by Walter Hsiang

With the anticipated arrival of monsoon season in Asia at the start of May, people have a right to be anxious. The annual summer monsoon is the major source of rain in India and much of South Asia, so it has a huge impact on environmental, social, and economic factors in those regions. For example, an overly strong or weak Indian summer monsoon can result in flooding or crop failures. Therefore, accurate monsoon predictions are important for everyone from farmers to politicians so that they may prepare accordingly.

India has an age-old relationship with the monsoon, and very few climate-related events around the globe can compare with the monsoon’s scale and its impact on the economy. The monsoon is estimated to influence 15% of India’s GDP, and the agriculture and energy sectors are most heavily affected. But beyond the economy, the monsoon greatly affects the livelihood of people who live in rural India. These people don’t have access to robust infrastructure and depend on farming for sustenance.

Because the monsoon season bears so much weight, the release of the India Meteorological Department’s long-range forecast (released this past week) has become an annual financial and political event. Private forecasting companies like Skymet have tried to capitalize on this anticipation by releasing their own forecast reports ahead of time.

This year, Skymet has predicted normal monsoon rainfall (102% of the long-term average), while the India Meteorological Department has forecast below-normal rainfall (only 93% of the long-term average). Skymet’s forecast had brought hope to the region, particularly after last year’s deficit monsoon which brought very little rainfall. But if the Meteorological Department is right, the region is in for another dry year — although their forecast of 93% of normal rainfall may not seem that bad, widespread drought characterized the 2012 monsoon which had a total rainfall very near that exact value. And it is good to remember that rainfall can vary regionally within India and temporally throughout the year;  unseasonal rains this past February damaged over 27 million acres of farmland in six regions of India.

The Indian economy is really a gamble on the monsoon. Seventy percent of India’s annual rainfall, which irrigates the country’s farmland, comes from the monsoon. The associated weather patterns affect productivity, industrial and agricultural output, health, and energy consumption. When monsoon season does not strike the delicate balance between not-too-much and not-too-little rainfall, it can increase food prices and reduce energy output, which worsens inflation.

Yet India’s reliance in recent years on the monsoon forecasting by the India Meteorological Department (IMD) has also been a gamble. Between 1988 and 2002, the IMD used a 16-parameter statistical prediction model that was claimed to be successful until it crumbled in a 2002 drought. Monsoons have been less predictable since then. The IMD has been working hard on new models that combine statistical and dynamic forecasts, but the average prediction error has only come down by 2% in the last decade. Just last year, the IMD’s prediction of monsoon rainfall was off by nearly 10%.  The current forecasts use both a 5-parameter statistical model and an experimental atmosphere-ocean dynamical model.

Despite Skymet’s and IMD’s monsoon prognosis, huge uncertainty remains. It calls into question India’s continued reliance on the monsoon rains, especially with the country’s fast development and modernization. Above all, it outlines a need to develop solutions that reduce India’s vulnerability to unexpected changes in the monsoon.

by Walter Hsiang

With the anticipated arrival of monsoon season in Asia at the start of May, people have a right to be anxious. The annual summer monsoon is the major source of rain in India and much of South Asia, so it has a huge impact on environmental, social, and economic factors in those regions. For example, an overly strong or weak Indian summer monsoon can result in flooding or crop failures. Therefore, accurate monsoon predictions are important for everyone from farmers to politicians so that they may prepare accordingly.

India has an age-old relationship with the monsoon, and very few climate-related events around the globe can compare with the monsoon’s scale and its impact on the economy. The monsoon is estimated to influence 15% of India’s GDP, and the agriculture and energy sectors are most heavily affected. But beyond the economy, the monsoon greatly affects the livelihood of people who live in rural India. These people don’t have access to robust infrastructure and depend on farming for sustenance.

Because the monsoon season bears so much weight, the release of the India Meteorological Department’s long-range forecast (released this past week) has become an annual financial and political event. Private forecasting companies like Skymet have tried to capitalize on this anticipation by releasing their own forecast reports ahead of time.

This year, Skymet has predicted normal monsoon rainfall (102% of the long-term average), while the India Meteorological Department has forecast below-normal rainfall (only 93% of the long-term average). Skymet’s forecast had brought hope to the region, particularly after last year’s deficit monsoon which brought very little rainfall. But if the Meteorological Department is right, the region is in for another dry year — although their forecast of 93% of normal rainfall may not seem that bad, widespread drought characterized the 2012 monsoon which had a total rainfall very near that exact value. And it is good to remember that rainfall can vary regionally within India and temporally throughout the year;  unseasonal rains this past February damaged over 27 million acres of farmland in six regions of India.

The Indian economy is really a gamble on the monsoon. Seventy percent of India’s annual rainfall, which irrigates the country’s farmland, comes from the monsoon. The associated weather patterns affect productivity, industrial and agricultural output, health, and energy consumption. When monsoon season does not strike the delicate balance between not-too-much and not-too-little rainfall, it can increase food prices and reduce energy output, which worsens inflation.

