Research

India's Groundwater Crisis

India is the world’s largest consumer of groundwater and its agriculture is critically dependent on it. But all over the country, groundwater is extracted faster than it is naturally replenished, water tables are falling and wells are drying up. Moreover, the increasing energy required to chase the   water table is straining the country’s entire energy economy. I work with a team from the Columbia Water Center that tries to understand this complex sustainability challenge and find ways to address it.

A Novel Policy for Enhancing Efficiency of Groundwater and Energy Use in India: 
Design and Evidence from a Field Pilot

This ten minute video describes our field work in Northern Gujarat, one of the most groundwater depleted regions of India. We are working with the local government on a field pilot of a novel mechanism to incentivize farmers to use energy and water more efficiently.   

Can Irrigation Buffer Agriculture from Rainfall Variability and Climate Change?

India's agriculture and economy has always been dependent on the vagaries of the Monsoon rains. One of the benefits of groundwater resources is that they can be used to provide alternative sources of irrigation water when the monsoon fails, so that crop production doesn't suffer. I try to understand how well irrigation has performed in this regard and how well it might help adapt agriculture to adapt to climate change in various geophysical and institutional environments.

Climate Change, Rainfall Variability and Adaptation through Irrigation: Evidence from India

Abstract: Alongside warmer temperatures, climate change is expected to also result in increasingly irregular and extreme precipitation patterns, and both of these trends can have potentially severe consequences for food production. Rain fed agriculture in developing countries is expected to be particularly vulnerable to these changes, leading many to argue that the expansion of irrigation is one of the best feasible and proven adaptation strategies for attenuating climate change's impacts. I combine detailed data on daily weather, irrigation and crop yields across India over the last four decades to evaluate the adaptive resilience achieved by the expansion of irrigation in the country during this time period. I begin by providing the first estimate of the impact of increased intra-seasonal rainfall variability on yields, and show that its magnitude and significance rival that of total seasonal rainfall. I then provide evidence that irrigated yields are less vulnerable to the impacts of rainfall irregularities, and estimate that the expansion of irrigation to cover all the rice cultivating farmland in India could eliminate 90\% of the projected precipitation-driven climate change impact on rice yields. I also provide evidence suggesting that farmers expand irrigation in response to adverse rainfall conditions, in accordance with a simple model reflecting the flat rate pricing of irrigation water in India. In contrast to its attenuation of precipitation shocks, I find that irrigation mitigates the impact of increased seasonal heat exposure only partially (in the case of wheat) if at all (in the case of rice). Because temperature increases turn out to drive most of the projected impact on rice yields, these results together suggest the expansion of irrigation, as actually practiced by farmers in India, has at best limited potential to adapt agriculture to the changing climate.

Over-Extraction from Shallow Bedrock versus Deep Alluvial Aquifers: 
Reliability versus Sustainability Considerations for India's Groundwater Irrigation
With Tobias Siegfried, Pradeep Raj, Vijay Modi and Upmanu Lall. 

Abstract
The excessive exploitation of groundwater aquifers is emerging as a worldwide problem but it is nowhere as dramatic and consequential as it is in India, the world's largest consumer, where hundreds of millions of people depend on it. Usually, the problem is framed in terms of a long-term decline in water tables and its consequence for extraction costs, resource depletion and the sustainability of irrigated agriculture. Here, a comparative analysis is provided of coupled groundwater, energy and irrigation dynamics in two groundwater intensive regions in India that differ in their underlying hydrogeology - the Indian Punjab with its deep alluvial aquifers and the Telangana region in south-central India, with its shallow hard rock aquifers. Using a simple modeling framework and Piezometric and agricultural time series, we show that in shallow aquifers, the sense in which extraction is excessive is different, and is related to the short term reliability of water supply rather than long-term sustainability. This has important repercussions for irrigated agricultural economies. 

Can Increased Agricultural Water Use Efficiency Save India’s Groundwater?
With Naresh Devineni and R. Raman

Abstract: 
Increased efficiency of scarce natural resources is sometimes advocated as a way of avoiding resource depletion. On the other hand, improvements in efficiency may, in some situations, also lead to higher returns and increased incentives to harvest. This note examines this issue in the context of groundwater use for irrigation in India, which is widely recognized to be both un-sustainable and highly inefficient. We explore the extent to which improvement in water use efficiency in agriculture, for which the potential is huge, can actually slow down or even halt the process of unsustainable depletion, under several technological scenarios. We find that application of proven existing technologies has significant potential to reduce depletion, but not in some of the most strategic areas for food production. Moreover, in the current regulatory structure, it is more likely that farmers will use efficiency improvement to expand irrigated areas before reducing water use. This will erode much of the potential reduction of depletion.



Theoretical Work on Long Term Investments

Heterogeneous Patience, Bargaining Power and Environmental Policy

Abstract: 
Because of the long time horizon involved, the optimal level of greenhouse emission reduction is highly sensitive to the choice of the discount rate. However, there is no reason to expect different countries to have the same discount rate, if only by virtue of their different growth rates. This paper departs from the usual assumption of a homogenous discount rate and uses a simple bargaining model to analyze the global emission reduction and division of costs negotiated by countries with heterogeneous patience. I show that relative bargaining power depends on the time horizon and shifts gradually from the patient to the impatient country as it increases. Thus, the familiar effect of patience on bargaining power (Rubinstein 1982) is overturned when the horizon is long. This can mean patient countries will pay a larger share of the costs and that global emission targets will be disproportionally influenced by the discount rate of the more impatient country.

Naive and Sophisticated Investment

Abstract
Environmental policy is often a compromise between myopic harvesting and far-sighted conservation. I model this tension through the public investment choices (e.g. in a renewable resource) of a sequence of planners that have declining discount rates and are unable to commit their successors. I show that the anticipation that future planners will exceed current harvesting plans can either decrease the rate of harvesting and increase inter-temporal welfare, or, perhaps more surprisingly, act in the opposite direction, depending on the strength of social preference for smoothing harvests over time.

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