Corroboration of Evapotranspiration and Infiltration Determined from Meteorological Time Series and Field Observations at the Rifle Site, CO, USA.

Net infiltration to the vadose zone, especially in arid or semi-arid climates, is an important control on microbial activity and solute and green house gas fluxes.  To assess net infiltration, we performed a statistical analysis of meteorological data as the basis for hydrological and climatic investigations and predictions for the Rifle site, Colorado, USA, located within a floodplain in a mountainous region along the Colorado River, with a semi-arid climate.  We carried out a statistical analysis of meteorological 30-year time series data (1985-2015), including: (1) precipitation data, taking into account the evaluation of the snowmelt, (2) evaluation of the evapotranspiration (reference and actual), (3) estimation of the multi-time-scalar Standardized Precipitation-Evapotranspiration Index (SPEI), (4) evaluation of the net infiltration rate, and (5) corroborative analysis of calculated net infiltration rate and groundwater recharge from radioisotopic (2013) measurements.  We determined that annual net infiltration percentage of precipitation varies from 4.7% to ~17.7%, with a mean of ~10%, and concluded that calculations of net infiltration based on long-term meteorological data are comparable with those from strontium isotopic investigations.  The evaluation of the SPEI showed the intermittent pattern of droughts and wet periods over the past 30 years, with a detectable decrease in the duration of droughts with time.