Bundelkhand, a geographical and cultural region in north-central India covering parts of Uttar Pradesh and Madhya Pradesh is one of the hotspots of poverty and malnutrition. The region has seen a decline in annual rainfall and experiences frequent droughts and intermittent long dry spells during monsoon and therefore, farmers are reluctant to cultivate kharif crops (i.e., cultivate during monsoon) due to uncertainty in rainfall pattern. They largely tend to cultivate a single crop during rabi season (i.e., cultivate during post-monsoon) using residual moisture for supplemental irrigation.
The traditional practices of decentralized rainwater harvesting locally called as haveli system has off late become dysfunctional due to social apathy and neglect. About 70–80 % of the region is dependent on shallow groundwater system for agricultural and domestic use which is largely under stress as these wells are functional for only a few months.
Farmers in the region generally follow the calendar based irrigation scheduling and still follow traditional technique of flood irrigation method which holds poor distribution efficiency and consume more energy.
Due to poor groundwater yield and prolonged well recovery period in the region, drudgery on women and children is increasing multifold and at the same time the cost of cultivation on irrigation application also increases as more labour has to be engaged on day-to-day basis.
In the absence of hydrological monitoring, most of the structural designs are based on empirical equations and those are not validated with variable topography, soil types, land degradation levels, and land use.
Moreover, there are no insights available on how the rain water management interventions are helpful in terms of well recovery period and associated energy consumption especially in shallow dug well system. Inadequate database on these aspects is also one of the reasons for demonstrating the efficacy of decentralized rainwater management initiatives and influence necessary policy interventions to guide prioritized investment in this area.
A recent paper Building resilient agricultural system through groundwater management interventions in degraded landscapes of Bundelkhand region, Central India by Singh et al looks at how rainwater harvesting interventions build groundwater resilience by diverting fraction of runoff into shallow aquifers. It quantifies the impact of rainwater management interventions on major water balance components, irrigation use, crop intensification and energy consumption and their interrelationships.
The study was conducted in three villages of Parasai-Sindh watershed located in Babina block of Jhansi district, Uttar Pradesh. Soils of this watershed (alfisols) have poor retention capacity (available water 100−120 mm/m) and farmers are mostly dependent on agriculture and livestock based activities.
Blackgram and greengram are cultivated under rainfed condition and groundnut with minimum supplemental irrigation during kharif season. Whereas, wheat, chickpea and barley are dominating crops during the rabi season, which was cultivated with the support of supplemental irrigation. The source of irrigation comprised of a total of 388 dug wells in the watershed.
New hydrological insights for the region
Rainwater management interventions can play an important role in mitigating the effects of climate change. This region is also characterized by hard rock geology and perched water table is formed during monsoon which is characterized by poor specific yield.
As the rainfall distribution in this region is highly skewed and the entire rainfall is received in about 20–40 days during a year (80% rainfall mostly between June and October), the rainwater management interventions provide opportunity to hold a fraction of water and facilitate for groundwater recharge. In the absence of rainwater management interventions, it is realized that the runoff generated is not available for the upstream users and besides leading to flooding in downstream areas.
Results from this study clearly show that once the perched water table is recharged, it can serve to meet water demand in the consecutive years. The perched water table also has its saturation limit (i.e., 120−130 mm) as water table in 2013 and 2016 reached almost the ground level in more than 90% of the wells and it was not possible for further harvest of recharge.
Water balance analysis shows that the rainwater management interventions enhanced groundwater availability from 45 mm to 80 mm. Enhanced availability of water triggered farmers to intensify their cropping system. The soil moisture in fallow lands was lost as non-productive evaporation before the project intervention. With improved groundwater availability these lands and the residual moisture held in them were converted into productive evapotranspiration thereby enhancing the overall land and water use efficiency.
This study also provides insights into the recovery ratio of groundwater pumping in shallow dug well systems. The recovery ratio is strongly correlated with the average hydraulic head of the watershed. With every 1m decline in hydraulic head, the recovery period increased by 50%. Improved groundwater table helped to reduce recovery period to 10−20h from 30 to 40h. Results show that energy consumption for irrigating 1 ha land was between 75 and 225 kWh/season depending on amount of annual rainfall and its distribution over seasons in respective years.
The haveli system holds an opportunity to harvest surface runoff in a decentralized manner so that the catchment and the command area are within the premises of the hydrological boundary.
In general, havelis are designed with 20−200 ha of catchment which submerges 1−10 ha (< 5% of the catchment) landscape on the upstream during monsoon. However, farmers whose lands get submerged as part of the haveli system during kharif season, do not lose much, as they cultivate rabi crop using residual soil moisture and with the support of supplemental irrigation which ensures an assured harvest, unlike the kharif crop which is often subjected to droughts and dry spells.
Besides, the fertility levels of the haveli fields are 30−40% higher than the normal fields due to the presence of high organic carbon and humus which compensates for their loss during the kharif season and at the same time, water harvested in the haveli system rejuvenates all nearby dug wells.
Rainwater management interventions harvested an additional 35 mm of surface runoff in various masonry structures and facilitated groundwater recharge from 720 mm rainfall received. The net groundwater recharge during monsoon season was estimated 75−80 mm; out of this, 25% (15−20 mm) was used in kharif and 75% (50−60 mm) in rabi season.
Groundwater recharge largely took place in wet and normal years due to rain water management interventions, which supported for meeting freshwater demand in recurring dry years. Increased groundwater recharge helped to enhance cropping intensity from 120% to 180% by converting significant fallow lands into productive cultivation.
The study shows a huge untapped potential for sustainable crop intensification by adopting a science-based natural resource management approach in fragile ecoregions of the semi-arid tropics.
The full paper is available in the Journal of Hydrology: Regional Studies, Volume 37, October 2021 here