From the sea, knowledge

South Asia’s agriculture, water management, and indeed much of the sub-continents’ way of life, is dependent on the mercy and whims of the South Asian Summer Monsoon rainfall and circulation. At the same time highly-varying and dependable (while it is certain to manifest each year, the amount and timing of the crucial rainfall can be shrouded in uncertainty), the monsoon is the subject of much continuous research that ever strives for better sub-seasonal, seasonal, and interannual forecasts, which can help South Asia’s people to better manage, and prepare, for its rains. In particular for agriculture, finding robust, reliable, predictors for monsoon variability is a crucial determinant for regional food production and security, as producers rely on advance weather information to decide what and when to plant, and how to allocate their management resources. If the natural variability, the monsoon’s ups and downs, baked into the system weren’t enough, the whole region stands be further impacted by rising temperatures and altered circulation patterns that accompany global climate change.

In this vein, a new study by Roxy et al. (2015) in Nature Communications has found a strikingly strong relationship between rising Indian Ocean sea surface temperatures (SSTs), and declining rainfall around the Indian sub-continent. The logic goes that as the Indian Ocean SSTs rise, particularly in the western portion of the basin, the major centers of convection (heated, moisture filled air that may rise high into the atmosphere, eventually contributing to rainfall) start to shift around the region, along with the transport of moisture by the canonical monsoon winds, for which the system is named. Roxy et al. suggest that as these SSTs increase, as they have been, the winds have concurrently weakened, causing less transport of moisture over the continent, leading to declines in rainfall over the land surface.

Sea surface temperatures (absolute, not anomalies) and land vegetation over the Indian Ocean are seen below in a visualization created with data from 1994 to 2005 from the Pathfinder satellite dataset. Impacts of rising Indian Ocean SSTs have also been linked to changes in rainfall over East Africa. Find more here: https://www.nasa.gov/topics/earth/features/indian_ocean_warm.html

Credit: NASA

In fact, the idea that changes in Indian Ocean SSTs can modulate the monsoon rainfall and circulation has been floating around for quite some time now. In 1999, Saji et al. and Webster et al. suggested that there was a source of internal variability (meaning, perhaps not forced by climate change, but occurring naturally) in the Indian Ocean, referred to as the Indian Ocean Dipole (IOD) Mode, or Equatorial Oscillation, among other names. In the simplest description, this “mode” seems to flip between alternating states that leaves the western Indian Ocean warmer (in the positive phase) or cooler (in the negative phase) than the eastern Indian Ocean, thereby also changing the overlying atmospheric convection and circulation. Since then, much research has been done to understand: how independent and reliable this IOD actually is; how the Indian Ocean varies with the better known El Nino Southern Oscillation (ENSO) cycle of altered SSTs and circulation in the Pacific; and how the Indian Ocean will “adjust” to rising global temperatures, both at the surface and in its deeper circulation (Gadgil et al., 2004; Ashok et al., 2004; Ihara et al. 2007; Ihara et al., 2008; Ummenhofer et al., 2011; and many more).

Monsoon rainfall forecasts seasonally issued for South Asian agriculture have historically relied heavily on ENSO indices, which, again historically, have explained approximately 30% of the interannual variability and are normally associated with below-normal rainfall totals. However, this relationship did not hold during the 1997/1998 major ENSO event, and the above studies suggest that other Indian ocean/atmosphere dynamics and interactions may be important for future study and forecasts. The uniqueness of the Roxy et al., study is that it demonstrates a surprisingly strong relationship between declining monsoon rainfall totals over portions of South Asia and rising (western) Indian Ocean SSTs. More work is called for to better articulate the mechanisms by which this may be occurring, further elucidating the series of interactions between the sea (and land) surface, the weakened monsoon circulation, and the declines in rainfall. As a relevant aside, the modification of the South Asian land surface via agricultural production may also be contributing to local, if not regional, shifts in circulation and rainfall patterns, and should also be considered (Douglas et al. 2006, 2009; Lee et al., 2008; Niyogi et al., 2010; Guimberteau et al., 2011; Shukla et al., 2014). Given these findings, and that historical ENSO-monsoon relationships are changing in their reliability (Krishna Kumar et al., 1999; and refs above), farmers and other agriculturalists therefore need additional metrics and predictors by which to plan their food production systems that fully consider the impact of changing Indian Ocean SSTs and interactions.

