[1] Primary productivity and vegetation cover are strongly related to how precipitation is partitioned into surface discharge, storage, and evapotranspiration (ET). Thus, quantifying feedbacks between changes in precipitation and vegetation at regional scales is a critical step toward predicting both carbon balance and water resources as climate and land cover change. We used a catchment-based approach to quantify partitioning of precipitation and compared these hydrologic fluxes to remotely sensed vegetation greenness (NDVI) in 86 U.S. catchments between 2000 and 2008. The fraction of precipitation potentially available to vegetation (catchment wetting; W) ranged from 0.64 to 0.99 demonstrating that up to 36% of precipitation was not available to vegetation. The ratio of ET:W (Horton Index (HI)), ranged from 0.07 to 1.0 demonstrating even greater variability in the fraction of catchment wetting used as ET. Negative slopes between annual Horton Index and maximum annual NDVI values indicated water limitation during dry years in most catchment ecosystems. Not surprisingly, grasslands were more sensitive to drying than forests. However, in nine of the wettest (HI < 0.66) catchment ecosystems, NDVI values increased as HI increased suggesting greater vegetation productivity under drier conditions. Our results demonstrate that catchment-scale hydrologic partitioning provides information on both the fractions of precipitation available to and used by vegetation. Their ratio ( HI) identifies shifts between water and energy limitation, and differential sensitivity to drying based on vegetation type within catchment ecosystems. Consequently, catchment-scale partitioning provides useful information for scaling point observations and quantifying regional ecohydrological response to climate or vegetation change.Citation: Brooks, P. D., P. A. Troch, M. Durcik, E. Gallo, and M. Schlegel (2011), Quantifying regional scale ecosystem response to changes in precipitation: Not all rain is created equal, Water Resour. Res., 47, W00J08,

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This study reviews and synthesizes the results from geochemical and isotopic case studies across Europe, North America, Antarctica, and Greenland to evaluate the effects of Pleistocene glaciation on continental-scale groundwater circulation in sedimentary basins. The most effective studies, in terms of delineating high-resolution records of paleorecharge to aquifers, combine solute chemistry, stable isotopes of water, age tracers, and dissolved noble gases. Some of the lowest d 18 O values ()22&), and noble gas temperatures (0°C), and high excess air concentrations were found in confined groundwaters in northern Estonia, likely derived from Scandinavian Ice Sheet subglacial recharge. These results are consistent with groundwater systems in North America that were recharged beneath the Laurentide Ice Sheet. Late Pleistocene precipitation may have also been an important source of recharge, as indicated by low-temperature, isotopically enriched groundwaters in several basins. Detectable age gaps have been observed in several aquifer systems in North America and Europe, likely caused by a hiatus of groundwater recharge in areas covered by permafrost during the Last Glacial Maximum (10-21 ka). Aquifers that were not covered by ice sheets or permafrost contain continuous records of Pleistocene to Holocene recharge with variable d 18 O values and low paleotemperatures (4-9°C lower than today). The maximum depth of glacial meltwater penetration into sedimentary basins is approximately 50-1000 m. Infiltration of dilute meltwaters dissolved large quantities of halite in evaporite-bearing basins. The presence of clay-rich glacial deposits and bedrock confining units enhanced the storage of meltwaters within low-permeability sediments and limited flushing of paleowaters in underlying aquifers. These results demonstrate the importance of continental glaciation as a driver for basinal-scale fluid and solute transport and have implications for long-term storage of radioactive waste and carbon dioxide at depth in high-latitude sedimentary basins.

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