scholarly journals Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa

2009 ◽  
Vol 5 (2) ◽  
pp. 853-878
Author(s):  
C. Cassignat ◽  
E. S. Gritti ◽  
O. Flores ◽  
R. Bonnefille ◽  
F. Chalié ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Deciduous Forest ◽  
Lake Victoria ◽  
Potential Effect ◽  
Mean Annual Precipitation ◽  
Pollen Data ◽  
Temperature And Precipitation ◽  
Equatorial Africa ◽  
Precipitation Seasonality ◽  
Climatic Scenarios

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.

scholarly journals Simulated effects of a seasonal precipitation change on the vegetation in tropical Africa

2010 ◽  
Vol 6 (2) ◽  
pp. 169-178 ◽  
Author(s):  
E. S. Gritti ◽  
C. Cassignat ◽  
O. Flores ◽  
R. Bonnefille ◽  
F. Chalié ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Deciduous Forest ◽  
Potential Effect ◽  
Dry Season ◽  
Mean Annual Precipitation ◽  
Pollen Data ◽  
Modern Pollen ◽  
Precipitation Regimes ◽  
Precipitation Seasonality ◽  
Annual Amount

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.

A 12 000 year palynological record of temperature and precipitation trends in southwestern British Columbia

1981 ◽  
Vol 59 (5) ◽  
pp. 707-710 ◽  
Author(s):  
Rolf W. Mathewes ◽  
Linda E. Heusser
Keyword(s):  
Transfer Functions ◽  
Late Glacial ◽  
Mean Annual Precipitation ◽  
Before Present ◽  
Pollen Data ◽  
The Core ◽  
Temperature And Precipitation ◽  
Maximum Temperatures ◽  
Reconstructed Precipitation ◽  
July Temperature

Transfer functions for converting pollen frequencies to estimates of mean July temperature and mean annual precipitation were applied to fossil pollen data from a sediment core in Marion Lake. The paleotemperature curve shows low July temperatures near 14 °C at the base of the core at about 12 000 before present (B.P.), rising rapidly between 10 400 B.P. and 10 000 B.P. to maximum values slightly above 16 °C. Maximum temperatures cluster between 10 000 B.P. and approximately 7500 B.P., declining steadily thereafter until 6000 B.P. Little change is apparent from 6000 B.P. to the present. The reconstructed precipitation curve also shows a three-part zonation, with moderately high values between 12 000 and 10 400 B.P. dropping rapidly to minimum Holocene values between 10 000 and 7500 B.P. Precipitation rises to modern levels near the Mazama ash bed. The informal term "early Holocene xerothermic interval" is applied to the pre-Mazama interval of maximum temperatures and minimum precipitation.The late-glacial age at the base of the core is confirmed by a new radiocarbon date of 11 920 ± 245 years B.P. (I-6857) on lodgepole pine needles screened from the basal clays.

Reconstruction of a semi-arid late Pleistocene paleocatena from the Lake Victoria region, Kenya

2015 ◽  
Vol 84 (3) ◽  
pp. 368-381 ◽  
Author(s):  
Emily J. Beverly ◽  
Steven G. Driese ◽  
Daniel J. Peppe ◽  
L. Nicole Arellano ◽  
Nick Blegen ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Homo Sapiens ◽  
Lake Victoria ◽  
Mean Annual Precipitation ◽  
Equatorial Africa ◽  
Lake Victoria Region ◽  
Rainfall Reduction ◽  
Few Data ◽  
Volcaniclastic Deposits ◽  
The Last Glacial

The effect of changing environment on the evolution of Homo sapiens is heavily debated, but few data are available from equatorial Africa prior to the last glacial maximum. The Karungu deposits on the northeast coast of Lake Victoria are ideal for paleoenvironmental reconstructions and are best studied at the Kisaaka site near Karunga in Kenya (94 to > 33 ka) where paleosols, fluvial deposits, tufa, and volcaniclastic deposits (tuffs) are exposed over a ~ 2 km transect. Three well-exposed and laterally continuous paleosols with intercalated tuffs allow for reconstruction of a succession of paleocatenas. The oldest paleosol is a smectitic paleo-Vertisol with saline and sodic properties. Higher in the section, the paleosols are tuffaceous paleo-Inceptisols with Alfisol-like soil characteristics (illuviated clay). Mean annual precipitation (MAP) proxies indicate little change through time, with an average of 764 ± 108 mm yr− 1 for Vertisols (CALMAG) and 813 ± 182 to 963 ± 182 mm yr− 1 for all paleosols (CIA-K). Field observations and MAP proxies suggest that Karungu was significantly drier than today, consistent with the associated faunal assemblage, and likely resulted in a significantly smaller Lake Victoria during the late Pleistocene. Rainfall reduction and associated grassland expansion may have facilitated human and faunal dispersals across equatorial East Africa.

