Dam floods

IMD forecast of Water Volume in River Basins: Can it help prevent Dam floods?

On Aug 16, 2019, a news report[i] announced that Pune IMD (India Meteorological Department) will now (from Aug 1, 2019) provide to CWC (Central Water Commission) forecasts of water volume that may accumulate in river basins across the India “In a bid to ensure effective reservoir management.”

Pulak Guhathakurta, head, Climate Application and User Interface at Climate Research and Service at IMD-Pune was quoted saying, “We will make use of our forecasts and rainfall information to calculate the total volume of water expected to accumulate in every river basin and sub-river basin on the basis of its area expanse. This information will then be shared with CWC and other authorities, like the department of irrigation. It will be handy and can be decisive while deciding the release of water from time to time, especially during the monsoon.” This statement again emphasised that this was being done to help reservoir management. The news report than mentioned the Kerala floods in 2018 and role of dams therein.

The news report quoted a senior IMD official saying, “Had this been available last year, the flooding in Kerala due to release of water from dams could have been avoided.” It would be great if information was available that help avoid such disasters.

IMD Pune website A visit to IMD Pune website[ii] showed that in the context of above announcement, IMD Pune website is offering following information:

  • Maps showing with color codes for different ranges, the volume of water (and Rainfall through a separate set of maps) that fell in different sub basins from June 1 to Aug 21 (when checked on Aug 26/27, 2019) and anomaly with respect to normal figure.
Sub Basin wise water volume received during 2019 SW Monsoon till Aug 21, 2019
  • Map showing Rainfall forecast range in each sub basin in color code for week 1 (Aug 22-28 when checked on above dates), week 2 (Aug 29-Sep 4), week 3 (Sep 5-11) and week 4 (Sep 12-18), and also cumulative rainfall for week 1 &2, week 1-3 and week 1-4.
Expected Water Volume for sub basins by IMD Pune on Aug 21 2019 for the coming four weeks

  • Map showing “Expected volume of water” (in TMC or Thousand Million Cubic Ft) forecast range in each sub basin in color code for week 1 (Aug 22-28 when checked on above dates), week 2 (Aug 29-Sep 4), week 3 (Sep 5-11) and week 4 (Sep 12-18), and also cumulative expected volume of water for week 1 &2, week 1-3 and week 1-4.

  • A table giving list of the 101 sub basins, their sub basin code and which of the basin the sub basin belongs to. It would have helped if the area of each of the sub basins and basins were also provided, since the water volume expected is essentially obtained, it seems from multiplication of the rainfall the area of the sub basin.

Basins/ Sub Basins covered When we go through the details of the list of basins and sub basins, we see that it includes 101 sub basins spread over 27 basins, as provided in the Annexure 1 below. From the list, one can see that it covers following regions.

  • NORTH WEST INDIA: 2 basins, 16 sub basins
  • GANGA BASIN: 1 basin, 19 sub basins.
  • NORTH EAST INDIA: 4 sub basins, 9 sub basins.
  • WEST FLOWING RIVERS: 6 basins, 21 sub basins.
  • EAST FLOWING RIVERS: 12 basins, 34 sub basins.
  • ISLANDS: 2 Basins, 2 sub basins.

Can this help Reservoir Management? So essentially, the additional information provided under this new initiative that apparently started on Aug 1, 2019 is the forecast of the rainfall and volume of water expected in each of the 101 sub basins (see the list in Annexure 1) in each of the next four weeks. While this additional information from this new initiative is certainly welcome, the question is how much can it help achieve better reservoir management, the main objective of this initiative?

Considering India has over 5000 big dams, on an average, each of the 101 sub basin would have about 50 dams. In fact, some of the sub basins would have many more than that, considering the greater dam concentration (say in Maharashtra, Madhya Pradesh and Gujarat, India’s top dam builder states) and size.

For particularly large sub basins (e.g. Brahmaputra Lower and Upper, Yamuna Lower, Krishna Upper, Cauvery Middle, Narmada Upper, Narmada Middle, Sone, Mahanadi Lower, Pariyar and others and other west flowing composite sub basins), each of them are known to have large number of dams, and where prudent reservoir management is very important, a lot of questions arise how this information will be useful and representative for the individual dam upstream and downstream area.

