Synoptic mechanisms behind historical rainfall records in Australasia: Cyclone Jasper and Auckland low

3.1 Methods

4.1 Key mechanisms responsible for heavy rainfall associated with TC Jasper

Jasper was weakening by 12:00 hours UTC 9 December 2023 and Fig. 2 (top frames) shows how it had by then 200-hPa westerly winds over it. Below this level, easterly winds drove the system in the opposite direction towards the Queensland coast. Time series of the intensity of Jasper from both the automatic Digital Dvorak Technique from the University of Wisconsin Meteorological Satellite Studies on Tropical Cyclones, see http://wisc.edu) and the Cooperative Institute for Research in the Atmosphere (CIRA) at Colorado State University in Fort Collins, CO, 2024sh03_dgtldvor_202312090000.gif, 1124 × 766, see https://rammb-data.cira.colostate.edu/tc_realtime/products/storms/2024sh03/dgtldvor/2024sh03_dgtldvor_202312090000.gif) show Jasper reaching a peak intensity at c. 00:00 hours UTC 8 December 2023 and then rapidly weakening. CIRA also showed that the ocean heat content was still favourable for TC intensification up to 00:00 hours UTC 10 December 2023, so it was the 200-hPa winds impinging on Jasper that caused it to rapidly weaken.

Fig. 2.

The top frames show how Jasper around the time of peak intensity weakens as a 200-hPa trough systems moves over it bringing 200-hPa westerly winds over its circulation. Below these high levels were easterly winds and the system continued moving towards the Queensland coast. In the lower two frames are Cairns radar images for 04:59 hours UTC (left) and 13:59 hours UTC 13 December 2023 with surface average (10-min) wind, temperature and dewpoint (°C) and mean sea level pressure observations close to the radar time. Images sourced from the Australian Bureau of Meteorology.

Jasper moved closer to the coast, increasing in intensity, with Low Isle reporting 50-knot (25.7 m s^–1) mean 10-min average winds at 05:00 hours UTC 13 December (Fig. 2 lower left frame). The reported heaviest rainfall in the 24 h to 23:00 hours UTC 13 December 2023 was north of Cairns closer to the cyclone centre, with Yandill reporting 624 mm, Diwan near Daintree 507 mm and Black Mountain 476 mm. From Fig. 2 (lower right frame), this was the period when the heavy rain evident along the western eye wall of Jasper moved onto the coast. The high-resolution Global Forecast System (GFS) charts (Fig. 3) show the ascent region from anticyclonic (anticlockwise) turning in wind direction from 850 to 500 hPa wrapping around the western eye wall at landfall. Also noted is the increased cyclonic circulation at 200-hPa leading to increased warming at that level, which has been found to be associated with intensification of TCs (Rivoire et al. 2016).

Fig. 3.

The 850- and 500-hPa winds (left frames) with ascent diagnosed by anticyclonic (anticlockwise) turning in direction with increasing height and the descent regions by clockwise turning and 200-hPa winds (right frames) for 12:00 hours UTC 12 December 2023 (top) and 06:00 hours UTC 13 December 2003 (bottom). Images sourced from https://weathernerds.org/.

From Table 2, Jasper produced torrential rain throughout northern Queensland, with seven stations reporting 5- or 6-daily totals exceeding 2 m. Below, the wind structure producing this extreme rainfall and is diagnosed and an explanation for the record 24-h rainfall is given for the period to 23:00 hours UTC 17 December 2023. From Fig. 4, coastal dew points north from Cairns were high at ~24–25°C. From the ACCESS analyses from 12:00 hours UTC 14 December to 06:00 hours UTC 17 December 2023 (Fig. 5), note the ascent from anticyclonic turning winds 850 to 500 hPa along the coast north from Cairns. While coastal dewpoints north from Cairns were high at ~24–25°C, which indicated the tropical nature of the airstream being lifted (Fig. 6). From Table 2, the heaviest rain fell in the 24 h to 23:00 hours UTC 17 December 2023 (09:00 hours AEST 18 December 2023), and the microwave images (Fig. 7) show a heavy rain area developing between Cairns and Wujal Wujal by 12:00 UTC 17 December 2023. The actual 24-h period with the heaviest reported rain was at Myola (elevation 340 m) near Cairns with 915 mm in the 24 h to 14:00 hours UTC 17 December 2023 (00:00 hours AEST local time). This of course was outside the traditional registration time of 23:00 hours UTC (09:00 hours AEST local time) and cannot be compared historically. From fig. 9 in Callaghan and Power (2016), the 700-hPa northerlies along the coast north of Cairns in Fig. 5 (lower two frames) and Fig. 8 help explain why the coastal rainfall was as intense as at the elevated sites on the eastern Tablelands (see Table 2). That is, orographic lifting has less effect when the 700-hPa winds are parallel to the ranges rather than flowing up the escarpment.

