Table 2.

Assumptions Used to Quantify Stakeholder Identified Adaptation Options

Adaptation options
13 stakeholder‐identified adaptation options (Workshop 1) were characterized and presented to stakeholders in Workshop 2. Two variants were developed for four options—urban rain/grey water harvesting, drip irrigation, and microirrigation which resulted in a total of 17 options. Their characteristics were converted into model‐relevant information. Each option was applied in January 2021 (in all Adaptation Scenarios), while for the Adaptation Pathways, the start‐up year followed the pathway‐specified sequence and timing (Figure 5). Mentioned below are the key assumptions for each adaptation option (with more detail in supporting information Figure S3). Options shaded grey (from 1 to 11) address water demand, while options shaded blue (12–17) address water supply issues.
1	25% Urban Grey Water Recycling	• 25% reduction in annual water use rate and water consumption. • Increase urban water demand from 43.8 m3/yr (current estimate) to 54.75 m3/yr for scenarios with increased urban water demand.
2	50% Urban Grey Water Harvesting	• 50% reduction in annual water use rate and water consumption. • Increase urban water demand from 43.8 m3/yr (current estimate) to 54.75 m3/yr for scenarios with increased urban water demand.
3	25% Urban Rain Water Recycling	• Same as 25% Urban Grey Water Recycling.
4	50% Urban Rain Water Harvesting	• Same as 50% Urban Grey Water Recycling.
5	Better Enforcement of Laws	• 10% reduction in annual urban water demand and a reduction of water consumed in urban areas by 33%.
6	Urban Water Pricing	• We assume an indicative 50% reduction in annual urban water demand and reduction in water consumed from the current 30% to 20%.
7	1.5 mha Microirrigation	• 50% reduction in demand in 1.5 mha (million hectares) of irrigated area.
8	2.5 mha Microirrigation	• 50% reduction in demand in 2.5 mha (million hectares) of irrigated area.
9	5% Drip Irrigation	• Change irrigated fraction of historically irrigated catchments. • Water demand reduces by 80% for 5% of the irrigated area.
10	10% Drip Irrigation	• Change irrigated fraction of historically irrigated catchments. • Water demand reduces by 80% for 10% of the irrigated area.
11	Agricultural Water Pricing	• A 25% reduction in crop water demand assumed in the irrigated command areas of the four major reservoirs: Krishnaraj Sagar Dam, Harangi Dam, Hemavati Dam, and Kabini Dam.
12	Interbasin Transfer (100 MCM)	• Water transfer from neighboring Netravathy basin to Hemavathy basin (tributary of Cauvery) of 100 Million Cubic Meters (MCM).
13	Interbasin Transfer (88 MCM)	• Water transfer from neighboring Netravathy basin to Hemavathy basin (tributary of Cauvery) of 88 MCM.
14	Cauvery Stage V—Phase I	• 500 Million Liters per Day (MLD) supply from Cauvery river to Bangalore.
15	Cauvery Stage V—Phase II	• Extension of Phase I by a further 270 MLD.
16	Urban Lake Restoration	• Off‐stream reservoir with 210 million cubic meter (MCM) in Bangalore and 10 MCM in Mysore. • We divert all city runoff to reservoirs. Water available is used to satisfy urban water demand, while excess water runs off to the river.
17	Urban and Rural Lake Restoration	• Urban and rural reservoirs (200 lakes with a total capacity of 420 MCM). • 10% of the runoff from the respective catchments is diverted to the reservoirs, the water is used to satisfy irrigation water demand.