Monsoon and it’s Forecasting in India
Indian economy which is still considered as an agricultural economy – is dependent on the amount of monsoon rains as large parts of the agricultural produce comes from the monsoon fed crops. Good monsoon always means a good harvest and brings in cheers all around the country. A weak or bad monsoon is always considered as a big set back to India’s economy and always results in a big loss in the country GDP levels.
Understanding the mechanisms driving global weather patterns leads us to question "what went wrong" when inconsistent weather conditions arise. Whenever periods of drought or flooding exceed than what is normally expected, driving forces in the weather have likely been either suppressed or enhanced in some manner.
As with any meteorological phenomenon, especially one demonstrating a periodic (cyclic, or recurring) tendency, attempts to forecast the monsoon have been underway for ages. Efforts to predict the performance of the monsoon based on correlations of observed weather features have been pursued since the late 1800s, when it was assumed that Himalayan snow-cover directly effected regional weather patterns. However, before forecasting can be attempted, knowledge of the phenomenon itself must be understood.
In the case of the Indian monsoon, what to look for in the period leading up to the monsoon onset as well as during the active monsoon itself are vital components of understanding the physical nature of the phenomenon.
IMD MethodologyIn the months prior to the expected start of the rainy season, the Indian Meteorological Department (IMD) predicts the onset date and rainfall potential of the monsoon using a statistical model that evaluates 16 "precursor" conditions, which indicate the potential strength of the monsoon circulation. Of the 16 parameters used, 6 regard temperature conditions, 3 wind or pressure field values, 5 pressure anomalies, and 2 snow-cover. The most important of these appear to be: 1) the position of the 500mb ridge centered over 75 E longitude averaged over the month of April; 2) monthly average temperatures over the Indian sub-continent (March and May monthly averages at different locations); and 3)El Niño /Southern Oscillation conditions. Independent studies have shown these parameters to have a high correlation separate from other fields, and are frequently used separately for unofficial pre-season forecasts.
Once the season has begun, forecasts of daily rainfall are attempted by observing and predicting the lengths of "active" and "break" periods. These are naturally occurring phases in the monsoon, lasting from 5 to 7 days, identified by fluctuations in the typical pattern. Several features associated with the active phase, brings rain to the northern Indian Plains and its west coast. They include tropical depressions in the Bay of Bengal, a low-level jet stream along the east African coast, and the variations in the monsoon trough, the area of low pressure that develops over India during the summer monsoon season.
The current monsoon forecast methods are generally either statistical or numerical. Statistical forecasts look at correlation or relationships between known phenomena and the event being analyzed, such as the earlier example of monsoon performance bases on the Tibetan Plateau snow pack. However, their strength lies in steering one towards a logical result rather in absolutes. For instance, in the case of the Asian drought of 1987, the monsoon was weak, resulting in one of the worst droughts of the century. But the El Niño which caused the disruption in world weather patterns was not as strong as the 1982-83. In contrast, a numerical model is a mathematical simulation of the atmosphere, represented by known physical relationships such as the equations of motion and thermo-dynamics etc. For example, the various models used by meteorologists to provide temperature and precipitation forecasts out to 5 days are numerical models, run on supercomputers due to the large amounts of data being processed.
Agricultural Planning for the Indian MonsoonTo ensure sustainable agriculture in a region, knowledge of the local climate is vital. Climatic limitations are a strong indicator of agronomic potential and can be used to determine which crops are best suited for a region, as rainfall and temperatures are two major variables affecting crop type and yield. Planning is especially critical in monsoon regions which experience distinct wet and dry seasons. Soil moisture prior to the beginning of the rainy season is usually negligible, a situation exacerbated by the preceding heat buildup and high evaporative losses. Except where irrigation is available, planting is consequently restricted to the beginning of the wet season.
In various parts of India, the onset of the south-west monsoon for a particular area is expected between June or July, depending on its location. The highest concentration of non-irrigated agriculture happens to be in western and southern oilseed, grain, and cotton areas while in the East, much of the rice is rain-fed. These crops suffer most from a late or weak start to therainy season , and could be considerably affected during an extended break in monsoon rains. Also, if the southwest monsoon withdraws from the region earlier than expected, late planted crops may be hurt during the filling stages due to lack of moisture. A late withdrawal or late-season rains, are on the other hand considered detrimental to maturing crops, especially cotton.
During the drought of 1987, kharif (summer planted) crop production was down as temperatures and rainfall were among the lowest on record in central and northern rain fed grain, oilseed, and cotton areas. Rabi (fall planted) crops, planted primarily in southern India and areas with adequate irrigation reserves, partially made up for the shortfall but also suffered some losses. In winter wheat areas of northern Pakistan and India, planting was delayed for months due to insufficient moisture availability for germination (although most of the crop is irrigated, low reservoirs and fuel shortages hampered irrigation efforts).
Conversely, a strong monsoon circulation can bring flooding, especially along the Ganges and Indus Rivers. Bangladesh encompasses most of the area considered the Mouths of the Ganges, with other major rivers (primarily the Brahmaputra and the Meghna) converging within its boundaries. Eastern India and Bangladesh are the least drought prone areas, indicating the consistency of the of the monsoon in that region . In fact, a certain level of flooding is expected each year, and local rice cropping patterns are dependent upon the seasonal abundance. In September of 1992, a late surge in the monsoon flooded cotton areas of Pakistan and generally soaked crops mostly in the open boll stage. Disease was also a problem as the spraying patterns were disrupted by the unseasonable heavy showers. However, while the rainfall was unusually heavy, it occurred only a few weeks later than normal, highlighting the hazard for the regions's cotton, which ripens so close to the end of the rainy season.
From the early 1950's to late 1970's, Indian food production outpaced population growth, owing to increased area cultivated as well as a number of technological factors including increased irrigation and fertilizer inputs. Over the past 20 years, course grain production has risen steadily despite dramatic decreases in area. Much of this area, predominately rain fed acreage in western India, is increasingly used for oilseed production, which has increased dramatically over the same period. This shift in agriculture, vital in meeting the nation's nutritional requirements, was possible due to the region's versatile climate. As stated earlier though, the rain ed crops are at greatest risk of failure in times of drought, especially in the drought-prone west. Advances in genetic research have been important in developing cultivators which would thrive in certain areas, balancing drought resistance and yield. In fact, some of the more drastic increases in production stem from improved germplasm, most notably wheat production, which has more than quadrupled over the last 30 years.
The monsoon climates are especially vulnerable to disruptions in global weather which could result in drought, flooding, or both in any given year. Decades of research on the driving forces behind the Indian monsoon circulation has resulted in a better understanding of weather extremes experienced, and their impact on agriculture. The benefits of good monsoon are certainly tempered by the risks of farming in such a volatile area, although forecast techniques currently being developed are helping to mitigate the impacts of poor monsoon performance.
- based on some research papers