The celebrations to mark the handing over to Panama of the Panama Canal a day or two ago were overshadowed by serious concern for its future viability. The canal, it seems, is running short of water.
When the canal was constructed 90 years ago, the Gatun Dam was built near the Caribbean outlet of the Rio Chagres. Behind it, and confined by the surrounding hills, the waters of the river rose to form a massive lake, whose surface was 80 ft above the level of the sea.
Gatun Lake is reached at either end by locks to form the longest and most important sector of the waterway.
It is, moreover, the only source of water for the canal, which needs a vast amount to keep it operational. It uses 52 million gallons to move a single ship from one end to the other, this fresh water ending up eventually in the ocean at either end.
The system posed no major problems for three-quarters of a century, but in recent years Gatun Lake has been suffering from an inconvenient and unaccustomed lack of water. Deforestation, interfering with the rainfall, is being blamed.
Moisture lost from the air in rainfall needs to be replaced. Most of the replenishment comes in the form of evaporation from the world's oceans, but a very important local source is the moisture that plants "breathe out" by transpiration.
Transpiration makes the local air more humid, which in turn allows clouds to form and more rain to fall, the moisture to be absorbed by trees again in the familiar cycle, but if you remove the trees, an important source of atmospheric moisture disappears, and in addition, water runs off the cleared areas much more rapidly than before, and this, too, reduces the amount available for evaporation.
Deforestation, therefore, results in less rain in the vicinity.
Tuesday's celebrations marked the culmination of a treaty made between the US and Panama in the late 1970s whereby the Canal Zone was to be gradually turned over to the Panamanian government. As they gained control of the territory adjacent to the canal, however, the Panamanians have been less successful than the Americans at preventing deforestation.
In 1947, more than 70 per cent of Panama was rain forest; now, less than 30 per cent remains forest and expectations are that the figure will be 15 per cent by the end of the century.
More than 2,000 acres of land are cleared each week, resulting in a decrease in average rainfall in the region - and in this particular case, it seems, less water in the catchment of the Rio Chagres to feed the Panama Canal.