S22

Tropical Hydrology

The purpose of this session is to review the state of scientific knowledge on tropical hydrology. The intertropical zone is the main energetic engine of climatic mechanics and can be characterized by the contrasting presence of tropical rainforest, tropical monsoon and tropical savanna climates. Convective phenomena are numerous and sometimes still poorly taken into account in climate models, making climate prediction more complex. However, the models agree on a trend towards global warming and an increase in extreme phenomena (excess rainfall and temperature, lack or scarcity of rainfall, etc.) whose consequences on hydrological regimes are sometimes unpredictable.
The impact of climate change on water resources depends not only on changes in the volume, timing, and quality of streamflow and recharge but also on system characteristics, changing pressures on the system, how the management of the system evolves, and what adaptations to climate change are implemented. Non-climatic changes may also have a greater impact on water resources than climate change, as it is mentioned in the Panta Rhei scientific decade 2013–2022 of IAHS, about changes in hydrology and society.
For example, since the 1970s, most of tropical Africa has been experiencing a decline in rainfall, with high evaporation due to the increasing temperature that became more pronounced in the early 1980s, with the repercussion of a decrease in water resources. However, since the 1990s, there has been a slight recovery in rainfall, which is still lower than that recorded in the 1950s in this environment of high evaporative demand. All this, combined with the degradation of the vegetation cover and the reduction in the number of rainy days (concentration of rainfall over short periods), leads to a heavy surface runoff in Sahelian areas and thus to the degradation of ecosystems. Paradoxically also in some tropical humid areas, flood peaks increased while average rainfall and groundwater resources did not. Those changes in precipitation and temperature, as well as non-linear effects on moisture, evapotranspiration and soil, have consequences on the quantity and quality of water resources, agriculture, fisheries and livestock.
Research related to the assessment of past and future climate change, as well as observed changes in hydrological regimes and/or watershed uses, are welcome in this session, including studies about actual and future assessment of evaporation and land-use/cover change interactions with surface runoff conditions.

Convener: Alain Dezetter | Co-Conveners: Ernest Amoussou, Pedro Luiz Borges Chaffe, Gil Mahé, Giovanny Mosquera
Orals
| Fri, 03 Jun, 08:30–18:00|Room Barthez 1
Posters
| Attendance Fri, 03 Jun, 15:00–16:30|Poster area

Orals: Fri, 03 Jun | Room Barthez 1

Chairpersons: Giovanny Mosquera, Pedro Luiz Borges Chaffe
08:30–08:45
|
IAHS2022-10
Ana Ochoa-Sánchez, Patricio Crespo, Galo Carrillo-Rojas, Adrián Sucozhañay, Franklin Marín, and Rolando Célleri

The paramo biome, located above 3300 m a.s.l. and covered mainly by tussock grasslands, provides ecosystem services for Andean cities, especially water resources used for drinking water, agriculture, hydropower generation and sustaining aquatic ecosystems. Even though research about the main components of the water cycle has increased substantially in the last decade, evaporation has remained unknown. In this study, we quantified for the first time daily, monthly and annual evaporation, its components (i.e. interception and transpiration) at event scale and its climatic drivers at a representative páramo catchment in Southern Ecuador (Figure 1). We used the eddy-covariance method to quantify evaporation. We additionally compared those measurements with lysimeters, water balance, energy balance, hydrological models (HBV-light and PDM) and the calibration of the Penman-Monteith equation in order to find easier and cheaper alternatives for estimating evaporation at the páramo (Figure 2).

Our results show that the paramo biome had a relatively low evaporation rate (annual ETa/P = 0.5, 1.7 mm/day) and is an energy-limited site, where net radiation is the primary control of evaporation (annual ETa/Rn = 0.47) (Figure 3). The secondary controls were wind speed, surface and aerodynamic conductance, especially important during dry periods. The maximum capacity of tussock grasslands to intercept water was 2 mm. During small events (P < 2 mm), between 100 and 80 % of precipitation was intercepted and released back to the atmosphere; while during large events (P > 2 mm), interception decreased from 80 to 10 %. During dry periods, transpiration rates ranged between 0.7 and 2.7 mm/day and on top, the fog and dew harvested by the vegetation contributed to the evaporation in around 30 %. When comparing eddy-covariance measurements with other methods, we found that the two hydrological models and the calibrated Penman-Monteith equation are robust alternatives for daily estimation of evaporation at the páramo. This study contributed to the understanding of the water cycle at the most important Andean ecosystem for its water resources.

Figure 1. Zhurucay ecohydrological observatory.

Figure 2. Methodology undertaken in the study.

Figure 3. Evaporation (ETa) and climatic variables at the study site.

How to cite: Ochoa-Sánchez, A., Crespo, P., Carrillo-Rojas, G., Sucozhañay, A., Marín, F., and Célleri, R.: Evaporation dynamics and partitioning in Andean tussock grasslands, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-10, 2022.

08:45–09:00
|
IAHS2022-23
Waldo Lavado-Casimiro

In this work, the simulation of the water supply has been carried out using the SWAT hydrological model to generate streamflows throughout Peru. For this purpose, 35 hydrological stations distributed in the 3 drainages of Peru have been used, simulating the entire country for the first time considering 4,355 sub-basins and 168 hydrographic units (HU); obtaining time series of streamflows for the period 1981-2016.
To evaluate the impact of climate change on water supply of Peru, three regional climate models based on dynamic regionalization have been used, obtaining time series from 1981 to 2065 with a spatial resolution of ~ 10 km. Based on these data, and using the delta change method, the streamflows generated in the period 2035-2065 versus 1981-2016 have been compared.
The results of the impact of climate change on water supply showed different results for each one of the 14 hydrological regions that Peru was divided. Spatially, the HUs with conditions towards a more marked decrease (increase) in flows are those located towards the center-south of the Pacific drainage and HUs dispersed in the Amazon drainage (north of the Pacific drainage). The uncertainties of hydrological modeling, as well as climate scenarios, are discussed in detail. All the results of this work can be accessed on the web portal https://idesep.senamhi.gob.pe/balance-hidrico/.

How to cite: Lavado-Casimiro, W.: Assessment of climate Change impact on water supply in Peru, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-23, 2022.

09:00–09:15
|
IAHS2022-128
Hydrometeorological assessment of ERA5 Land and GPCC climatological products over tropical watersheds
(withdrawn)
Thibault Mathevet, Audrey Valéry, and Théophile Yvert
09:15–09:30
|
IAHS2022-752
Hydrology of High-Elevation Grasslands in the Tropical Andes
(withdrawn)
Giovanny Mosquera, Franklin Marin, Peggy Stern, Vivien Bonnesoeur, Boris Ochoa-Tocachi, Francisco Román, and Patricio Crespo
09:30–09:45
|
IAHS2022-89
Yao Morton Kouamé, N'diaye Edwige Hermann Meledje, Tanina Idrissa Soro, Gneneyougo Emile Soro, Destyle Van Kombyla, Kouakou Lazare Kouassi, Bi Tié Albert Goula, Jean Emmanuel Paturel, Arona Diedhiou, and Ernest Amoussou

The streamflow is important for planning et decision-making of development activities  related to water resource. The hydrological mathematical models are frequently used to simulate the transformation of rainfall into streamflow as well as Artificial Neural Networks (ANNs. In order to contribute to the establishment of an adequate framework for water resource management in the Davo river basin, this study presents an intercomparison between streamflow estimations from conventional hydrological modelling and ANN analysis. The Davo River basin is located in the southwestern forest of Côte d'Ivoire. The hydrological models used are the HEC-HMS model (Hydrologic Engineering Center-Hydrologic Modeling System) and the GR4J model (Rural Engineering with four daily parameters), while the data-driven ANN model is developed in MATLAB. The three tools receive the same data and their parameters are calibrated using the same objective functions. The quality of the simulations is measured in the control phase using several statistical criteria. For the assesment of the impacts of climate change on hydrological regime of the Davo river basin, the AFRICA-CORDEX (Coordinated Downscaling Experiment for Africa) data under two RCP (representative concentration pathway) scenarios   RCP4.5 and RCP8.5 are integrated in the three tools of modelling. The approach developed in this study allows a considerable improvement of the outils performances developed in calibration and validation. In addition, the results of the current study provide valuable feedback for water resources’ planners in Côte d’Ivoire and the developing regions.

