scholarly journals Holocene changes in African vegetation: tradeoff between climate and water availability

2014 ◽  
Vol 10 (2) ◽  
pp. 681-686 ◽  
Author(s):  
C. Hély ◽  
A.-M. Lézine ◽  
APD contributors
Keyword(s):  
West Africa ◽  
Water Availability ◽  
Regional Scale ◽  
Plant Distribution ◽  
Climate Conditions ◽  
Tropical Plants ◽  
Plant Migration ◽  
Spatio Temporal ◽  
The Individual ◽  
Instrumental Records

Abstract. Although past climate change is well documented in West Africa through instrumental records, modeling activities, and paleo-data, little is known about regional-scale ecosystem vulnerability and long-term impacts of climate on plant distribution and biodiversity. Here we use paleohydrological and paleobotanical data to discuss the relation between available surface water, monsoon rainfall and vegetation distribution in West Africa during the Holocene. The individual patterns of plant migration or community shifts in latitude are explained by differences among tolerance limits of species to rainfall amount and seasonality. Using the probability density function methodology, we show here that the widespread development of lakes, wetlands and rivers at the time of the "Green Sahara" played an additional role in forming a network of topographically defined water availability, allowing for tropical plants to migrate north from 15 to 24° N (reached ca. 9 cal ka BP). The analysis of the spatio–temporal changes in biodiversity, through both pollen occurrence and richness, shows that the core of the tropical rainbelt associated with the Intertropical Convergence Zone was centered at 15–20° N during the early Holocene wet period, with comparatively drier/more seasonal climate conditions south of 15° N.

scholarly journals Holocene changes in African vegetation: tradeoff between climate and water availability

2013 ◽  
Vol 9 (6) ◽  
pp. 6397-6427
Author(s):  
C. Hély ◽  
A.-M. Lézine ◽  
APD contributors
Keyword(s):  
West Africa ◽  
Water Availability ◽  
Regional Scale ◽  
Plant Distribution ◽  
Climate Conditions ◽  
Tropical Plants ◽  
Plant Migration ◽  
Spatio Temporal ◽  
The Individual ◽  
Instrumental Records

Abstract. Although past climate change is well documented in West Africa through instrumental records, modeling activities, and paleo-data, little is known about regional-scale ecosystem vulnerability and long term impacts of climate on plant distribution and biodiversity. Here we use paleohydrological and paleobotanical data to discuss the relation between available surface water, monsoon rainfall and vegetation distribution in West Africa during the Holocene. The individual patterns of plant migration or community shifts in latitude are explained by differences among tolerance limits of species to rainfall amount and seasonality. Using the probability density function methodology, we show here that the widespread development of lakes, wetlands and rivers at the time of the "Green Sahara" played an additional role in forming a network of topographically defined water availability allowing for tropical plants to migrate north from 15 to 24° N (reached ca. 9 cal ka BP). The analysis of the spatio-temporal changes in biodiversity, through both pollen occurrence and diversity, shows that the core of the tropical rainbelt associated with the Intertropical Convergence Zone was centered at 15–20° N during the early Holocene wet period with comparatively drier/more seasonal climate conditions south of 15° N.

Analysis of Mean Climate Conditions in Senegal (1971–98)

2006 ◽  
Vol 10 (5) ◽  
pp. 1-40 ◽  
Author(s):  
Souleymane Fall ◽  
Dev Niyogi ◽  
Fredrick H. M. Semazzi
Keyword(s):  
West Africa ◽  
Large Scale ◽  
Regional Climate ◽  
Linear Regression Analysis ◽  
Regional Scale ◽  
Regional Climate Change ◽  
Warming Trend ◽  
Positive Trend ◽  
Local Climate ◽  
Climate Conditions

