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On Fri, 30 May 2025 13:14:41 -0700,  Siri Cruz says...  

> 
> On 30/5/25 12:37, AlleyCat wrote:
> > CO2 is good for agriculture... More proof.
> >
> > India wheat, rice production to rise to record high, government says
> >
> 
> Wheat continues by dying where the sea rises and growing where it 
> does not.

"Wheat continues by dying".

Dude... put the bottle down, you mommy's basement-dwelling nerd.
 
> And you cheer as humans drown.

If ANYONE is drowning, it's because they're third world stupid, living in flood zones.

Sea level rise in an inter-glacial!!!???

Say it ain't so!
 
> <https://www.unicef.org/stories/flooding-affects-millions-bangladesh-india-and-nepal>

Learn what's REALLY causing the flooding.

People's Perception Of LAND SUBSIDENCE, Floods, And Their Connection: A Note Based On Recent Surveys In A Sinking Coastal 
Community In Jakarta

Highlights

LAND SUBSIDENCE exacerbates flooding. Their connection is scientifically obvious.

However, it is not clear whether ordinary people perceive the progress of LAND SUBSIDENCE as their own issue.

Nearly half of the respondents living in a rapidly sinking coastal community were not aware of the ongoing LAND SUBSIDENCE.

Severe flood and LAND SUBSIDENCE are not clearly recognized as interlinked problems by local citizens.

Awareness building programs should be promoted to articulate the significance of stopping groundwater extraction.

Abstract

LAND SUBSIDENCE has triggered severe coastal floods in Jakarta, whose mechanism has been extensively investigated by researchers 
and engineers. The government has also recognized this fact, which has partially contributed to the recent announcement that the 
capital will be relocated to East Kalimantan. However, it is not clear whether ordinary people perceive the progress of land 
SUBSIDENCE as their own issue. To ascertain this, a field survey was conducted after a major coastal flood that took place in 
December 2017, which revealed that nearly half of the people living in a rapidly sinking coastal community were not aware of the 
ongoing LAND SUBSIDENCE under their own houses. Severe flood and LAND SUBSIDENCE were not strongly recognized as interlinked 
problems by local citizens. Rain-induced flooding is common in the community, and this may explain why a quarter of respondents 
did not fear the 2017 coastal flood, despite their houses being flooded, in some cases to a depth above their heads. Land 
SUBSIDENCE has an adverse effect on flooding. Awareness building programs for normal citizens should be promoted, in order to 
articulate the significance of stopping groundwater extraction for mitigating LAND SUBSIDENCE and the flooding it induces.

Graphical abstract

"Do you feel your house is sinking?" This figure shows the results of our survey in March 2018, consisting of interviews with 29 
residents on flood triggered by the 2017 flood event and perception on LAND SUBSIDENCE. The ground elevation was estimated based 
on our survey in November 2017. About half of the population do not recognize that LAND SUBSIDENCE is ongoing under their own 
houses. Three respondents in this figure who experienced the highest floods (almost 2 m high) believed that their houses are NOT 
sinking. We initially hypothesized that the experience of suffering severe inundation would make people establish connection 
between flood and LAND SUBSIDENCE. However, this connection appears not to be straightforward for local inhabitants.


Introduction

Jakarta is one of the most densely populated cities in the world, with a population exceeding 10.35 million in 2018 (Pusat 
Pelayanan Statistik, 2019), plus approximately over 1.2 million daily commuters from the adjacent cities (BPS, 2019), and a total 
land area of 662 km2 (Djaja et al., 2004; Firman et al., 2010). By 2030 Greater Jakarta is expected to overtake the position of 
Tokyo as the most populated megacity in the world, with an expected population of almost 36 million people (Euromonitor 
International, 2018). An accessible and ample supply of clean water resources is required to maintain any level of human 
activity. However, the percentage of households with water access is only 24.3% (Hartono, 2018), and the urban poor have to buy 
it from local vendors. It is estimated that the city's poorer households spend 13-25% of their income for buying water, and thus 
often pump up groundwater to fulfill their basic water requirements, even though nearly 90% of shallow groundwater has been 
contaminated with domestic waste (The Jakarta Post, 2015). This groundwater extraction has caused LAND SUBSIDENCE, increasing the 
extent of flooded areas (Braadbaart and Braadbaart, 1997).