Keywords: Climate change, Streamflow, Artificial Neural Networks, HEC-HMS, GR4J, Davo river basin, Côte d’Ivoire

How to cite: Kouamé, Y. M., Meledje, N. E. H., Soro, T. I., Soro, G. E., Kombyla, D. V., Kouassi, K. L., Goula, B. T. A., Paturel, J. E., Diedhiou, A., and Amoussou, E.: Artificial Neural Networks (ANNs) and Hydrological Models to Simulate Streamflow in a context of climate change: Case of Davo river basin in Côte d’Ivoire, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-89, 2022.

09:45–10:00
|
IAHS2022-134
Marc Auriol Amalaman, Gil Mahe, Ibrahim Beh Diomande, Zamble Armand Tra Bi, Nathalie Rouche, Zeineddine Nouaceur, and Benoit Laignel

The objective of this study is to analyze the links between climate indices and the variability of precipitation and flow series. In order to better understand the non-stationarity of the different stations, the flow and rainfall data used concern the Tortiya station (1960-1996) and the Lafigué station (1977-1996). The climate indices coupled to these series are the NAO (North Atlantic Oscillation) and ENSO (El Niño - Southern Oscillation) over the same study period. The methodology of this work consisted in applying wavelet analysis and wavelet coherence on the different time series. These methods highlighted the different modes of variability occurring in the time series, namely : the sub-annual mode (< 1 year), the annual mode (1 year) and the interannual mode (1-2 years ; 2-4 years; 4-8 years). Firstly, the results of the present analysis show that the variability of the signal is explained at high frequencies (6 months to 1 year) in the different time series. At this frequency, it is the annual mode (1 year) that records all the signal variability between 30% and 70%. On the other hand, this work presents signals on other frequencies and periods but fairly, especially 2-year frequency, in the 1990s at the Lafigué station (8.2%). Wavelet analysis revealed that the dominant signal is very broadly significant  at the annual cycle level. In addition, the use of wavelet coherence between climate indices (ENSO, NAO) and precipitation, flow indicates a strong influence of NAO on rainfall and flow series.

Key words : Wavelet, coherence, periodicity, variability, upstream Tortiya watershed 

How to cite: Amalaman, M. A., Mahe, G., Diomande, I. B., Tra Bi, Z. A., Rouche, N., Nouaceur, Z., and Laignel, B.: WAVELET ANALYSIS OF TIME SERIES AT RAINFALL AND FLOW STATIONS IN THE UPSTREAM TORTIYA WATERSHED (Northern Ivory Coast), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-134, 2022.

Coffee break
Chairpersons: Ernest Amoussou, Gil Mahé
10:30–10:45
|
IAHS2022-19
Coffi Justin Noumon, Domiho Japhet Kodja, Ernest Amoussou, Luc Olliver Sintondji, and Euloge Kossi Agbossou

Low flows and irrigation in Mono River basin at Athiéme outlet (West -Africa)

1Coffi Justin Noumon, 2Domiho Japhet Kodja, 2Ernest Amoussou, 1Luc O. Sintondji,1 Euloge K. Agbossou.

1Laboratoire d’Hydraulique et de Maîtrise de l’Eau (LHME), Institut National de l’Eau, Université d’Abomey Calavi 01 BP 526 Cotonou (Bénin).

2Laboratoire Pierre Pagney Climat Eau Ecosystèmes et Développement (LACEEDE), Institut de Géographie et Aménagement du Territoire et de l’Environnement, Université d’Abomey Calavi 01 BP 526 Cotonou (Bénin).

Auteur correspondant: 1Coffi Justin NOUMON (justinoum2001@yahoo.fr)

Abstract

The basic goal of this survey is the assessment of water resources of Mono River at Athiémé outlet in low flow period where it availability for agriculture uses is problematic. Therefore, daily data (precipitations, ETP, flows) from 1971 to 2016 are collected. It allows to simulate low discharge with GR4J model. Field survey permits the characterization of agriculture uses and the assessment of water requirement for irrigation. Low flows of Mono River at Athiémé outlet simulation with GR4J showed a good performance of the model to simulate low discharges before the construction of Nangbéto dam in 1988. Criteria values of Nash-Sutcliffe before dam establishment are 69% (calibration) and 71% (validation). The performance of the model is less for the period after the dam establishment: The change in the hydrological regime of the river due to water jets from Nangbéto dam can explain this low performance. Water requirement for irrigated areas estimation has given 42 587 596 m3 in 2020 and 73 007 308 m3 in 2030 mainly for the constraint period production which came from february to may. The comparison of water availability/water requirement shows that the water needs are closely covered monthly but a fine decade period analysis revealed some deficit decades. These results involve a great attention and consequent investments for deep knowledge of the resource in order to plan it sustainable management.

Key words: Mono basin, Low flow, GR4J, Irrigation.

How to cite: Noumon, C. J., Kodja, D. J., Amoussou, E., Sintondji, L. O., and Agbossou, E. K.: Low flows and irrigation in Mono River basin at Athiéme outlet (West -Africa)., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-19, 2022.

10:45–11:00
|
IAHS2022-59
Kouakou Christian Junior Yao, Modeste Kacou, Ehouman Serge Koffi, Amidou Dao, Clément Dutremble, Maurice Guilliod, Bamory Kamagaté, Luc Neppel, Jean-Emmanuel Paturel, Jean-Louis Perrin, Christian Salles, Luc Séguis, and Eric Pascal Zahiri

In recent decades, floods are recurrent and intensifying in African major cities. Every year, rains cause material damage and human losses, in Abidjan (Ivory Coast). This study contributes to the characterization of the rain hazard in the District of Abidjan. The available data are made up of daily rainfall from a historical station "Abidjan airport" (1961-2014) and an academic network of 21 rain gauges progressively implemented in Abidjan since 2016.

 The annual rainfall observed from 2016 to 2021 on the sites of this network are representative of the interannual variability of the historical station. An analysis (date of occurrence, rainfall depth, mean intensity of wet days and number of rainy days) on the Highest Cumulative Rainfall Periods (HCRP:15, 30 and 60 days) is conducted on the long-term station, in order to characterize the periods of highest risk of flooding occurrence during the long and short rainy seasons. Date of HCRP occurrence during long rainy season is relatively stable over time. It tends to occur later in the short rainy season. In recent years, the mean intensity of wet days remains steady despite intensifying flooding.

The current network of rain gauges permits to discuss the spatial variability of the date of HCRP over Abidjan. It can be seen that the date of HCRP occurrence in the long rainy season is uniform across the area of Abidjan, whereas it appears more variable during the short rainy season. At the daily scale and for 60 days- HCRP of the two rainy seasons, the extreme quantiles are determined and their evolution analysed over the historical period.  With the current network, the experimental variograms of extreme rainfalls allows to evaluate their spatial extensions according to the rainy season.

Beyond this analysis of daily rainfall, the next step will consist in the characterisation of rainfall events at the sub-daily scale in order to update the intensity-duration-frequency curves and the design storm, which is a prerequisite for a better estimation of floods and sizing of structures.

How to cite: Yao, K. C. J., Kacou, M., Koffi, E. S., Dao, A., Dutremble, C., Guilliod, M., Kamagaté, B., Neppel, L., Paturel, J.-E., Perrin, J.-L., Salles, C., Séguis, L., and Zahiri, E. P.: Rainfall risk over the city of Abidjan (Ivory Coast): First contribution to the joint analysis of daily rainfall from a historical record and a recent network of rain gauges., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-59, 2022.

11:00–11:15
|
IAHS2022-690
Valerie Borrell, Eugène Kouacou, Ahmat Abdoulaye, Brice Konan Kouame, Alex Zile Kouadio, Jean-Emmanuel Paturel, Bernard Dje, Andrew Ogilvie, and Eric Servat

In Africa, floods have become “classic” hazards (David, 2004) due to climate change. If this trend continues, modeling predicts that in 2050 West Africa will experience a warming of 0.5 to 2 ° C with dramatic consequences. Galloping and poorly regulated urbanization amplifies urban runoff, exposure of the most precarious habitats and modifies the water cycle through massive deforestation and the modification of the destination of associated land uses (Montanari et al. 2013) , (Jourdan, 2019). Over a million and a half people are affected each year in Africa by flooding following heavy rains. Over the period from 2009 to 2014, there were a total of 74 deaths caused by flooding in the District of Abidjan.

