I SOMETIMES tell newcomers to California that we do not have weather - just climate. We can expect rain in the winter and early spring; otherwise, it will be dry. The coastal summer will be kept cool by the fogbank just offshore. But the joke is increasingly on us, now, as signs of climate change appear everywhere. The one we are seeing now is drought.

This rainy season is nearly half over, without having yielded significant precipitation. The days are unusually warm. The vegetation is as confused as the people, and cherry trees and flowering quinces are in full bloom weeks before their usual time. One hears a repeated refrain of pleasure mixed with guilt: "Lovely weather we're having; but I guess I shouldn't really be enjoying it. We need rain."

As a city-dweller, I can almost ignore it. The worst thing we have to worry about just now is a bit of water rationing - something we have learned to live with, in past droughts. My sister, on the other hand, has a vineyard that depends entirely on rainfall for water. Larger issues are in the balance for a state that is not only a wine producer, but also the source of much of the nation's fresh produce.

The year 2013 was our driest on record, but formal records go back only to the late 19th century. The typical pattern of this period has been that droughts last only a couple of years. Now we know, however, from investigations that take the matter further back, with the help of tree rings and other data, that it is possible for droughts in the American west to go on for a century or more.

Water has long been the most precious resource here, the focus of long-term planning and ever-renewed conflict. Long canals carry water from the wetter north to the more populous south. Shortages pit farmers against urban dwellers, and both against the need to respect the natural environment.

Every period of drought creates anxiety, but this one more so than usual, because it is more severe, and because we are newly conscious that climate is not immune to change. The difference between climate and weather, it turns out, is not that one is immutable and the other changeable; the difference is more a matter of the scale and pace of change.

And there is strong evidence that climate is changing more rapidly now, thanks to human interventions. In some parts of the United States, there is still a kind of obscurantist denial that anything is amiss, much less that humans are contributing to the problem. By this time, however, there is little sympathy for such a view in California.

California has long been a leader in efforts to improve air quality. We had Los Angeles smog to serve as a warning bell. Now, the difficult process of not only managing but reducing water usage across the board is beginning to impose itself, and we will have to learn to accommodate.

We Californians are in no position to ask the rest of the world to feel sorry for us. The consequences of global warming are far less severe for us than for, say, the Sahel, or the small island nations of the world. We are getting a strong reminder, however, that we are intrinsically no less vulnerable to the uncertainties of the near future than anyone else. No one is exempt.

The Revd Dr Bill Countryman is Professor Emeritus of New Testament at the Church Divinity School of the Pacific in Berkeley, California, in the United States.