Even normal Monsoon 2017 may not save dwindling reservoir status in South India

Southwest Monsoon 2017 has made timely onset over southern parts of Kerala on May 30. With this, we now expect rains to pick up pace across Kerala and over parts of Karnataka and Tamil Nadu. These rains are eagerly awaited owing to the dwindling status of water reservoirs in southern parts of the country. According to the statistics, these reservoirs are reporting acute shortage of water i.e. below 10%.

This has cited major cause of concern for the agriculture sector for the region down south, which is also already battling worst drought of the decade. Moreover, lack of irrigation has further worsened the situation.

Must watch: Checkout the onset date of Monsoon 2017 in your city

Blame it all on the fluctuating Monsoon rains during the last three years. While 2014 and 2015 were the severe drought years, 2016 despite recording normal Monsoon rains left the southern region parched.

Last year, Kerala was deficit by 34%, South Interior Karnataka-21%, Coastal Karnataka 21% and Tamil Nadu by 19%.

However, this year, Skymet Weather has predicted Southwest Monsoon to be marginally below normal at 95% with an error margin of +/- 5%. In fact, weather models are indicating that June is likely to witness good Monsoon rains.

But we are still afraid that even good Monsoon rains from June-September will not be enough to improve the situation. So, let us see how the forecast rains for the monsoon 2017 will change the current status of reservoir at the end of the season.

As per the data released by the Central Water Commission on May 25, 2017, the southern region has 31 reservoirs having total live storage capacity of 51.59 BCM. The Southern region includes states of Andhra Pradesh, Telangana, Karnataka, Kerala and Tamil Nadu. As per Reservoir Storage Bulletin, the total live storage available in these reservoirs is 3.92 BCM which is 8% of total live storage capacity of these reservoirs.

The storage during corresponding period of last year was 11% and average storage of last ten years during corresponding period was 17% of live storage capacity of these reservoirs. Thus, storage during current year is less than the corresponding period of last year and is also less than the average storage of last ten years during the corresponding period.

Region Wise Reservoir Storage Status as on May 26, 2017

Situation is very tough for southern states as reservoirs have reached to dead storage. There is no water left for agriculture.

Now to assess the meteorological drought of southern states, Skymet Weather has calculated the Standardized Precipitation Index (SPI), a widelyused index to characterize meteorological drought on a range of timescales. On long timescales, the SPI is closely related to groundwater and reservoir status. On short timescales, the SPI can be related to soil moisture or the agricultural drought. Generally, SPI varies between +3 to -3. Positive values suggest floods and negative drought.

SPI analysis is done over 3 scenarios. In first scenario, we have assumed that the rainfall will be normal. Whereas the second and third scenarios are generated for 5% and 10% extra rainfall till December 2017. The averaged SPI over few meteorological subdivisions are plotted.

Through the combined analysis, it can be said that under assumed scenario of forecasted precipitation, the water availability issue in these sub divisions will remain severe in the season. From agricultural point of view, water backlog may not be filled in this region.

So, we can see in both sub-divisions for 9-monthly and 12-monthly SPI that if normal or 5% more than normal or 10% more than normal rainfall occurred from June-2017 to Dec-2017 than also hydrological drought won’t be fulfil.

Image credit: CWC

Any information taken from here should be credited to skymetweather.com