WETSYS, un modèle de système dynamique pour évaluer les compromis entre les services écosystémiques des zones humides à l'échelle locale

This report presents an integrated dynamic simulation model that represents wetland functioning. The model can be used for analysing trade-offs between the provision of ecosystem services and ecosystem integrity and resulting land use changes in the Ga-Mampa wetland in the Limpopo basin in South Africa. The purpose of the analysis is to generate knowledge that can assist decision-makers and local communities in managing wetland ecosystems in a sustainable manner. The model was developed using the STELLA platform and comprises seven interactive sectors namely: hydrology (itself sub-divided into three sub-sectors: natural wetland, cultivated wetland and irrigation scheme), crop production, crop economics, irrigation management, natural resources use, land use change decision, and community well-being. These sectors are inter- linked and changes in one sector impact on other sectors through feedback loops between sectors. Key parameters in the model are community demand for food, demand for income, and biophysical drivers (soils, rainfall, groundwater and surface flows). Taking into account these factors, the local community makes choices about uses of different categories of land and water resources available to them (irrigation scheme and wetland). These activities impact on the wetland functioning, which in turn influences economic returns of wetland related activities and ultimately livelihoods. The report describes each sector in details, including a presentation of input data and results of calibration. The model is intended to be used to simulate several management options in the valley under various localised scenarios of global changes

Impact de l'usage agricole du Bas Fonds de Ga Mampa sur l'hydrologie du Bas Fonds et de la rivière Mohlapitse

Wetlands in southern Africa support the livelihoods of many poor people through agriculture for both food production and income. They are used to mitigate the problem of low crop yields associated with low rainfall and droughts. However, wetlands are complex and sensitive ecosystems, and they fulfill important environmental functions. Conversion of wetlands to agriculture has potential impacts not just within the wetland but also in downstream areas. While further development of wetlands for agriculture is difficult to prevent when alternative livelihood opportunities are lacking, it is important to ensure that this does not compromise the provision of goods and services by the wetlands. This paper investigates the possible contributions by the GaMampa wetland to stream flow in the Mohlapetsi River, a tributary of the Olifants River during low flow periods and the impact of the wetland use for agriculture on the hydrological functioning of the wetland. The GaMampa wetland comprises less than 1 % of the Mohlapetsi catchment and an even smaller portion of the Olifants catchment. Yet hydrological records show that the Mohlapetsi River contributes a significant amount of the Olifants flow particularly during the dry season. Because of the connectivity between wetlands and their surrounding catchments, hydrological processes upstream of wetlands impact the water balance of the wetlands, and processes within the wetlands impact on areas down stream. The results presented in this study are based on ongoing hydrological investigation focusing on rainfall, groundwater, and stream flow monitoring and analysis to understand hydrological processes within the GaMampa wetland. Further study is required to confirm them, but the preliminary results indicate that groundwater is a significant contributor to the dry season flow in the Mohlapetsi River, but there is little contribution directly from the wetland

Modelling trade-offs between livelihoods and wetland ecosystem services: the case of Ga-Mampa wetland,South Africa

International audienceThis paper presents an integrated dynamic simulation model that represents the functioning of a small South African wetland. The model was developed using the STELLA platform and comprises six interactive sectors namely: hydrology, crop production, crop economics, use of natural wetland resources, land use decision and community well-being. These sectors are inter- linked and changes in one sector impact on other sectors through feedback loops between sectors. Key parameters in the model are demand for food, demand for income, and biophysical drivers (soils, rainfall, groundwater and surface flows). Taking into account these factors, the local community makes choices about uses of different categories of land and water resources available to them (irrigation scheme and wetland). These activities impact on the wetland functioning, which in turn influences economic returns of wetland related activities and ultimately livelihoods. The model is used to simulate several land management options under various localised scenarios of global changes

Compromis entre subsistance des populations et services écosystémiques des zones humides: un modèle dynamique intégré de la zone humide de Ga-Mampa en Afrique du Sud