Fig. 4.

Cairns radar images for 12:04 hours UTC 14 December 2023 (left) and 05:59 hours UTC 15 December 2023 with surface average (10-min) wind, temperature and dewpoint (°C) observations close to the radar time. Images sourced from the Australian Bureau of Meteorology.

Fig. 5.

ACCESS winds at 850 hPa in the left frames, 700-hPa winds in the centre frames (with red circles highlighting where winds turned anticyclonic from 850 to 500 hPa), and 500-hPa winds in the right frames, where ‘C’ marks the location of Cairns. These are for 12:00 hours UTC 14 December 2023 in the top row, 06:00 hours UTC 15 December 2023 in the second top row, 06:00 hours UTC 16 December 2023 in the third row, and 06:00 hours UTC 17 December 2023 in the bottom row. Charts sourced from the Bureau of Meteorology, with annotations by the author.

Fig. 6.

Cairns radar images with surface average (10-min) wind, temperature and dewpoint (°C) observations close to the radar time. These are for 05:59 hours UTC 16 December 2023 (top left) and 21:24 hours UTC 16 December 2023 (top right), and for 04:09 hours UTC 17 December 2023 (bottom left) and 06:04 hours UTC 17 December 2023 (bottom right). Images sourced from the Australian Bureau of Meteorology.

Fig. 7.

Naval Research Labotatory – Monterey Global Precipitation Measurement Imager rain images 06:00 hours UTC 17 December 2023 to 12:00 hours UTC 17 December 2023.

Fig. 8.

Reanalyses charts with mean flow over period 13–19 December 2023 for 850-hPa (top left), 700-hPa (top right), 500-hPa (bottom left) and 700-hPa mean temperature contours (K) for period 17–18 December 2023 (bottom right). NCEP, National Centers for Environmental Prediction; NCAR, National Center for Atmospheric Research. Images sourced from the NCEP NCAR Reanalysis (see https://psl.noaa.gov/data/composites/hour/).

The mean flow over the heavy rain period from reanalyses charts (Fig. 8) shows a ridge (between easterly and westerly flow) near 25°S latitude at 850 and 700 hPa and at these levels, the easterlies in the circulation of Jasper are stronger than the monsoon westerlies. Therefore, at these lower levels, this would tend to move Jasper westward. However, at 500 hPa, there is no sub-tropical ridge and westerly flow dominates, and this would tend to move the storm eastwards. This gave the centre of Jasper over the period a slope eastward with an 850-hPa centre just over the Gulf of Carpentaria tilting to a 500-hPa centre over Cape York Peninsula. A result of this tilt was a westerly 850–500-hPa shear with WAA at 700 hPa east of the centre and CAA west of the centre. This concentrated the heavy rain near and north of Cairns (green area in Fig. 8, top right frame, east of the centre). The mean winds show a WAA structure around Cairns with north-easterlies at 850 hPa turning anticlockwise through northerlies at 700 hPa to north-westerlies at ~500 hPa. In Fig. 8 (lower right frame), a cold 700-hPa trough can be seen extending up towards the rain area over 17 and 18 December 2023 (the period of heaviest rainfall). As shown in Appendix 1, these cold features enhanced the Cairns rainfall by increasing the instability of the high-moisture onshore flow. Therefore, an explanation of the record rainfall north from Cairns is that the high-moisture onshore flow was being lifted by the turning wind structure and by 17 December 2023, this was occurring in an atmosphere that became very unstable owing to cool middle-level air extending up to north Queensland.

During the record rain at Bellenden Ker mentioned above, nearby Cairns upper winds had a strong easterly wind component at 700 hPa that was turning anticlockwise with height from the 850- to 500-hPa level. Compare this wind structure with the winds in the lower two frames of Fig. 5 where northerly 700-hPa winds (also turning anticlockwise with height) delivered extreme rainfall to the low-lying coastal stations.

