Water Storage Secures Harvest 

In Nepal, the success or failure of crops in both rainfed and irrigated agriculture is closely linked to the rainfall pattern. Though the irrigated areas in the country are reported to be 1,435,302 hectares (ha), most of the irrigation systems are characterised by low performance, and not all the cultivated areas even under the irrigation systems' commands get an assured supply of irrigation water. This implies that rainwater has an important role to play, not only in rainfed farming but also even in areas having irrigation infrastructures.

The amount of rainfall in most parts of the country is adequate to support at least one monsoon season rice crop and the rain showers along with the residual soil moisture help to grow other less water-demanding crops in the winter and pre-monsoon seasons. But the variability in time, amount and distribution in rainfall limits the yields of rainfed crops. The extent of such variations also prevents farmers from going for a low-risk, low-input cropping pattern, which ultimately puts them in subsistence brackets. Such farmers have only seasonal employment on farms and thus are generally poverty-stricken.

Rainwater conservation could help mitigate this problem. The average rainfall in the country is around 1,500 mm. Though rainfall varies in time and space, it remains the primary and direct source of irrigation for crop production. However, ranging from 70 to 80 per cent of rainfall falls in June to September, and a large portion of it is lost as surface runoff.  Even in pre-monsoon season, a fairly good amount of rainfall occurs in the country. Though the average amount of rainfall in the pre-monsoon season is about 230 mm, this year it far exceeded that amount to almost 340 mm. Conservation of this valuable resource, be it in the monsoon or in the pre-monsoon seasons, and its proper use should therefore be an important activity of the irrigation and agricultural agencies and the farmers.

The most efficient and inexpensive way of conserving rainfall is to hold it at the site of incidence. Farmers in South and Southeast Asia have developed rice fields which are the most efficient soil and water conservation systems. Evaporation losses are considerably reduced when the rainwater is stored in the soil rather than in a physical structure with a free water surface. Plants take only the water that is stored in the soil. 

However, rainfed crops often suffer from periodic dry spells/droughts, resulting in yield reductions. Cultural practices like proper tillage, land levelling, field bund management and mulching can conserve a great deal of soil moisture and avert the risk of crop failure to a certain extent. The irony is, so far, there is no specific agency in Nepal working in this important field of soil and water conservation.

Another very important means of rainwater conservation and utilisation is the provision of on-farm reservoirs (OFRs). In many South Asian and Southeast Asian countries, like Bangladesh, India, the Philippines, and Indonesia, the OFR technology of conserving rainwater has been a means to alleviate soil water deficit problems in rainfed and inadequately irrigated areas. The OFRs of about 800-5,000 square metres in area and 1.3 metres in depth have been used by farmers in the Philippines to store rainwater and runoff for supplemental irrigation. 

The OFRs are also used for raising fish. We also have reservoirs and ponds in Nepal which are used for raising fish and wallowing buffaloes. There are also cases where farmers have tapped rainwater and small spring sources and conserved them in ponds, allowing the water to recharge groundwater as much as possible rather than being quickly drained away. The stored water’s ultimate use is mainly for irrigation.  To put it the other way round, the OFRs also act as infiltration galleries for recharging the groundwater aquifers and help reduce overland flows. Groundwater recharge can reduce flood risks while also increasing water availability during droughts. 

Research results in several countries reveal that the OFRs are very attractive economically. As an example, in the Philippines the average benefit-cost ratio of OFR was found to be 5.1, and the wet season rice yields increased by about 15 per cent and enabled the production of an early rice crop or vegetables in a portion of the farm and made a good harvest.

In the context of Nepal, since a large portion of the cultivated area will remain rainfed even after developing the conventional type of irrigation facilities for all the irrigable area and also a big chunk of area under the irrigation command is not receiving adequate year-round irrigation, it will be worthwhile to go for the development of OFRs or water storage structures, including the impoverished ponds. 

It is suggested that the Department of Water Resources and Irrigation and the Department of Agriculture should jointly plan programmes of developing the OFRs so that the risk of crop failure can be minimised, and in the face of climate change.  As part of climate-smart agriculture, the government plans to promote resilient crop varieties, the OFR technology could be instrumental for adopting simple water conservation technologies like direct seeding, alternate wetting and drying irrigation methods, and rainwater harvesting techniques, which will eventually reduce the climate-related risks. 

The OFRs have much scope for substantial increases in agricultural crop production through relatively small investments within a shorter timeframe. A cluster of OFRs could be developed and the technology transferred to a wider area. The potential for increased production and on-farm income with the use of OFRs will facilitate the technology dissemination to both the farmers and the policymakers. 

Climate change poses significant threats to agricultural systems all around the globe. To ensure climate resilience, multifaceted approaches, including crop diversification, crop rotation, and improved water management are necessary. Increasing organic matter in the soil improves its water-holding capacity, nutrient retention, and resilience to extreme weather events. Besides, planting cover crops helps to protect the soil from erosion, improve soil structure, and add organic matter. Minimising soil disturbance by adopting no tillage or minimal tillage rather than following the conventional repeated tillage practice also reduces soil erosion, preserves soil moisture, and promotes microbial activity.

Agro-forestry, which implies integrating trees with crops, can provide shade, reduce soil erosion, and enhance biodiversity. 

Likewise, precision agriculture using technology to monitor and manage agricultural inputs more precisely can optimise resource use and reduce environmental impacts. Further, climate-resilient crop varieties that are more tolerant to floods, drought, heat and pests can help improve resilience. 

On top of many such simple but highly significant techniques, early warning systems and disaster preparedness can minimise agricultural losses and facilitate the crop recovery process. On all this, the three tiers of government can play a crucial role in creating enabling policies that support climate-resilient agriculture, such as providing incentives for promoting sustainable practices. For all this, strengthening agricultural research institutions and extension services can help farmers access information and adopt climate-smart technologies.

(The author is an irrigation management specialist.)