How Droughts And Worsening Soil Health Can Increase Carbon Emissions

Climate science researchers have been concerned with amplifying feedback loops that exacerbate the effects of climate change. Amplifying or positive feedback loops are mechanisms that increase the warming effects caused by an initial event. For example, the melting of Arctic sea ice due to warming temperatures further increases warming because the melted water has a lower albedo (fraction of light reflected by a surface) compared to ice.

To gain a more realistic understanding of global temperature changes and climate tipping points, researchers are increasingly emphasising that these feedback loops need to be accounted for. A recent study published in Environmental Research Letters highlights one such feedback loop which is overlooked in current climate dialogues — the loop connecting drought, soil desiccation and carbon dioxide emission.

Soil is home to 80% of the terrestrial carbon and the study postulates that under conditions of drought and soil surface cracking or desiccation, this carbon is exposed to oxidation, thereby increasing the carbon dioxide emitted into the atmosphere.

Understanding this feedback loop could be vital in devising measures to mitigate global warming and prevent droughts.

Droughts and soil health

“Soil health plays a crucial but often underappreciated role in climate change,” says Farshid Vahedifard, lead author of the study and Professor and Louis Berger Chair in Civil and Environmental Engineering, Tufts University. “This role is critical in both [climate] adaptation and mitigation.”

The study explains that drought has complex consequences on soil health, reducing soil water retention, increasing weathering and erosion, and affecting plant nutrient availability. Droughts also expose the micro and macroflora (bacteria, fungi, earthworms, and so on) of soil to greater environmental stresses, affecting the soil’s nutrient cycling, leading to further carbon loss.

Understanding these complex interplays will help reduce significant inaccuracies when predicting climate change and encourage action towards healthy soils, explains Vahedifard. “Healthy soils are potent carbon sinks. Practices like cover cropping, reduced tillage, and organic farming increase soil organic matter content, enhancing its ability to store carbon. By increasing the organic carbon content, soils not only capture carbon dioxide but also improve their structure, aeration, water retention, and nutrient content, leading to a virtuous cycle of benefits,” he says. Beyond carbon, healthy soils can help regulate other greenhouse gases, such as methane and nitrous oxide, he adds.

The study explains that the feedback loop will also reduce methane emissions but will increase the emission of nitrous oxide, a more potent greenhouse gas. A pound of nitrous oxide warms the atmosphere 265 times more than a pound of carbon dioxide.

The authors of the study state that focused interdisciplinary research is vital to fully comprehend the ramifications of this feedback loop.

Getting to the bottom of droughts

While analysis of historical data shows that droughts are a natural part of the Earth’s weather cycle, a recent study by the Tyndall Centre for Climate Change Research has established that increasing temperatures due to global warming will lead to more prolonged and frequent droughts. The research also shows that limiting global warming to 1.5°C will reduce the exposure to severe droughts across land covers.

Understanding drought needs a lot of expertise, says Vimal Mishra, Professor, Civil Engineering and Earth Sciences, Indian Institute of Technology, Gandhinagar. “There are different kinds of droughts—meteorological droughts caused by a rainfall deficit, agricultural droughts when soil moisture is depleted and hydrological droughts with reduced water flow instreams, rivers, and reservoirs. Finally, there is the socio-economic drought resulting from the droughts outlined above, when crop production will go down due to less water for irrigation, which will impact incomes and purchasing power of the people,” explains Mishra.

In January 2024, Mishra and his team published the Drought Atlas of India, documenting the country’s droughts at the state, district and taluk levels. Based on data analysis between 1901 and 2020, the atlas revealed that the most severe monsoon drought occurred during the summer monsoon of 2002. The calamity caused crop losses worth $8.7 billion and affected 300 million people. The team notes that India has seen an increase in the duration, frequency and severity of droughts over the recent decades, and the trends point to worsening conditions with climate change.

Drought monitoring in India is based on mandatory and impact indicators which are outlined in the Ministry of Agriculture and Farmers’ Welfare’s Manual for Drought Management, explains K. Sreenivas, Deputy Director, Remote Sensing Applications Area, National Remote Sensing Centre (NRSC), Indian Space Research Organisation (ISRO). Mandatory indicators like rainfall deviation, standardised precipitation index (SPI) and dry spells are used to set off what is called the first drought trigger. This is followed by an analysis of impact indicators based on agriculture, remote sensing, soil moisture and hydrological factors that aid in assessing the drought and its severity. Droughts that are ascertained as severe or moderate set off the second trigger, leading to a field verification process to determine the extent of loss and damage. Based on these observations, the state governments declare droughts.

