[1] Vertical and horizontal water fluxes in the unsaturated zone near intermittent streams critically affect ecosystems, water supply, and contaminant transport in arid and semiarid regions. The subsurface near the Oro Grande Wash is typical in having great textural diversity, pronounced layer contrasts, and extremely low hydraulic conductivities associated with nearly dry media. These features prevent a straightforward application of the Darcian method for recharge estimation, which has provided high-quality flux estimates at simpler, wetter sites. We have augmented the basic Darcian method with theoretical developments such that a small number of core sample unsaturated hydraulic property measurements, combined with additional, easily obtained data (e.g., drillers' logs) can provide useful flux estimates and knowledge of two-dimensional water behavior beneath the wash.

Jurisdictions are in the process of establishing regulatory systems to control greenhouse gas emissions. Short‐term and sometimes long‐term emissions reduction goals are established, as California does for 2020 and 2050, but little attention has yet been focused on annual emissions targets for the intervening years. We develop recommendations for how these annual targets—which we collectively term a “compliance pathway”—can be set, as well as what flexibility sources should have to adjust in light of cost uncertainties. Environmental effectiveness, efficiency, equity, adaptability, and encouraging global participation are appropriate criteria by which these intertemporal policy alternatives should be judged. Limited but useful knowledge about costs leads us to recommend a compliance pathway characterized by increasing incremental reductions along it. This can be approximated by discrete linear segments, which may fit better with global negotiations. Although the above conclusion applies to any long‐term GHG regulatory program, many jurisdictions will rely heavily on a cap‐and‐trade system, and the same pathway recommendation applies to its time schedule of allowances. Furthermore, borrowing constraints in cap‐and‐trade systems can impose substantial unnecessary costs. To avoid most of these costs, we recommend that sources be allowed early use of limited percentages of allowances intended for future years. We also find that a three‐year compliance period can have substantial benefit over a one‐year period. © 2010 by the Association for Public Policy Analysis and Management.