In the framework of operational and scientific research actions around the updating of hydrological standards in West Africa (ActNAO Project) funded by the Institute of Research for Development, the University of Montpellier and the UNESCO ICIREWARD center, and in response to the WMO call, we carried out a study the aim of which is to define a method for characterizing the hydrological response of the watersheds of Abidjan in the face of intense rain, interpreting the states of surface and d 'land use, applicable at the level of the municipality and the district, and adapted to the nature and availability of data. The impact of past and future climate and land uses changes are studied. Ultimately, this study should make it possible to determine the runoff scenarios under various constraints of global changes and the conditions of resilience of the territory.

How to cite: Borrell, V., Kouacou, E., Abdoulaye, A., Kouame, B. K., Zile Kouadio, A., Paturel, J.-E., Dje, B., Ogilvie, A., and Servat, E.: Floods in Abidjan and global changes at the neighborhood level, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-690, 2022.

11:15–11:30
|
IAHS2022-274
Koffi Claude Alain Kouadio, Ernest Amoussou, Arona Diedhiou, Talnan Jean Honoré Coulibaly, Houebagnon Coulibaly, Regis Didi, and Issiaka Savané

This study was conducted in the White Bandama watershed (WBW) in Côte d’Ivoire (West Africa). The objective is to assess the impacts of future climate change (CC) on the hydropower potential (HPP) of the WBW. The methodology is based on coupling the SWAT (Soil and Water Assessment Tool) hydrological model with the Geographic Information System (GIS) QGIS to assess HPP on streams and evaluate the impacts of future CC on HPP of the watershed. Historical and climate projection data (precipitation, minimum and maximum temperature) for a set of three Regional Climate Models (RCM) from CORDEX-AFRICA (CCCma-CanRCM4, CCLM4-8-17 and REMO 2009) under RCP 4.5 were used. The biases of the ensemble mean were corrected by the Delta-change method. The relative change of streamflow discharge and HPP was assessed as the relative difference between the projection periods (2041-2070 and 2071-2100) and the reference period (1976-2005). The results showed a total of 22 future hydropower potential sites in the watershed. These sites were identified, geolocated and classified according to their potential capacity of generation in 82% as small (1 MW-25 MW potential capacity), 9% as medium (25 MW-100 MW potential capacity) and 9% as large (more than 100 MW potential capacity) hydropower. The climate models’ ensemble projected an upward trend for both the annual mean discharge of rivers and HPP of the WBW according to RCP 4.5 for the periods 2041-2070 and 2071-2100. The variation in flow rates is projected to have a positive impact on the HPP of the WBW. On the annual cycle, the months of August and September will record the highest monthly mean flows between 150 and 200 m3/s while the months from November to April will record low monthly mean flows on the WBW.

How to cite: Kouadio, K. C. A., Amoussou, E., Diedhiou, A., Coulibaly, T. J. H., Coulibaly, H., Didi, R., and Savané, I.: Using of hydrological model and geospatial tool to assess climate change impact on the hydropower potential of the White Bandama watershed in Côte d’Ivoire (West Africa), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-274, 2022.

11:30–11:45
|
IAHS2022-149
Papa Malick Ndiaye, Ansoumana Bodian, Serigne Bassirou Diop, Lamine Diop, Alain Dezetter, Andrew Ogilvie, and Koffi Djaman

Analysis of reference evapotranspiration (ET0) trends is essential for understanding the impacts of climate change on water resources. Thus, despite the continuous rise in temperatures, a decrease in evapotranspiration is noted in some parts of the world. This contrast is called the "evaporation paradox" and is thought to be related to the variation in wind speed, relative humidity and solar radiation. The objective of this work is to analyze, based on the Reanalysis weather data from the NASA Langley Research Center (LaRC) POWER project, the annual and seasonal trends of ET0 and climate variables at the scale of the Senegal, Gambia and Casamance rivers basins over the period 1984-2019. Mann Kendall's test and Sen slope were used to analyze trends in ET0 and climate variables. Results show that on annual scale, ET0 increases significantly in 32% of the Senegal basin and decreases in less than 1% of it. In contrast, in the Casamance and Gambia basins, the annual ET0 drops by 65% and 18%, respectively. On an annual scale, temperature and relative humidity show an increasing trend over all basins while wind speed and radiation decrease significantly. This confirms the existence of the "evaporation paradox" in the three basins. This phenomenon is explained by the increase in relative humidity and the decrease in wind speed.

Keywords: Reference evapotranspiration, Penman-Monteith, Mann Kendall test, Senegal, Gambia and Casamance River Basins.

How to cite: Ndiaye, P. M., Bodian, A., Diop, S. B., Diop, L., Dezetter, A., Ogilvie, A., and Djaman, K.: Trend analysis of reference evapotranspiration and climate variables in the main hydrosystems of Senegal: Senegal, Gambia and Casamance River Basins, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-149, 2022.

11:45–12:00
|
IAHS2022-152
Ansoumana Bodian, Papa Malick Ndiaye, Serigne Bassirou Diop, Lamine Diop, Alain Dezetter, Andrew Ogilvie, and Koffi Djaman

Reference evapotranspiration (ET0) is an essential parameter for hydrological modeling, irrigation planning and for studying the impacts of climate change on water resources. The Penman-Monteith method is recommended for estimating ET0 under all climatic conditions. But its application is limited in regions where data are difficult to access. The alternative is to use methods that incorporate fewer climatic parameters. The objective of this work is to evaluate twenty alternative methods of estimating ET0 and to calibrate and validate the best ones in order to adapt them to the climatic context of the basins of Senegal, Gambia and Casamance. This tree basins are the main hydrosystems of Senegal. The KGE and the PBIAS were used to evaluate the performance of the methods. The results show that the methods of Valiantzas 1, Doorenboss & Pruitt and Penman are the most robust for the estimation of ET0 in the three basins. The calibration/validation allowed the improvement of the methods of Trabert, Valiantzas 2 and Hargreaves & Samani for the estimation of the reference evapotranspiration in the basins of Senegal, Gambia and Casamance.

Keywords: Reference evapotranspiration, Penman-Monteith, Alternative Methods, Calibration/validation, Senegal, Gambia and Casamance Basins.

How to cite: Bodian, A., Ndiaye, P. M., Diop, S. B., Diop, L., Dezetter, A., Ogilvie, A., and Djaman, K.: Evaluation and calibration of Twenty alternative methods for estimating reference evapotranspiration in main hydrosystems of Senegal: Senegal, Gambia and Casamance River Basins, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-152, 2022.

Lunch break / Exhibition for the public
Chairpersons: Alain Dezetter, Ernest Amoussou
13:30–13:45
|
IAHS2022-212
Chandrakant Singh, Lan Wang-Erlandsson, Ingo Fetzer, and Ruud van der Ent

The tropical terrestrial ecosystems naturally exist as alternative stable states, commonly referred to as forest and savanna ecosystems. However, these ecosystems, especially forests, are currently threatened by the risk of drought-induced forest-to-savanna transitions across the tropics and subtropics. Therefore, a better understanding of ecosystem dynamics and characteristics behind these alternative stable states is crucial in predicting their response to future hydroclimatic changes. Previous studies have analyzed these alternative stable states against precipitation predominantly based on space-for-time substitution. However, such a substitution provides a partial picture of ecosystem adaptation dynamics and associated ecosystem structural change over time.

Here, we empirically study the transient state of tropical ecosystems and their hydroclimatic adaptations by examining remotely sensed tree cover and root zone storage capacity over the last two decades in South America and Africa. Tree cover represents the above-ground ecosystem structure's density, and is derived directly from MODIS satellite data. Whereas root zone storage capacity is the maximum amount of soil moisture that the vegetation can access for transpiration is derived using daily precipitation and evaporation data.

