Earth & Sky

Do we have enough fresh water?

Johan Rockstrom says we do, if we use it correctly.

Johan Rockstrom is Associate Professor in Natural Resources Management at Stockholm University and Executive Director of Stockholm Environment Institute (SEI). He has 12 years of research and development work in developing countries, with more than 40 scientific publications in areas of water resource management, agricultural development, environmental management, systems research and resilience research.

In March, 2006, Dr. Rockstrom spoke with Earth & Sky’s Jorge Salazar about the important role of fresh water in the effort to feed the world’s growing population.

Salazar: How big is the scope of the world’s water needs?

Rockstrom: United Nations Secretary General Kofi Annan stated very clearly that humankind is facing a global fresh water crisis. Fresh water is finite in the world. We just have one given volume of fresh water, while population growth and demand for water is increasing very fast. And the main driver of that demand is the water that’s needed to produce food.

No human activity consumes so much water as producing food. Ninety percent of the fresh water requirements of an adult human is water to produce food. There are such huge volumes of water required behind every kilo of food, that the fresh water challenge is central to the hunger challenge.

The U.N. has said that each human being requires around 3,000 kilocalories per day. So, for you and me, feeding ourselves just one day consumes roughly four cubic meters of fresh water, or 4,000 liters of fresh water, or four tons of water.

Salazar: What’s the current fresh water situation?

Rockstrom: We know that there are six billion people in the world today. We know that the withdrawals of fresh water today, for irrigated agriculture, amounts to roughly 4,000 cubic kilometers per year.

The key concern is that we are taking out a very worrying volume of water. Already many rivers are running dry. The Yellow River doesn’t reach the ocean anymore. The Limpopo River, in southern Africa, is dry due to large withdrawals of water for irrigation.

When you are confronted with 800 million hungry people in the world today, and 3 billion newborn people during the next 30 years, of which 95% are born in developing countries, the question is, is there enough fresh water to produce food for a growing population? That is, in a nutshell, one of the world’s largest environment development challenges.

Salazar: How much water will we need to feed that future population?

Rockstrom: According to one of the most recent research analyses that we’ve done, presented at the U.N. Millennium Summit in June of last year, halving the number of hungry by 2015 would require a staggering 2,200 cubic kilometers of fresh water, new fresh water, to be allocated to agriculture. The shocking magnitude of that number is that the whole volume of consumptive use and irrigation today, in the whole world, lies around 1,800 cubic kilometers per year.

It is a challenge that is enormous, but it’s also very worrying because so far in the Millennium Development process, nobody’s really listing this issue of fresh water behind the food challenge. The focus is on fertilization, on new seed, on management of land, on crops and markets, but very little is discussed around the massive, massive pressure on fresh water to achieve the goals.

Salazar: You’ve written about the importance of what’s called “green” and “blue” water. Can you talk about that?

Rockstrom: The dilemma in water resource policy today is the narrow focus on managing runoff, the “blue” water. That’s the water that flows down our rivers, reaches our groundwater, and fills our lakes. That’s the water that we plug, and tap into large dams. That’s the water that we use to supply industry and households. That water constitutes roughly 40% of the world’s fresh water.

But in poor tropical countries, in dry tropical regions of the world, blue water is often just 5 to 10 percent of what we call the water balance, the total amount of water that circulates from rainfall, to land, back to the atmosphere.

The flow that we call the “green” water flow is the water that, when a rainfall reaches the soil, enters the soil. It either returns to the atmosphere directly as evaporation, which doesn’t produce any food, or it enters the soil, is taken up by roots, and goes through the leaves and goes back to the atmosphere and contributes to biomass production.

Rain–fed agriculture in the world feeds on green water. It feeds on the soil moisture, and it feeds on the soil, consumes that water, and contributes to biomass production.

Salazar: So you are looking at trying to use this green water more effectively to produce food?

Rockstrom: Yes. And the aim when trying to produce more food in the rain–fed sector is to maximize the infiltration of rainfall into the soil. How do you assure that you don’t generate blue water, i.e., don’t generate runoff from the soil surface?

