TWO-DIMENSIONAL EVALUATION: THE ENVIRONMENTAL AND SOCIOECONOMIC IMPACTS OF MEXICO' S PAYMENTS FOR HYDROLOGICAL SERVICES PROGRAM December, 2012 Jennifer M. Alix-Garcia a Katharine R.E. Sims b Patricia Yanez-Pagans a Elizabeth N. Shapiro c a. Agricultural and Applied Economics, University of Wisconsin, Madison b. Department of Economics, Amherst College c. Nicholas School of the Environment, Duke University