A better understanding of these Indian Ocean interactions would lead to the development of new, and additional, indices that account for interannual, and perhaps seasonal and sub-seasonal, monsoon rainfall variability. Krishna Kumar et al., 2004 demonstrates how influential Indian Ocean SSTs are in retrospectively understanding changes in interannual crop yields, particularly in the central and western portions of India. The body of work investigating the interactions between the Indian Ocean, the Pacific Ocean, and the monsoon system has since made great strides and continues to develop, and more studies should be undertaken to understand how these interactions, such as the findings of Roxy et al., control agricultural production.  Furthermore, we should move to incorporate these emerging insights into better, more sophisticated, forecasts and assessments - at the stakeholder level - for current and future South Asian agricultural production.

References:

Ashok K, et al. (2004) Individual and combined influences of the ENSO and Indian Ocean dipole on the Indian summer monsoon. J. Clim. 17 3141–55

Douglas EM, et al. (2006) Changes in moisture and energy fluxes due to agricultural land use and irrigation in the Indian Monsoon Belt. Geophys Res Lett 33:L14403. doi:10.1029/2006GL026550

Douglas EM, et al. (2009) The impact of agricultural intensification and irrigation on land-atmosphere interactions and Indian monsoon precipitation—a mesoscale modeling perspective. Global Planet Change 67:117–128

Gadgil S, et al. (2004) Extremes of the Indian summer monsoon rainfall, ENSO and equatorial Indian Ocean oscillation. Geophys. Res. Lett. 31 L12213

Guimberteau M, et al. (2011) Global effect of irrigation and its impact on the onset of the Indian summer monsoon. Clim Dyn. doi:10.1007/s00382-011-1251-5

Ihara C, et al. (2007) Indian summer monsoon rainfall and its link with ENSO and Indian Ocean climate indices. Int. J. Climatol. 27 179–87

Ihara C, et al. (2008) July droughts over homogeneous Indian Monsoon region and Indian Ocean dipole during El Niño events. Int. J. Climatol. 28 1799–805

Krishna Kumar K, et al. (1999) On theweakening relationship between the Indian monsoon and ENSO. Science 284 2156–9

Krishna Kumar K., et al. (2004) Climae Impacts On Indian Agriculture. Int. J. Climatol 24:1375-1393.

Lee E, et al. (2008) Effects of irrigation and vegetation activity on early Indian summer monsoon variability. Intl J Climatol. doi: 10.1002/joc.1721

Niyogi D, et al. (2010) Observational evidence that agricultural intensification and land use change may be reducing the Indian summer monsoon rainfall. Water Resour. Res. 46 W03533

Roxy MK., et al. (2015) Drying of Indian subcontinent by rapid Indian Ocean warming and a weakening land-sea thermal gradient. Nature Comm. DOI: 10.1038/ncomms8423

Saji N H, et al. (1999) A dipole mode in the tropical Indian Ocean. Nature 401 360–3

Shukla SP., et al. (2013) The response of the South Asian Summer Monsoon circulation to intensified irrigation in global climate model simulations. Clim Dyn. DOI:10.1007/s00382-013-1786-9

Ummenhofer CC., et al. (2011) Multi-decadal modulation of the El Nino-Indian monsoon relationship by Indian Ocean variability. Environ. Res. Lett. 6:034006

Webster P J, et al. (1999) Coupled ocean–atmosphere dynamics in the Indian Ocean during 1997–98. Nature 401 356–6

For a cup of tea

The hills of Ooty. Picture by Mathew McDermid

On my many visits to Tamil Nadu, India, I would often visit the Nilgiri Hills, by way of Ooty and Coonoor, where my uncle maintains a farm. The Nilgiris are a startling juxtaposition of beauty and ugliness, order and chaos, the controlled and the wild. The region is characterized as subtropical highland, and hosts a Biosphere Reserve, including populations of tigers, elephants, bucks, monkeys, and a host of bird species, as well as the dense, stunted, tropical montane Shola forest - dark as night when you stroll under its canopy.

