Carbon, Land and Water: A Global Analysis of the Hydrologic Dimensions of Climate Change Mitigation through Afforestation/Reforestation

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"Climate change and global warming have become familiar notions throughout the world, as the profound impact that human activities have made on global biogeochemical cycles is increasingly recognized. The global carbon cycle has received much international attention as it has become increasingly obvious that increased levels of CO2 in the atmosphere are causing changes in our climate at an alarming rate. The Kyoto Protocol is an international effort aimed at mitigating climate change through the reduction of greenhouse gas emissions into the atmosphere. Within the Kyoto Protocol, the Clean Development Mechanism (CDM) is an instrument which is intended to reduce greenhouse gas emissions, while assisting developing countries in achieving sustainable development, with the multiple goals of poverty reduction, environmental benefits and costeffective emission reductions. The CDM allows for a small percentage of emission reduction credits to come from reforestation and afforestation (CDM-AR) projects. "In this report, we articulate the hidden water dimensions of international efforts to mitigate climate change through multilateral treaties through a global analysis of land suitability and water use impacts of CDM-AR carbon sink projects. Large amounts of land were identified globally as biophysically suitable and meeting the CDM-AR eligibility criteria. The eco-sociologic characteristics of these suitable areas were examined, with results showing that much of this land is under rain-fed and/or subsistence agriculture or savannah land. Large amounts of suitable land exhibited relatively low population densities. Generally, most of this land is below 1,000 meters (m) in elevation and of moderate productivity. "If converted to forest, large areas deemed suitable for CDM-AR would exhibit increases in actual evapotranspiration and/or decreases in runoff, i.e., a decrease in water potentially available off-site for other uses. This is particularly evident in drier areas, the semi-arid tropics, and in conversion from grasslands and subsistence agriculture. However, major direct impacts of CDM-AR at the global and regional scales on water resources and food security are ascertained as unlikely, primarily due to the UNFCCC mandated cap on CDM-AR at one percent per annum of total emission obligations. However, significant changes in CDM-AR rules affecting the number of projects or amount of land that could eventually be under CDM-AR, should take into account these potential impacts on the hydrological cycle, and related food security issues. At the local and project level scale, impacts on water use was substantial. It was evident that CDM-AR projects can benefit from identifying locally optimal locations for tree plantations that maximize the positive aspects of increased green water vapor flows and reduced runoff. "This report highlights the potentially significant impacts on the hydrologic cycle and the importance of considering secondary effects, particularly with regard to water, resulting from the widespread adoption of global climate change mitigation measures. It is recommended that the implicit hydrologic dimensions of climate change mitigation should be more formally articulated within the international environmental conventions, and recognized within future UNFCCC negotiations on the CDM-AR provisions."
climate change, afforestation, reforestation, land tenure and use, water resources, trees, forests, ecosystems