Climate change and crop yields: what we really know
Assam tea garden
It’s obvious that disruptions of rain and temperature patterns are affecting tea farming and the impact is sure to grow. Drought in Africa has reached crisis levels. In Northern Kenya, over a million people face starvation. Intense rainfall is eroding slopes and damaging plantings in India. Low-lying areas of China’s farms are being covered with dust that blocks sunshine.
The glaciers of the Himalayas, the water towers of Asia, have been melting since 2000 at twice the rate of the preceding twenty years.
These are macro-level “Big Picture” figures. What is less clear is the micro, local view on the ground. What impacts are the changes creating in individual farms? Which of these are immediate rather than accumulating over the long-term? What are the most critical climatic variables? What can farmers, rather than policymakers do?
A useful study that provides answers from detailed tracking of crop yields in Assam was published at the end of 2016 and draws on 10 years of data collection. “Observing climate impacts on tea yield in Assam, India”: Applied Geography journal). It captures the structural dynamics of the climate-yield relationship.
Assam remains the largest tea-growing region of the world, accounting for a fifth of global production and half of India’s crop. Tea provides employment to 1.2 million workers. The region faces increasingly difficult times, especially in upgrading its quality of tea to compete with its main export rivals, China, Kenya, and Sri Lanka. Input costs have increased 8% a year since 2013 but prices have grown just 1% annually.
Obviously, climate change drives many of the problems for its tea growing businesses: the 800 large plantations and over 100,000 smallholders who now produce around half Assam’s output. The tea yield study is especially helpful in its use of data at the business unit level. This was gathered from 82 gardens and showed monthly yields from 2004-2013 with daily figures on weather temperature and precipitation. It thus adds a microfocus to support and extend the macro research findings. Those tend to address policy issues; the yield investigation is more relevant to management ones.
The macro analysis uniformly shows that the long term regional warming trend is consistent and reduces yield. Econometric models confirm that the changes in monsoon seasonality are having a long-term impact. The Assam study disaggregates the figures to show that the main source of yield decrease is from the short-term variability of temperature and precipitation within an individual month. On average, the main weather patterns over a year have been January as the coolest month, with the monsoons arriving in June, and the highest precipitation coming in June-September. The immediate effects on yield come from within a month, particularly any five consecutive days of non-precipitation.
The management messages from the study are that priorities must center on reducing the sensitivity of bushes to variability in precipitation:
Speed up the planting of drought-resistant cultivars;
Improve irrigation infrastructures (fertigation drip versus manual field spraying for example);
Increase shade tree protection of bushes to retain moisture; and
Improve pruning practices. The study concludes that this combination of good practices provides immediate and adaptive payoffs.