LAND SUBSIDENCE has occurred in the past or is currently occurring in major cities in Asia, with Jakarta's LAND SUBSIDENCE being 
the most prominent (Fig. 1). LAND SUBSIDENCE was observed as early as 1978, when many cracks were found in buildings and a bridge 
in Jakarta (Djaja et al., 2004). In recent years, LAND SUBSIDENCE in Jakarta has reached up to 20 cm per year in the worst 
affected places. The SUBSIDENCE is especially fast on the lowlands in the northern part of the city, where economic activity 
concentrates, such as Nizam Zachman Fishing Industry Zone (JICA, 2019). It has been estimated that the total extent of the 
potential coastal flooded area in Northern Jakarta could expand by 110.5 km2 by 2050. LAND SUBSIDENCE is responsible for 88% of 
this increase, which is much greater than the contribution of global sea-level rise (Takagi et al., 2016a). In fact, the regional 
sea-level rise in Indonesian waters is 3.3 mm/yr on average (Fig. 1). Therefore, the rate of LAND SUBSIDENCE is up to 60 times 
faster than the rate of sea-level rise.

The Emergency Events Database (EM-DAT) indicates that Jakarta has experienced 23 major floods in the past 40 years (Fig. 2). 
Twelve of these floods have occurred in the past ten years, which demonstrates how frequently floods have occurred in recent 
times. The 2013 flood was particularly severe, causing $3000 million in economic damage across Jakarta. Along with land 
SUBSIDENCE, land-use changes could also greatly affect fluvial and pluvial floods in the future (Moe et al., 2017). However, 
coastal flooding is not very common in Jakarta, especially compared to intense rainfall, which is the most typical cause of urban 
floods (Esteban et al., 2017a). In November 2007, North Jakarta suffered from its first major coastal flood (Ningsih et al., 
2011), caused by an abnormal high tide during an annual spring tide period (Takagi et al., 2016a). Moreover, questionnaire 
surveys conducted on past disaster experience showed that 86% of 200 respondents had experienced some sort of damage to their 
houses or other properties due to the coastal ?oods in North Jakarta (Esteban et al., 2017a).

In order to address coastal flooding, the master plan referred to as the National Capital Integrated Coastal Development (NCICD) 
was established jointly by multiple Indonesian governmental agencies in 2014, in association with the Government of the 
Netherlands. The 2014 NCICD report highlighted how LAND SUBSIDENCE of 7.5 cm per year on average was one of the fundamental 
reasons that was exacerbating coastal floods (NCICD, 2014). However, a mitigation plan for LAND SUBSIDENCE was not adequately 
incorporated into the plan (Colven, 2017). The most noteworthy component of this project is known as the Giant Seawall, which 
aims to close Jakarta Bay with a long offshore ring-shaped dike designed with a similar shape to the national symbolic bird Great 
Garuda. The dike was also meant to serve as a 43-km highway. Prior to the construction of the offshore seawall, it was planned 
that the existing dike would be progressively raised to keep up with the pace of sea-level rise and SUBSIDENCE (NCICD, 2014). The 
revised version of the master plan more explicitly addressed the significance of LAND SUBSIDENCE (NCICD, 2018). As a matter of 
fact, the number of newspaper articles discussing LAND SUBSIDENCE has been increasing (Octavianti and Charles, 2018).