Yet India’s reliance in recent years on the monsoon forecasting by the India Meteorological Department (IMD) has also been a gamble. Between 1988 and 2002, the IMD used a 16-parameter statistical prediction model that was claimed to be successful until it crumbled in a 2002 drought. Monsoons have been less predictable since then. The IMD has been working hard on new models that combine statistical and dynamic forecasts, but the average prediction error has only come down by 2% in the last decade. Just last year, the IMD’s prediction of monsoon rainfall was off by nearly 10%.  The current forecasts use both a 5-parameter statistical model and an experimental atmosphere-ocean dynamical model.

Despite Skymet’s and IMD’s monsoon prognosis, huge uncertainty remains. It calls into question India’s continued reliance on the monsoon rains, especially with the country’s fast development and modernization. Above all, it outlines a need to develop solutions that reduce India’s vulnerability to unexpected changes in the monsoon.

By Julia Rothchild

Russians don’t usually worry about monsoons. But a new study says maybe they should. Research suggests that deforestation in the far north could significantly impact South Asian monsoon rainfall.

The study, published last month in the Proceedings of the National Academy of Sciences, used an idealized climate model to show how cutting down trees at high latitudes might change monsoon circulations.

The researchers found that heavy deforestation would shift what is called the Intertropical Convergence Zone (ITCZ) towards the south. The ITCZ is a band of clouds and precipitation circling the globe where the northeast and southeast trade winds converge and rise. It hovers near the equator, but migrates hundreds to thousands of miles north and south of the equator during the course of the seasonal cycle. The ITCZ’s movement determines where and when monsoons occur.

The ITCZ lies north of the equator during June, July, August, and September, when the northern hemisphere’s summer occurs and the warm, rising air lies in the northern hemisphere. During that time, monsoons occur north of the equator. In December, January, February, and March, the ITCZ moves south, and showers the southern hemisphere with monsoon rain during its summer.

Deforestation would push the ITCZ south by providing a remote forcing. Cutting down dark green forests exposes land, and bare land reflects more sunlight than the original forests. In other words, deforestation increases the albedo of the Earth’s surface. The result is less solar absorption, and an energy deficit in the northern hemisphere’s high latitude systems. This causes the ITCZ to shift away from the imposed energy sink.

The idea that the ITCZ might move to the north or south in response to a high-latitude heat source or sink is not new. Numerous studies have shown that an expansion of reflective ice cover in the northern hemisphere would shift the ITCZ southward. It is thought that the decades-long drought in Africa’s Sahel resulted from a southward shift in Africa’s monsoon precipitation, which was caused by temperature changes in the Atlantic Ocean – cooling north of the equator, and warming south of it. These and other studies relating shifts in tropical precipitation to cross-equatorial gradients in energy sources were reviewed here.

A southward shift of the ITCZ would mean that many places in the northern hemisphere that rely on monsoon rains would receive less precipitation. These places include North America, North Africa, and South Asia. In the study’s ideal climate model, northern deforestation causes the rainfall over India in particular to decline by 18%. Correspondingly, the southern hemisphere monsoon regions – South Africa, South America, and Australia – would experience a precipitation increase. It should be noted that the model assumed drastic, major deforestation, in which all trees north of 50 degrees latitude were eliminated and replaced by grasses. But in places that rely on monsoons for life, even a precipitation change of less than 18% would have major impacts on livelihood: droughts and floods plague India when the summer rainfall is only ten percent weaker or stronger than usual.

The study found that far-away deforestation actually has more of an impact on the South Asian monsoon region than does local land surface changes in South Asia. In other words, land changes in India might have less effect on Indian monsoons than deforestation in Russia. We focus on Russia because that particular country has the most forested area of any state on Earth. About 20,000 square kilometers in Russia alone are deforested every year.

The upshot is that people living in India might have less environmental control over the monsoons than people in Russia. This seems not only unintuitive, but politically inconvenient: the people who may be most affected by northern latitude deforestation – Indians, for example – have little say in its occurrence.

The idea that land surface albedo changes might affect monsoons is not new, and it is unclear whether realistic amounts of deforestation would have an appreciable effect on monsoons. Still, this study emphasizes the truly global nature of climate change issues. Maintaining a climate that is healthy for human populations cannot be accomplished by one country alone.

From September 3 – 7, about 12 inches of rain fell in the India-Pakistan region of Kashmir.  The resulting flooding has resulted in a death toll of at least 200, and well over 100,000 people were rescued by the military.  NASA’s Terra satellite shows the dramatic expansion of the region’s rivers between August 31 and September 11 to 10 km-wide channels stretching for hundreds of kilometers:

This torrential rainfall was produced by a monsoon depression — a type of storm that is substantially weaker than a typhoon but can pass over land without loss of intensity.  An average of 5 or 6 monsoon depressions form every year in the Indian region, with most originating over the ocean east of India and then propagating to the northwest.  This particular one seems to be fairly intense (animation compiled from images obtained from Yoshi Kajikawa’s monsoon site at the University of Hawaii):

There is some discussion of this monsoon depression interacting with an eastward-propagating midlatitude disturbance, thereby producing the extreme rainfall observed in the region.  Further analysis is needed to understand the meteorology of this event, why it produced such unusually strong rainfall in what has this season been an otherwise fairly dry region, and how often similar extreme events should be expected in the future.