4.2 Driving forces behind the rainfall associated with the Auckland Low

According to NIWA, Auckland airport received more than its average monthly rainfall for January (201 mm or 7.9″) within 1 day on 27 January 2023. By 22:00 hours (19:00 hours UTC) on 27 January, other locations in Auckland had reported record daily rainfalls before the day was over; the Museum of Transport and Technology (MOTAT) had 238.4 mm (9.39″), Albany had 260.6 mm (10.26″) and highest daily rainfall occurred in Mangere (Auckland Airport), with a total of 265 mm (10.4″). The three automatic weather stations covered the whole Auckland urban area from MOTAT in the north and Albany in central areas to the airport in the south. 27 January 2023 was declared the wettest day at Auckland airport on record, exceeding the previous record of 161.8 mm (6.37″).

The flooding in Auckland on 27 January affected 25 suburbs in the city, closed major motorways and left 6000–8000 homes in need of damage assessment. NIWA reported that emergency services in Auckland responded to 719 weather incidents, answered 2242 emergency calls and made 126 rescues on Friday and Saturday morning. A total of 811 water-damaged cars had to be manually removed from roads, and 20 water damaged buses were removed from service.

The New Zealand Insurance Council predicted that the event would result in the highest number of weather-related insurance claims on record, with insurance companies expecting that this will be the costliest weather event in New Zealand ever. Over 57,000 insurance claims were made in relation to the floods. The floods were its largest vehicle claims event in history, with an estimated 10,000 cars expected to be written off. The event also surpassed the total cost of NZ$351 million of weather-related insurance claims in New Zealand during the entirety of 2022, which was previously the highest number in a year ever.

New Zealand authorities say four people died during the record rainfall. On Friday 27 January in the evening, more than 150 mm of rain fell in just 3 h around the city, and at Auckland airport in Mangere, 71 mm was dumped in the space of 1 h. The rain closed highways and poured into homes. Auckland, New Zealand’s largest city of 1.6 million people, remained in a state of emergency. The tropical low responsible for the rain developed near Townsville in north-east Australia and travelled in a large arc across the Coral and Tasman Seas to New Zealand (Fig. 1b). Wind analyses from the 850–500-hPa levels during the heavy rain (Fig. 9) show the strong lift the flow was experiencing as it moved down into Auckland and the North Island of New Zealand. Additionally, the radiosonde data received from the soundings at Whenuapai Airforce base in the northern suburbs of Auckland showed the strong ascent from anticlockwise turning winds with height and atmospheric instability associated with the flow into Auckland.

Fig. 9.

US reanalyses winds 850 hPa (left), 700 hPa (centre) (with red circles highlighting where winds turned anticyclonic from 850 to 500 hPa) and 500 hPa (right frames) with contours labelled in metres per second. These are for 06:00 hours UTC 27 January 2023 in the top row and 06:00 hours UTC 28 January 2023 in the bottom row. Images sourced from the NCEP NCAR Reanalysis (see https://psl.noaa.gov/data/composites/hour/).

Whenuapai winds and temperatures at 21:00 hours UTC on 26 January 2023 were 850-hPa temperature 12.4°C, dew point 12.4°C and wind 020/22.65 m s⁻¹; 700-hPa temperature 3.60°C, dew point 2.8°C and wind 005/15.96 m s⁻¹; 511-hPa wind 360/8.75 m s⁻¹; 500-hPa temperature −11.90°C, dew point −12.10°C and wind 005/8.75 m s⁻¹.

Total Totals 48.6 and lifted index −1.22 were indicative of strong instability conducive to forming significant thunderstorms.

Whenuapai winds and temperatures at 09:00 hours UTC on 27 January 2023 were 850-hPa temperature 14.20°C, dew point 11.50°C and wind 015/14.41 m s⁻¹; 700-hPa temperature 3.80°C, dew point −1.10°C and wind 340/11.33 m s⁻¹; 500-hPa temperature −11.30°C, dew point −12.90°C and wind 330/9.27 m s⁻¹.

Total Totals 48.3 and lifted index −1.77 indicative of strong instability conducive to forming significant thunderstorms.