We found that ecosystems at high (>75%) and low (<10%) tree cover adapt to changing precipitation by instigating considerable subsoil investment while experiencing limited tree cover change over time. For these ecosystems, the below-ground investment does not come at the cost of changing the above-ground ecosystem structure. Thus, we deem these ecosystems as stable since ecosystems' adaptive dynamics keep the structural characteristics intact. In contrast, unstable ecosystems at intermediate (30-60%) tree cover were unable to exploit the same level of adaptation as stable ecosystems, thus showing considerable changes to their above-ground ecosystem structure. We also found that ignoring this adaptive capacity of the ecosystem can underestimate the resilience of the forest ecosystems, which we find is largely underestimated in the case of the Congo rainforests. The results from this study emphasize the importance of the ecosystem's temporal dynamics and adaptation in inferring and assessing the risk of forest-savannah transitions under rapid hydroclimatic change.

How to cite: Singh, C., Wang-Erlandsson, L., Fetzer, I., and van der Ent, R.: Transient ecohydrology of the rainforests under changing climate, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-212, 2022.

13:45–14:00
|
IAHS2022-244
Mosisa Tujuba Wakjira, Nadav Peleg, Daniela Anghileri, Darcy Molnar, Tena Alamirew, Johan Six, and Peter Molnar

Temporal distribution of rainfall is a crucial climatic factor that controls seasonal biomass productivity and crop yield, particularly in tropical semi-arid and sub-humid climates where agriculture is primarily rainfed. This study explores the relationship between temporal rainfall attributes – seasonality, timing, and duration of the wet season -- and cereal crop productivity in the rainfed agriculture (RFA) areas of Ethiopia using the CHIRPS rainfall. In the first step, we determined the rainfall seasonality using an entropy-based dimensionless seasonality index (DSI), defined the dates of onset and cessation from the cumulative rainfall anomalies, computed the duration of the wet season, and assessed the anomalies and trends in these attributes and their associations to El Niño–Southern Oscillation (ENSO) over the period 1981-2010. In the second step, we analyzed the correlation between de-trended total cereal production (the sum of maize, teff, sorghum, wheat, barley, millet, oats, and rice productions) during the main growing season (April - September), and anomalies of the temporal rainfall attributes during 1995-2010. We also estimated the effects of variabilities in the rainfall timing attributes on cereal production using a univariate linear regression model. We show that rainfall in the northern RFA areas of Ethiopia is highly seasonal and unimodal whereas the southern and southeastern parts are characterized by low seasonality and a bimodal regime. Anomalies in the onset dates and DSI are meaningfully related with ENSO: 54% of late-onset events and 50% of negative DSI anomalies during 1981-2010 were observed in El Niño years. The response of crop production to changes in the temporal rainfall attributes depends on the rainfall regime. In regions with unimodal and highly seasonal rainfall regimes, we found that cereal production is mostly correlated with the onset (median ρ=-0.39) and duration (ρ=0.24) of the rainy season, whereas in regions with semi-arid bimodal rainfall regime, cereal production is more correlated with the rainfall seasonality (ρ=0.21). The median cereal production losses due to late-onset and shorter duration over the RFA areas are estimated to be ∼1.5% and 1.1% per 5-day period respectively, but much larger losses of up to 12% can be experienced in some regions.

How to cite: Wakjira, M. T., Peleg, N., Anghileri, D., Molnar, D., Alamirew, T., Six, J., and Molnar, P.: The connections between rainfall regimes and crop production in semi-arid and sub-humid climates: an example from Ethiopia, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-244, 2022.

14:00–14:15
|
IAHS2022-314
The Waza-Logone plain floodings in the context of high rainfall return: Hydro-climatic and remote sensing approaches (Lake Chad basin)
(withdrawn)
Frédéric Saha and Manuela Grippa
14:15–14:30
|
IAHS2022-475
Ralph Bathelemy, Pierre Brigode, Dominique Boisson, Emmanuel Tric, and Vazken Andréassian

Recent floods have highlighted the high vulnerability of Haitian territories to hydro-meteorological hazards. For example, the coastal city of Cayes (southern Haiti) has been heavily impacted by the torrential rainfall of October 5 to 6, 2018, with numerous damaged buildings. In Haiti, the only time period of continuous observations of both rainfall and streamflow lasts from 1920 to 1940. The concomitance of rainfall and streamflow observations at daily timestep enable the characterization of Haitian catchment hydrological response over that 20-year period. However, Haiti has experienced massive deforestation over the last century, and the Caribbean is a hotspot of climate change impacts such as warmer air and sea surface temperatures, leading to stronger hurricanes. Hence, the relevance of the characteristics estimated over the 1920-1940 period is questionable for present-time studies.

The objectives of this work are firstly to estimate flow characteristics of gauged Haitian catchments considering 1920-1940 temporal series, and secondly to use this historical information to estimate present-time hydrological characteristics. After digitalization and quality control tests of daily rainfall and streamflow temporal series, two types of hydrological characteristics were estimated on each gauged Haitian catchment. First, the catchment annual water balance was described by calculating the ratio between mean annual precipitation, evapotranspiration and runoff (using Turc-Budyko representation). Then, daily flood characteristics were estimated with a rainfall-runoff event-based study, focused on rainfall event duration and amount, peak streamflows and runoff ratio. Finally, present-time flow characteristics were estimated using a global rainfall-runoff model (GR4J) calibrated on the digitalized series, and then fed by the MSWEP dataset. This global database is available at the daily time step from 1979 to 2017, and merges gauge, satellite, and reanalysis data. The uncertainties related to the temporal stability of the rainfall-runoff model parameters and the potential impact of the deforestation on flow characteristics were then discussed.

How to cite: Bathelemy, R., Brigode, P., Boisson, D., Tric, E., and Andréassian, V.: Climate change and deforestation in Haiti: are historical hydro-meteorological observations relevant to describe present catchment hydrological characteristics?  , IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-475, 2022.

14:30–14:45
|
IAHS2022-69
Yetchékpo Patrick Gbohoui, Roland Yonaba, Tazen Fowé, Jean-Emmanuel Paturel, Harouna Karambiri, and Hamma Yacouba

Abstract:

Runoff simulation in highly anthropized watersheds is complex, but essential for water management, especially in poorly gauged and data-scarce hydrosystems of the West African Sahel. In this study, the physically-based and semi-distributed hydrological model SWAT (Soil and Water Assessment Tool) was applied to simulate daily runoff in the Nakanbé watershed at Wayen (21,178 km2) in Burkina Faso over the period 2006-2012. The data used concerned 9 water reservoirs, 5 hydrometric stations, 15 rain gauges, 3 synoptic stations, a digital elevation model (spatial resolution: 30m), a soil map (scale: 1:5,000,000), a land use and land cover map (scale: 1:200,000). The 5 hydrometric stations (Tougou, Dombré, Rambo, Ramsa and Wayen) gauge 5 nested watersheds ranging in size from 38 to 21,178 Km2. The added value of nested watersheds was assessed through the following three calibration/validation (C/V) schemes: one-site C/V (OS) at the watershed outlet (Wayen); multi-sites C/V considering nested sub-basins (MS1) and multi-sites C/V without considering nested sub-basins (MS2). The results at the watershed outlet (Wayen) indicated that the three C/V schemes (OS, MS1, MS2) are overall satisfactory (KGE above 0.7). However, MS2 scheme (KGE = 0.75) performed better as compared to the traditional one-site calibration scheme (OS: KGE = 0.73). On the other hand, the MS1 scheme (KGE =0.71) performed worse than the OS scheme. The water balance analysis at Wayen showed that 60 to 90% of the annual rainfall is lost as evapotranspiration whereas 5 to 8% contributes to surface runoff, groundwater recharge remaining very low. The comparison of the three calibration/validation schemes provides evidence that accounting for nested sub-basins does not necessarily improve the quality of rainfall-runoff simulations. Yet, multi-sites modeling remains the best scheme when the watersheds used are not nested. The availability of higher resolution data might allow a better understanding of spatial scale effects.

Keywords:

Nested watersheds, SWAT model, Nakanbé, West Africa Sahel, Burkina Faso.

How to cite: Gbohoui, Y. P., Yonaba, R., Fowé, T., Paturel, J.-E., Karambiri, H., and Yacouba, H.: Comparison of One-Site vs Multi-Sites calibration/validation schemes for hydrological modelling of nested watersheds in the West African Sahel, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-69, 2022.