The climatic, topographic and litho-tectonic characteristics of badlands in Turkey

2021 ◽  
Author(s):  
Aydogan Avcioglu ◽  
Tolga Gorum ◽  
Abdullah Akbas ◽  
Mariano Moreno de las Heras ◽  
Omer Yetemen
Keyword(s):  
Critical Role ◽  
Sedimentary Rocks ◽  
Spatial Coherence ◽  
Google Earth ◽  
Controlling Factors ◽  
Mean Annual Precipitation ◽  
Rainfall Erosivity ◽  
Data Set ◽  
Anatolian Plateau ◽  
Precipitation Seasonality

<p>Badland areas are present in all continents, excluding Antarctica, and play a critical role in establishing local erosion and sedimentation rates. The presence of unconsolidated rocks (e.g., marls, sandstone, mudstone etc.) is a major driver controlling the distribution of badlands, which together with other environmental components, such as climate, tectonics, vegetation, and topography, determine their forms and processes. The mutual interaction of controlling factors in badlands areas provides a basis for developing a holistic approach to clarify their distribution patterns. Turkey's geodynamic evolution has led to the emergence of marine sedimentary rocks, pyroclastics, and continental clastics, especially in line with the uplift of the Anatolian Plateau and volcanism during the last 8 Ma.</p><p>This study aims to explore the country-scale distribution of badlands and the controlling factors of this badland distribution in Turkey. Remarkably wide badlands landscapes (4494 km<sup>2</sup>) have been visually inspected using Google Earth Pro<sup>TM</sup> to further digitize and extract geomorphological units by applying high-resolution multispectral images provided by WorldView-4/Maxar Technology and CNES/Airbus. To obtain exact boundaries, we eliminated contiguous flat areas surrounding the identified badlands by using red relief image map (RRIM) mosaics that express surface concavity and convexity combined with topographic slope derived from a digital elevation model of 5-m spatial resolution. Last, to determine the controlling factors of badlands distribution, we have compiled a global data set comprising 1-km resolution layers of mean annual precipitation, temperature and precipitation seasonality, aridity, NDVI, rainfall erosivity factor, elevation, and majority values of regional lithology in sub-catchments units. The enhanced investigation of the complex relationship that expresses the controlling factors of badlands distribution, has been conducted by K-means unsupervised cluster analysis.</p><p>Our comprehensive regional analyses exploring the distribution and environmental attributes of major Turkish badlands identified five different groups or clusters of badlands that display spatial coherence with climatic and tectonic settings. We argue that Turkey's climatic and topographic transition zones, varying from Mediterranean climate dominated areas to the more arid Central Anatolian Plateau, and tectonically‑induced topographic barriers play a relevant role in discriminating these groups of badlands. Moreover, the Anatolian diversity of sedimentary rocks, which consists of Neogene and Paleogene continental clastics, volcano clastics & pyroclastics, and lacustrine deposits, makes an essential contribution to the identified, extensive badland distribution.</p><p>This study has been produced benefiting from the 2232 International Fellowship for Outstanding Researchers Program of the Scientific and Technological Research Council of Turkey (TUBITAK) through grant 118C329. The financial support received from TUBITAK does not mean that the content of the publication is approved in a scientific sense by TUBITAK.</p>

Ecological Niche Modeling Predicting the Potential Distribution of African Horse Sickness Virus from 2020 - 2060

2021 ◽  
Author(s):  
Ayalew Assefa ◽  
Abebe Tibebu ◽  
Amare Bihon ◽  
Alemu Dagnachew ◽  
Yimer Muktar
Keyword(s):  
Solar Radiation ◽  
Ecological Niche ◽  
Annual Precipitation ◽  
Maximum Temperature ◽  
Mean Annual Precipitation ◽  
African Horse Sickness ◽  
Diurnal Range ◽  
Annual Minimum Temperature ◽  
Precipitation Seasonality ◽  
Vector Borne

Abstract African horse sickness is a vector-borne, non-contagious and highly infectious disease of equines caused by African Horse Sickness viruses (AHSv) that mainly affect horses. The occurrence of the disease causes huge economic impacts because of its fatality rate is high, trade ban and disease control costs. In planning of vectors and vector borne diseases, the application of Ecological niche models (ENM) used an enormous contribution in exactly delineating the suitable habitats of the vector. We developed an ENM with the objective of delineating the global suitability of AHSv outbreaks retrospective based on data records from 2005–2019. The model was developed in R software program using Biomod2 package with an Ensemble modeling technique. Predictive environmental variables like mean diurnal range, mean precipitation of driest month(mm), precipitation seasonality (cv), mean annual maximum temperature (oc), mean annual minimum temperature (oc) mean precipitation of warmest quarter(mm), mean precipitation of coldest quarter (mm) mean annual precipitation (mm), solar radiation (kj /day), elevation/altitude (m), wind speed (m/s) were used to develop the model. From these variables, solar radiation, mean maximum temperature, average annual precipitation, altitude and precipitation seasonality contributed 36.83%, 17.1%, 14.34%, 7.61%, and 6.4%, respectively. The model depicted the sub-Sahara African continent as the most suitable area for the virus. Mainly Senegal, Burkina Faso, Niger, Nigeria, Ethiopia, Sudan, Somalia, South Africa, Zimbabwe, Madagascar and Malawi are African countries identified as highly suitable countries for the virus. Besides, OIE-listed disease-free countries like India, Australia, Brazil, Paraguay and Bolivia have been found suitable for the virusThis model can be used as an epidemiological tool in planning control and surveillance of diseases nationally or internationally.

