Status of climate and water resources at Tumacácori National Historical Park: Water year 2015

Gwilliam, Evan; Filippone, Colleen; Hubbard, J.

Climate and hydrology are major drivers of ecosystems. They dramatically shape ecosystem structure and function, particularly in arid and semi-arid ecosystems. Understanding changes in climate, groundwater, streamflow, and water quality is central to assessing the condition of park biota and key cultural resources. This report combines data collected on climate, groundwater, and surface water at Tumacácori National Historical Park (NHP) to provide an integrated look at climate and water conditions during water year 2015 (October 2014–September 2015). Globally, 2015 was the hottest year on record. By contrast, local conditions at Tumacácori NHP were mixed, with cool-season minimum and maximum air temperatures generally well above normal, followed by a relatively cool fore-summer (May–June), and monsoon maximum temperatures typically below normal. Annual precipitation was nearly 150% of normal, with the largest increases occurring in June—a month in which little to no rainfall typically occurs. Increased rainfall and mixed air temperatures reduced the reconnaissance drought index relative to recent years, indicating a degree of recovery from the drought of the early 2000s. Water levels in the shallow aquifer at Tumacácori were at the lowest on record (June 2007– present) during the pre-monsoon period (May–early June) in WY2014. However, monsoon events near the end of WY2014, coupled with the above-average precipitation during the winter and late spring of WY2015, brought shallow-aquifer water levels back to near average. Four sampling visits were made to the Santa Cruz River index site for water quality monitoring in WY2015, one during each quarter. There were 247 individual analysis of water samples, 88 of which were associated with Arizona state water quality standards. There were no exceedances observed, and nutrient concentrations remained low—a dramatic improvement over conditions at the park five years ago. In addition, more than 15,000 measurements were collected from a logging multiparameter probe, deployed for 2–3 weeks during each of three quarters of WY2015. These data showed that the median value of temperature (°C) and dissolved oxygen concentration were within the expected range during all three deployments. The median values for pH and specific conductivity were outside the expected range during three quarters, for reasons that are uncertain. During WY2015, the amount of river flow was lower than the mean gage record in every month except September, likely due to reduced effluent contributions from the Nogales International Wastewater Treatment Plant, which is a major source of flow for the Santa Cruz River.

Status of climate and water resources at Tumacácori National Historical Park: Water year 2015

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