However, as the offshore seawall would close Jakarta Bay, the NCICD masterplan has received a great deal of criticism regarding 
its environmental impacts (Wulp et al., 2016). Also, formal adaptation strategy is often decoupled from informal adaptation, and 
residents of major cities in Asia tend to be excluded from the decision-making processes (Cao et al., 2021). The 2018 NCICD 
estimated that the upgraded coastal dikes would work against future floods if SUBSIDENCE can be stopped in the short term (NCICD, 
2018). However, a 3-m dyke would only be able to cope with present-day conditions, and would eventually lose its ability to 
protect against coastal floods by 2040, unless SUBSIDENCE is stopped (Takagi et al., 2017a). Therefore, a comprehensive and long-
term adaptation strategy is essential for coping with coastal flooding induced by LAND SUBSIDENCE. In this regard, it is worth 
noting that Tokyo has successfully overcome the huge challenges brought about by SUBSIDENCE in the 1950's ~1960's by establishing 
effective regulations against groundwater extraction, as well as developing key infrastructure to ensure adequate freshwater 
supply (Esteban et al., 2020).

Despite the efforts to raise the existing dike up to 2 m, 10 years after the 2007 event North Jakarta suffered another severe 
coastal flood in December 2017 (NCICD, 2018). Fig. 3 shows a comparison of the local tide record at Tanjung Priok with the 
expected astronomical tide. Although the tide station did not completely record the tide throughout the flooding period, an 
abnormal tidal anomaly of at least 40 cm could be identified. As Jakarta is not directly affected by tropical cyclones (given its 
proximity to the equator), the height of coastal dikes is usually very low compared with those in typhoon-prone countries/regions 
(Esteban et al., 2019). Hence an abnormal tide, even if it is only in the order of ~50 cm, is enough to cause substantial 
inundations in many of the densely populated communities along the coast of Northern Jakarta.

In April 2019, Indonesia's president announced that the national capital will move from Jakarta to East Kalimantan on Borneo 
Island. LAND SUBSIDENCE and frequent floods appear to be two of the triggering factors for the government to decide to relocate, 
in addition to extreme traffic congestion (Bendix, 2019).

From the point of hydrology, the interdependency between LAND SUBSIDENCE and the extent of flooding is obvious. In a previous 
study on flooding along the Jakarta coast (Takagi et al. 2016b), the authors conducted a detailed flood analysis and pointed out 
that (due to LAND SUBSIDENCE) the velocity of coastal flooding can be faster than 1 m/s. Furthermore, if the ground sinks another 
2 m in the future, and if the coastal dike collapses for some reason, the momentum of flooding would be similar to that of a 
tsunami or a flash flood. However, it is not clear if ordinary citizens recognize the connection between LAND SUBSIDENCE and 
flooding, and some people may be reluctant to recognize that their own prodigal use of groundwater contributes to SUBSIDENCE and 
the consequent flooding (Rodolfo and Siringan, 2006).

In order to investigate the progress of LAND SUBSIDENCE and the perception coastal residents regarding this issue and floods, the 
authors carried out field surveys in a coastal community in North Jakarta before and after the 2017 coastal flood event. Based on 
the observations made, this short communication concludes that the connection between LAND SUBSIDENCE and coastal flood is not 
necessarily recognized by local citizens, contrary to scientific common sense on the obvious relationship between these two. The 
NCICD has been active in constructing large polder systems, but seems reluctant to take measures against LAND SUBSIDENCE (Colven, 
2017). In flood-prone areas, many residents tend to call for the construction or reinforcement of dikes (Takagi et al., 2017a, 
2019), generally neglecting attempts that could slow down the rate of LAND SUBSIDENCE. To improve the resilience of communities 
and ensure their long-term sustainability, awareness building programs amongst them is needed to implement.

Field Survey in Pluit Ward before and after 2017 Coastal Flood.

The authors conducted a series of field surveys along the entire coastline of Jakarta in January 2015, May 2015, September 2015, 
and February 2016, and have identified the potential hazards present in the coastal region (Takagi et al., 2016a, 2016b, 2017a; 
Esteban et al., 2017a, 2019,2020). As a result, a community in Pluit ward was clearly identified as one of the most vulnerable 
within Jakarta. This area is not only important from the point of view of how vulnerable the local population is, but also due to 
the potential threat it poses to Greater Jakarta if an adjacent pump station is flooded, as this infrastructure is critical to 
the city as a whole (Takagi et al., 2016b).

