Another Subpar Monsoon Season Likely for India in 2019

It’s been 25 years since India has had a significantly wetter-than-average monsoon, and 2019 is unlikely to break this streak, according to new outlooks from the Indian Meteorological Department (IMD) and The Weather Company, an IBM Business (TWC). The IMD’s latest monsoon outlook, issued on May 31, projects that total national rainfall during the monsoon season (June-September) will end up at 96%, or at the low end of the normal range (96-104%). The margin of model error in the IMD outlook is 4% in either direction—which implies the odds are almost even that 2019’s monsoon rainfall will actually fall below the normal range.

IMD predicted that the monsoon will reach far southwest India (Kerala) on or around June 6, close to a week later than average. Thus far, the monsoon has been running about a week late in its trek across the southeast Bay of Bengal (see Figure 1). Monsoons that drag their heels advancing through India tend to produce less total rainfall than early-onset monsoons.

Figure 1. Typical progress of the Indian monsoon in its northwestward push during June and July (red dashed lines) and the progress of the 2019 monsoon (solid green lines at lower right of map). Image credit: India Meteorological Department.

The Weather Company’s latest outlook for the Indian monsoon, issued on May 31, is just a touch drier than IMD’s. The TWC outlook is calling for 94% of average seasonal rainfall.

Both IMD and TWC expect that the early part of the monsoon, especially June, will be the driest part relative to normal, with conditions moving closer to average by late summer.

These outlooks take into account model projections that the weak El Niño episode simmering in the Pacific since late 2018 will diminish by later this year. The Indian monsoon is typically suppressed by downward motion fostered by El Niño across and near the western tropical Pacific. NOAA’s last monthly El Niño/Southern Oscillation (ENSO) outlook, issued on May 9, called for a 70% chance of El Niño conditions extending through summer and only a 55-60% chance that El Niño would make it into autumn. A downwelling phase of the Madden-Julian Oscillation is currently enhancing subsurface warm water in the western equatorial Pacific, which could give a mild boost to El Niño, but that influence is likely to fade within a few weeks.

IMD and TWC also agree that this year’s monsoon rains will be closest to average in southern India, with drier-than-normal conditions more pronounced as you move toward the north (except during August).

Update (June 6): There are signs that the Indian Ocean Dipole (IOD), a pattern of warmth and cooling similar to ENSO, is moving toward a positive phase, which could work to enhance monsoon rains later this summer. In a follow-up email, IMD stated that they believe any influence from the weak El Niño will be counterbalanced by the monsoon-enhancing effects of the positive phase of the IOD.

Figure 2. The Weather Company’s month-by-month forecast of precipitation in and near India, expressed as percentages of the long-term average. Image credit: Todd Crawford/TWC.

The last time an Indian monsoon produced rainfall 10% or more above the long-term average was in 1994. Since then, five monsoons have come in with a rainfall deficit of more than 10% below average (2002, 2004, 2009, 2014, 2015); three of these years were in the past decade. Drought linked to the blockbuster El Niño of 2015-16 caused at least $5 billion in losses in India, making it by far the nation’s most expensive drought in history. A later-than-average monsoon in 2012 contributed to one of the world’s biggest-ever power outages.

Based on the multidecade trend toward less-than-stellar monsoon rains, “it is sensible to skew any prediction of the monsoon towards the dry side,” said TWC’s Todd Crawford. In addition, TWC is employing a new technique this year to calibrate the output from the ECMWF (European) model’s seasonal climate forecasts, shifting them closer to the range of observed outcomes from past years. In the case of this year’s Indian monsoon, the calibration process is pushing the ECMWF guidance toward a drier outcome, according to Crawford.

Figure 3. Monsoon rainfall by year, averaged across all of India for the period June through September. The 2018 monsoon (not shown) produced 91% of average rainfall. Image credit: D.R. Kothawale and Jayashree Revadekar, Indian Institute of Tropical Meteorology.

