When it Rains it Pours: Seminar Sum-Ups

The Indian Monsoon is an important and powerful meteorological phenomena that ensues over June to September every year. The monsoon triggers changes to precipitation and wind patterns that lead to significant social, environmental and economic effects over South Asia (Figure 1). Despite being very well researched the Indian monsoon processes are not well understood and very difficult to predict. The monsoon precipitation is notoriously variable with drastic flooding or severe droughts possible with too much or too little precipitation. Millions of people are affected by the monsoon and rely on it for agricultural produce and freshwater. The monsoon can change the social and economic status of the area dramatically with a good or bad year. To protect the people and their environment it is so important to try and understand the complex process and patterns of the Indian Monsoon especially as climate change threatens to add yet more intricacy. 

Figure 1: Location of the Indian Monsoon Rainfall, (Wikipeadia)


Dr. Jennifer Fletcher is a senior research scientist at the University of Leeds and has worked on many projects surrounding the Indian Monsoon dynamics. Her seminar ‘Characterising Indian Monsoon Rainfall’ provided a fantastic overview into her research and this captivating meteorological process. Jennifer discussed three factors influencing monsoon rainfall:

1) Synoptic scale low pressure systems

2)  Orographic Effects

3) Irrigation effects in the Ganges Basin


Monsoon Depressions and Dry Intrusions


Monsoon Depressions (low pressure systems) trigger variability in the monsoon precipitation and Jennifer and her team wanted to look at how much of the monsoon rainfall is accounted for by these features. They concluded that 80% of summer rainfall in North India is from Monsoon Depressions. However, they found periodic incursions of dry air that they found dramatically reduce the Monsoon Depression rainfall. These North-westerly Dry Intrusions therefore bring another aspect of irregularity. This is very important as lowering rainfall could mitigate hazardous flooding associated with the monsoon but also prevent very arid areas from receiving essential water supplies.

Orographic Effects

Note: Orographic Effect – Often at a mountain front air is forced to move from low to high elevation. With higher altitude the air cools, create clouds and leads to precipitation, known as orographic lift and effect. 

Jennifer embarked on a field excursion in June 2016 to establish the processes associated with Indian Monsoon rainfall at the Western Ghats Mountains (Figure 2). They collected flying aircraft data information on temperature, humidity, wind speed and more. During their excursion the Boreal Summer Intraseasonal Oscillation (BSISO) passed over. The BSISO is another way in which rainfall is moderated in the Indian Monsoon. Their results showed two distinct periods of this moderation; an offshore and coastal phase. The Offshore phase when the BSISO is ‘active’ leads to very heavy rainfall over the East Arabian Sea and supressed rainfall at the coast and mountains. The coastal phase displays the opposite. They concluded that in the coastal phase high humidity is pushed by strong winds to the mountains, bringing lots of moisture. This leads to orographic precipitation enhancing the mountain rainfall during this phase. This is important as it indicated that not all the precipitation patterns in the are related to orography.
Figure 2: Location of the Western Ghats, the aircraft utilised in the fieldwork and the scenic views of the area.

Irrigation in the Ganges Basin

Note: Irrigation - Applying controlled amounts of water to plants to increase agricultural productivity, especially in arid areas. Supplied by the Ganges river and its tributaries.

Finally the last aspect of the Indian monsoon rainfall covered is how the irrigation (Figure 3) effect on surface conditions affects atmospheric circulation as this is often not included in climate models. Irrigation cools the surface which weakens the thermal difference between land and sea, hypothetically reducing the Indian monsoon as it relies on this contrast. Previous studies in the Ganges Basin (Figure 3) concluded irrigation weakens the circulation and reduces rainfall. Jennifer and her team found irrigation does weaken circulation but forecast climate models showed an increase in rainfall especially over the Himalayas. The results are not inconsistent with previous climate model results as they suggest a wetter surface will enhance rainfall in the pre-monsoon season.


Figure 3: Location of the Ganges basin and a view of the Ganges Canal irrigation system.

Wider Context

Jennifer described three processes that affect the Indian Monsoon rainfall and has gained a better understanding of each influencing factor. It is clear the processes determining the Indian Monsoon occur on a range of scales and vast amount of different phenomena are varying it. All of these separate processes are interacting and why it is so difficult to understand and determine the Monsoon processes correctly. 


However, all the work by Jennifer provides positive steps in the  right direction. The more we learn now the better prepared we will be for the future adversities that will come. Hopefully in the next decade we will have an even better scope of knowledge on the Indian Monsoon to help protect and prosper the people and environments impacted by this incredible event. 

Meg




Links you might be interested in:
Relevant papers by Jennifer and her team:
Fletcher, J.K., Parker, D.J., Hunt, K.M., Vishwanathan, G. and Govindankutty, M., 2018. The interaction of Indian monsoon depressions with northwesterly midlevel dry intrusions. Monthly Weather Review, 146(3), pp.679-693.


Fletcher, J.K., Parker, D.J., Turner, A.G., Menon, A., Martin, G.M., Birch, C.E., Mitra, A.K., Mrudula, G., Hunt, K.M.R., Taylor, C.M. and Houze, R.A., 2018. The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP. Quarterly Journal of the Royal Meteorological Society.





Comments

Post a Comment

Popular posts from this blog

Not Just a Pretty Face (Picture): Seminar Sum-Ups

Image
As technology advances so to does our understanding of the planet. Penny How perfectly demonstrated this at a seminar I recently attended all about her PhD thesis.  Aims Using time-lapse photography Penny aimed to better understand the methods of dynamic alteration at the terminus of two tidewater glaciers (Fig 1). Figure 1 : Example of a Tidewater Glacier, Kronebreen in Svalbard, (Penny How's Blog) Note: Tidewater Glacier - Glaciers that flow into the ocean. Why So, why is it important to understand glacier processes? Climate change or more specifically global warming leads to ice loss from glaciers and this impacts global sea level rise. However, there is still a limited understanding of how glacial change will affect sea level rise especially within different emission scenarios. There are two main ways in which ice transfers from glacier to ocean: 1) High temperatures promote glacier melting and surface melt channels funnel water into the oceans. Melt...
Read more

Water Scarcity- The economic impacts focusing on Scotland: Seminar Sum-Ups

Image
Historically water has been very important for the growth of civilisations including driving technology advances and agricultural production. Today every aspect of our modern economy utilises water and therefore any environmental changes that impact the hydrological cycle will bring global and regional challenges. Global population increase and diminishing water resources due to climate change is a serious hazard that could have consequences even for water rich countries such as Scotland. As water is vital for economic success it is therefore so important to understand the possible consequences of water scarcity in the future.   A recent seminar I attended by Dr Scott J. McGrane focused on the regional economic impacts of a water scarce future for Scotland. Currently his work at Strathclyde University employs multi-disciplinary methods to improve environmental monitoring of climate dynamics and impacts for regional economic forecasts. The economy is linked to wate...
Read more