14:45–15:00
|
IAHS2022-702
René Bodjrènou, Jeanmartial Cohard, Bernard Ahamidé, Basile Hector, Emmanuelagnidé Lawin, Yekambessoun Ntchampo, and Félicien Badou

West-Africa has undergone serious precipitation deficits in the second half of the XXe century, together with land use and land cover changes. While in the Sahel, runoff has mostly increased despite the drought and because of land clearing, in the sub-humid soudanian area streamflows have decreased relatively more than rainfall despite concomitant land clearing. In some areas of the Sahel, this has led an increase in groundwater levels, while the impacts on groundwater in the soudanian areas are still unclear. A better understanding and ability to simulate what happened in the soudanian area is needed to anticipate future trajectories.

We use the integrated, physics-based ParFlow-CLM model to simulate the water fluxes in the Ouémé hydrosystem in Benin, forced with climate reanalysis (ERA5), and land cover maps (1975, 2000, 2013). This was made possible after 1) evaluating locally the model performance against observations (groundwater, soil moisture, evapotranspiration, streamflow) from the AMMA-CATCH observatory when forced with observed meteorological and radiative forcings, and for the major land cover types; 2) evaluating the model sensitivity to forcings on a smaller catchment; 3) evaluating differences in ERA5 and ground-based observations (precipitation, temperature, longwave and shortwave incoming radiation); 4) Apply bias correction to the most sensitive forcing field (precipitation intensities); 5) Running a full simulation over the Ouémé catchment and quantify discrepancies with national monitorings (groundwater, streamflows).

In this communication, we present a synthesis of these different steps and show the first estimate of land cover changes impacts on the different compartments of the Ouémé hydrosystem (evapotranspiration, streamflow, groundwater, soil moisture).

How to cite: Bodjrènou, R., Cohard, J., Ahamidé, B., Hector, B., Lawin, E., Ntchampo, Y., and Badou, F.: Investigating land cover change impacts on the Oueme hydrosystem (Benin) using an integrated, physics-based model, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-702, 2022.

Break
Chairpersons: Gil Mahé, Pedro Luiz Borges Chaffe
16:30–16:45
|
IAHS2022-478
Sakaros Bogning, Raphael Onguene, Frédéric Frappart, Gil Mahé, Adrien Paris, Michel Tchilibou, Jacques Etame, and Jean-Jacques Braun

This study examines the relationship between rainfall variations in the Ogooué River Basin (ORB) and sea surface temperature (SST) of the tropical oceans. Due to its location crossing the equator, the ORB receives abundant annual precipitation (mean annual precipitation ranging from over 1000 mm to less than 3000 mm/year). Although it rains heavily throughout the basin, the rainfall is far from uniform. Due to the multiplicity of influencing factors, characterizing local precipitation at spatio-temporal scales is often a challenge. Among these factors, the SST of tropical ocean basins has been consistently reported in many studies. In this study, maximum covariance analysis is used to represent broadly coupled spatial patterns over as much of the spatial domains analyzed as possible. The method is efficient to implement numerically because it does not require pre-filtering of the fields. Results from the first modes of analysis show significant links between the southeastern equatorial SST with an extension along the equator into the Atlantic Ocean, off the coast of Peru over the El Nino Southern Oscillation (ENSO) zone of influence, and over the broader Indian Ocean including the areas of the Western Tropical Indian Ocean (WTIO) index and the Southeast Tropical Indian Ocean (SETIO) index.

How to cite: Bogning, S., Onguene, R., Frappart, F., Mahé, G., Paris, A., Tchilibou, M., Etame, J., and Braun, J.-J.: Teleconnection patterns between tropical sea surface temperature and rainfall in coastal equatorial Africa: a focus on the Ogooué River basin, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-478, 2022.

16:45–17:00
|
IAHS2022-496
Francisco Amaral, Nicolas Gratiot, and Thierry Pellarin

A good understanding of the hydrological cycle, and discharge in particular, in tropical tidal rivers enables reliable forecasting and decision making by researchers and policy makers.

The study proposes a low-cost technique to estimate tidally-influenced river discharge based on high frequency in-situ measurements. This technique pursues the work of Camenen et al. 2021 and estimates discharge based on a stage-fall-discharge rating curve, which requires the estimation of the river’s slope.

The application to the Saigon river (Vietnam) shows that its hydrological dynamics are ruled by a complex combination of atmospheric, continental and oceanic factors and pointed out unexpected hydrological behaviour: the 2018 rainy season was marked by heavy precipitations during four months, especially in November (typhoon USAGI). These high precipitations were associated with an increased water level; but surprisingly, the net water discharge decreased substantially during the same period (figure 9a, 9c). 

We propose an in-depth study of in-situ water level time series at several locations including in the Mekong delta, in the Saigon river and in the surrounding coastal area. The tidal signal obtained via harmonic analysis is extracted from the water level time series and the residual signal is then filtered using a low-pass filter as proposed in Trinh et al. 2020. This discriminates non-tidal fluctuations of water level and thus, permits the analysis of the impact of non-tidal signal such as storm surge or precipitation.

Our analysis supports that the coastal water level dynamics actually control the slope of the Saigon river and thus, its net discharge. Additionally, the coastal water level might be itself regulated by the seasonal flood of the Mekong delta, so that the Mekong river discharge management would indirectly influence the Saigon river dynamics, even if these two basins are hydrologically disconnected. 

The technique developed will help in better understanding the hydrological pattern of complex tropical estuarine rivers and disentangle the factors that influence their discharges as well as provide insights on tidal river interactions with coastal waters.

 

How to cite: Amaral, F., Gratiot, N., and Pellarin, T.: The Saigon's river response to coastal dynamics, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-496, 2022.

17:00–17:15
|
IAHS2022-532
Hero Marhaento, Martijn J. Booij, and Noorhadi Rahardjo

The aim of this study is to assess the impacts of climate change and forestation on the hydrology of a tropical catchment in Java, Indonesia. The study area is an exemplary case in Indonesia where a forestation programme has been implemented at the catchment scale. The hydrological effects of this forestation programme, in combination with climate change effects, have not been assessed. The individual and combined effects of climate change and forestation on the hydrology are assessed by employing a calibrated Soil and Water Assessment Tool (SWAT) model. Different water balance components are considered including streamflow, surface runoff, lateral flow, base flow and evapotranspiration. The results show that the forest area has increased from 2.7 to 12.8% of the catchment area from 2006 to 2019. In the same period the mean annual and seasonal temperature, rainfall and streamflow have increased as well. The SWAT simulations show that the effects of forestation on the annual and seasonal water balance components were relatively small, while the effects of climate change on these components were more pronounced. The combined effects of climate change and forestation show the dominant influence of climate change and both opposite effects of climate change and forestation on water balance components (e.g. for streamflow) and similar effects (e.g. for evapotranspiration). The outcomes of this study indicate that the forestation programme has small impacts on water balance components in the study catchment on an annual scale compared to the impacts of climate change. However, seasonally, forestation has resulted in a decrease in streamflow and surface runoff during the wet season which may reduce the flood risk. At the same time, the effects of forestation on severe drought events in the dry season should be carefully monitored. In conclusion, this study showed the relative importance of climate change and forestation impacts on water balance components and the potential of forestation programmes to flatten extreme events on a seasonal scale.

How to cite: Marhaento, H., Booij, M. J., and Rahardjo, N.: Impacts of climate change and forestation on the hydrology of a tropical catchment in Indonesia, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-532, 2022.

17:15–17:30
|
IAHS2022-590
Representing buffer effect induced by landscape fragmentation in a large-scale hydrological model
(withdrawn)
Daniel Andres Rodriguez and Lucas Garofolo Lopes
17:30–17:45
|
IAHS2022-593
Luc Descroix, Sylvie Paméla Manga, Arame Dièye, Ange Bouramanding Diedhiou, Kadiatou Diallo, Yaya Sakho, Ababacar Fall, Julien Andrieu, Andrew Ogilvie, Oumar Marega, Ousmane Diouf, and Bakary Faty

Le Fouta Djallon est considéré comme le « château d’eau » de l’Afrique de l’Ouest. La plupart des grands cours d’eau d’Afrique de l’Ouest y prennent leur source. Les eaux provenant de ce massif constituent l’essentiel du débit des grands cours d’eau apportant de l’eau douce à la bande sahélo-soudanienne, en particulier, d’ouest en est, la Gambie, le Sénégal et le Niger.

