Stream Temperature Responses to Summer Urban Rain Events Along the Savannah River

Joseph E. Wermter, Savannah River National LaboratoryFollow
Vivian L. Turner, Savannah River National LaboratoryFollow
Max K. Appelbaum, University of WyomingFollow
James M. Shepherd, University of GeorgiaFollow
Jacob Z. Lott, Phinizy Center for Water SciencesFollow

Article Type

Full Research Article – Regular Issue

Volume

Issue

Abstract

The hydrological urban heat island (HUHI) is a recent facet of the urban heat island (UHI), describing thermal enhancement of bodies of water in response to urbanization. Although the forefront of this work has been studied for large Metropolitan areas, this effect on developing cities is currently unknown. To locally measure and quantify HUHI effects in a developing city, we utilized Multi-Radar Multi Sensor (MRMS) radar-derived rainfall data to estimate rainfall in the Augusta Metropolitan Area (AMA) and the Savannah Metropolitan Area (SMA), two developing communities adjacent to the Savannah River. We analyzed mean temperature trends of two stream gauges measuring temperature at, and downstream of the central AMA and the SMA. Results show overall peak stream temperatures within AMA are reached within a 2hr timeframe with surge temperatures between 1-2 K, perhaps assisted by the presence of the Augusta Shoals further upstream. The SMA appears to have little HUHI effects due to urban greening and impacts to coastal meteorology. It is suggested that Moderate rainfall events (10-25mm of rainfall) have a significant correlation (~0.1 correlation coefficient with a significance level of 0.05) between stream temperature and rainfall, indicating potential warmer runoff input into the Savannah River. Although results seem promising, further research into moderate rainfall events are needed to determine the extent of the HUHI for AMA.

Takeaway(s)

We have found that there is a suggested relationship between rainfall and stream temperature in the AMA, potentially being an impact for further study on the ecology of the Savannah River as well as being a consideration for urban heat mitigation strategies.

Recommended Citation

Wermter, Joseph E.; Turner, Vivian L.; Appelbaum, Max K.; Shepherd, James M.; and Lott, Jacob Z. (2025) "Stream Temperature Responses to Summer Urban Rain Events Along the Savannah River," Journal of South Carolina Water Resources: Vol. 10 : Iss. 1 , Article 1.
Available at: https://open.clemson.edu/jscwr/vol10/iss1/1

AugAMAfig.png (6563 kB)
Figure 1. A map of the AMA and SMA overlayed onto a Landsat derived land cover/land use map from 2020. A map contextualizing the location of the metropolitan areas within the USA is displayed on the lower left.
Figure_2.png (8476 kB)
Figure 2. Locations of the areal domains within the (a) AMA and (b) SMA in which the MRMS data is averaged as well as the locations of the Savannah River stream temperature gauges. The counts of (c) daily QPE and (d) hourly QPE for each domain is derived and displayed in labeled bar charts.
AGS_UHI.png (1473 kB)
Figure 3. Landsat-derived maximum land surface temperatures over the AMA during JJA 2019-2021, subtracted from the rural mean of surrounding counties over the same period.
Figure_4.png (2033 kB)
Figure 4. Deviation of stream temperatures in the 12 hour period surrounding a rain hour detected through MRMS data for (a-d) RM202, and (e-h) RM190, separated by magnitude of rain hour denoted by the header above each panel. The black solid lines indicate the mean temperature deviation for each magnitude of rain hour, with the red dashed lines indicating the first (below; Q1) and third (above; Q3) quartiles.
Figure_5.png (1587 kB)
Figure 5. Deviation of stream temperatures in the 12 hour period surrounding a rain hour detected through MRMS data for (a-d) Usace, and (e-h) Elba Island, separated by magnitude of rain hour denoted by the header above each panel. The black solid lines indicate the mean temperature deviation for each magnitude of rain hour, with the red dashed lines indicating the first (below; Q1) and third (above; Q3) quartiles.
Figure_6.png (1359 kB)
Figure 6. Stream temperature surges following MRMS rain hours for (a-d) RM202, (e-h) RM1905, (i-l) Usace, and (m-p) Elba Island, with the magnitude of rain hour denoted by the header of each subplot.
Figure_7.png (963 kB)
Figure 7. Lag correlations at AMA between MRMS 1-hour QPE at 15-minute intervals and the stream temperature at gauges (a-f) RM202 and (g-l) RM190, separated into bins of computed daily rainfall denoted by the header above each panel. Areas marked by a green background show where p-values fall within the critical significance threshold of 0.00-0.05 and are considered statistically significant.
Figure_8.png (959 kB)
Figure 8. Lag correlations at SMA between MRMS 1-hour QPE at 15-minute intervals and the stream temperature at gauges (a-f) Usace and (g-l) Elba Island, separated into bins of computed daily rainfall denoted by the header above each panel. Areas marked by a green background show where p-values fall within the critical significance threshold of 0.00-0.05 and are considered statistically significant.

Download