In November 2017, the authors conducted a precise topographical survey at this community, using laser range finders (TruPulse 
360; Laser Technology, Inc.) and other equipment. Aerial photos of the area were also obtained using a drone (Phantom 4 Pro; DJI 
Technology Co. Ltd.). Fig. 4 shows the ground elevations measured along pedestrian corridors, with the elevations indicated on it 
using the high-tide level of the year 2017 as the reference datum. The land appears to be situated -3 m below the highest tide 
level, but there is a noticeable difference in elevation even within this small area (~0.01 km2). The ground elevation 
immediately behind the coastal dike (upper part of Fig. 4d) was relatively high, whereas the lowest elevation was found slightly 
inland of it.

After a week of this survey, in December 2017, a severe coastal flood took place in the area, essentially a recurrence of the 
2007 coastal flood event. This flooding was widely broadcasted through international media. The authors carried out a follow-up 
survey in March 2018. This was done to clarify the extent of the 2017 flooding, in addition to collecting opinions regarding land 
SUBSIDENCE from the local population. The questions included the inundation depths at their houses and feelings of fear during 
the flood, and "Do you feel your house is sinking?". One of the authors administered a questionnaire survey to residents 
encountered while walking in the area. A total of 29 respondents agreed to answer, all of whom were residents/householders living 
in this particular community, excluding commuters from other areas. The questionnaire was originally drafted in English and was 
then translated into Bahasa Indonesia - the official language of Indonesia. Any possible relationship between SUBSIDENCE and 
flooding was not explained in advance, in order to investigate the unbiased perceptions of the respondents.

Fig. 5 shows the distribution of the flood depths, as indicated by the accounts of the 29 respondents. The flooding was not 
uniformly distributed. The deepest inundation height (nearly 2 m) was observed in slightly inland locations, whereas it was lower 
than waist level immediately behind the dike. Fig. 6 shows a comparison of inundation depth and elevation along a road starting 
from the dike (the path a-a' shown in Fig. 5). It can be seen that the elevation is the lowest at approximately 70 m from the 
dike, which is almost coincident with the location of the deepest reported flood. Essentially, this shows that the deeper 
flooding occurred at lower elevations, though other factors should also play minor localized effects (such as the location of 
concentrated overflow and blockage effects due to the accumulation of debris at the entrance of the narrow pedestrian corridors). 
In any case, it can be said that the flood damage is not uniform even within a small area.


Results and discussion

Fig. 7 summarizes the result of the two surveys in December 2017 and March 2018. One axis indicates the response on land 
SUBSIDENCE, which can be related with the flood depth and ground elevation. Although the community is small in space, the number 
of samples we were able to collect is also small. Therefore, the margin of the statistical error E is calculated by the following 
formula, which assumes a finite population with size N.


Conclusion

The latest IPCC report of Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) projects the global mean sea 
level rise will be 0.84 m (0.61-1.10 m, likely range) by 2100 under the RCP8.5 scenario. In Jakarta, this range of change in 
water levels is already happening each decade due to LAND SUBSIDENCE caused by groundwater extraction, which has been ongoing 
since at least 1978. The government understands that LAND SUBSIDENCE is a fundamental threat to the metropolitan area, 

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to 
influence the work reported in this paper.

Acknowledgements

This research was funded by a grant awarded to Tokyo Institute of Technology (Japan Society for the Promotion of Science, 
16KK0121 and 19K04964) and was also supported by the Environment Research and Technology Development Fund (S-14) of the 
Environmental Restoration and Conservation Agency of Japan. A part of the present work was performed as research activities of 
the Research Institute of Sustainable Future Society, Waseda Research Institute for Science and Engineering, Waseda University.

=====

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