India tends to dominate the monsoon-related news this time of year, despite the fact that there are multiple other monsoon regions that may be experiencing hydrological events that are just as extreme.  This year is a case in point:  about 80% of the recent links in a Google news search on “monsoon” relate to India and Nepal, in particular to the floods and landslides that killed at least 50 people there.  The other 20% refers mostly to the North American monsoon, in particular to the U.S. portion.  (Note that the recent precipitation events in India, though deadly, are part of several rainy episodes occurring since mid-July that have brought India as a whole up from 40% below normal precipitation to “only” 17% below normal.)

Our point is that there are fairly severe droughts in other world monsoon regions that have gotten comparatively little attention.  Equatorial Africa and South America are currently experiencing dry anomalies even stronger than the one in India.  That can be seen on our website here, as well as in this map of precipitation anomalies in the last 6 months:

Rainfall is particularly below normal in Venezuela, but it is interesting that this was predicted and seemingly planned for to some degree.  Back in early June the Venezuelan government predicted half the normal precipitation for the 2014 rainy season because of the effects of the developing El Nino.  Perhaps this can be viewed as a successful prediction, even though that El Nino event has thus far proven to be weak, at best.  Nevertheless, there is still suffering, with news articles reporting reduced crop planting and elevated cattle mortality in the severe drought.  News coverage of this, though, is fairly scant.

We also mentioned that equatorial Africa has less rain than usual, especially parts of Nigeria, Cameroon, and the Congo.  But it is difficult to find reports of widespread severe drought in those regions via the usual web searches, and the Famine Early Warning System Network (FEWS NET) is not reporting agricultural drought there.  So one wonders if this below-average rainfall is just not that much of a stress because the average rainfall is so high, or if there is perhaps some error in some of the gauge-based rainfall dataset that we have been using, or if news agencies simply haven’t picked up on local conditions.

Finally, the drought in at least some of the Korean peninsula seems to have been lessened by, unfortunately, torrential rains that have led to floods.  These floods have led to deaths, displacements, and destruction of farmland and residences.

These were just a few words to bring attention to some of the hydrological extremes happening in monsoon regions outside of India.  Over time we hope to build a collection of links to other websites that provide real-time updates on tropical weather events and their impacts; we don’t currently know of any single site that does this, but suggestions are very welcome.

The precipitation anomalies that began this summer’s monsoon season have mostly persisted:  a large dry anomaly over central and northern India and a band of dryness over northeast coastal China and the Korean peninsula.  These can be seen in maps of anomalous precipitation over the past 30 days:

These dry anomalies seem to be predominantly part of a spatial shift in the normal maximum, from India toward the east over Bangladesh and Myanmar, and from the Korean peninsula toward the south.  Although India does not seem to be in a formal “drought” yet, there are widespread reports of impacts from high temperatures and dryness over much of the region, with some large-scale economic effects.   North Korea does seem to be in a severe drought state, with media reporting the driest conditions in over a decade and deleterious effects on agriculture.

What has caused these dry conditions?  Is the dryness in Korea and India related, or is it just a coincidence that the normal rainfall maximum have shifted eastward over South Asia and southward over East Asia?  While it is not possible to answer these questions definitively without much more detailed investigation than I can do on a blog, it is intriguing that sea surface temperatures (SSTs) are warmer than usual over the tropical West Pacific:

In the above map of SST anomalies for the past month, you can see warm anomalies in the equatorial East Pacific associated with what might be the development of an El Nino event, as well as warm anomalies of about 1 K in the West Pacific.  Perhaps the warm West Pacific is essentially causing an eastward shift of the South Asian rainfall maximum and a southward shift of the East Asian maximum.  The latter is organized in what is called the Maiyu-Baiu front, an east-west band of precipitation that stretches from China to the east of Japan, and this band seems to be shifted south of its normal position so that it now lies more over the cold SST anomalies just south of Japan.  So an auxiliary question is:  are the cold SSTs a response to the cloudiness of the shifted Maiyu-Baiu front, or is the front responding to the SST anomalies?  There has been some research into connections between this front and SST, although I am not very familiar with this and there seem to be many open questions.  Or perhaps the cause of the Asian rainfall anomalies is the warm SST in the equatorial East Pacific, or something altogether different from SST.

It will be interesting to see if some of these precipitation anomalies continue, especially if we head further toward an El Nino state.  Current predictions from the Indian Institute of Tropical Meteorology are for enhanced monsoon rainfall over central and northern India in the coming week or so, with the west part of India remaining dry for the next two weeks.  The U.S. forecast model (NCEP’s GFS) is also predicting above-normal rain over central India over the next week, but continued dryness over N. and S. Korea:

Let’s check back in a week or two to see what has happened with Indian and Korean drought.