Abstract This paper presents a GIS-based analysis of climate variability over Senegal, West Africa. It responds to the need for developing a climate atlas that uses local observations instead of gridded global analyses. Monthly readings of observed rainfall (20 stations) and mean temperature (12 stations) were compiled, digitized, and quality assured for a period from 1971 to 1998. The monthly, seasonal, and annual temperature and precipitation distributions were mapped and analyzed using ArcGIS Spatial Analyst. A north–south gradient in rainfall and an east–west gradient in temperature variations were observed. June exhibits the greatest variability for both quantity of rainfall and number of rainy days, especially in the western and northern parts of the country. Trends in precipitation and temperature were studied using a linear regression analysis and interpolation maps. Air temperature showed a positive and significant warming trend throughout the country, except in the southeast. A significant correlation is found between the temperature index for Senegal and the Pacific sea surface temperatures during the January–April period, especially in the El Niño zone. In contrast to earlier regional-scale studies, precipitation does not show a negative trend and has remained largely unchanged, with a few locations showing a positive trend, particularly in the northeastern and southwestern regions. This study reveals a need for more localized climate analyses of the West Africa region because local climate variations are not always captured by large-scale analysis, and such variations can alter conclusions related to regional climate change.

scholarly journals Effects of climate variability on savannah fire regimes in West Africa

2015 ◽  
Vol 6 (1) ◽  
pp. 161-174 ◽  
Author(s):  
E. T. N'Datchoh ◽  
A. Konaré ◽  
A. Diedhiou ◽  
A. Diawara ◽  
E. Quansah ◽  
...  
Keyword(s):  
West Africa ◽  
Large Scale ◽  
Southern Oscillation ◽  
Regional Scale ◽  
Fire Regimes ◽  
Burned Area ◽  
Climate Conditions ◽  
Burned Areas ◽  
Seasonal Analysis ◽  
Biomass Availability

Abstract. The main objective of this work is to investigate at regional scale the variability in burned areas over the savannahs of West Africa and their links with the rainfall and the large-scale climatic indexes such as the Southern Oscillation Index (SOI), Multivariate ENSO Index (MEI), North Atlantic Oscillation (NAO) and sea surface temperature gradient (SSTG). Daily satellite products (L3JRC) of burned areas from the SPOT Vegetation sensor at a moderate spatial resolution of 1 km x 1 km between 2000 and 2007 were analyzed over the West African savannah in this paper. Results from seasonal analysis revealed a large increase in burned areas from November to February, with consistent peaks in December at the regional scale. In addition, about 30% of the pixels are burned at least four times within the 7-year period. Positive correlations were found between burned areas and rainfall values obtained from the TRMM satellite over savannahs located above 8° N, meaning that a wet rainfall season over these regions was favorable to biomass availability in the next dry season and therefore may induce an increase in burned areas in this region. Moreover, our results showed a nonlinear relationship between the large-scale climatic indexes SOI, MEI, NAO and SSTG and burned-area anomalies. Positive (negative) correlations between burned areas and SOI (MEI) were consistent over the Sahel and Sudano-Sahelian areas. Negative correlations with Atlantic SSTG were significant over the Guinea subregion. Correlations between burned areas over Sudano-Guinean subregion and all the large-scale indexes were weak and may be explained by the fact that this subregion had a mean rainfall greater than 800 mm yr−1 with permanent biomass availability and an optimal amount of soil moisture favorable to fire practice irrespective of the climate conditions. The teleconnection with NAO was not clear and needed to be investigated further.

SPATIO-TEMPORAL VARIATION OF NONLINEARITY IN TROPOSPHERIC ZENITH WET DELAY OVER WEST AFRICA

2020 ◽  
Vol 79 (11) ◽  
pp. 1009-1016
Author(s):  
S. T. Ogunjo ◽  
J. B. Dada ◽  
I. A. Fuwape
Keyword(s):  
West Africa ◽  
Temporal Variation ◽  
Zenith Wet Delay ◽  
Spatio Temporal

scholarly journals Investigating the Spatio-Temporal Variation of Soil Moisture and Agricultural Drought towards Supporting Water Resources Management in the Red River Basin of Vietnam

2021 ◽  
Vol 13 (9) ◽  
pp. 4926
Author(s):  
Nguyen Duc Luong ◽  
Nguyen Hoang Hiep ◽  
Thi Hieu Bui
Keyword(s):  
Soil Moisture ◽  
River Basin ◽  
Temporal Dynamics ◽  
Regional Scale ◽  
Dry Season ◽  
Red River ◽  
Agricultural Drought ◽  
Severe Drought ◽  
Red River Basin ◽  
Spatio Temporal

