Large scale high resolution modelling of the West African rivers and aquifers

2020 ◽  
Author(s):  
Alban Depeyre ◽  
Jean-Martial Cohard ◽  
Basile Hector ◽  
Reed Maxwell ◽  
Thierry Pellarin
Keyword(s):  
Water Resources ◽  
West Africa ◽  
Large Scale ◽  
River Flow ◽  
Hydrological Cycle ◽  
Soil Parameters ◽  
Global Changes ◽  
The West ◽  
Main Challenge

<p>West Africa has been classified as one of the most vulnerable regions in the world for water resources to face global changes, both climatic and demographic. The population is expected to double by 2050 leading to increased pressure on the use of water resources. In this context, it is necessary to understand the dynamics of major African hydrosystems as large rivers (Niger river, Senegal river...) and transboundary aquifers in order to predict the fate of water resources for the next decades. The ParFlow-CLM physical-based model was chosen for its ability to simulate surface water and groundwater dynamics in a coupled manner. This type of modelling makes it possible to represent the main hydrological processes observed over the whole West Africa region. It operates at a relatively fine spatial resolution (1 km²). The main challenge is to determine the hydrodynamic parameters of the soil for the entire region and on a 100 m thickness (i.e. 3.5 million pixels times 11 layers).</p><p>As a first step, the model was implemented on two catchments monitored by the AMMA-CATCH observatory. These two watersheds are representative of the major and contrasted processes found in WA : being respectively representative of Sudanian and Sahelian climates. In order to assess the relevance of the regional databases (SoilGrids and GLHYMPS), simulations were carried out with original and adjusted (based on observations) soil parameters and results were evaluated with local measurements. It appears that the deep weathered lithology is not considered in databases for most of hard-rock areas in intertropical areas with no tectonic uplift. Aquifer thicknesses, permeabilities and porosities have to be significantly enhanced for the model to represent the correct flow paths. Furthermore, in the Sahel where most of the annual precipitation falls during a dozen events only, a crust layer (consistent with observations) has been added to represent the large runoff coefficients which lead to the early season floods.</p><p>In a second step, the model was implemented at the West Africa scale using the adjusted soil parameters. These parameters were obtained using a simple linear law that have been applied uniformly over the entire domain and a mask over a part of the Sahel representative of the crusting zones. Results will be compared with both remotely sensed and in situ data : GRACE provides water stock variations at a very large scale, MERRA and ERA reanalysis provide evapotranspiration data. Altimeters and in situ measurements provide river flow data. In the near future the launch of the SWOT satellite will bring new observations to complete the current one. The evaluation of the different compartments of the hydrological cycle should reveal spatial discrepancies in the model's ability to represent processes, highlighting the points on which further work should focus.</p>

scholarly journals A GCM study of the response of the atmospheric water cycle of West Africa and the Atlantic to Saharan dust radiative forcing

2009 ◽  
Vol 27 (10) ◽  
pp. 4023-4037 ◽  
Author(s):  
K. M. Lau ◽  
K. M. Kim ◽  
Y. C. Sud ◽  
G. K. Walker
Keyword(s):  
West Africa ◽  
Radiative Forcing ◽  
Large Scale ◽  
Water Cycle ◽  
Deep Convection ◽  
Saharan Dust ◽  
Caribbean Region ◽  
Atmospheric Water ◽  
The West ◽  
Dust Layer

Abstract. The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence of an "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feedback triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Eastern Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while longwave has the opposite response. The elevated dust layer warms the air over West Africa and the eastern Atlantic. As the warm air rises, it spawns a large-scale onshore flow carrying the moist air from the eastern Atlantic and the Gulf of Guinea. The onshore flow in turn enhances the deep convection over West Africa land, and the eastern Atlantic. The condensation heating associated with the ensuing deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in a northward shift of the West Africa precipitation over land, increased low-level westerly flow over West Africa at the southern edge of the dust layer, and a near surface westerly jet underneath the dust layer over the Sahara. The dust radiative forcing also leads to significant changes in surface energy fluxes, resulting in cooling of the West African land and the eastern Atlantic, and warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