The winds show the anticyclonic turning of the winds from 850 to 511 hPa at 21:00 hours UTC 26 January 2023 and from 850 to 500 hPa at 09:00 hours UTC 27 January 2023. The Total Totals values of 48 or more (an indicator of warm moist low levels overlain by cool mid-levels of the atmosphere) indicated strong instability or buoyancy while the negative lifted index showed that the atmosphere over Auckland was easily lifted.

Thus, like the atmosphere over Cairns with Jasper, the onshore flow was subjected to large-scale ascent while the air parcels within this flow were buoyant and easily lifted.

From the reanalyses winds in Fig. 9, Auckland is well embedded in the ascent region at 06:00 hours UTC 27 January 2023 but on the western fringe by 06:00 hours UTC 28 January 2023 when the onshore ascent flow is focussed further east. At 06:00 hours UTC 27 January 2023 (Fig. 10 top frame), note the strong north-east flow onto Northland with high dew points (19–20°C) and an opposing west-north-westerly wind at Auckland forming strong localised convergence in Auckland. This convergence zone is examined more closely from the hourly observations at Auckland airport below during 27 January 2023. At 04:00 hours UTC, Auckland reported light rain with strong east-north-east winds. The rainfall rate then became strong as these winds weakened and became more variable, opposing the strong east-north-east winds. These east-north-east winds picked up again at Auckland airport and the rainfall rate became light.

Fig. 10.

Mean sea level pressure analyses for 06:00 hours UTC 27 January 2023 (top) and 06:00 hours UTC 28 January 2023 (middle) showing mean winds (10-min) plots (normal plotting convention), isobars (hPa), dewpoints (°C) and green circles indicating rain at analysis time at the station. The bottom frame shows the radar image of disastrous Tropical Cyclone Gabrielle passing close to Auckland at 12:00 hours 13 February 2023 with mean winds, dewpoints (in red) and mean sea level pressures displayed. Auckland reported 61.6 mm in the 24 h to 00:00 hours UTC 14 February 2023. Top two images created by the author, bottom image sourced from the National Institute of Water and Atmospheric Research, New Zealand, with wind plots added by the author.

Station: Auckland Aero Automatic Weather Station (AWS) (elevation 7 m, 37°00′S 174°48′E):

By 06:00 hours UTC 28 January 2023 (Fig. 10 middle frame), this north-east onshore flow had weakened, and the rain was easing. This is shown in Fig. 11 displaying 24-h rainfall to 12:00 hours UTC 27 January 2023 in the Auckland and adjacent region; the next day (24-h rainfall to 12:00 hours UTC 28 January 2023), the heavy rain had slipped south-east and led to the devastating floods in Hawkes Bay from TC Gabrielle. Fig. 10 (lower frame) shows the disastrous TC Gabrielle passing close to Auckland but producing only moderate rainfall in the 24 h near Auckland. Note the lower dew points compared with the top two frames in Fig. 10 and the lack of direct onshore flow into the Auckland area. TC Gabrielle went on to claim 11 lives in the Hawkes Bay floods following on from similar devastation from TCs striking New Zealand from the north.

Fig. 11.

The 24-h rainfall (mm) to 11:00 hours UTC 27 January 2023 (left), and 11:00 hours UTC 28 January 2023 (right); light blue, greater than 50 mm; green, greater than 100 mm; red, greater than 150 mm; and mauve, greater than 200 mm. Image sourced from the Met Service New Zealand.

4.3 Analysis of climate drivers

The Southern Oscillation Index, or SOI, gives an indication of the development and intensity of El Niño or La Niña events in the Pacific Ocean. The SOI is calculated using the pressure differences between Tahiti and Darwin and is positive for La Niña events and negative during El Niño events (McBride and Nicholls 1983). From Tozer et al. (2023), one should expect dry conditions in El Niño and wet in La Niña for eastern Australia. The region associated with Jasper was under the influence of a weakening El Niño, the SOI showing a weakening trend with −13.6 in September 2023, −6.8 in October 2023, −8.6 in November 2023 and −2.4 in December 2023. Another driver, The Madden–Julian Oscillation (MJO), was not expected to have much influence in this case as at the time, it was over the Indian Ocean and was moving from there over to the maritime continent. Appendix 1 shows the equatorial surface winds and temperature means leading into the Jasper event, comparing it with both major El Niño and La Niña events. From these analyses, the Jasper extreme rainfall event was not under the influence of a typical El Niño event. The Southern Annular Mode (SAM) was positive, having more an effect of increased rain in south-east Australia. The Indian Ocean Dipole (IOD) was positive, having no effect on rain from Jasper.