Record pre-monsoon heat and intense dryness is gripping northwest India

The last few days have seen a deadly heat wave over the arid landscape of northwest India that’s been brutal even by the usual torrid standards of pre-monsoonal weather. Paving the way for the heat was an unusually parched pre-monsoonal period. For March through May, as reported by the Times of India via weather.com, an average of 99 millimeters (3.90”) of precipitation fell across India, the lowest total for that period since 2012 and the second lowest since 1954.

Figure 4. The India Meteorological Department’s observing site in Churu, Rajasthan, where a high of 50.8°C (123.4°F) was recorded on June 1, 2019. Image credit: Money Sharma /AFP/Getty Images.

On Saturday, June 1, the temperature at Churu in northwest India’s Rajasthan province hit 50.8°C (123.4°F), which is the province's all-time high, the nation’s highest temperature on record for June, and the second-highest temperature ever reliably measured in India. In fact, the reading may actually be a new all-time high for the nation, according to international weather records expert Maximiliano Herrera. The reason: India’s official record high of 51°C—set in Phalodi on May 19, 2016—was only measured to the nearest 0.5°C, which means it could have been as low as 50.5°C.

Figure 5. Trend in maximum temperature of the hottest day of the year for the period 1971–2012. Image credit: “The heat wave in Phalodi, Rajasthan, India, 19 May 2016,” Climate and Development Knowledge Network/World Weather Attribution initiative.

How is climate change related to India’s pre-monsoonal heat?

A 2017 study conducted by the Climate and Development Knowledge Network and the World Weather Attribution initiative looked at whether such localized heat events could be directly attributed to climate change. Examining data at 103 stations from 1971 to 2012, as well as output from global climate models, the study found that annual temperatures are rising across India, consistent with human-produced climate change. Heat waves are becoming significantly more frequent and more intense in northwest India (including Rajasthan), but not elsewhere in the country.

Moreoever, the study notes, “the analysis did not find that human-induced climate change played a role in these individual heat waves. This runs counter to studies done on similar extreme heat events in other parts of the world. The lack of a detectable climate change trend may be due to the masking effect of aerosols on warming, and increased use of irrigation.”

Aerosols (air pollution particles) inhibited sharp temperature rises in Europe before pollution came under greater control there in the 1980s. Similarly, the authors conclude, “it is likely that aerosols are helping to offset the surface warming trend over India—particularly when it comes to maximum temperatures in the pre-monsoon season.” Importantly, they add: “High temperatures with polluted air kill many more people than high heat alone. This means that the impacts of heat waves may well have become worse, even if the maximum temperatures have not shown strong trends.”

Figure 6. A farmer prepares his pumping set to irrigate his wheat field on the outskirts of Allahabad, India, on February 1, 2018. Image credit: Sanjay Kanojia/AFP/Getty Images.

Irrigation may be another factor trimming the intensity of pre-monsoonal heat across parts of northern and central India, the report finds. Across irrigated lands, more of the intense sunlight of late spring is used to evaporate moisture, which reduces how much air temperatures can rise (although increases in water vapor and the heat index can themselves take a toll on health).

Irrigation may even be influencing the monsoon itself. A 2010 study led by Dev Niyogi (Purdue University) found that intensified agriculture from irrigation may, ironically, weaken the very heat-driven updrafts that help pull monsoon flow inland.

The Weather Channel becomes The Water Channel

Wednesday is the start of a temporary takeover of weather.com: it's now the website for "The Water Channel", part of The Weather Channel Forecast: Change campaign to raise awareness about the issue of global clean water scarcity. In collaboration with this campaign, IBM will contribute a total market value of $1 million to two groups—charity: water and The Nature Conservancy—to help provide and protect clean water for those in need. 

The Water Channel website includes my writeup on water scarcity and climate change, "Where Will All the Water Go?"

Dr. Jeff Masters contributed to this report.