The influence of termite-induced heterogeneity on savanna vegetation along a climatic gradient in West Africa

2012 ◽  
Vol 29 (1) ◽  
pp. 11-23 ◽  
Author(s):  
Arne Erpenbach ◽  
Markus Bernhardt-Römermann ◽  
Rüdiger Wittig ◽  
Adjima Thiombiano ◽  
Karen Hahn
Keyword(s):  
West Africa ◽  
Plant Species ◽  
Large Scale ◽  
Regional Scale ◽  
Soil Conditions ◽  
Soil Parameters ◽  
Climatic Gradient ◽  
Termite Mound ◽  
Savanna Vegetation ◽  
Bioclimatic Variables

Abstract:Termites are renowned ecosystem engineers. Their mounds have been described as an important element of savanna vegetation dynamics, but little is known about their large-scale impact on vegetation composition. To investigate the influence of termite-induced heterogeneity in savannas along a climatic gradient in West Africa termite mound vegetation was compared with adjacent savanna vegetation using 256 paired plots (size of the termite mound and a corresponding savanna area) in five protected areas from northern Burkina Faso to northern Benin. On each plot vegetation and soil sampling was performed. Additionally bioclimatic variables from the WORLDCLIM database were used. The vegetation on the mounds and the surrounding savanna differed within all study sites (DCA length of gradient 3.85 SD) and showed complete turnover along the climatic gradient (DCA length of gradient 5.99 SD). Differences between mounds and savanna were significantly related to termite-induced changes in soil parameters, specifically clay enrichment and increased cation concentrations (base saturation). On a local scale, termite-induced differences in soil conditions were found to be the most important factor affecting mound vegetation, while on a regional scale, annual precipitation showed the strongest significant correlations. However, with increasing precipitation, differences between mounds and the surrounding matrix became more pronounced, and the contribution of mounds to local phytodiversity increased. Eleven plant species were identified as characteristic termite mound species. In the more humid parts of the gradient, more characteristic plant species were found that may benefit from favourable soil conditions, good water availability, and a low fire impact in the mound microhabitat.

scholarly journals A Mathematical Framework for Analysis of Water Tracers. Part II: Understanding Large-Scale Perturbations in the Hydrological Cycle due to CO2 Doubling

2016 ◽  
Vol 29 (18) ◽  
pp. 6765-6782 ◽  
Author(s):  
Hansi K. A. Singh ◽  
Cecilia M. Bitz ◽  
Aaron Donohoe ◽  
Jesse Nusbaumer ◽  
David C. Noone
Keyword(s):  
Moisture Transport ◽  
Large Scale ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Global Climate ◽  
Global Climate Model ◽  
Mathematical Framework ◽  
Surface Evaporation ◽  
And Shifts

Abstract The aerial hydrological cycle response to CO2 doubling from a Lagrangian, rather than Eulerian, perspective is evaluated using information from numerical water tracers implemented in a global climate model. While increased surface evaporation (both local and remote) increases precipitation globally, changes in transport are necessary to create a spatial pattern where precipitation decreases in the subtropics and increases substantially at the equator. Overall, changes in the convergence of remotely evaporated moisture are more important to the overall precipitation change than changes in the amount of locally evaporated moisture that precipitates in situ. It is found that CO2 doubling increases the fraction of locally evaporated moisture that is exported, enhances moisture exchange between ocean basins, and shifts moisture convergence within a given basin toward greater distances between moisture source (evaporation) and sink (precipitation) regions. These changes can be understood in terms of the increased residence time of water in the atmosphere with CO2 doubling, which corresponds to an increase in the advective length scale of moisture transport. As a result, the distance between where moisture evaporates and where it precipitates increases. Analyses of several heuristic models further support this finding.

scholarly journals WETCHIMP-WSL: intercomparison of wetland methane emissions models over West Siberia