Ce massif est caractérisé par une forte hydraulicité. Ceci est lié avant tout à une forte pluviométrie, à des pentes appréciables et à une lithologie peu perméable. Les roches sont en effet peu poreuses, ce qui s’oppose grandement à la nation de « château d’eau ». de fait, les réserves sont faibles, et essentiellement liées à la présence de 8000 petites zones humides qui stockent des volumes d’eau permettant de garantir des écoulements faibles en fin de saison sèche, mais pérennes sur de nombreux cours d’eau.

La couverture végétale du Fouta Djalon n’est pas très dense, du fait d’une lithologie peu propice. Mais elle ne montre pas, ni sur le court ni sur le long terme de signes de dégradation pouvant menacer sa résilience.

Après la période hyper humide 1950-1967 et la longue sécheresse de 1968 à 1993, la pluviométrie annuelle est en croissance au point de dépasser, dans de nombreuses régions d’Afrique de l’Ouest, la moyenne de long terme. Mais les débits mettent du temps à rejoindre ceux de la période antérieure à la phase hyper humide, du fait de la reconstitution des stocks d’eau suite à leur vidange progressive durant la phase sèche où elles ont longtemps soutenu les étiages.

Cette recherche vise à déterminer les conditions de la résilience hydrologique du massif du Fouta Djalon, source majeure d’alimentation en eau douce de la bande sahélo-soudanienne.

How to cite: Descroix, L., Manga, S. P., Dièye, A., Diedhiou, A. B., Diallo, K., Sakho, Y., Fall, A., Andrieu, J., Ogilvie, A., Marega, O., Diouf, O., and Faty, B.: Le château d’eau de l’Afrique de l’Ouest est-il hydrologiquement résilient ?, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-593, 2022.

17:45–18:00
|
IAHS2022-701
The value of water resources reanalysis products for water security assessment in ungauged basins 
(withdrawn)
Elias Nkiaka

Posters: Fri, 3 Jun, 15:00–16:30 | Poster area

Chairpersons: Giovanny Mosquera, Ernest Amoussou, Pedro Luiz Borges Chaffe
P31
|
IAHS2022-79
Salif Koné, Gil Mahé, Fatogoma Bamba, Jean Emmanuel Paturel, Alain Dezetter, and Eric Servat

La géostatistique, qui permet de comprendre l’inférence spatiale existante au sein de la distribution d’une variable, conduit au développement d’une méthodologie hydro-géostatistique, pour l’estimation des paramètres de modèle en hydrologie, sur 15 sous-bassins du haut Niger à Koulikoro. Nous avons « dé-corrélé » la différence de performance des modèles par rapport à la variabilité spatiale des données d’une propriété physique du sol – spécifiquement la capacité de rétention du sol en eau (Water Holding Capacity ou WHC). Cette dé-corrélation passe par l’application d’un coefficient de pondération des lames d’eau (simulées) en modélisation semi-distribuée ; l’amélioration apportée au modèle hydrologique semi-distribué est alternativement évaluée à travers un procédé dénommé protocole inter-modèles : un coefficient de corrélation (entre la série formée par les différences relatives de performance de deux versions de modèle et celle formée par les coefficients de dispersion relative des WHC par bassin versant) qui passe de 0.80 à 0.21 en valeur absolue pour le modèle hydrologique SimulHyd. Ce modèle est issu d’une modification de GR2M, en remplaçant la constante A (la capacité maximale du  réservoir sol  au sein du modèle GR2M) par le terme 1/X1.WHC ; avec X1 le paramètre interne de GR2M qui module les données d’entrée de la modélisation ; le coefficient  de pondération, utilisé au sein de SimulHyd semi-distribué, est bâti à partir de l’information de la variance empirique (dispersion) des valeurs de WHC entre les mailles du bassin versant. Nous proposons un protocole inter-bassins dont la vocation est de bâtir un espace dénommé NASH-WHC, différent de l’espace géographique habituel, où un modèle semi-distribué avec coefficient de pondération s’illustre mieux ; ce qui se traduit par une meilleure corrélation (un coefficient de 0.48) pour la structure spatiale des point-bassins dans cet espace, (au lieu de 0.36 lorsque le coefficient de pondération n’est pas utilisé). La méthodologie hydro-géostatistique constitue un prolongement géostatistique de ce protocole inter-bassins, où les outils et démarches de la géostatistique classique sont appliqués pour la modélisation et la simulation des valeurs des paramètres des modèles hydrologiques dans cet espace NASH-WHC ; et ceci, partant des bassins jaugés pour une application sur des bassins non-jaugés. 

How to cite: Koné, S., Mahé, G., Bamba, F., Paturel, J. E., Dezetter, A., and Servat, E.: Utilisation de la Géostatistique pour l’Estimation de Paramètres des Modèles Hydrologiques sur des sous-bassins versants du haut Niger à Koulikoro., IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-79, 2022.

P32
|
IAHS2022-116
Ibouraïma Yabi, Talahatou Tabou, and Tchabi Bruno Akin

Abstract

Located in a tropical environment, the Okpara sub-basin is influenced by human actions and natural hazards while it plays an important socio-ecological role. On the basis of socio-anthropological investigations, this research analyzes community perceptions associated with the dynamics of hydro-ecological resources in this sub-basin and considers solutions for integrated and sustainable management of said resources.

The information used relates to community knowledge of hydro-ecological resources such as water, soil, vegetation and fauna (availability, uses, threat pressures, sustainability solutions). A sample of 240 people made up of the main actors, namely farmers, breeders, fishermen and hunters, was drawn up in a reasoned manner. The individual and group interviews as well as the field observations were organized, furnished the field investigations. Descriptive statistics parameters were used for data processing. Likewise, the Informant Consensus Factor (FCI) is used to test the consistency of responses.

According to respondents, the most used resources are water (100%), soil (100%), vegetation (85%) and wildlife (60%). According to the respondents, these different resources are necessary for the conduct of socio-economic activities such as agriculture, animal husbandry, fishing and hunting, which provide food, financial and medicinal resources. The degradation of plant cover (100%), the scarcity of woody species with high use values ​​(85%), the scarcity of water resources (85%), the disappearance of several animal species (75%), the of land (75), are the trends perceived by the communities. The human causes are the most cited as responsible without forgetting the drought and the runoff of water. Adaptation measures concern the adjustment of practices based on endogenous knowledge and suggestions from rural management, reforestation initiatives, the creation of community protected areas, irrigation schemes. Taking these initiatives into account will make it possible to design participatory measures for the sustainable management of hydro-ecological resources in the sub-basin studied.

Keywords: Okpara River (Benin), hydro-ecological resources, degradation, sustainable management measures

How to cite: Yabi, I., Tabou, T., and Akin, T. B.: Perceptions communautaires de la dynamique des ressources hydro-écologiques du sous bassin de l’Okpara dans la Commune de Tchaourou Centre du Bénin, Afrique de l’Ouest), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-116, 2022.

P33
|
IAHS2022-118
Jérôme Demarty, Hassane Bil-Assanou Issoufou, Jordi Etchanchu, Alain Dezetter, Ibrahim Mainassara, Monique Oï, Bassirou Adamou, Aubin Allies, Hélène Barral, Jean-Philippe Chazarin, and Bernard Cappelaere

To project the future of natural resources, the modeling of continental surfaces is identified as a key tool. In this study, an emphasis is given to the modeling of water and vegetal resources, whose interactions cannot be finely apprehended by current models. To this end, an agro-eco-hydrological model is proposed to quantify both the energy, water and carbon exchanges and the plant productivity of natural and agricultural ecosystems encountered in the agropastoral Sahel: millet cultivation and shrub fallow. This model is based on the physically-based SVAT model, SiSPAT (Braud et al., 2005). It mechanistically simulates vertical energy and water transfers in the continuum, and its high capability in the Sahelian zone has been fully demonstrated (Velluet et al., 2014). Processes specific to plant functioning and to carbon cycle were now added to the model: photosynthesis, stomatal regulation, seasonal plant phenology, and organ carbon allocation. This step was carried out for the millet crop using the formalisms described in the agronomic models SARRA-H from CIRAD (Dingkuhn et al., 2003) and STICS from INRAE (Brisson et al., 1998). Similarly, the description of natural ecosystems will soon be drawn from the ecological models STEP (Mougin et al., 1986) and TREEGRASS-2 (Boulain et al., 2014); all these models dedicated to vegetation having successfully been tested in the Sahelian context. The new version of the model has now the ability to simulate the seasonal development of agrosystems as a function of climate and energy and water availability. A first phase of exploitation of the integrated model has just been carried out in order to evaluate the robustness and relevance of the developments. It was conducted at the scale of a millet plot and with the support of multi-year observations acquired at the Wankama site (Cappelaere et al., 2009). The presentation will focus on the results as well as some perspectives of applications in future climatic changes.