According to NIWA, Auckland would expect more rainfall in summer under La Niña conditions. The Auckland event occurred during the tail end of a prolonged La Niña event, with the SOI figures for December 2022 being +20.0, January 2023 +11.8 and February 2023 +10.5. For Auckland, the MJO was weak, being in the central to eastern Pacific. The SAM index only briefly dipped to negative levels. The IOD was neutral, making the La Niña event the main influence for Auckland’s rain. See Appendix 1 Fig. A1 for a time series of the 30-day moving SOI for January 2022 to April 2024.

5.1 Earlier disastrous rainfall events in Australia as a comparison with TC Jasper

On the escarpment south of Cairns, Bellenden Ker Top station of Cairns (elevation 1555 m) recorded 1947 mm in the 48-h period ending 23:00 hours UTC 4 January 1979 and a 5-day total of 2457 mm to that date. Violent winds at times prevented the rain gauges being analysed every 24 h. The bottom station at Bellenden Ker (elevation 97 m) recorded 1907 mm in the 4 days to 4 January 1979, indicating the effect of orographic lifting in this case. The Australian official 24-h record of 907 mm was recorded at Crohamhurst, latitude 26.81°S, elevation 200 m, in south-east Queensland on 3 February 1893. The Crohamhurst 4-day reading was 1964 mm. These Crohamhurst data were associated with the largest ever Brisbane City flood, and 14 days later, another event of almost identical magnitude struck the city (Callaghan and Power 2014).

In Australia’s largest city, the greatest recorded floods were in the 19th Century (Callaghan and Power 2014). The largest flood in Sydney in the Hawkesbury and Nepean Rivers system was in 1867 (41 fatalities) when a low remained slow-moving over the Blue Mountains for 3 days whereas the largest Georges River floods in Sydney (the catchment with Australia’s densest population) also occurred in the 19th Century (Callaghan and Power 2014). Other 24-h rainfall records in NSW are: Newcastle Nobbys Pilot, 283.7 mm 19 March 1871; Maitland West, 375.4 mm 9 March 1893; Bulahdelah, 502.9 mm 16 April 1927; Coffs Harbour, 404.6 mm 28 April 1963, and Kempsey, 314.5 mm 28 April 1963.

In south-east Queensland, record 24-h rainfall was recorded at Brisbane, 464 mm 1 January 1887; Nerang, 401.3 mm 6 February 1931, and Southport, 426.2 mm 6 February 1931. In Victoria, the largest Yarra River and largest Gippsland floods occurred in 1934 (Callaghan 2021c), claiming 37 lives, 17 from freshwater flooding and 20 at sea. The worst floods and record rainfall occurred on the west coast of Victoria during February 1946 when there were seven drowning fatalities; as an example, Port Fairy recorded 189.7 mm in 24 h. From Callaghan (2020a), the largest Murray River flood occurred in 1870. The worst Tasmanian floods occurred in north-east Tasmania in April 1929, when 22 people died and 5000 were made homeless. There were 2000 buildings damaged and 100 destroyed, and 25 bridges were destroyed. The Hobart City record 24-h rainfall of 156.2 mm occurred on 15 September 1957. Adelaide’s record 24-h rainfall occurred on 7 February 1925, with 141.5 mm at West Terrace and 163.6 mm at North Adelaide. In Perth, the record 24-h rainfall was recorded on 9 February 1992 with 120.6 mm in the city and 132.0 mm at the airport.

As an example of extreme rainfall inland penetration, one of Australia’s worst flooding disasters occurred when a TC brought extreme rainfall into the dry interior of tropical Queensland. At 23:00 hours UTC 25 December 1916, a severe TC passed over the Dent Island lighthouse just north of Mackay, where a central pressure of 958 hPa was recorded. By 11:00 hours UTC 27 December, the night of commencement of the flood, it was located ~90 km north of Clermont. Disastrous flooding occurred and the final death toll in Clermont was somewhere between 61 and 70. The lower part of the town was never rebuilt, and settlement shifted to higher ground. Most of this rain fell over the 15-h period from 08:00 hours UTC to 23:00 hours UTC 27 December 1916 (Callaghan 2021b). The heaviest rainfall was in a zone 30–60 km east of the track of the cyclone, with totals to 597 mm. These rainfall totals are staggering for an inland location when you consider the record daily rainfall for Tully, one of the wettest locations in Australia, is 606 mm, less than the rainfall rate of 597 m in ~15 h. Obviously, the TC kept its inner core structure intact as it made its way towards Clermont and this is a sobering message for the inundation potential when a unique set of circumstances simultaneously occur. An example during 2008 provided evidence how the Clermont disaster may have occurred. From Callaghan (2021b), a tropical low formed into a cyclone tracking overland between Townsville and inland regions while under the influence of a wind structure described above as WAA, and went on to produce rainfall while still under the influence of this wind structure in the Central Highlands (where Clermont is located) with an annual recurrence interval of 2000 years or 0.05% annual exceedance probability.