2015 ◽  
Vol 12 (2) ◽  
pp. 1907-1973 ◽  
Author(s):  
T. J. Bohn ◽  
J. R. Melton ◽  
A. Ito ◽  
T. Kleinen ◽  
R. Spahni ◽  
...  
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Methane Emissions ◽  
High Latitudes ◽  
The West ◽  
Wetland Area ◽  
Forward Models ◽  
Ch4 Emissions ◽  
In Situ Observations

Abstract. Wetlands are the world's largest natural source of methane, a powerful greenhouse gas. The strong sensitivity of methane emissions to environmental factors such as soil temperature and moisture has led to concerns about potential positive feedbacks to climate change. This risk is particularly relevant at high latitudes, which have experienced pronounced warming and where thawing permafrost could potentially liberate large amounts of labile carbon over the next 100 years. However, global models disagree as to the magnitude and spatial distribution of emissions, due to uncertainties in wetland area and emissions per unit area and a scarcity of in situ observations. Recent intensive field campaigns across the West Siberian Lowland (WSL) make this an ideal region over which to assess the performance of large-scale process-based wetland models in a high-latitude environment. Here we present the results of a follow-up to the Wetland and Wetland CH4 Intercomparison of Models Project (WETCHIMP), focused on the West Siberian Lowland (WETCHIMP-WSL). We assessed 21 models and 5 inversions over this domain in terms of total CH4 emissions, simulated wetland areas, and CH4 fluxes per unit wetland area and compared these results to an intensive in situ CH4 flux dataset, several wetland maps, and two satellite inundation products. We found that: (a) despite the large scatter of individual estimates, 12 year mean estimates of annual total emissions over the WSL from forward models (5.34 ± 0.54 Tg CH4 y-1), inversions (6.06 ± 1.22 Tg CH4 y-1), and in situ observations (3.91 ± 1.29 Tg CH4 y-1) largely agreed, (b) forward models using inundation products alone to estimate wetland areas suffered from severe biases in CH4 emissions, (c) the interannual timeseries of models that lacked either soil thermal physics appropriate to the high latitudes or realistic emissions from unsaturated peatlands tended to be dominated by a single environmental driver (inundation or air temperature), unlike those of inversions and more sophisticated forward models, (d) differences in biogeochemical schemes across models had relatively smaller influence over performance; and (e) multi-year or multi-decade observational records are crucial for evaluating models' responses to long-term climate change.

scholarly journals The hydrological cycle in the high Pamir Mountains: how temperature and seasonal precipitation distribution influence stream flow in the Gunt catchment, Tajikistan

2014 ◽  
Vol 2 (2) ◽  
pp. 1155-1215 ◽  
Author(s):  
E. Pohl ◽  
M. Knoche ◽  
R. Gloaguen ◽  
C. Andermann ◽  
P. Krause
Keyword(s):  
Remote Sensing ◽  
Stream Flow ◽  
River Flow ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Climatic Variability ◽  
Glacier Mass Balance ◽  
In Situ Data ◽  
Glacier Melt