Moreover, some of the sub basins are themselves composites of more than one basins, including those in the west flowing rivers and east flowing rivers and also in the North and North East. Here again the question will arise as to how representative is the forecast for each of the constituent of the sub basin.

Similarly, while the forecast of four weeks is welcome, it is well known that as the length of the forecast time increases, the accuracy % drops. More significantly, for dam operation, daily and sometimes even more disaggregated forecast is required, one hopes we slowly move in that direction.

It would help if IMD Pune were to upload on the same website, the comparison of actual vs forecast rainfall and its representativeness across the sub basins for each of the forecast week for each of the sub basin.

Most important issue is how is the CWC going to use this? There is no information or indication of that on CWC flood forecasting website[iii] or the CWC website[iv] as yet. Similarly, there is no clarity as to how the state water resources departments or individual dam managers are going to use this information.

Was IMD already providing river basin wise information to CWC? According to Chapter 17 titled “Verification of Quantitative Precipitation Forecast (QPF) 2018 during SW Monsoon over River Sub-basins of India” of the IMD’s 2018 monsoon monograph[v], IMD has already been providing sub basin wise quantitative QPF since about 2013. In fact, this chapter provides a map of the region for which QPF have been provided, which covers only part of India, not whole of India, see the map below.

Moreover, this QPF are provided for 146 sub basins, compared to 101 sub basins covering whole of India that IMD Pune is providing. The following screenshot from the monograph provides some details of the 146 sub basins.

A section of IMD website[vi] says that this is provided by ten Flood Meteorological Offices (FMOs at Agra, Ahmedabad, Asansol, Bhubaneshwar, Guwahati, Hyderabad, Jalpaiguri, Lucknow, New Delhi. Patna) provide this information, covering basins are given below. An option for more information provided here[vii] for each of these ten FMOs and three additional ones (Bhakra Beas MB, DVC Kolkata and Jhelum River Basin), but no information could be accessed on any of these pages.

It’s possibly barred for general public viewing and accessible only to official agencies. The IMD monograph of 2018 says that forecast of rainfall for each of the next three days is provided for all these 146 sub basins throughout the monsoon period for some years now.

The basic question is, if this information was already provided by IMD for some years now and that too for 146 sub basins, then why is that not used to also provide Expected Water Volume in each of these 146 sub basins and may be add the remaining sub basins, so that we have information for smaller unit areas? The new initiative is to provide weekly forecasts for next four weeks (rather than only daily for next three days as was the case till now). It may be useful to provide both daily- 3 day – and weekly (4 weeks) forecasts.

In Conclusion While the new initiative of IMD Pune providing four week weekly forecasts for rainfall and water accumulation in 101 sub basins in India is welcome, a lot of questions remain how it will be used by the CWC, states and dam managers and how helpful it will be in averting dam induced flood disasters, which is the objective of this initiative. We have to wait and see.

However, this cannot be replacement for robust and rigorous, transparent, accountable dam operation governance for each of the large dam in India. If we have such a governance, all such initiatives can be put to good use. And without such governance, there is little hope of good use of any such initiative.

Himanshu Thakkar (ht.sandrp@gmail.com)

Annexure 1.


