duration-Frequency (IDF) curves before and after 1980 have been computed and compared. For the city of Toronto, it is shown that the rainfall intensities after 1980 are lower than those from before this date. This is especially clear for those of short duration. Comparing our results with those of other authors, it appears that, for the moment, no general law on the impact of global warming on the curves intensity duration frequency cannot be made. It appears that the impact of global warming on rainfall varies with geographic location and that it is not possible to draw some general conclusions across the planet.
Tropical Precipitation Estimated by GPCP and TRMM PR Observations
LI Rui,FU Yunfei,
LI Rui
,FU Yunfei

大气科学进展 , 2005,
Abstract: In this study, tropical monthly mean precipitation estimated by the latest Global Precipitation Climatology Project (GPCP) version 2 dataset and Tropical Rainfall Measurement Mission Precipitation Radar (TRMM PR) are compared in temporal and spatial scales in order to comprehend tropical rainfall climatologically. Reasons for the rainfall differences derived from both datasets are discussed. Results show that GPCP and TRMM PR datasets present similar distribution patterns over the Tropics but with some differences in amplitude and location. Generally, the average difference over the ocean of about 0.5 mm d-1 is larger than that of about 0.1 mm d-1 over land. Results also show that GPCP tends to underestimate the monthly precipitation over the land region with sparse rain gauges in contrast to regions with a higher density of rain gauge stations. A Probability Distribution Function (PDF) analysis indicates that the GPCP rain rate at its maximum PDF is generally consistent with the TRMM PR rain rate as the latter is less than 8 mm d-1. When the TRMM PR rain rate is greater than 8 mm d-1, the GPCP rain rate at its maximum PDF is less by at least 1 mm d-1compared to TRMM PR estimates. Results also show an absolute bias of less than 1 mm d-1 between the two datasets when the rain rate is less than 10 mm d-1. A large relative bias of the two datasets occurs at weak and heavy rain rates.
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