Spatiotemporal Trend and Variability of Precipitation in Taiwan Based on Multi-dimensional Ensemble Empirical Mode Decomposition (MEEMD)

2021 ◽  
Author(s):  
Chun-Hsiang Tang ◽  
Christina W. Tsai
Keyword(s):  
Time Series ◽  
Empirical Mode Decomposition ◽  
Ensemble Empirical Mode Decomposition ◽  
Intrinsic Mode Functions ◽  
Short Term ◽  
Time Frequency ◽  
Spatial Locality ◽  
Temperature And Precipitation ◽  
Mode Decomposition ◽  
Climatic Scenarios

<p>Abstract</p><p>Most of the time series in nature are nonlinear and nonstationary affected by climate change particularly. It is inevitable that Taiwan has also experienced frequent drought events in recent years. However, drought events are natural disasters with no clear warnings and their influences are cumulative. The difficulty of detecting and analyzing the drought phenomenon remains. To deal with the above-mentioned problem, Multi-dimensional Ensemble Empirical Mode Decomposition (MEEMD) is introduced to analyze the temperature and rainfall data from 1975~2018 in this study, which is a powerful method developed for the time-frequency analysis of nonlinear, nonstationary time series. This method can not only analyze the spatial locality and temporal locality of signals but also decompose the multiple-dimensional time series into several Intrinsic Mode Functions (IMFs). By the set of IMFs, the meaningful instantaneous frequency and the trend of the signals can be observed. Considering stochastic and deterministic influences, to enhance the accuracy this study also reconstruct IMFs into two components, stochastic and deterministic, by the coefficient of auto-correlation.</p><p>In this study, the influences of temperature and precipitation on the drought events will be discussed. Furthermore, to decrease the significant impact of drought events, this study also attempts to forecast the occurrences of drought events in the short-term via the Artificial Neural Network technique. And, based on the CMIP5 model, this study also investigates the trend and variability of drought events and warming in different climatic scenarios.</p><p> </p><p>Keywords: Multi-dimensional Ensemble Empirical Mode Decomposition (MEEMD), Intrinsic Mode Function(IMF), Drought</p>

Pollen Response-Surface Estimates of Late-Quaternary Changes in the Moisture Balance of the Northeastern United States

1993 ◽  
Vol 40 (2) ◽  
pp. 213-227 ◽  
Author(s):  
Robert S. Webb ◽  
Katherine H. Anderson ◽  
Thompson Webb
Keyword(s):  
Soil Moisture ◽  
Water Level ◽  
Late Quaternary ◽  
Response Surfaces ◽  
Water Level Fluctuations ◽  
Annual Precipitation ◽  
Mean Annual Precipitation ◽  
Northeastern United States ◽  
Pollen Data ◽  
Moisture Balance

AbstractQuantitative estimates of late-Quaternary climate in the northeastern United States are reconstructed from fossil pollen data to evaluate changes in the regional moisture balance inferred from water-level fluctuations. We use environmental response surfaces to calibrate modern pollen data (for 17 different taxa) to an index of effective soil moisture and mean annual precipitation. We apply these response surfaces to fossil pollen data from 60 sites in the region to reconstruct changes in soil moisture and mean annual precipitation at 3000-yr intervals from 12,000 yr B.P. to present. The mapped reconstructions of soil moisture and mean annual precipitation illustrate how the regional moisture balance of the Northeast may have changed over the last 12,000 yr in response to changing climate. Reconstructions of annual precipitation show a gradual increase from 30% below modern values at 12,000 yr B.P. to near-modern values by 6000 yr B.P. and then remain relatively constant thereafter. Reconstructed changes in the index of effective soil moisture, however, show a pattern of near-modern values at 12,000, 6000, and 3000 yr B.P., with significantly lower values estimated for 9000 yr B.P., the time of maximum pine pollen abundances in the Northeast. This pattern of change is similar to the change in regional moisture balance inferred from stratigraphic records of water-level fluctuations. These results confirm previous interpretations, based on records of water-level fluctuations, that conditions in the Northeast were significantly drier during the early to middle Holocene than at other times during the last 12,000 yr.

