Eighty-four years ago Europe watched aghast as the Schlieffen Plan was implemented, and the Imperial German Army advanced relentlessly through Belgium on its way to Paris. "The lights are going out all over Europe," said Sir Edward Grey. "We shall not see them lit again within our lifetime." Meanwhile, in the other hemisphere, life continued pretty much as usual, and indeed exciting things were happening: on August 3rd, 1914, an ambition that was centuries old was realised when the SS Ancon became the first ship to navigate the Panama Canal.
Work on the project had begun a decade previously. Central to the scheme, in every sense, was a river called the Rio Chagres that ran right across the route proposed for the canal, and which, in the rainy season, swelled into a torrent that provided plentiful supplies of water. Near the Caribbean outlet of this river, the Gatun Dam was built; behind it, and confined by the surrounding hills, the Chagres waters rose to form a massive lake, whose surface was 80 ft above the level of the sea. Gatun Lake is accessed at either end by locks to form the longest and most important sector of the waterway. The system posed no major problems for three-quarters of a century, but in recent years Gatun Lake is reputed to be suffering from an inconvenient and unaccustomed lack of water. Deforestation, interfering with the rainfall, has been blamed.
The column of the atmosphere directly above our heads contains enough moisture to provide about an inch of rainfall, which is, on average, the quota for a mere 12 days. It follows that any moisture lost from the air as rainfall is replaced. Most of the replenishment comes in the form of evaporation from the oceans; a little is absorbed from lakes and rivers, dew and puddles and such things; but a very important source is the moisture that plants "breathe out" - moisture which they have taken in through their roots, and which they lose again by "transpiration".
This loss of water by transpiration has an effect upon the nearby weather. It makes the local air more humid, which in turn allows clouds to form and 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.
Moreover, 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 - and it may well be that this is why the Panama Canal is short of water