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. 2020 May 14;22(5):549.
doi: 10.3390/e22050549.

Complex Extreme Sea Levels Prediction Analysis: Karachi Coast Case Study

Faisal Ahmed Khan  1 , Tariq Masood Ali Khan  1 , Ali Najah Ahmed  2 , Haitham Abdulmohsin Afan  3 , Mohsen Sherif  4   5 , Ahmed Sefelnasr  4 , Ahmed El-Shafie  4   6
Affiliations

Complex Extreme Sea Levels Prediction Analysis: Karachi Coast Case Study

Faisal Ahmed Khan et al. Entropy (Basel). .

Abstract

In this study, the analysis of the extreme sea level was carried out by using 10 years (2007-2016) of hourly tide gauge data of Karachi port station along the Pakistan coast. Observations revealed that the magnitudes of the tides usually exceeded the storm surges at this station. The main observation for this duration and the subsequent analysis showed that in June 2007 a tropical Cyclone "Yemyin" hit the Pakistan coast. The joint probability method (JPM) and the annual maximum method (AMM) were used for statistical analysis to find out the return periods of different extreme sea levels. According to the achieved results, the AMM and JPM methods erre compatible with each other for the Karachi coast and remained well within the range of 95% confidence. For the JPM method, the highest astronomical tide (HAT) of the Karachi coast was considered as the threshold and the sea levels above it were considered extreme sea levels. The 10 annual observed sea level maxima, in the recent past, showed an increasing trend for extreme sea levels. In the study period, the increment rates of 3.6 mm/year and 2.1 mm/year were observed for mean sea level and extreme sea level, respectively, along the Karachi coast. Tidal analysis, for the Karachi tide gauge data, showed less dependency of the extreme sea levels on the non-tidal residuals. By applying the Merrifield criteria of mean annual maximum water level ratio, it was found that the Karachi coast was tidally dominated and the non-tidal residual contribution was just 10%. The examination of the highest water level event (13 June 2014) during the study period, further favored the tidal dominance as compared to the non-tidal component along the Karachi coast.

Keywords: Pakistan coast; annual maximum method; complex system prediction; extreme sea level prediction; joint probability method.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Bathymetry, topography and the location of the tide gauge at Karachi port, along the Pakistan coast.
Figure 2
Figure 2
Tracks of all four of the tropical cyclones during the study period (2007 to 2016).
Figure 3
Figure 3
Spectral density of the tide gauge data.
Figure 4
Figure 4
Hours from the highest water event at 11:00 PST (local time) on 13 June 2014 in the Karachi coast during the study period (i.e., years 2007–2016).
Figure 5
Figure 5
The track of Cyclone “Yemyin”, June 2007.
Figure 6
Figure 6
The signatures of the storm surges are seen in the tidal analysis of the Karachi Data during the period 20–28 June 2007 (Cyclone Yemyin).
Figure 7
Figure 7
Return period by using the AMM (annual maximum method).
Figure 8
Figure 8
Estimated return period of extreme sea level utilizing the AMM and the JPM (joint probability method) for Karachi, Pakistan. The vertical lines show 95% confidence limits.
Figure 9
Figure 9
Annual mean and extreme sea levels for the Karachi tide gauge data from the year 2007 to 2016.
See this image and copyright information in PMC

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