scholarly journals Air Temperature and Precipitation on the Greenland Ice Sheet

1960 ◽  
Vol 3 (27) ◽  
pp. 558-567 ◽  
Author(s):  
Marvin Diamond
Keyword(s):  
Air Temperature ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Warming Trend ◽  
The Arctic ◽  
Mean Annual Precipitation ◽  
The West ◽  
West Side ◽  
Temperature And Precipitation ◽  
Mean Annual Air Temperature

AbstractMean annual air temperatures and precipitation on the Greenland Ice Sheet, as estimated from snow profile studies and long-term meteorological records at coastal stations, have been used to prepare mean annual air temperature and mean annual precipitation charts for the Greenland Ice Sheet. It is shown that melting of surface snow may occur at elevations of about 1,300 m. in north Greenland and up to 2,700 m. in south Greenland. The warming trend in the Arctic, as indicated by increases in mean annual air temperature, may have occurred to a lesser extent on the ice sheet than at sea-level coastal stations. Annual accumulation of precipitation is two or three times as great at 2,700 m. on the west side of the ice sheet as at the crest. South of lat. 66° N., precipitation may be about twice as great on the east side of the crest as on the west side.

Multivariate Statistical Estimates of Holocene Vegetation and Climate Change, Forest-Tundra Transition Zone, NWT, Canada

1979 ◽  
Vol 11 (1) ◽  
pp. 125-140 ◽  
Author(s):  
Paul A. Kay
Keyword(s):  
Boreal Forest ◽  
Vegetation Change ◽  
Transfer Functions ◽  
Climatic Data ◽  
Tree Line ◽  
Pollen Data ◽  
Multivariate Statistical ◽  
Statistical Estimates ◽  
Pollen Rain ◽  
Forest Limit

Newly derived fossil pollen data were obtained from four sites along a transect from the boreal forest limit into tundra in the eastern Northwest Territories. Multivariate statistical analyses were employed to interpret the pollen assemblages. Transfer functions were constructed between the pollen data and climatic data, and paleoclimatic estimates were derived. The objective nature of the reconstructions provides an independent verification of the general outlines of the chronology of tree-line movements during the mid- and late-Holocene as established in previous paleosol and pollen studies. Boreal forest extended to approximately 62°N, associated with mean July temperatures 1 to 3°C above modern means, from at least 5500 to 3700 yr B.P. Although a major episode of southward displacement of tree line at about 3700 yr B.P. is recorded, later events are not clearly represented. Considerations of the statistics, the time scales, and the nature of the pollen rain suggest only conservative interpretations of the results are possible. It is suggested that the pollen sites may have been sensitive recorders of regional vegetation change only when they were near the ecotone, corresponding to a climatic threshold.

Pollen and Radiolarian Records from Deep-Sea Core RC14-103: Climatic Reconstructions of Northeast Japan and Northwest Pacific for the Last 90,000 Years

1985 ◽  
Vol 24 (1) ◽  
pp. 60-72 ◽  
Author(s):  
Linda E. Heusser ◽  
Joseph J. Morley
Keyword(s):  
Deciduous Forest ◽  
Northwest Pacific ◽  
Mean Annual Temperature ◽  
Modern Pollen ◽  
Temperature And Precipitation ◽  
Glacial Environments ◽  
Summer Temperatures ◽  
Broadleaf Deciduous Forest ◽  
Northeast Asian ◽  
High Degree

Using modern pollen and radiolarian distributions in sediments from the northwest Pacific and seas adjacent to Japan to interpret floral and faunal changes in core RC14-103 (44°02′N, 152°56′E), we recognize two major responses of the biota of eastern Hokkaido and the northwest Pacific to climatic changes since the last interglaciation. Relatively stable glacial environments (∼80,000–20,000 yr B.P.) were basically cold and wet (<4°C and ∼1000 mm mean annual temperature and precipitation, respectively) with boreal conijers and tundra/park-tundra on Hokkaido, and cool (<16°C) summer and cold (<1.0°C) winter surface temperatures offshore. Contrasting nonglacial environments (∼10,000–4000 yr B.P.) were warm and humid (>8°C and >1200 mm mean annual temperature and precipitation, respectively), supporting climax broadleaf deciduous forest with Quercus and Ulmus/Zelkova, with surface waters in the northwest Pacific characterized by warm (>1.5°C) winter and cold (10.4°–14.3°C) summer temperatures. Climatic evidence from RC14-103 shows a high degree of local and regional variation within the context of global climatic change. Correlative ocean and land records provide the detailed input necessary to assess local/regional responses to variations in other key elements (i.e., solar radiation, monsoonal variations) of the northeast Asian climate system.

Sign in / Sign up

Export Citation Format

Share Document