5.2 Coral Sea TCs affecting New Zealand

New Zealand suffers disastrous effects from TCs moving onto the islands from the Coral Sea. As referred to above, TC Gabrielle followed soon after the 2023 Auckland low with floods devastating the Hawkes Bay region, resulting in 11 fatalities. Other examples from Callaghan (2021a) include TC Bola, which created some of the heaviest rainfall totals for a single storm in the history of New Zealand; one station recorded 419 mm (16.5″) in a 24-h period (Sinclair 1993) and three people perished. TC Giselle in April 1968 claimed 26 lives, including 51 from the sinking of the inter-island ferry Wahine. From another NIWA report in 1936, a TC formed south of the Solomon Islands on 28 January 1936. On 1 February, the cyclone was centred near Norfolk Island. It then interacted with a cold front like Giselle, which caused it to intensify prior to hitting the North Island of New Zealand on 1 February. During the night, it increased in speed and intensity, with the centre passing over Auckland. By 09:00 hours NZ time on 2 February 1936 it was located near Kawhia (55 km south-west of Hamilton); 12 people died and it brought high winds, heavy rain, flooding and rough seas to the whole North Island and Marlborough, which caused widespread damage. Damage in 2008 New Zealand dollars was reported as being over NZ$1 billion.

5.3 Anthropogenic effects and global warming

Warming sea surface temperatures with rising sea levels are expected to continue thus enhancing floods and coastal sea damage into the future (Fox-Kemper et al. 2021). In coastal areas between Brisbane and the Victorian border, the largest incidence of major flooding occurred during the 1890s and the 1950s (Callaghan 2023), indicating periods of unique events over those decades. If these occurrences continue, we can expect catastrophic events to occur. This will be exacerbated owing to this area having the fastest growing population in Australia. For example, the 1954 cyclone (Callaghan 2023) caused 36 fatalities in southern Queensland and north-eastern New South Wales and produced rainfall records still standing in those locations today. A 24-h rainfall registration of 900.4 mm broke all-time records at Springbrook Forestry (elevation 806 m), falling in the 24 h to 12:45 hours UTC 20 February 1954, and 250 mm fell between 07:00 and 11:30 hours UTC, which was the most intense period (Brunt 1956). Not long after, the current NSW 24-h record was set during this cyclone at Myrtle St Dorrigo (elevation 740 m) of 809.2 mm to 23:00 hours UTC 20 February 1954. The track through NSW is shown in fig. 19 of Callaghan (2023) with the sea surface temperatures (SSTs) in fig. 20. From this, it was shown that SSTs in 1954 were warmer than those in February 2022 (Callaghan 2023). There is no reason to suspect the 1954 SST figures as the area is part a busy shipping lane between Australia and Asia. The SSTs were a factor in making this event unique and show that marine heat waves occurred in the past. The Gold Coast–Tweed region then had a population of ~30,000, whereas today it is ~800,000 or more, so the impact from such a storm would be unthinkable. Quickly following this event were the NSW floods of 1955 (Bond and Wiesnern 1955), with 25 fatalities and enormous stock losses. Then, the largest Murray Darling floods since 1870 occurred during 1956 (Callaghan 2020a).

Rapidly increasing population and increased urbanisation significantly affect rainfall runoff, leading to a larger volume of runoff and a decrease in infiltration. This occurs because urbanisation replaces natural, permeable surfaces like soil and vegetation with impervious surfaces like roads, buildings and parking lots. As a result, rainwater flows more rapidly across these surfaces and into drainage systems rather than being absorbed into the ground (Bárdossy and Anwar 2023).