Status of climate and water resources at Tumacácori National Historical Park: Water year 2018

Gwilliam, Evan; Palacios, Laura; Raymond, Kara

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 2018 (October 2017–September 2018). Overall annual precipitation was 74% of normal. Rainfall was higher than normal in February and near normal in June–August. All other months received substantially less rainfall than normal. Temperatures at Tumacácori NHP tended to be warmer than normal—except during the summer months, which were slightly cooler. The reconnaissance drought index indicated that the drought that began in 2000 continued through WY2018, while the five-year running mean of total annual precipitation indicated the drought has been less severe during the last five years. Two monitored wells at Tumacácori NHP (MW-1 Deep and the Mission unit’s water supply well) indicated that mean groundwater levels in WY2018 were generally higher than the mean of the data record for each well (0.21–1.35 ft). The third well, MW1-Shallow, was missing data for nearly a quarter of the year, and an annual mean was not calculated. Water levels in both the shallow- and deep-aquifer wells peaked after a large storm event in February, then dropped in response to dry spring conditions, and quickly increased with monsoon precipitation and flow events. Seasonal variability was more dramatic in the shallow aquifer. Streamflow data for this report were recorded at USGS gauge 09481740, on the Santa Cruz River at Tubac, Arizona. This gauge is located five kilometers downstream from the index sampling site in Tumacácori NHP. Streamflow on the Santa Cruz River through the park was slightly below average in WY2018. Peak flow occurred on August 23. There were several smaller flow events on August 9, August 14, and September 19. Recorded discharge was typical for October–May, then decreased through the pre-monsoon, dry, hot period of late May and June. The pre-monsoon period, along with a slight decrease of discharge during the monsoon, led to the decreased mean and median values for WY2018 compared to the gage record. Water samples were collected from the Santa Cruz River at the Santa Gertrudis index site. Of 90 individual analyses associated with Arizona surface-water criteria, there were two exceedances: one for E. coli, and one for cyanide; that is, almost 98% of samples were compliant with state standards. Relative to macroinvertebrates, the Arizona Index of Biological Integrity value has been at or below impaired status since WY2012 (although there is not an established index threshold for effluent-dominated streams in Arizona). Fish were collected during collaborative sampling at the Santa Gertrudis index reach. The metric for longfin dace (Agosia chryogaster) decreased in WY2018. In WY2018, workers collected and summed the number of fish from the family Poeciliidae, including Gila topminnow and western mosquito-fish. The metric for Poeciliidae increased in WY2018 (35.78 fish/minute) from previous years. The continued presence of longfin dace and Poeciliidae are positive indicators of the animals’ response to improved water quality and habitat features on this reach.

Status of climate and water resources at Tumacácori National Historical Park: Water year 2018

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