How to cite: Demarty, J., Issoufou, H. B.-A., Etchanchu, J., Dezetter, A., Mainassara, I., Oï, M., Adamou, B., Allies, A., Barral, H., Chazarin, J.-P., and Cappelaere, B.: Interactions between energy, water and carbon cycles: A new agro-eco-hydrological model to study impacts of global changes in the agropastoral Sahel, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-118, 2022.

P34
|
IAHS2022-135
Ibikunlé Alain Agué, Cyr Gervais Eténé, Somiyabalo Pilabina, and Ibouraïma Yabi

Surface water resources are exposed to the effects of climate change, which poses a threat to agricultural activities in particular and socio-economic development in general. This study aims to characterize the effect of current and future climate change on surface water resource in the Alibori sub-watershed at the Yankin outlet. The historical data cover the period from 1965 to 2015 and include climate and hydrometric series respectively from the Meteo-Benin and the General Water Directorate databases. The simulation data are those of the HadGEM2-ES climate model under Representative Concentration Pathways (RCP) 4.5 and 8.5 for the horizons 2050 (time period 2041 - 2060) and 2070 (time period 2061 - 2080). These data were processed by descriptive statistics methods and the global conceptual hydrological model GR2M was used to evaluate the flow of the Alibori River for each climate scenario at the horizons 2050 and 2070. The results reveal two breaks in the flow series in 1970 and 1993, hence the consideration of the time periods 1965-1970, 1971-1993 and 1994-2015 for the analysis of current variations. Between the time periods 1965-1970 and 1971-1993, the rainfall decrease by 13% and the flow decrease by 55%. On the other hand, between the time periods 1971-1993 and 1994-2015, these two terms of the hydrological balance have experienced increases estimates at 7% for rainfull and 84% for flow, resulting in flooding phenomena that have become annual in recent decades in the sub-watershed. Similarly, by 2050 and 2070, and regardless of the RCP 4.5 or RCP8.5 scenario, the variations induced by climate change seriously affect the volume of runoff. There is a very significant increase in the average monthly flow, especially from July to October, while the annual hydrological pattern remains unchanged. Faced with this situation, appropriate strategies should be sought in conjunction with the local populations and authorities.

Keywords: Surface water resource, Climate change, Hydrological balance, Alibori sub-watershed at Yankin, Benin  

How to cite: Agué, I. A., Eténé, C. G., Pilabina, S., and Yabi, I.: Impacts of climate change on surface water resource availability in Alibori sub-watershed at the Yankin outlet (Northern Benin/West Africa), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-135, 2022.

P35
|
IAHS2022-332
Deen Dayal, Ashish Pandey, Praveen Gupta, and Yogesh Mahanandaiah

Efficient management of water resources is crucial for sustainable development, protection of the environment, and growth of the nation. However, this is quite challenging in developing countries like India, mostly due to the lack of watershed-wide hydrological data from in-situ platforms. Under such circumstances, hydrologic models forced with widely available satellite-based datasets can be very useful. Keeping this in view, Variable Infiltration Capacity (VIC), a physically-based distributed model is set up over the Upper Ganga Basin up to Garhmukteshwar gauging site. Daily calibration and validation of the VIC model were carried out for the years 2009 and 2010. The streamflow simulation was sensitive to mainly two parameters i.e., infiltration parameter and soil layer depth when evaluated with different objective functions. Model performance in the terms of coefficient of determination (R2) and Nash-Sutcliffe Efficiency (NSE) during calibration was found to be 0.76 and 0.65, respectively, while for the validation period, they were 0.78 and 0.73, respectively. A good agreement between the simulated and observed hydrographs for discharge justifies the performance and utility of the VIC model. The spatial distribution of the simulated water balance components (i.e., runoff, ET, and soil moisture) generated from the successfully validated model are presented. The study reveals that the VIC model is capable of simulating hydrological fluxes for the Upper Ganga Basin.

How to cite: Dayal, D., Pandey, A., Gupta, P., and Mahanandaiah, Y.: Applicability of VIC model for hydrological simulations over Upper Ganga Basin, India, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-332, 2022.

P36
|
IAHS2022-424
Masashi Kiguchi

South Asian countries are recognized as a vulnerable area of water-related disasters. Due to the recent climate change, the precipitation trends have been changed in some regions. Of course, it is important to examine changes in heavy precipitation because it will cause a flood, but it is also important to describe variation in weak precipitation because weak rainfall is one of the important water resources in agriculture sectors during non-monsoon seasons. Recently Endo et al. (2015) analyzed the precipitation trends in Bangladesh from 1950 to 2008. They showed that as for the total amount of precipitation and the number of the wet day appeared to be increasing over the country. Heavy rain was also increasing in some stations. During the pre-monsoon, seasonal total rainfall, the number of the wet days and weak precipitation were increasing. Heavy rainfall indices showed that inter-annual and decadal variations dominated. The objective is to analyze the long-term rainfall data (1891-2016), and detect the time series variation in Bangladesh and compare with the previous studies.
The results were generally matched with the previous one. By analyzing the short-term trend, it was showed that significant change detected in the research is due to the recent rainfall characteristics change. It implies recent climate change is significant. Trends showed spatial characteristics. Both rainfall amount and intensity are increasing mainly in southern Bangladesh. It will suggest that more active ITCZ could move southward, and this trend will continue. There were different changing trends among seasons. Also, we expand to analyze in Sri Lanka.

How to cite: Kiguchi, M.: Change of Rainfall Characteristics in Bangladesh and Sri Lanka using more than 100-years Record, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-424, 2022.

P37
|
IAHS2022-544
Loukou Alexis Brou, Affoué Berthe Yao, Zilé Alex Kouadio, Bérenger Koffi, and Kouakou Lazare Kouassi

The aim of this paper is to characterize the bottom sediments of the Cavally River bed in order to determine the appropriate roughness coefficient of said river, in a context of clandestine gold panning in the locality of Zouan-Hounien. To achieve this, fifteen (15) sediment samples are periodically taken from the Cavally River bed, precisely in the area of influence of the activities of the Société des Mines de Ity (SMI). These samples are taken from the Bakatouo meander (upstream) to downstream of the Colline Sud meander. Sediment sampling is done with a Van Veen grab sampler. The collected sediments are carefully preserved in labeled bags. The granulometric analysis of these sediments is carried out at the laboratory using a column of sieves with AFNOR series. Analysis of the particle size curves of all samples suggests that Cavally sands are generally medium to heavy. Moreover, these particle size curves could show that the sands are transported mainly by bedload. However, these observations should be taken with great caution, since gold mining activities have a very great influence on the distribution of sediments in the river.

How to cite: Brou, L. A., Yao, A. B., Kouadio, Z. A., Koffi, B., and Kouassi, K. L.: Characterisation of the morphology of Cavally River sediments in a context of anthropisation at Zouan-Hounien (West-Côte d'Ivoire), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-544, 2022.

P38
|
IAHS2022-575
Safiétou Soumaré, Luc Descroix, Barnabé Ephrem Diémé, Julien Andrieu, Ababacar Fall, and El Hadji Bamba Diaw

La Casamance, une région qui se situe au sud du Sénégal, dispose d'importantes ressources agroécologiques et forestières pour son développement socio-économique. C'est une région qui dispose d'un climat de type soudano-guinéen et est caractérisée par deux types de paysages nettement contrastés, à savoir la terre ferme beaucoup plus diverse, dont la composition varie suivant la latitude en fonction du climat, et elle connaît de très nombreuses formations (savanes, forêts et palmeraies) ; et les mangroves qui occupent une grande partie des vasières soumises aux battements de la marée. Néanmoins, depuis quelques années, la mangrove, en Afrique de l'Ouest particulièrement celle de la Casamance, connait d'importantes mutations en réaction plus ou moins directe aux évolutions du climat et aux activités anthropiques (Soumaré et al. ; 2021 ; Lombard et al., 2021 ; Andrieu, 2018 ; Tappanet al., 2004 ; Vasconcelos et al ., 2002 ; Michel, 1990). Cela produit de forts changements d'usage des sols et de couverts végétaux, ce qui provoque des modifications notoires (une réduction drastique de fait, le plus souvent) de la capacité de rétention en eau des sols, des champs, des terroirs et des bassins versants.