Abstract. Complex climatic interactions control hydrological processes in high mountains that in their turn regulate the erosive forces shaping the relief. To unravel the hydrological cycle of a glaciated watershed (Gunt River) considered representative of the Pamirs' hydrologic regime we developed a remote sensing-based approach. At the boundary between two distinct climatic zones dominated by Westerlies and Indian summer monsoon, the Pamir is poorly instrumented and only a few in situ meteorological and hydrological data are available. We adapted a suitable conceptual distributed hydrological model (J2000g). Interpolations of the few available in situ data are inadequate due to strong, relief induced, spatial heterogeneities. Instead we use raster data, preferably from remote sensing sources depending on availability and validation. We evaluate remote sensing-based precipitation and temperature products. MODIS MOD11 surface temperatures show good agreement with in situ data, perform better than other products and represent a good proxy for air temperatures. For precipitation we tested remote sensing products as well as the HAR10 climate model data and the interpolation-based APHRODITE dataset. All products show substantial differences both in intensity and seasonal distribution with in-situ data. Despite low resolutions, the datasets are able to sustain high model efficiencies (NSE ≥0.85). In contrast to neighbouring regions in the Himalayas or the Hindukush, discharge is dominantly the product of snow and glacier melt and thus temperature is the essential controlling factor. 80% of annual precipitation is provided as snow in winter and spring contrasting peak discharges during summer. Hence, precipitation and discharge are negatively correlated and display complex hysteresis effects that allow to infer the effect of inter-annual climatic variability on river flow. We infer the existence of two subsurface reservoirs. The groundwater reservoir (providing 40% of annual discharge) recharges in spring and summer and releases slowly during fall and winter. A not fully constrained shallow reservoir with very rapid retention times buffers melt waters during spring and summer. This study highlights the importance of a better understanding of the hydrologic cycle to constrain natural hazards such as floods and landslides as well as water availability in the downstream areas. The negative glacier mass balance (−0.6 m w.e. yr−1) indicates glacier retreat, that will effect the currently 30% contribution of glacier melt to stream flow.

scholarly journals Pemakaian Model Diterministik Untuk Transformasi Data Hujan Menjadi Data Debit Pada Das Lahor

2012 ◽  
Vol 9 (1) ◽  
Author(s):  
Ernawan Setyono
Keyword(s):  
Water Resources ◽  
River Flow ◽  
Deterministic Model ◽  
Hydrological Cycle ◽  
Performance Model ◽  
Data Series ◽  
Tank Model ◽  
Water Resources Development ◽  
Advantages And Disadvantages ◽  
Resources Development

Hydrologic analysis is an important stage in water resources development activities, therefore the output of the general hydrological analysis will determine the direction of water resources development strategy in a comprehensive and more narrow scale will determine the dimensions and characteristics of the necessary infrastructure. Determination of hydrological quantities are actually not too difficult when the data for analysis is available in sufficient quantity and quality. Classical problems in developing countries, including Indonesia, the availability of river flow data series is quite a separate issue, so the solution must be done by to specification climate variables into a variable flow. So far this has been developed conceptual model, of course, each has advantages and disadvantages because basically models were developed according to local hydrological conditions. All models are basically developed from the same basic concept, namely the hydrological cycle. Basic things that sets it apart is the way to interpret the process until the rain began to flow. This is what would need to be studied further in this study.This study is an attempt to determine the performance model determinstic of FJ Mock, NRECA, and Tank model and can explain the comparative level of performance of the deterministic model in Reservoir Lahor.Results of research on Lahor Reservoir indicated that the tank model is able to present the relationship of climate data and data streams very well. In this research obtained on the model RMSE value of model NRECA is 7.854 m3/sec, model FJ Mock for 18.696 m3/sec and Tank Model for 7.823 m3/sec.Keywords: discharge, NRECA model, fjmock model, model tank

Investigating global changes in snow dynamics and the impact on water resources

2020 ◽  
Author(s):  
Adrià Fontrodona Bach ◽  
Joshua Larsen ◽  
Ross Woods ◽  
Bettina Schaefli ◽  
Ryan Teuling
Keyword(s):  
Water Resources ◽  
Hydrological Cycle ◽  
Snow Accumulation ◽  
Global Changes ◽  
Hydrological Models ◽  
Winter Snow ◽  
Long Term Trends ◽  
And Shifts ◽  
The Impact

