Shillong, Sep 21: Meghalaya’s Mawsynram and Cherrapunji, among the world’s wettest places, are facing a growing drought risk as climate change brings heavier rain, fewer rainy days and rising temperatures, a new study has found.
The study, published in Theoretical and Applied Climatology recently, analysed projected climate and hydrological data for the state and adjoining areas for the period 1981-2100 to understand the apparent paradox of increasing rainfall intensity alongside rising drought vulnerability.
Researchers Ashesh Rudra Paul and Pankaj Kumar Roy found that rainfall is becoming concentrated in intense spells, while light rain and the number of rainy days are declining.
The study recorded an increase in the Simple Daily Intensity Index (SDII), with a maximum local rise of 0.08 mm per day per year.
The number of rainy days, meanwhile, declined by an average 0.40 days per year.
SDII is a climate index that measures the average amount of rainfall on a “wet day” over a specific period, usually given in millimeters per day (mm/day).
“Contrary to the conventional expectation that increased precipitation alleviates drought,” the researchers said, the findings showed “a clear tendency toward elevated drought risk” in Meghalaya.
The changing rainfall pattern is particularly significant for Meghalaya because of its steep terrain and shallow soils, the researchers said.
Intense rain causes rapid surface runoff instead of being absorbed into the soil, reducing groundwater recharge. As a result, large amounts of monsoon rain may not translate into enough water being available during drier months.
“Such rainfall concentration enhances surface runoff and reduces infiltration,” the study said.
Rising temperatures are adding to the pressure by increasing evapotranspiration, or water loss from soil, vegetation and other surfaces. Minimum temperatures were found to be rising by as much as 0.08 degrees Celsius per year.
The researchers said higher temperatures increase atmospheric water demand and accelerate soil-moisture loss during rain-free periods.
To assess drought, the researchers used the Standardized Precipitation Evapotranspiration Index, or SPEI, at a three-month timescale. The analysis indicated an increasing frequency and intensity of moderate, severe and extreme drought events, particularly under the high-emission SSP585 scenario.
The study projected that drought occurrences would generally increase from the near future to the far future under the scenarios examined, with the strongest rise occurring under SSP585.
The findings were also reflected in projections for river flows.
Using hydrological modelling, the researchers examined the Sari-Gowain and Surma-Meghna river basins, both of which originate in or receive significant flows from Meghalaya.
The model projected a maximum decline of 9.8 per cent in mean annual streamflow in the Sari-Gowain basin in the far future under SSP585. For the Surma-Meghna basin, the projected maximum decline was 11.6 per cent under the same scenario.
SSP585 is a high-emissions climate change scenario used by researchers to model a future with rapid economic growth heavily reliant on fossil fuels.
The researchers said river flows would remain heavily concentrated during the monsoon, peaking around June and July before declining, potentially increasing the risk of hydrological drought later in the year.
The study did not account for human-induced factors such as deforestation, urban expansion, land-use change and groundwater extraction, which can also affect water availability.
The researchers called for water-management strategies that consider not just the total rainfall, but also its intensity and distribution, rising temperatures and basin-level water flows.
“Collaboration between scientists, policymakers, and local communities will be vital,” the study said.
Local observations also point to increasing water stress.
Residents of Sohra and Mawsynram said several waterbodies and waterfalls have been drying up faster this year, with the trend visible as early as mid-September.
P Hujon, a Mawkisyiem resident who runs a guest house, said, “Many waterfalls in Sohra area are getting dried, and I am seeing this as early as mid September.” (PTI)