  1. Indus (Upto Border)
    1. Upper Indus
    2. Lower Indus
    3. Gilgit
    4. Chautang and others
    5. Shyok
    6. Jhelum
    7. Chenab
    8. Ravi
    9. Beas
    10. Sutlej Upper
    11. Sutlej Lower
    12. Ghaghar and others
    13. Barmer
    14. Churu
  2. Area of N Ladakh not draining into Indus
    1. Shaksagam
    2. Sulmar
  3. Brahmaputra
    1. Brahmaputra Lower
    2. Brahmaputra Upper
  4. Barak and others
    1. Barak
    2. Kynchiang and other south flowing rivers
    3. Naoch Chara and others
  5. Minor rivers draining into Bangladesh
    1. Karnaphuli and others
    2. Muhury and others
  6. Minor rivers draining into Mynmar
    1. Imphal and others
    2. Mangpui Lui and others
  7. Ganga
    1. Above Ramganga Confluence
    2. Ramganga
    3. Ghaghara
    4. Ghaghra confluence to Gomti Confluence
    5. Upstream of Gomti Confluence to Muzaffarnagar
    6. Gomti
    7. Gandak and others
    8. Sone
    9. Tons
    10. Kosi
    11. Damodar
    12. Bhagirathi and others (G Lower)
    13. Banas
    14. Kalisindh and others upto confluence with Parbati
    15. Chambal Upper
    16. Chambal Lower
    17. Yamuna Upper
    18. Yamuna Middle
    19. Yamuna Lower
  8. W flowing rivers of K and S including Luni basin
    1. Bhadar and other west flowing rivers
    2. Shetrunji and other east flowing rivers
    3. Luni Upper
    4. Luni Lower
    5. Saraswati
    6. Drainage of Rann
  9. Mahi
    1. Mahi Upper
    2. Mahi Lower
  10. Sabarmati
    1. Sabarmati Upper
    2. Sabarmati lower
  11. Narmada
    1. Narmada Upper
    2. Narmada Middle
    3. Narmada Lower
  12. Tapi
    1. Tapi Upper
    2. Tapi Middle
    3. Tapi Lower
  13. W flowing rivers south of Tapi
    1. Bhatsol and others
    2. Varrar and others
    3. Vasishti and others
    4. Netravati and others
    5. Periyar and others
  14. Brahmani and Baitarni
    1. Baitarni
    2. Brahmani
  15. Subarnarekha
    1. Subarnarekha
  16. Mahanadi
    1. Mahanadi Upper
    2. Mahanadi Middle
    3. Mahanadi Lower
  17. East flowing rivers between Mahanadi and Godavari
    1. Nagvati and others
    2. Vamsadhar and other
  18. Godavari
    1. Pranhita and others
    2. Manjra
    3. Wardha
    4. Weinganga
    5. Indravati
    6. Godavari Upper
    7. Godavari Middle
    8. Godavari Lower
  19. East flowing rivers between Godavari and Krishna
    1. East flowing rivers between Godavari and Krishna
  20. Krishna
    1. Bhima Upper
    2. Bhima lower
    3. Krishna Upper
    4. Krishna Middle
    5. Krishna Lower
    6. Tungabhadra Upper
    7. Tungabhadra Lower
  21. East flowing rivers between Krishna and Pennar
    1. East flowing rivers between Krishna and Pennar
  22. Pennar
    1. Pennar Upper
    2. Pennar Lower
  23. East flowing rivers between Pennar and Cauvery
    1. Palar and other
    2. Ponnaiyar and other
  24. Cauvery
    1. Cauvery Upper
    2. Cauvery Middle
    3. Cauvery Lower
  25. East flowing rivers south of Cauvery
    1. Pamba and others
    2. Vaippar and others
  26. Lakshadweep
    1. Drainage area of Lakshadweep Islands basin
  27. Andaman and Nicobar
    1. Drainage area of Andaman and Nicobar islands basin


[i] https://indianexpress.com/article/cities/pune/imd-starts-forecast-of-water-volume-in-river-basins-5906665/

[ii] http://www.imdpune.gov.in/index.html

[iii] http://ffs.tamcnhp.com/ffs/

[iv] http://cwc.gov.in/flood-forecasting-hydrological

[v] http://www.imdpune.gov.in/Links/monsoon_report_2018.pdf

[vi] http://www.imd.gov.in/pages/services_hydromet.php

[vii] e.g. http://www.imd.gov.in/pages/services_fmo.php?adta=agra

3 thoughts on “IMD forecast of Water Volume in River Basins: Can it help prevent Dam floods?

  1. 25 East flowing rivers south of Cauvery.
    Pamba and others
    Vaippar and others

    How the Kerala river Pamba flows to East. It flows west and join lake Vembanad near Arabian sea in Kochi area. Please correct this error.


  2. Your analysis of each River basin will help to mitigate floods in future.Water retention capacity of each River basin should be increased by removal of sand and aggregate.


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