<p>Snow is a key component of the hydrological cycle in many regions of the world, providing a natural storage of water by accumulating snow in winter and releasing it in spring. Many ecosystems, societies and economies rely on this mechanism as a water resource. There is strong evidence in the literature that global warming leads to decreasing snowfall and snow accumulation and shifts the onset of the melt season to earlier in the year. However, little is known about how rising temperatures affect snowmelt rates and timing, and how these can have an impact on water resources for instance by changing the time and magnitude of streamflow. Some studies predict slower snowmelt rates in a warmer world, due to the onset of melt being earlier when there is less energy available for melt, but there is not yet an observation-based study showing such trends. As a first step, here we present preliminary results of observed long term trends in snowmelt rates from different climates. We use a dataset that has already shown strong decreasing signals for winter snow accumulation. Here we also present potential avenues to investigate the sensitivity of snowpacks and snowmelt regimes in different climatic settings to further rising temperatures using modeled snow dynamics. A few possibilities on how to link the snowpack dynamics to impacts in water resources are also discussed, for instance by comparing modelled dynamics to hydrological models and observations.</p>

scholarly journals Rainfall and Water Resources Variability in Sub-Saharan Africa during the Twentieth Century

2009 ◽  
Vol 10 (1) ◽  
pp. 41-59 ◽  
Author(s):  
Declan Conway ◽  
Aurelie Persechino ◽  
Sandra Ardoin-Bardin ◽  
Hamisai Hamandawana ◽  
Claudine Dieulin ◽  
...  
Keyword(s):  
Water Resources ◽  
West Africa ◽  
Southern Africa ◽  
River Flow ◽  
Data Availability ◽  
Sub Saharan Africa ◽  
Spatial And Temporal Variability ◽  
Rainfall Runoff ◽  
River Flows ◽  
Sub Saharan

Abstract River basin rainfall series and extensive river flow records are used to characterize and improve understanding of spatial and temporal variability in sub-Saharan African water resources during the last century. Nine major international river basins were chosen for examination primarily for their extensive, good quality flow records. A range of statistical descriptors highlight the substantial variability in rainfall and river flows [e.g., differences in rainfall (flows) of up to −14% (−51%) between 1931–60 and 1961–90 in West Africa], the marked regional differences, and the modest intraregional differences. On decadal time scales, sub-Saharan Africa exhibits drying across the Sahel after the early 1970s, relative stability punctuated by extreme wet years in East Africa, and periodic behavior underlying high interannual variability in southern Africa. Central Africa shows very modest decadal variability, with some similarities to the Sahel in the adjoining basins. No consistent signals in rainfall and river flows emerge across the whole of the region. An analysis of rainfall–runoff relationships reveals varying behavior including strong but nonstationary relationships (particularly in West Africa); many basins with marked variations (temporal and spatial) in strength; weak, almost random behavior (particularly in southern Africa); and very few strong, temporally stable relationships. Twenty-year running correlations between rainfall and river flow tend to be higher during periods of greater rainfall station density; however, there are situations in which weak (strong) relationships exist even with reasonable (poor) station coverage. The authors conclude for sub-Saharan Africa that robust identification and attribution of hydrological change is severely limited by data availability, conflicting behavior across basins/regions, low signal-to-noise ratios, sometimes weak rainfall–runoff relationships, and limited quantification of the magnitude and effects of land use change.

scholarly journals A study of large-scale vertical motion over West Africa

MAUSAM ◽  
2021 ◽  
Vol 43 (2) ◽  
pp. 175-182
Author(s):  
OLUWAGBEMIGA O. JEGEDE
Keyword(s):  
West Africa ◽  
Large Scale ◽  
West African Monsoon ◽  
Vertical Motion ◽  
Velocity Fields ◽  
West African ◽  
The West ◽  
Surface Weather ◽  
Kinematic Method ◽  
Plane Technique

Three separately recorded cases of thundery weather over West Africa that occurred during the conduct of the West African Monsoon Experiment (WAMEX) of 1979, are investigated with the kinematic vertical p-velocity field. The scheme employed here is based on a least-squares-plane technique which has been desribed in Jegede and Balogun (1991), as a variant to the similar methods used by Kung (1972, 1973), and Pedder (1981).   The aim in this study is to demonstrate the practicability of the kinematic method for interpreting observed surface weather. In all the three cast-s, there was some consistency noted between the precipitation patterns and the computed vertical velocity fields within the sub-region.    

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