Impact of climate change on agriculture irrigation and way forward
The face of agriculture in India has gone through a sea change in the past decades since independence. There has been a marked upgradation in both the scale and technological adoption by farmers in the country, for the better. However, Climate Change is another inevitable force to reckon with, that needs urgent introspection and attention. Water is one natural resource that can impact numerous spheres of industry and people, all at the same time.
The International Panel on Climate Change (IPCC) has observed increasing trends in the global surface temperature and changes in precipitation due to climate change that affect food, energy, and water availability. Irrigation being consuming the lion’s share of the water used, it is inevitable to study the link between the impacts of climate change on irrigation. Lack of adequate infrastructure, inappropriate water management has created a situation where only 18-20 per cent of water is presently used.
India’s annual rainfall is around 1183 mm, out of which about 75 per cent is received in a short span of four months during the monsoon season (June to September). This results in a significant amount of runoff during the monsoon and calls for irrigation investments for the rest of the year. The population of India is likely to be 1.6 billion by 2050, resulting in increased demand for water, food, and energy. Hence the effect of climate change on water needs to be critically analysed for agriculture, especially from an irrigation perspective.
Scenario of agricultural water use
Globally, food demands from the ever-rising population have led to the withdrawal of water resources that increased by about 6 times, from 500 km3 per year in 1900 to 3000 km3 per year in 2000. Since the beginning of the 21st century, extreme climatic events drive water withdrawal and it has reached 4000 km3 per year in 2010. The largest consumer is the agriculture sector, with a global accounting of about 72 per cent. Added to the population growth, global climate change is altering the hydrological cycle by changing the Spatio-temporal characteristics of rainfall and raising the evaporative demands of the atmosphere due to rising temperatures. The compounding effects of these factors put the freshwater resources vis-à-vis agriculture at great risk.
In India, the annual precipitation including snowfall, which is the main source of water, is estimated to be of the order of 4000 km3. Due to various constraints of topography, and uneven distribution of resources over space and time, it has been estimated that only about 1122 km3 (690 km3 from surface water and 432 km3 from groundwater) out of the total potential can be available for use. The country nourishes about 17 per cent of the world population, endowed with only ~ 4 per cent of the global freshwater
resources and ~ 2.4 per cent of the world’s total area. In spite of these limited natural resources, the country is self-reliant in its food requirements (the second-largest producer of rice and wheat in the world), and is also a major exporter. In the year 2010, according to one of the estimates, the water consumed by agriculture, domestic, industry, energy and other sectors are 557, 43,
37, 19 and 54 km3, respectively. Thus, presently agriculture consumes about 78 per cent of the total water withdrawal.
How will climate change impact water resources?
The effect of climate change on water resources is based on temperature, rainfall and water yield. Various studies on the impacts of climate change on water resources availability indicate that climate change is likely to affect the hydrological cycle, which will result in (i) more rainfall in lesser time; (ii) a decrease in the number of rainy days; (iii) overall increase in precipitation; (iv) increased glacial-melt-runoff initially and then afterwards decrease; (v) increase in runoff thereby less groundwater recharge; (vi) increase in extreme climatic events such as floods and droughts; (vii) increase in landslide events in hilly areas etc. Climate change is likely to affect groundwater availability in terms of both quantity and quality due to changes in precipitation, runoff and evapotranspiration. Increased rainfall intensity may lead to higher runoff and possibly reduced groundwater recharge. All these will significantly affect irrigation water availability and thereby agriculture.
Irrigation in India
In the backdrop of acute food scarcity in the 1960s, several multi-purpose dams and reservoirs were constructed across major river basins to expand irrigation in order to grow food grains. However, the growth in the area under surface irrigation started slowing down since the 1980s, coinciding with a faster rise in area under groundwater irrigation (Fig.1). Groundwater played a pivotal role in the alluvial aquifer of northern India, reinforcing the agricultural intensification programme ‘Green Revolution’ that ultimately ensured food security in India. However, its large-scale use has a climatic explanation too, as it started to rise phenomenally since the beginning of the drying phase in the mid-1980s. Smallholder agriculture dominates the food production system in India, which is largely rainfed and rely mostly on the rational distribution of the monsoon rainfall. In turn, the warming-induced acceleration of the hydrological cycle has resulted in more extreme rainfall events, at the expense of the frequency of moderate rainfall days that actually fulfils the irrigation requirement of rainfed agriculture. Thus, in the changing climate scenario, groundwater irrigation proliferated sinking more than 19 million wells.
Surface and groundwater irrigated area in India during 1950-2011
Currently, India extracts the world’s largest volume of groundwater to irrigate a record area of about 40 million ha annually which is more than double the irrigated area under surface
water. Most of this extracted groundwater is non-renewable in nature, and thus groundwater depletion is taking place at a faster rate compared to any country, questioning the long-term sustainability of aquifers. The key question then― whether groundwater can buffer the emerging hotter droughts. In order to achieve the Millennium Development Goals for an expected population of 1.6 billion by 2050, it is therefore the right time to adopt more sustainable measures of water management.
Further, per capita, dam storage capacity in India is one of the lowest in the world (200 m3/capita as compared to 5000 m3/capita in the USA, 1000 m3/capita in China, and around 900 m3/capita in South Africa) and needs to be substantially enhanced to offset the seasonal and long term resource availability fluctuations and make efficient use of available surface water resources.
Impact of Climate Change
Given the changes in temperature and rainfall pattern in India, the obvious question comes is that isn’t climate change affecting crop productivity in India? The changes in climatic factors directly affect the physiology, phenology, and morphology of plants. Indirectly it affects soil fertility, irrigation availability, and natural calamities like floods and droughts. Since water mediates much of the climate change impacts on agriculture, increased water scarcity in many regions presents a major challenge for climate adaptation. The scope for adaptation in rainfed agriculture is determined largely by the ability of crop varieties to cope with shifts in temperature and to manage soil water deficits. Irrigation allows cropping calendars to be rescheduled and intensified, thus providing a key adaptation mechanism for land that previously relied solely on precipitation.
Irrigation water demand, which is a major share of the total water demand of the country, is considered more sensitive to climate change. A change in field-level climate may alter the need and timing of irrigation. Increased dryness may lead to increased demand, but demand could be reduced if soil moisture content rises at critical times of the year. It is projected that most irrigated areas in India would require more water around 2025 and global net irrigation requirements would increase, relative to the
situation without climate change, by 3.5–5 per cent by 2025, and 6–8 per cent by 2075. In India, roughly 52 per cent of irrigation consumption across the country is extracted from groundwater; therefore, it can be an alarming situation with a decline in groundwater and an increase in irrigation requirements due to climate change. To obtain a better quantitative assessment of the climate change impact, a more accurate ‘damage due to flood’ and ‘damage due to drought’ relationship must be established and updated periodically. More studies are needed in different basins, aquifers, and agro-climatic regions of India to assess the sensitivity of the basin response to climate change.