Evaluation of climate variability on sustainability for transboundary water supply in Chihuahua, Mexico

Study region: This is study of the Rio Conchos Watershed, Chihuahua, Mexico. Study focus: This study provides assessment of climate variability from analysis of instrumental climate and reservoir operations data, plus nearby tree-ring indices in Chihuahua, Mexico. Water demand include international treaty deliveries, growing agricultural land use, and intensified crop production. Analysis of climate cycles includes frequency analysis of local multidecadal instrumental hydrologic time series and multi-century tree-ring indices. In addition, tree-ring indices were compared with 14C content in tree rings to assess the presence of the millennial solar cycle.New hydrological insights for the region: Most of the climate variability within inter-annual to interdecadal periods are aligned with Pacific Decadal Oscillation (PDO)-like climate cycles. New multi-century climate cycles were discovered from tree-ring indices that have a profound impact on sustainability of food and water security. Historical droughts of 8-year average duration within PDO-like cycles that span longer (12-43 year) periods were newly identified which are longer than the 5-year delivery cycles used in the 1944 International Treaty of the Rivers. Mega-droughts were discovered to occur within multi-century climate cycles. Multi-century cycles identified in tree-ring indices were likely driven by solar luminosity changes from the millennial solar cycle and not just recent anthropogenic climate change. Climate variability and temperature increases will further amplify cycles of supply and demand and exacerbate sustainability, mitigation, and management strategies. Conjunctive use combined with reservoir operations will broaden sus-tainability portfolio of options, reducing demand effects as well as enhance supply options and replenishment effects.