A tool for community-based assessment of the implications of development on water security in hillside watersheds

Development and population growth in Latin American countries with steep sl ope farming arc likely to further increase pressures on water and land reso urces. A methodology was developed for assessing water availability and use under different development pathways at a watershed scale to determine whe ther water security is a potential problem, and if so, under what condition s it is likely to occur. This methodology makes use of a GIS-based spatial water budget model for simulating stream water availability, water use and stream flow control on a daily basis at a watershed scale. Here, we analyse d water availability under three plausible development scenarios for the 32 46 ha Cabuyal River watershed in southwest Colombia in the year 2025: Corpo rate Farming (CF), Ecological Watershed (EW), and Business as Usual (BU). S imulated average river flows at the watershed outlet were, respectively, 87 4, 796 and 925 1 s(-1) for the CF, EW and BU scenarios, The contribution of base flow to river flow (base flow index) was on average, 80.8, 85.6 and 7 7.9%, respectively, for the three scenarios. The watershed had the potentia l to meet the anticipated increase in water use under each explorative scen ario. However, dams were necessary to store irrigation water in the CF scen ario, otherwise over 60% of the available water would have been used during the dry season, Such a high figure raises concerns about effects on aquati c and riparian ecology, concentrations of potential contaminants, water res erves for especially low rainfall years, and the watershed resilience to me et temporarily hi.-her water needs during the day. Analyses indicated that current water-use conflicts in the watershed can be resolved if irrigation water supply is separated from drinking water supply. This study helped red uce some of the complexity associated with the interdependencies between la nd and water resources, the impact of using them, and spatial linkages with in the watershed. Results of this study can be used for teaching local stak eholders about basic landscape responses and helping multi-institutional al liances to become proactive and to guide development to the benefit of loca l communities. (C) 2001 Elsevier Science Ltd. All rights reserved.