The challenge is to enable plants to take up as much water as possible. There is a very interesting momentum throughout the world over the last 20 years, progressively abandoning conventional plowing in favor of what we call “conservation tillage”, which is a tillage system that tries to disturb the soil as little as possible, which helps build organic matter and helps build better structure, and thereby maximizes rainfall infiltration.

Salazar: Can you give me an example of this?

Rockstrom: Arusha is a place just on the slopes of Kilamanjaro in Tanzania. It’s a region that has been subject to massive land degradation over decades, particularly related to large–scale heavy plowing. That has caused soil compaction, loss of organic matter, and plow pans, which are hard pans in the soil due to plowing at the same depth, year after year after year.

In this region, we’ve worked with farmers during many, many years introducing innovative ways of tilling the land. Instead of turning the land, which you do when you plow, we introduce systems of conservation tillage, such as just going through with a knife, to only open the soil to maximize rainfall infiltration, while still minimizing the disturbance.

This leads to a double benefit. One is that you harvest water. The second is that by not turning the soil, you reduce the exposure of the soil to wind and sun. You help build organic matter in the soil, which helps increase water–holding capacity in the soil and productivity of the soil. That has resulted in major increases in yield levels, often more than doubling, from less than one ton per hectare to over two tons per hectare. Also, interestingly, it’s reduced the labor needs, particularly in terms of tractors and oxen to pull your plow. Because now you can till much less.

And by increasing yield levels in small scale agriculture that was producing very low yields, by covering the ground with much better leaf area and much better biomass growth, you actually reduce the non–productive evaporation in favor of productive transpiration, without reducing blue water flow downstream. You can actually produce more food, without necessarily reducing the water going down the river.

Salazar: Would you tell me about some other techniquies that increase the efficiency of water use?

Rockstrom: Sure. Most of the poor people of the world live in rural areas, and they live in tropical countries. Rainfall is extremely erratic, with very, very poor distribution. This leads to many periods of what we call dry spells, which are short periods of drought during the rainy season. These dry spells lead to crop failure in large tracts of Africa, India, South Asia, and Latin America.

The challenge then, in places where small–scale rain–fed agriculture doesn’t have large dams, is to collect runoff generated upstream in areas above the agricultural areas, in small dams, or into the soil for storage, or in small subsurface tanks for supplemental irrigation – to “top up” your rain–fed agriculture with small, small volumes of water to bridge dry spells.

In a vast number of both direct farm practices and research stations across the tropical world, these opportunities have more than doubled yield levels, while still improving the efficiency of water use.

Salazar: What are some examples of how this is carried out?

Rockstrom: One example is work that we are currently carrying out in Kenya, in a semi–arid region just southeast of the capital, Nairobi, in the Machakos district. It’s a typical semi–arid savannah in Africa, with a short rainy season, highly intensive rainfall, and recurrent, frequent periods of dry spells.

There, together with farmers, we have developed small microdams, not much larger than two, three swimming pools, which can store water collected from small, degraded grazing areas upstream of that small dam, which is then placed a couple of hundred meters above farmers fields, and farmers in these regions cultivate primarily maize. The runoff collected from just a couple of hectares – 10 or 20 thousand square meters – of land in small, hand–dug ponds, are then used for supplementary irrigation during short periods of dry spells.

The results of these experiments are very exciting. In the year 2000, for example, the president at the time declared a state of emergency and the need for food aid, due to what was proclaimed, politically, as a drought. We were actually able to produce two to three tons of maize per hectare during that exact same year.

Because the reality was – which it often is in Africa – that even when you talk about a drought, there has often been quite substantial rain. There was a massive rainfall event in the beginning of the rainy season, where most of the water was either evaporated or ran off the land, causing major erosion.

But we instead collected that water, thanks to the fact that these small microdams were in place. And this water was then used for supplemental irrigation. The rains picked up at the end of the season. Most farmers had complete crop failure. But the farmers that had these small dams had what the farmers themselves considered to be a bumper harvest.

And this continues consistently, rainy season after rainy season, collecting small amounts of runoff for use during dry spells. It’s an example of a system that not only increases yield levels for farmers, but also stabilizes yields. And that’s important. Because when the yields can be stabilized, farmers can dare take a risk to invest in fertilizers, which are expensive, which are very needed. But farmers hesitate in investing because of the risk of rainfall–induced crop failure.