International audienceThis paper presents an integrated dynamic simulation model that represents wetland functioning and will be used for trade-off analysis. The model was developed using the STELLA platform and comprises five interactive sectors namely: hydrology, crop production, use of natural wetland resources and community well-being. These sectors are inter- linked and changes in one sector impact on other sectors through feedback loops between sectors. Key parameters in the model are demand for food, demand for income, and biophysical drivers (soils, rainfall, groundwater and surface flows). Taking into account these factors, the local community makes choices about uses of different categories of land and water resources available to them (irrigation scheme and wetland). These activities impact on the wetland functioning, which in turn influences economic returns of wetland related activities and ultimately livelihoods. The model will be used to simulate several management options in the valley under various localised scenarios of global change

Une étude de l’hydrologie des zones humides et la fourniture de services écosystémiques : la zone humide de GaMampa, Afrique du Sud

International audienceThe GaMampa wetland is typical of many small wetlands in the Limpopo River basin. These wetlands support the livelihoods of many poor people through agriculture for both food production and income from the sale of crops. They also contribute to livelihoods through the provision of natural food products and medicines, as well as materials for construction and handicrafts. The wetlands are complex and vulnerable ecosystems, fulfilling important environmental functions that benefit both local and downstream stakeholders. Conversion of a wetland to agriculture therefore has potential impacts not just within the wetland itself, but also downstream. In this paper we report the findings of an integrated study, comprising both hydrological and socioeconomic investigations of the GaMampa wetland in South Africa. The GaMampa wetland comprises less than 1% of the Mohlapitsi catchment and an even smaller portion of the Olifants River catchment; a major tributary of the Limpopo. Yet hydrological records show that the Mohlapitsi River contributes up to 16% of the dry season flow in the Olifants River. This has perpetuated the belief that, regardless of its small size, the GaMampa wetland provides an important regulating service, contributing significantly to the Mohlapitsi and Olifants River flows. The contribution of the GaMampa wetland to dry season flow in the Mohlapitsi River and the impact of wetland conversion to agriculture on its hydrological functioning were investigated. The economic analyses showed that the total net financial value of the wetland equates to an average of US$211 per household of which agriculture comprises 38$ dont 38% correspondent à l’agriculture. Les analyses hydrologiques ont montré que la rivière Mohlapitsi contribue en moyenne pour 16% au débit de la rivière Olifants en saison sèche. Cependant, la zone humide contribue à 12% au plus de l’augmentation du débit observé en saison sèche sur la portion de la rivière sur laquelle la zone humide est située. Le reste de l’augmentation provient de l’eau souterraine qui coule au travers de la zone humide. Par ailleurs, malgré la conversion de 50% de la zone humide en terres agricoles depuis 2001, il n’y a pas eu de réduction statistiquement significative du débit de saison sèche de la rivière Mohlapitsi. Ces résultats soulignent combien il est important de comprendre la nature de la gamme complète de services fournis par une zone humide, afin de prendre des décisions éclairées pour une gestion appropriée

Le cadre d'aide à la décision du projet WETwin

The overall objective of the WETwin project is to enhance the role of wetlands in basin-scale integrated water resources management (IWRM), with the aim of improving the community service functions while conserving good ecological status. Wetland management strategies will be identified for (i) integrating wetlands into river basin management; (ii) utilizing the drinking water supply and sanitation potentials of wetlands for the benefit of people living in the basin, while maintaining (and improving as much as possible) the ecosystem functions; (iii) adapting wetland management to changing environmental conditions; and (iv) improving stakeholder participation and capacity building with the aim of supporting sustainable wetland management. The envisaged wetland management strategies are planned to be developed with the help of a Decision Support (DS) Framework. The primary aim of this report is to provide a detailed description about this framework, and also to give guidance on how to apply it at case studies. The report consists of two main parts. In the first part the Conceptual Framework is introduced. This is followed by the detailed description of the embedded Decision Support Framework in the second part

Evaluation of different methods for delineation of wetlands in Limpopo River Basin using Landsat ETM + and SRTM data

In Proceedings, GlobWetland: Looking at Wetlands from Space, Frascati, Italy, 19-20 October 200