Evaluating agricultural sustainability in tropical watersheds : an integrated geographical approach

Abstract

A framework for evaluating agricultural sustainability in tropical watersheds was established using spatial multi-criteria analysis. This GIS-based decision support system was able to integrate localised sustainability indicators and reflect the vulnerability of the watershed's resources to land degradation processes. The derived spatial sustainability indices may now be able to support design of alternatives towards interventions for long-term productivity that could ensure food security to the community while at the same time preserving the environment. The high poverty incidence among staple crop farmers and persistent low productivity that could barely support the needs of the growing population within the province motivated a watershed-scale approach in investigating for enhanced sustainable farming practices that could help address the pressing concerns in the locality. This research is a component of initiatives aimed to develop suitable management practices for demonstration and subsequent adoption by low-income crop farmers. Hence, the overall contribution of this study has been to evaluate the degree of agricultural sustainability and map out alternatives or options for long-term sustainability, best utilising the watershed's limited resources. An integral component was the selection and identification of applicable sustainability indicators that could locate vulnerable areas when aggregated in a flexible and intuitive decision support framework. The integration of derived indicators was carried out to allow calculation of sustainability indices in a geographical manner. An operationalisation for a case and site specific meaning of agricultural sustainability and its breakdown into functional units was key to the establishment of localised sustainability indicators. A systems approach was employed for a holistic description of what would constitute agricultural sustainability for the particular watershed as perceived by the local stakeholders. Achievable sustainable management options that could be implemented for the existing farming systems were then generalised to reflect the long-term sustainability goals which essentially became the operational components of agricultural sustainability. Further, systems analysis using causal loop diagramming illustrated the interactions among factors affecting the farming system which were eventually transformed into stocks and flows to facilitate the development and selection of the sustainability indicators. The localised definition, as a result of the systems analysis, describes agricultural sustainability as determined by an appropriate combination of cropping systems employing suitable erosion and runoff interventions to help preserve soil and water resources while sustaining agricultural productivity and consequently ensuring at least subsistence food security and financial income for farmers. The identification of realistic indicators was further validated by the availability of limited datasets for the entire watershed area. Soil erosion and runoff were identified as the main factors of land degradation affecting the study area of the upper Inabanga watershed in Bohol, Philippines. High runoff and soil loss were pronounced over the watershed, especially in extensively cultivated areas of corn and cassava. Mapping the spatial extent of probable risks to high erosion and runoff as well as incorporating other vital contributing factors constituted the most important collective indicator for agricultural sustainability evaluation. Available agro-socioeconomic parameters associated with the likelihood of communities to overexploitation of resources and inappropriate farming practices were also considered a critical indicator group that contributed to the deterioration of the environment. For water resources, the rapid decline in hydrologic conditions of a gauged sub-watershed, which were found comparable with other ungauged sub-watersheds, exhibited trends towards unsustainability if not mitigated immediately. And importantly, information extracted from a multi-temporal analysis of remotely sensed imageries indicating changes in land use conditions over time revealed a range of human activities that could have significant impacts on susceptibility to environmental degradation. The integration of all identified sustainability indicators enabled development of a comprehensive and powerful decision support tool for sustainable management of an agriculture dependent tropical watershed. The logical structure for the aggregation and hierarchies of the input indicators was organised in a user-defined criteria tree addressing a goal of locating vulnerable areas to land degradation processes. The entire procedure involved standardisation and assigning of weights to each input parameter prior to a weighted summation technique in the calculation of the resulting composite index map. The process was facilitated through utilisation of a GIS application termed Spatial Multi-Criteria Evaluation. The data driven approach in setting up the sustainability criteria and the exercise of value judgement rendered this framework more flexible for problem-solving and decision-making. The derived spatial sustainability indices illustrated varying degrees of vulnerability which could then be applied in prioritisation for the application of sustainability interventions. Strategies for employing site specific conservation measures particularly for dealing with high runoff and soil loss in cultivated areas were also developed and identified through scenario simulations of suitable input parameters for the spatial multi-criteria analysis.

Date of Award	2011
Original language	English