(In Part 1, data analysts explained how they arrived at a definition of water security. In Part 2, the analysts explained the methodology used in estimating the Cauvery index and the results have been obtained. In continuation, part 3 will explain the methodology used in estimating the remaining indices and its results)

Groundwater index

Borewell count: The OpenCity borewell dataset was used to map borewells into Bruhat Bengaluru Mahanagara Palike (BBMP) wards and compute the number of borewells per ward. Assuming an average yield of 5,000 litres/day, water supply from borewells was normalised with ward population and the wards were ranked by this normalised supply.

Groundwater extraction: Data from the Dynamic Groundwater Resources of Karnataka as of March 2022 was used to assess the groundwater extraction. The relevant table for Bengaluru (Annexure -VB [Page 114]) is reproduced below:

The wards were then mapped to the respective taluks. Lower groundwater extraction is desirable and hence wards with lower over extraction percentage were assigned a higher rank.

Groundwater quality: Data from the Karnataka State Groundwater Quality Evaluation Report -2018 was used. Table -12 water quality Data of Bengaluru Urban DIstrict 2018-2019 from the report has been reproduced below:

The wards were then mapped to the respective taluks. As with the groundwater extraction, wards with a lower non-potable probability were assigned a higher rank.

Lake/tank area coverage: We analysed the BBMP wards dataset with QGIS to determine the percentage of area covered by lakes and ponds in each ward, using the Lakes and Ponds data from Open City.

Results

The ranks at the variable level were then added up and the wards were ranked again to arrive at the groundwater index. The results are plotted in the heatmap below:

A higher area covered by lakes and tanks is good in terms of groundwater rechargeability. Hence, wards with a higher area covered by lakes and tanks were assigned a higher rank.

The results are displayed in the heatmap below:

• The blue end of the spectrum represents the best-performing wards
• The white end represents the worst-performing wards

• Wards which have been historically serviced by Cauvery water and hence less dependent on borewell supply appear to be ranked quite low in this index
• Some wards in the eastern and the south western areas rank very low, this is likely due to inadequate data on the actual number of borewells present

Land use index

Built up area: We used the land use maps – built-up vs unbuilt to arrive at the unbuilt area in each ward. Wards were ranked in ascending order of unbuilt area percentage – the more unbuilt area in a ward, the higher the ranking.

Results

The ranks for each variable (built-up area and commercial area) were then summed up individually. These totals were ranked again to determine the land use index/rank. The ward with the best performance in terms of the identified variables is ranked 1, while the ward with the worst performance is ranked 225. The table below provides the variable values and ranks for the top 10 and bottom 10 wards.

The values plotted on to a heatmap is presented below:

• The blue end of the spectrum represents the best performing wards
• The white end represents wards which perform the worst

The peripheral areas particularly on the southern and eastern edges perform better on this index owing to less built-up and commercial area.

Governance index

The Bangalore Water Supply and Sewerage Board (BWSSB) contacts were obtained from their website and their office location details were geocoded. We then assigned these locations to their respective wards. We located the following wards where a BWSSB liaison officer was available.

Having access to a BWSSB liaison officer is desirable. Therefore, the wards mentioned in the table above were assigned a rank of 1, while the rest of the wards ranked at 2.

(Part 4 of the series will highlight how to address the gaps in data to enhance Bengaluru’s water security)

(The other team members who contributed their insights for this article are: Swati Ganeshan, VishnuPriya Viswanathan, Ritika Gupta, Aniket Sawant, and Chandanapriya Dhanraj)

Also read:

• Insights from K-RERA: Large real estate projects add to Bengaluru’s water stress 
• Real estate developers face few hurdles in getting environment clearance