Climate plays a critical role in human survival. Where there is water no matter what the physical conditions, there is life. Water has been important for the development of cultural complexity in human society during the Holocene (last 10,000 years) and earlier. Numerous civilizations evolved along the banks of water bodies or in areas with abundant rainfall. The archaeological and historical records show many instances of societal collapse, attributed to a combination of social, political and economic factors. However, recent studies have implicated climate change and drought as the primary agent in human migration, cultural separation, population dislocation and collapse of prehistoric and early historic societies. Natural springs, river valleys, and coasts have remained favoured locations for both hominids and modern man. Particularly, aquatic and maritime adaptations such as coastal occupation, fishing and seafaring played a significant role in demographic as well as geographic expansion of modern humans during the late Quaternary period.
The Indian summer monsoon, an important feature of the tropics, is the lifeline of the people of the Indian subcontinent. Abrupt changes, including monsoon failures or intense monsoonal rainfall may cause havoc to human life and economic growth of one of the most densely populated regions of the world. Complex and extreme climate events such as aridity, droughts, heat waves, floods, cyclones, stormy rainfall or hurricanes are expected to leave a much greater impact on human society than gradual changes in climate that may generate widespread response to adapt and mitigate the sufferings associated with the extremes. Societal and cultural responses to prolonged droughts include population dislocations, cultural separation, habitation abandonment, and societal collapse. A typical response to local aridity is human migration to safer areas with abundant water availability. People may also modify dwelling environments by adapting to new strategies to optimise the utility of available water by harvesting rain rather than migrating to newer areas. A recent review of paleoclimatological evidence for climate change during the Holocene found a good correlation between archaeological and historical records of rain water harvesting structures such as ponds, tanks and lakes at times of monsoon failures throughout India
Monsoon variability and rain water harvesting
Response to increased aridity in the Indian region over the last few millennia has given rise to traditional village tanks, ponds and earthen embankments. The antiquity of human occupation of Thar desert goes back to late Pleistocene as indicated by the discovery of hand axe from Late Acheulian site and microlithic site with pottery of early to mid-Holocene (i.e. between 7000 and 6000 years ago). Even after the disappearance of river Saraswati due to drainage disorganisation and subsequent increase in aridity, people continued to occupy the region by adapting to climate change through rain water harvesting. Thar is the most densely populated desert in the world and every settlement has often more than one water collection pond and numerous Khadins (earthworks) to harvest rain, developed over the last 5500 years of continuous and dynamic adaptation to climate change.
Rain water harvesting in the present day Rain water harvesting matters more today than any other time in the Holocene. Faster growth of human population as compared to the increases in the amount of accessible fresh water, per capita availability of fresh water, and climate change will cause a general intensification of the Earth’s hydrological cycle in the next century or so, with generally increased precipitation, evapotranspiration, and occurrence of storms, and significant changes in biogeochemical processes influencing water quality. As summers get hotter and anthropogenic climate changes exert further strain on economic, social and natural systems, water scarcity is likely to grow in India and elsewhere. Widespread arsenic poisoning is another case in point where rain water harvesting has a high potential as a possible solution. In West Bengal, alluvial Ganges aquifers used for public water supply are polluted with naturally occurring arsenic, which adversely affects the health of millions of people by causing arsenicosis, increasing the risk of cancer. Addressing water problem holds the promise in future for a world with decreasing water-impounding area of traditional tanks due to urbanisation. Under these circumstances, harvesting rain shall be critical. Rain water harvesting is a better option to provide arsenic free safe water in a cost effective and accessible manner, particularly for drinking and food preparation.
The history of rain water harvesting as an adaptation to climate change in India is deep rooted. Earliest examples of rain water systems in India include the Havelis of Jabalpur, Bandh and Bandhulia of Satna, Virda of Gujarat, Khadins of Rajasthan, Ahar-pynes of Bihar, Eri of Tamil Nadu, Dhora of Aravalis and similar other earthworks throughout the country. As these earthworks still continue to survive and serve the society, scientific studies such as C-14 dating of sediment cores of ponds, tanks and lakes would be useful to understand the dynamics of rain water harvest and climate relationship in diverse geographic regions throughout India. In a world confronting local and global changes, building societal endurance of human society to absorb shock, learn and develop would depend on sound knowledge of the historical adaptive processes that are still functional.
Although there is renewed interest in the revival of rain water harvesting which continues to be practiced globally, the systems nonetheless have fallen to disrepair. It would be worthwhile to investigate if declining interest in this time tested adaptation, in India for example, is due to economic reasons or as a climatic response to increasing strength of southwest monsoon during the past 400 years. Whatever the case, climate policy and water policy would require to be streamlined to promote rain water harvesting in the water scarce regions. We believe that neither the water policy nor the climate policy discussions seem to notice the worth of rain water harvesting as an adaptation to climate change especially in urban areas where water resources are fast depleting due to rapid increase in the population growth, construction of widespread permanent structures leaving little space for groundwater recharges, and unrestricted use of water. Studies of historical societal adaptations to climate fluctuations provide insights into possible responses of modern societies to future climate change and sustainable management of water resources for better economic growth.