The increasing serious droughts recently might have significant impacts on socioeconomic development in the Red River basin (RRB). This study applied the variable infiltration capacity (VIC) model to investigate spatio-temporal dynamics of soil moisture in the northeast, northwest, and Red River Delta (RRD) regions of the RRB part belongs to territory of Vietnam. The soil moisture dataset simulated for 10 years (2005–2014) was utilized to establish the soil moisture anomaly percentage index (SMAPI) for assessing intensity of agricultural drought. Soil moisture appeared to co-vary with precipitation, air temperature, evapotranspiration, and various features of land cover, topography, and soil type in three regions of the RRB. SMAPI analysis revealed that more areas in the northeast experienced severe droughts compared to those in other regions, especially in the dry season and transitional months. Meanwhile, the northwest mainly suffered from mild drought and a slightly wet condition during the dry season. Different from that, the RRD mainly had moderately to very wet conditions throughout the year. The areas of both agricultural and forested lands associated with severe drought in the dry season were larger than those in the wet season. Generally, VIC-based soil moisture approach offered a feasible solution for improving soil moisture and agricultural drought monitoring capabilities at the regional scale.

scholarly journals Simulating Spatio-Temporal Patterns of Bicycle Flows with an Agent-Based Model

2021 ◽  
Vol 10 (2) ◽  
pp. 88
Author(s):  
Dana Kaziyeva ◽  
Martin Loidl ◽  
Gudrun Wallentin
Keyword(s):  
Regional Scale ◽  
Evidence Base ◽  
Wide Field ◽  
Traffic Patterns ◽  
Agent Based Model ◽  
Validation Data ◽  
Agent Based ◽  
Mobility Behavior ◽  
Spatio Temporal ◽  
Models Validation

Transport planning strategies regard cycling promotion as a suitable means for tackling problems connected with motorized traffic such as limited space, congestion, and pollution. However, the evidence base for optimizing cycling promotion is weak in most cases, and information on bicycle patterns at a sufficient resolution is largely lacking. In this paper, we propose agent-based modeling to simulate bicycle traffic flows at a regional scale level for an entire day. The feasibility of the model is demonstrated in a use case in the Salzburg region, Austria. The simulation results in distinct spatio-temporal bicycle traffic patterns at high spatial (road segments) and temporal (minute) resolution. Scenario analysis positively assesses the model’s level of complexity, where the demographically parametrized behavior of cyclists outperforms stochastic null models. Validation with reference data from three sources shows a high correlation between simulated and observed bicycle traffic, where the predictive power is primarily related to the quality of the input and validation data. In conclusion, the implemented agent-based model successfully simulates bicycle patterns of 186,000 inhabitants within a reasonable time. This spatially explicit approach of modeling individual mobility behavior opens new opportunities for evidence-based planning and decision making in the wide field of cycling promotion

Combining static and dynamic environmental factors at various scales to predict shallow landsliding in South Tyrol, Italy – The Proslide project

2021 ◽  
Author(s):  
Robin Kohrs ◽  
 Lotte de Vugt ◽  
Thomas Zieher ◽  
Alice Crespi ◽  
Mattia Rossi ◽  
...  
Keyword(s):  
Regional Scale ◽  
Remote Sensing Data ◽  
Predisposing Factors ◽  
Physical Models ◽  
Data Driven ◽  
Catchment Scale ◽  
Heterogeneous Model ◽  
South Tyrol ◽  
Daily Precipitation Data ◽  
Spatio Temporal

<p>Shallow landslides in alpine environments can constitute a serious threat to the exposed elements. The spatio-temporal occurrence of such slope movements is controlled by a combination of predisposing factors (e.g. topography), preparatory factors (e.g. wet periods, snow melting) and landslide triggers (e.g. heavy precipitation events).  </p><p>For large study areas, landslide assessments frequently focus either on the static predisposing factors to estimate landslide susceptibility using data-driven procedures, or exclusively on the triggering events to derive empirical rainfall thresholds. For smaller areas, dynamic physical models can reasonably be parameterized to simultaneously account for static and dynamic landslide controls.  </p><p>The recently accepted Proslide project aims to develop and test methods with the potential to improve the predictability of landslides for the Italian province of South Tyrol. It is envisaged to account for a variety of innovative input data at multiple spatio-temporal scales. In this context, we seek to exploit remote sensing data for the spatio-temporal description of landslide controlling factors (e.g. precipitation RADAR; satellite soil moisture) and to develop models that allow an integration of heterogeneous model inputs using both, data-driven approaches (regional scale) and physically-based models (catchment scale). This contribution presents the core ideas and methodical framework behind the Proslide project and its very first results (e.g. relationships between landslide observations and gridded daily precipitation data at regional scale). </p>

