Data: All-India Water Storage Level in Reservoirs Was Below Average for Almost All of Last 12 Months

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The Central Water Commission (CWC)’s reservoir water storage data is based on reports received from the State Governments & Project Authorities. The water storage level in reservoirs at an All-India level was below average for most of the last 12 months, going above average only towards the end of July 2024.

Extreme weather patterns have become increasingly common in recent years, characterized by erratic rainfall and intense heatwaves. This year’s monsoon season, in particular, underscored these changes, leading to severe flooding and significant loss of life across several regions, including Andhra Pradesh, Telangana, Assam, and Delhi. The erratic rainfall has caused water levels in dams and reservoirs to fluctuate wildly, with rapid increases during heavy downpours and dramatic drops during dry spells. In this backdrop, we examine the data on water levels in these water bodies over the years to analyse how these trends have evolved and assess the impact of extreme weather on water management and flood control.

The data for this story is sourced from Dataful’s collection on Water Storage Data in Dams, Reservoirs, Barrages and Others, which is collated from the Central Water Commission (CWC)’s reports on monitored reservoirs. CWC’s data is compiled based on reports received from the State Government/Project Authorities.

The definition of some of the key terms used in the story is as follows:

In 2019, the CWC monitored 120 reservoirs across the country. As of 22 August 2024, the number of monitored reservoirs has increased to 155. Out of these reservoirs, 20 reservoirs are hydro-electric projects.

There is a cyclic pattern in the live storage levels of reservoirs in the country

The analysis of the live storage levels (current) in reservoirs across India for the period from August 2019 to September 2024 shows a cyclic pattern influenced by seasonal changes and precipitation events. Every year, from early July to mid-October, there is a clear trend of increasing reservoir storage as the year progresses, reflecting the seasonal impact of the monsoon.

Towards the end of June, just towards the end of Summer and around the time Monsoon hits the country, the water levels in the reservoirs are the lowest. In the previous years, the lowest water levels recorded in June were between 45 to 55 billion cubic meters (BCM) whereas in 2024, it was just 36.37 BCM, the lowest in many years. While the numerical values might not be immediately understandable to the layman, this year has witnessed severe water shortages in several states, including Karnataka, Kerala, and Gujarat, as reported by various media outlets.

Nonetheless, the most significant rise in reservoir storage occurred during the peak of the monsoon season. By early August, the water level increased to 115.736 BCM, with a notable increase to 124.016 BCM by mid-August. The upward trend continued into late August and early September, peaking at 147.337 BCM on 05 September 2024, due to increased precipitation during the monsoon.

For better understanding, we use the percentage departure of current storage from normal storage in the story as it provides a clear and contextualized view of how current reservoir levels compare to historical averages. For instance, if a reservoir has a live storage of 50 BCM, and the normal storage for this time of year is 40 BCM, the percentage departure might show a positive value, indicating that current storage is above average. Conversely, if the live storage is 30 BCM with the same normal storage, the percentage departure will show a negative value, indicating a shortfall.

In the last one year, the water storage was below average in the reservoirs

The data on the percentage departure from normal storage for reservoirs measures the fluctuations in water levels relative to the average storage over the past decade. At the national level, the data indicates that between August 2023 and July 2024, the overall water storage in the reservoirs dropped less than the average of the last 10 years for the corresponding period.

The storage was 14% below average on 06 September 2023 which improved to only 4% below average as on 04 April 2024. Since then, it progressively worsened, reaching its lowest point in June (15% below average). It was only in August 2024 that the storage level became above average. This trend is unlike in the previous years. The lowest deviation from the average water level in 2020 and 2021 was -6% in the first week of August in the respective years. On the other side, the storage was more than average by 71% towards the end of June in the year 2020. During the same period in 2021, the storage was 43% more than average. In 2022, the spike was witnessed in the third week of July.

Contrasting trends in water levels seen across regions

Regional trends reveal that the northern region witnessed average or below average storage for almost two years from August 2020 to July 2022, and since January 2024 onwards. Between August 2022 and July 2023, the storage was above average and went up to 80% above average in July 2023. Meanwhile, in the eastern region, the storage was nearly double the average in June 2020. However, since then, it has dropped and has been below average for most of the time, except for occasional peaks.

In contrast to the eastern region, the western region has been having average or above average water storage in the reservoirs throughout the year. The lowest level was in the first week of September 2021, when the shortfall was 13%.

The central region witnessed a continuous rise in the water level compared to the average until June 2020 when the water level was double the average. Since then, the region has had average to above-average water levels (up to 30%) till June 2024. Following a 21% below-average storage in July 2024, the water level has now risen back to above average.

The trend in the southern region has been similar to that at all India levels with below-average water levels between June 2023 and July 2024. In the monsoon of 2021 and 2022, the water level was 100% more than the average.

Within a region, there is a significant difference in water levels in each state

While the trends are more or less similar in the states in the northern region with increasing water levels from a significant shortfall between June 2022 to July 2023, there is a stark difference in the patterns in the eastern region. Data available for a single year for Assam revealed an above-average water level in the state, with 250% more than average storage in February 2024. During the same period, Odisha and West Bengal recorded below-average storage, even 50% below average. Bihar saw a significant shortfall in water levels, recording up to 95% below average during the same period.

Meanwhile, the western states of Gujarat and Maharashtra saw seasonal spikes in water levels in July each year. Uttar Pradesh in the central region, has only had below average water levels since the beginning of 2023, until August 2024 when it became above average for the first time in about 20 months. The situation wasn’t this bad in the remaining central states.

In the southern states, around the monsoon season, there is a spike in the water levels. The rise was around 100% above average storage at least at one point of time during the season every year, except in Karnataka and Kerala. As seen in the overall water levels in the region, there was a considerable shortfall in the water levels post-monsoon of 2023 and in the summer of 2024.

Data on water storage levels in reservoirs reveals a significant impact of extreme weather patterns, including erratic rainfall and heatwaves. While the monsoon season typically leads to a rise in reservoir levels, 2023 and 2024 saw sharp fluctuations, with levels peaking in August 2023 and declining sharply by mid-2024. This trend underscores the challenges of managing water resources amid increasing weather variability and regional disparities. Understanding these emerging patterns is essential for managing water resources, predicting availability for agricultural, industrial, and domestic needs, and also preparing for potential flood risks.