Sreenivas stated that the National Agricultural Drought Monitoring and Assessment System (NADAMS) was developed by ISRO and has been operational since 1990. Subsequently, the methodology was transferred to the Ministry of Agriculture and Farmers’ Welfare for regular monitoring and has undergone further improvements.

Karun Kumar Choudhary, head of the Crop Assessment Division at the NRSC explains that NADAMS performs monthly drought monitoring in India’s most drought-prone areas, providing data at the sub-district level. Since 2012, NADAMS has been implemented by the Mahalanobis National Crop Forecast Centre, Ministry of Agriculture and Farmers’ Welfare.

However, as the Drought Manual explains, several Indian states continue to follow the traditional monitoring system (known as the annewari/paisewari/girdwari method), which looks at the value of the crops obtained. Also, multiple datasets and assessment methods further complicate the analysis of droughts, says Mishra. “People think drought occurs only in dry areas, but that’s not true. You can have droughts even in Cherrapunji, Meghalaya, a place known for its high annual precipitation levels,” he adds.

Additionally, Mishra’s research also shows that anthropogenic warming and variations in summer monsoons will increase India’s risk of flash droughts — droughts caused by the rapid depletion of soil moisture — leading to devastating impacts on agriculture and irrigation demands.

Holistic solutions

In light of the identified feedback loop and India’s growing challenges with droughts, the need of the hour is climate-smart agricultural practices, says Vahedifard. “This includes the integration of crop diversification, agroforestry, and precision farming techniques to optimise the use of water and nutrients, thereby reducing the stress on the land and minimising soil desiccation,” he explains.

Sreenath Dixit, Principal Scientist and Strategic Advisor, International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) adds that the path forward must include a combination of traditional practices and modern techniques that benefit the soil and add to our understanding of a region’s adaptability to droughts.

ICRISAT has been conducting long-term studies that look at retaining and increasing soil organic carbon by incorporating crop residues into the soil. In a recent publication, researchers from the institute show that the addition of crop residues in both conventional farming and minimum tillage farming increases the soil organic carbon and improves soil health. This also prevents the burning of crop residues, thus reducing emissions and agricultural waste, the authors state. While the study looked at maize-chickpea sequential and maize-pigeonpea intercropping, it underscores the need to protect soil from high atmospheric temperatures by using residues and mulch.

Choudhary also shares that the NRSC team is working on making drought assessment more specific from a geographical and agricultural point of view. “We are improving the approach to see if we can go from the district to the taluk or gram panchayat level. Currently, drought reports are crop generic, and further research is needed to make the assessment crop-specific. If we say that a district is drought-affected and there are two crops that grow in the region, how do these differ in their response to the drought? This is also important information for drought management and assessing its impacts,” he adds.

Sreenivas shares that the Centre is also focused on long-term analysis to identify drought-prone regions to allow mitigation measures to be implemented accordingly. But most importantly, they are working on devising an early-warning system that can aid in responding swiftly to deteriorating conditions and will greatly benefit people and ecosystems.

Early-warning systems are an urgent need, emphasises KJ Joy, activist, researcher and one of the founding members of the Society for Promoting Participative Ecosystem Management (SOPPECOM). Having worked with drought-affected farmers in Maharashtra, Joy says that farmers need information on rainfall distribution to plan their cropping. “It is not the quantity of rainfall alone that matters. It is also the gap between two rain events. When this gap widens, it leads to disastrous consequences for farmers,” he says.

Joy adds that drought assessments need to be more data-driven and weather parameters must be collected across villages using a standard protocol, which can aid farmers in making informed decisions.

Over and above, educating the general public, farmers and policymakers on soil health’s pivotal role in climate change mitigation and adaptation is crucial, says Vahedifard. He shares, “We must engage local communities in planning and implementing adaptation strategies that address specific local needs and vulnerabilities. Empowering communities through education and resources to adopt sustainable practices can significantly contribute to mitigating the adverse effects of interplay between drought, soil desiccation cracking, and greenhouse gas emissions in a changing climate.”

(Published under Creative Commons from Mongabay-India. Read the original article here)