Encroaching upon these natural ecosystems - and dominating them, in fact - are the endless tea plantations that were instated during British rule, not unlike those of Darjeeling and Assam. These plantations cover hectare after hectare, as bush after bush is carefully curated and managed, forming a rich green carpet of tea in any and all directions. As tea tends to burn easily, particularly as young leaves, they are sparsely interspersed with beautiful, yet somewhat solitary silver oaks, whose leaves provide them the necessary shading. 

The boundary between tea and forest is often abrupt and jagged, as pictured above. In many areas, there is hardly a buffer zone separating, and shielding, the natural ecosystems from the heavily managed monoculture. As such, there is a tension between these systems that manifests in many forms, from water use to erosion (1). Landslides in the region are quite common and highly disruptive, requiring that the roads and infrastructure be constantly repaired. 

That said, there are movements emerging to upscale conservation efforts in the region, from maintaining and expanding wildlife refuges, to conserving water, to managing and preventing the copious amounts of erosion. My uncle's farm is among these initiatives as he is organically growing herbs selected for their heartiness on the exposed hillsides, and has implemented a range of management techniques designed to precisely and minimally utilize his water resources. He does this while maintaining natural ecosystems around his farm, allowing for re-growth and a healthy riparian buffer towards the bottom of his sloped fields, where lies a river that attracts the many types of species that roam freely throughout the region. While this has been a fruitful undertaking for him, he however admits that such a venture can prove expensive under current economic pressures, and the scaling-up of such farming techniques proves challenging. However, the explorations of such initiatives, along with appropriate policy measures and economic incentives, may eventually help pave the way for healthier regional agro-ecosystems.

1. Kumar and Bhagavanulu (2008) Effect of deforestation on landslides in the Nilgiri district - A case study. J. of the Indian Soc. of Remote Sensing, 36:1, 105-108

Tea bushes are given some (minimal) shading by silver oaks and other trees that are planted among them. Heartiness to full-sun conditions can also depend on the tea variety. Photo by Mathew McDermid

My uncles herb farm, planted on previously cleared hills. These herbs require less water, and are organically grown. Natural vegetation is allowed to re-grow along the farm boundaries and down toward the river at the bottom of the slope. Photo by Mathew McDermid

Seed-funding to explore agro-ecosystems in India

To have longevity, present and future agricultural adaptation solutions to climate change must fulfill multiple objectives: they must make farms resilient to future environmental change, they must allow farmers to derive a liveable income from their farms, even in the face of socio-economic shocks, and they must be sensitive to the surrounding natural ecosystems and their services. Taking an “agro-ecosystems” approach, that measures the amount and quality of a farm’s overall production and returns, while also monitoring important environmental and ecosystem interactions, can help to place value on the “whole farm system”, rather than just on the primary crop grown.

In steering my own research, this approach is increasingly becoming my guiding principle, and I’m actively seeking new avenues to apply this thinking. I, along with my esteemed colleagues, recently obtained seed funding for a project exploring how small-scale farmers in Madhya Pradesh, India make decisions about what crops to plant, and how those decisions both help them deal with climate variability (and change) and impact the surrounding environment. We’ll be working in the southeastern region of Madhya Pradesh, which has not had much in the way of dedicated field experiments by which we can calibrate our models. To help us do this, and also help us to understand the farmers’ decision-making processes and the local natural ecosystems, we’ll be working with the Foundation for Ecological Security (https://fes.org.in/), an NGO dedicated to sustainability in and between the agricultural and natural ecosystems. Such NGOs are critical to farmers in finding and implementing adaptation solutions that help make their farms more resilient to climate and economic change, while also being mindful of how the chosen farming practices impact the natural environment.

I’m thrilled to be taking on this project, particularly in an area that hasn’t seen much in the way of this type of research (with our modeling and satellite-based methods). However, we can learn from a number of similar initiatives that are taking place across the developing world, too. In particular are the efforts of the Kusamala Institute in Malawi (https://www.kusamala.org/) and the ESRI Conservation Program (https://www.conservationgis.org/), who are taking an “agro-ecosystems” perspective of achieving food security (the concept of “permaculture” can fall under this umbrella). The goal behind such endeavors (including ours) is to create a robust, nutritive agricultural system that also maintains – even protects – the natural environment and ecosystem services. The principles, methods and technologies exist to achieve all these objectives, and in doing so, these communities may truly thrive.