THE SPACES OF MYTH IN KAZUO ISHIGURO’S THE REMAINS OF THE DAY: EXPLORING THE INTERSECTIONS OF MEMORY AND HISTORY

Ensemble ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 234-242
Author(s):  
Medha Bhadra Chowdhury ◽  
Keyword(s):  
Identity Politics ◽  
Cultural Beliefs ◽  
Traditional Values ◽  
Confined Space ◽  
Spatial Dimensions ◽  
Temporal Expressions ◽  
Spatio Temporal ◽  
Post War ◽  
The Individual ◽  
Historical Past

Kazuo Ishiguro’s The Remains of the Day (1989) reconstructs the experiences of an ageing butler, Stevens, trapped within the confined space of the house he has served in for many years. The contours of memory are drawn along the spatial dimensions of the house which serve as a space of contestation between traditional values and emergent cultural beliefs in the post-war period. Physical modifications on the architecture produce continuities and alterations within the subject, who inhabits the space. This paper seeks to explore the dynamics of remembering and forgetting which are determined by the sites of memory and which trace historical changes as well as shifts in identity politics in Ishiguro’s novel. The paper critically assesses the idea of space, its functional dimension and mythic commemoration in relation to a symbolic historical past. It examines the development of subjectivity through the expansion of memory embodied in material form and the complex relationship between history and myth-making, which complicates individual identity. This paper further proposes that these spatio-temporal expressions can be understood as not only confined to the individual but may be extended to the domain of public memory and contextualized in a post-war British cultural politics of grief.

Spatio-Temporal Gaussianization Flows for Extreme Event Detection

2021 ◽  
Author(s):  
Miguel-Ángel Fernández-Torres ◽  
J. Emmanuel Johnson ◽  
María Piles ◽  
Gustau Camps-Valls
Keyword(s):  
Event Detection ◽  
Land Surface ◽  
Extreme Event ◽  
Learning Approaches ◽  
Proposed Model ◽  
Individual Contributions ◽  
Current Context ◽  
Spatio Temporal ◽  
The Individual ◽  
Anomaly Score

<p>Automatic anticipation and detection of extreme events constitute a major challenge in the current context of climate change. Machine learning approaches have excelled in detection of extremes and anomalies in Earth data cubes recently, but are typically both computationally costly and supervised, which hamper their wide adoption. We alternatively present here an unsupervised, efficient, generative approach for extreme event detection, whose performance is illustrated for drought detection in Europe during the severe Russian heat wave in 2010. The core architecture of the model is generic and could naturally be extended to the detection of other kinds of anomalies. First, it computes hierarchical appearance (spatial) and motion (temporal) representations of several informative Essential Climate Variables (ECVs), including soil moisture, land surface temperature, as well as features describing vegetation health. Then, these representations are combined using Gaussianization Flows that yield a spatio-temporal anomaly score. This allows the proposed model not only to detect droughts areas, but also to explain why they were produced, monitoring the individual contributions of each of the ECVs to the indicator at its output.</p>

Spatio-temporal dynamics of suitable habitats for Detarium microcarpum Guill. & Perr. (Caesalpiniaceae), a priority food tree species in Benin (West Africa)

2018 ◽  
Vol 5 (2) ◽  
pp. 595-604 ◽  
Author(s):  
Relique Ignace Agbo ◽  
Rodrigue Idohou ◽  
Romaric Vihotogbé ◽  
Antoine Abel Missihoun ◽  
Rollande Aladé Dagba ◽  
...  
Keyword(s):  
West Africa ◽  
Tree Species ◽  
Temporal Dynamics ◽  
Detarium Microcarpum ◽  
A Priority ◽  
Spatio Temporal ◽  
Suitable Habitats
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