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Can hot water discharged from industrial processes enhance the likelihood of waterspouts?

Valerio Capecchi, Bernardo Gozzini, Mario Marcello Miglietta

Abstract

Italy and the surrounding seas are recognised as one of the European hotspots for tornadoes and waterspouts. In recent years, the town of Rosignano Solvay (on the Northern Tyrrhenian coast) experienced repeated waterspouts affecting the same areas, raising local concern about the possible influence of heated wastewater discharged into the sea by a nearby industrial site. We reconstruct the mesoscale meteorological conditions of four intense waterspouts near Rosignano Solvay using a limited-area weather model at high-to-very-high resolution (inner domain grid spacing 500 m; sensitivity tests at 100 m). At the reported event times, the intensity of key mesoscale precursors (low-level wind shear, 1 km storm-relative helicity, maximum updraft intensity, and lifting condensation level) is consistent with the values typically associated with EF1 (or stronger) tornadoes and waterspouts. The model systematically predicts the peak of instability indices 2-3 hours earlier than the reported event times. For one case study, we conduct two sea surface temperature sensitivity experiments to assess the potential atmospheric impact of heated wastewater discharge (temperature increases of +1.5 K and +5 K over a 10 km$^2$ area). The resulting changes in instability indices are marginal, with differences of at most 3\% relative to the control run. A simple mass-balance estimate for the modified sea patch suggests that, given the reported discharge rates, a plausible impact of the warm water released from the industrial site could lead to an increase in the local sea surface temperature of approximately +0.7 °C over two months. We conclude that synoptic and mesoscale conditions primarily govern waterspout initiation in this region, while the direct effect of the small, warm coastal plume from the industrial discharge appears to be minor.

Can hot water discharged from industrial processes enhance the likelihood of waterspouts?

Abstract

Italy and the surrounding seas are recognised as one of the European hotspots for tornadoes and waterspouts. In recent years, the town of Rosignano Solvay (on the Northern Tyrrhenian coast) experienced repeated waterspouts affecting the same areas, raising local concern about the possible influence of heated wastewater discharged into the sea by a nearby industrial site. We reconstruct the mesoscale meteorological conditions of four intense waterspouts near Rosignano Solvay using a limited-area weather model at high-to-very-high resolution (inner domain grid spacing 500 m; sensitivity tests at 100 m). At the reported event times, the intensity of key mesoscale precursors (low-level wind shear, 1 km storm-relative helicity, maximum updraft intensity, and lifting condensation level) is consistent with the values typically associated with EF1 (or stronger) tornadoes and waterspouts. The model systematically predicts the peak of instability indices 2-3 hours earlier than the reported event times. For one case study, we conduct two sea surface temperature sensitivity experiments to assess the potential atmospheric impact of heated wastewater discharge (temperature increases of +1.5 K and +5 K over a 10 km area). The resulting changes in instability indices are marginal, with differences of at most 3\% relative to the control run. A simple mass-balance estimate for the modified sea patch suggests that, given the reported discharge rates, a plausible impact of the warm water released from the industrial site could lead to an increase in the local sea surface temperature of approximately +0.7 °C over two months. We conclude that synoptic and mesoscale conditions primarily govern waterspout initiation in this region, while the direct effect of the small, warm coastal plume from the industrial discharge appears to be minor.
Paper Structure (15 sections, 3 equations, 19 figures, 4 tables)

This paper contains 15 sections, 3 equations, 19 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Data and methods
  3. Description of the waterspout cases
  4. The 17DEC2011 case
  5. The 27NOV2012 case
  6. The 10SEP2017 case
  7. The 25SEP2020 case
  8. Experimental design of the Meso-NH model for the numerical reconstruction of the four events
  9. Meteorological parameters
  10. Results
  11. Discussion
  12. Conclusions
  13. Appendix A
  14. Appendix B
  15. Appendix C

Figures (19)

  • Figure 1: Zoom on the Rosignano Solvay area belonging to the Rosignano Marittimo municipality. The red square delineates the integration domain for the higher-resolution Meso-NH simulation, which employs a grid spacing of 100 m and is applied to the 25SEP2020 case only. The white trapezoid indicates the region where sea surface temperatures were modified in the sensitivity experiments. Such trapezoid covers an approximate area of 11 km$^2$. The black line represents the path of the ditch that discharges water from the industrial facility, which is indicated with the black polygon and is located less than 1 km inland from the coastline. Satellite image from Sentinel-2 cloudless © EOX IT Services GmbH.
  • Figure 2: 1-30 September 2020 hourly data from the Solvay Chimica Italia discharge ditch: (a) flow (unit of measure is ${m^3}$/hour) indicated with black triangles and (b) water temperature (unit of measure is degree Celsius) indicated with black circles. In both plots the red line indicates the 24-hour moving average and the black vertical line indicates midnight of the 25th of September 2020. Data courtesy of Solvay Chimica Italia.
  • Figure 3: 850-hPa equivalent potential temperature, $\theta_E$ (unit of measure degree Celsius), and wind speed (unit of measure knots) and direction from ERA5 data at the approximate time of the waterspout for the 17DEC2011 (a), 27NOV2012 (b), 10SEP2017 (c) and 25SEP2020 (d) case. Barbs are shown for wind speed greater than 20 knots. The approximate location of Rosignano Solvay is indicated with the black point ($\bullet$).
  • Figure 4: 17DEC2011 case: (a) surface pressure reduced at sea level and fronts at 06 UTC (plot courtesy of UK MetOffice) and (b) 850-hPa wind speed and direction (barbs), relative humidity (shaded colours) and temperature (white contour) at 06 UTC (ERA5 data). The approximate location of Rosignano Solvay is indicated with the black point ($\bullet$).
  • Figure 5: 27NOV2012 case: (a) surface pressure reduced at sea level and fronts at 12 UTC (plot courtesy of UK MetOffice) and (b) Meteosat infrared image at 10.45 UTC with superimposed lighting strikes observed by the Blitzortung network. The approximate location of Rosignano Solvay is indicated with the black point ($\bullet$).
  • ...and 14 more figures