Modeling the Rhine
Pinpointing weaknesses in existing water barriers is just a first step toward understanding the Netherlands’ flood risk. Rising sea level is, of course, the elephant in the room. But for the moment, the elephant is moving slowly enough to rank lower on the list of Dutch concerns than certain near-term threats. One is that the Rhine could burst its banks in areas such as Rotterdam. And as peat decomposes, land is sinking faster than the sea is rising. (To make matters worse, peat decomposition, triggered by centuries of Dutch land drainage, throws off greenhouse gases.) Finally, new roads and developments could increase runoff, and population growth could put more people in the path of disaster.
At Wageningen University’s Alterra research institute, 20 earth scientists and climate scientists are trying, among other things, to develop an accurate way of forecasting the water level of the Rhine. The goal is to understand the entire river as a system, from its headwaters in the Swiss Alps, through Germany, and finally through Rotterdam to the North Sea–to figure out how much precipitation it receives, what hydrological processes shape it and its watershed, and how development will change these factors. The Alterra group is trying to integrate meteorological and hydrological models and use them to evaluate various scenarios of climate and land-use change. “All the different components of the model are available somewhere,” says Eddy Moors, a hydrometeorologist at Alterra. “There’s a Dutch model, a German model, a hydrological model, a meteorological model. It’s a matter of finding a way to combine those components, more than inventing something new.”
One of the factors the researchers are considering is that radical changes are expected in European land use. Dutch planners say that by 2050, European agricultural land totaling an area larger than Germany will give way to development or, in some cases, revert to forest. That, in turn, will affect the way floods propagate–by altering the ability of the land to absorb water, for example. “If we take these changes into account and look into land use, we can perhaps promote some land-use changes which will assist us,” says Moors. “We want to see the feedback of those changes.” As part of his study, Moors has even been investigating how trends in land use might change the local weather. By running meteorological models, he found that turning farmland into forest is likely to stimulate more local precipitation. Whether this is good or bad depends on whether it happens during a summer drought or a winter flood. Either way, analyzing such effects is important to understanding the larger system.
In addition to forecasting the effects of changing land use, the Alterra group is trying to predict the effects of intensified weather extremes. The Intergovernmental Panel on Climate Change, the U.N.-sponsored body whose work represents the global scientific consensus on the subject, recently predicted that warmer temperatures worldwide could make droughts harsher and precipitation more intense. And in winter, precipitation will tend to fall more as rain than snow in some areas, including the Swiss Alps, at the Rhine’s headwaters. As a result, wintertime river flooding–already a problem in the Netherlands–could get far worse. Buffer systems of some kind will probably be required. These might be impoundment areas upriver, perhaps even in Germany, or underground tanks beneath Dutch developments. But planners need to know where to put these buffer systems, and how to manage them so they’re empty when deluges are expected but full when droughts are near. This calls for better long-range forecasts. “To adapt, it is important to have forecasting systems,” says Moors. “To be able to do that, you have to couple meteorology and hydrology models.”
Developing these sharper predictive tools is a pursuit common to planners in The Hague, New York City, and California (see “Planning for a Climate-Changed World,” May/June). But in the Netherlands, the need is acute. “Our whole country is at stake,” says Piet Dircke, director of the water program at Arcadis, an engineering and consulting firm based in Maastricht that is participating in national planning efforts. “So we are moving from an engineering kind of approach to a systems approach. You never know which part is going to change, and which one will be relevant, until you look at the complete system.”