Adapting to Climate Change: Hypothesis of Hope

"What ICRISAT Thinks" December 2009 by Director General William D Dar

We live in a warming world. How bad will it get? We can´t say for sure, but it seems clear that the drylands poor will be especially hard-hit. The Intergovernmental Panel on Climate Change (IPCC) has concluded in its most recent assessment that "At lower latitudes, especially in seasonally dry and tropical regions, crop productivity is projected to decrease for even small local temperature increases (1-2°C), which would increase the risk of hunger."

But even the highly sophisticated models that are cited by the IPCC are uncertain, predicting a range of possible temperature and rainfall trends. Furthermore, the scales at which these models operate — global and regional — are too imprecise to help people whose livelihoods are determined at the levels of the farm, village, and district. How can farmers adapt to a future that is so fuzzy?

Drawing lessons from the past

Rather than betting the future on one uncertain prediction or another, ICRISAT scientists decided to sample across a range of possible futures and draw lessons from broad response patterns, comparing them against the variations in temperature and rainfall that already occur over years in strategic locations across Africa and India. This in-depth analysis was based on the painstaking collection of many thousands of meteorological station measurements by different institutions over the past 30-50 years.

How could such large and complex data sets be handled scientifically? Scientists drew on the power of computer-based climatic and crop production models, built using data gathered during decades of intensive laboratory and field works by a wide range of institutions.

Projecting the future

Two computer simulation models, the Agricultural Production System Simulator (APSIM) and Decision Support System for Agro-Technology Transfer (DSSAT), found that one of the most important effects of rising temperatures would be to increase the rate of evaporation of water from soils and crops, shortening the length of the growing period (LGP). For example, the mid-point of the curves in the figure illustrate that under average rainfall conditions in Makindu, Kenya (50% probability point) a 3°C rise in temperature would be expected to cause a reduction in LGP of 8%, shortening average LGP from 108 to 101 days. Shorter LGP results in lower grain yield, because the crop has less time to convert sunlight into carbohydrate.

What is especially striking and noteworthy, though is that this 8% reduction pales in comparison to the variation in LGP that farmers already experience due to the wide variation that occurs in rainfall from season to season, causing LGP to vary from well under 80 days to more than 130 days.

The key message of hope that this finding delivers is that the study of how farming systems cope with current rainfall variation is likely to yield important clues for adapting to future climate change.

What are those adaptations, though and how can they be harnessed for the future?

Managing moisture

Since warming will dry out soils more quickly, two strategies to increase soil water storage were modeled using APSIM under Makindu conditions. The practices were i) planting a maize crop on soil formed into ridges across the slope to reduce the runoff of rainfall water, and ii) leaving residues from the previous crop on the soil surface to reduce runoff and evaporation (mulching). The model predicted that these two water management techniques would remarkably improve and stabilize yields relative to the wide climatic variations experienced over the past 50 years. In fact, further model analyses indicate that even with a 3°C temperature rise, mulching would effectively extend LGP beyond the current average of 108 days, to 113 days at this typical location.

Exploiting evolution

Even when water losses are countered, another problem arises. Higher temperatures accelerate the development of plants, causing them to mature too quickly before they´ve fully utilized available water and sunlight to produce grain.

Fortunately though, crops have evolved wide genetic variations in their inherent ´development clocks´. Based on our germplasm and breeding research combined with model predictions, we are confident that sustained effort will identify varieties whose development cycles are well-matched with the warmer temperatures that farmers will face. In parallel, since extreme temperatures can still cause considerable damage at sensitive growth stages, the search for temperature-resistance genes needs to be intensified.

Countering climate change

As serious as it is, climate change is just one of a host of challenges that threaten to reduce grain yields in the drylands of the future. For example, the impact of a 3°C temperature increase on maize yield is likely to be relatively smaller than the impact of continuing low rates of application of nitrogen fertilizers. This suggests yet another strategy for countering climate change: redouble our efforts to make fertilizer more readily available to poor farmers.

Looking ahead

These hints of hope illustrate how modern science can cut through the fog of uncertainty, complexity, and pessimism on a crucial global issue. Strategic, longer-term research of this type must be strengthened. Computer simulation models must be continually improved. The effects of heat on many different farming system dynamics must be better understood. Precious genetic diversity must be vigorously collected, conserved and characterized. Human capacities must be strengthened in all these areas at national as well as international levels. Conditions for the adoption of adaptive technologies must be fostered.

With your support and partnership, ICRISAT´s Hypothesis of Hope will continue to enrich the insights, options, and actions needed to help the poor to adapt to climate change.

The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) is a non-profit, non-political organization that does innovative agricultural research and capacity building for sustainable development with a wide array of partners across the globe. ICRISAT´s mission is to help empower 600 million poor people to overcome hunger, poverty and a degraded environment in the dry tropics through better agriculture. ICRISAT is supported by the Consultative Group on International Agricultural Research (CGIAR). www.icrisat.org ICRISAT-Patancheru Patancheru 502 324, Andhra Pradesh, India Tel +91 40 30713071 Fax +91 40 30713074 - With editing