Cependant, depuis les années 1990, on assiste à un renversement de certaines tendances environnementales. Depuis les années 1990 s'opère une reprise des précipitations (Diémé, 2018 ; Descroix et al ., 2015 ; Bodian, 2014 ; Ali et Lebel, 2009 ; Nicholson, 2005 ; Prince et al., 1998 ; Kerr 1998) qui, d 'après la littérature, se traduit par un « reverdissement » du Sahel (Dardel, 2014, Fensholt et al ., 2011, Lebel et al. , 2009, Hermann et al ., 2005 ; Anyamba et al ., 2005, Olsson et al . ., 2005). Dans ce contexte, l'objectif de cet article est de montrer en quoi l'évolution pluviométrique récente explique la dynamique hydrologique de la Casamance. Des méthodes de cartographie multiscalaire (télédétection et enquêtes) et des techniques statistiques simples seront utilisées pour mettre en évidence l'évolution pluviométrique sur la période récente à nos jours (cumuls annuels, pluies extrêmes, date de début et de fin et durée de la saison des pluies).

How to cite: Soumaré, S., Descroix, L., Diémé, B. E., Andrieu, J., Fall, A., and Diaw, E. H. B.: Changement climatique et évolution de la mangrove en Casamance (Basse et Moyenne Casamance), IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-575, 2022.

P39
|
IAHS2022-576
Modeling River hydro-morphological responses to Land Use Land Cover Change in Tropical Regions, case of Sebeya catchment, Rwanda.
(withdrawn)
Naomie Kayitesi Manishimwe and Gregoire Marirthoz
P40
|
IAHS2022-594
Potential scenarios of land use and cover change and its hydroclimatic impacts in Brazilian Southeast
(withdrawn)
Lucas Garofolo, Isabel Pilotto, and Daniel Andres Rodriguez
P41
|
IAHS2022-608
Garance Tanguy, Lydie Sichoix, and Christophe Bouvier

The tropical volcanic Island of Tahiti is prone to heavy rainfalls and flash floods which can generate very severe damages. Hydrological response here appears highly variable from one catchment to the other, in terms of runoff production as well as peak flow amplitude. There is a strong need for an operational method able to estimate well the design flood metrics on any Tahitian catchment, taking into account the variability of their response. This study deals with five small catchments (surface range between 0.6 and 1.4 km²). It aims at adjusting the equations of the production function of the Soil Conservation Service – Lag and Route (SCS-LR) model in order to improve its flexibility until it is able to reproduce the hydrological responses. In practice for each catchment, a few dozens to a hundred of rainfall-runoff events were extracted from available records and then event cumulated rainfall and runoff were calculated and plotted to characterize the asymptotic behavior. The theoretical equation of the SCS production function was successively adjusted for the five catchments. Original SCS equations well fitted rainfall-runoff events for one particular catchment (linear determination coefficient R² of 0.85) while weak fits were obtained for the other catchments. We applied modified equations of SCS inspired by Mishra and Singh (with introduction of parameter M in SCS equations) and better regressions with R² ranging between 0.52 and 0.87 were estimated. However when using this modified model, compensation of cumulated rainfall by the optimization of the initial condition parameter S decreased values of correlation coefficient. Further exploitation of asymptotic behaviors must be undertaken to modify and render SCS equations more adapted to Tahitian hydrological variability.

How to cite: Tanguy, G., Sichoix, L., and Bouvier, C.: Adapting an Event-based, Distributed and Conceptual Model to the Hydrological Response of Small Catchments in the Island of Tahiti, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-608, 2022.

P42
|
IAHS2022-654
Alain Dezetter, Jerôme Demarty, Jordi Etchanchu, Andrew Ogilvie, Ansoumana Bodian, Papa Malick Ndiaye, Lamine Diop, and Hassane Bil Assanou Issoufou

This project, financed by ICIREWARD UNESCO center of Montpellier, is part of his WP2 "Large-scale hydrosystem processes to assess changes in the availability and quality of water resources caused by climate change" of the UNESCO centre's project. It also includes a skills transfer component for permanent or future researchers and training for doctoral students and students.

Evapotranspiration (ET) is a surface process that ensures the recycling of water and the redistribution of incident energy to the near atmosphere. In this way, it links the major continental water and energy cycles and is a major variable of interest for studies on the management and monitoring of hydro(geo)logical and plant resources (closure of water balances, monitoring of water tables, irrigation management, crop forecasting, etc.). This is all the more the case in West Africa, where ET accounts for more than 85% of rainfall (Velluet et al., 2014) and where the human pressures on the environment in terms of land use and occupation are real societal issues. These significant changes in the territory, coupled with the current and future effects of climate change, exacerbate the pressures on sensitive ecosystems where the balance of natural resources is already fragile. The proposal of methodologies to monitor and anticipate changes in green water resources (including ET) is therefore a major scientific challenge.

Satellite data acquired in the thermal infrared range provide access to a key energy balance variable, i.e. the surface temperature (ST). This variable is correlated, depending on the intensity of water stress, with ET. Over the last few decades, several algorithms have been proposed to exploit this link, and consequently to estimate ET from ST. In spite of this popularity, the current challenge is the ability of these algorithms to generate sufficiently robust, accurate and frequent products to establish annual-scale balances.

This project aims to assess the potential of the different types of satellite-based ET approaches currently applied in West Africa, not only by comprehensively reviewing and testing the ET products available in the region, but also by actively contributing to the generation of new and more reliable products.

How to cite: Dezetter, A., Demarty, J., Etchanchu, J., Ogilvie, A., Bodian, A., Ndiaye, P. M., Diop, L., and Issoufou, H. B. A.: Evap’Eau project: Estimating actual evapotranspiration from remote sensing in Senegal and Niger, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-654, 2022.

P43
|
IAHS2022-759
Santiago Yépez, Francisca Salas, José Vargas, Victor Osores, and Rolando Rodriguez

The phenomena associated with global climate variability may lead to more intense extreme events, thus causing an increase in floods and prolonged droughts. In view of this situation, the Chilean Directorate of Hydraulic Works (DOH) has the task of selecting the works to be executed with the highest priority with the annual budget, to control and mitigate the effects of floods. Hence the need for a tool that includes the evaluation of fluvial morphodynamics, which allows the management of hydraulic works compatible with the processes of response and adjustment of the channels. The objective of this study is to characterize the fluvial styles of the Duqueco River based on its geomorphology, to understand the character and behavior of the fluvial corridor in a semi-automatic way applying GIS techniques and Python geoprocessing. The first stage of the River Styles framework is applied through the South Rivers Toolbox program, which characterizes and classifies fluvial styles based on hydromorphological attributes measured at segment scale, implementing a semi-automatic approach that reduces expert judgment. Previously, the disaggregation and aggregation framework is used, which determines channel attributes at a local scale, and then aggregates them with a statistical test in larger reaches. The whole process is performed in a semi-automated way with tools from the South Rivers Toolbox set within the QGIS software. As results, 36 main fluvial styles and 47 complementary styles are classified and characterized, and the river channel is analyzed in 3 zones. The upper zone is characterized by being mostly confined, mono-channel, with a bed of boulders and blocks, being highly intervened by power generation works; the middle zone is still mostly confined and mono-channel, with a change in the type of bed towards boulders. Finally, the lower zone is more diverse in styles, mostly unconfined, with a high presence of geomorphic units that give way to multichannel and transition zones.

How to cite: Yépez, S., Salas, F., Vargas, J., Osores, V., and Rodriguez, R.: Morphological characterization using South Rivers Toolbox in the Duqueco river: A support tool for river management, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-759, 2022.