Temps, water & quality wine
Rainfall patterns will be affected, and may require vintners to irrigate where they haven't previously done so, wetter areas may dry out, etc. But one way to visualize the possible changes would be to compare the California Coast to it's much hotter (and drier) Central and San Joaquin valleys.
Since today's date is 6/6/06, it seemed as good of day as any to put them side by side for a fiendish comparison...
[we'll look at Santa Rosa for a spot representing the North Coast, Monterey both because it represents the central coast area and also because it's on nearly the same latitude as Fresno, and of course -Fresno!- because it's a perfect example of the typical San Joaquin Valley environment...]
Here we have the 4:00 AM PDT relative humidity (%RH) which will help illustrate the drying effects of the different areas...(uncontrolled dehydration is not a good thing if you're trying to keep the sugars from shooting skyward while you await maximum flavor development...)
Note that both Monterey and Santa Rosa start at 96% RH (which means there isn't really any dehydration to speak of during this time)...Now we see 7 AM PDT and the areas are starting to warm up & their %RH drops - but faster when you're away from the more humid coastal area...Fresno now starts to drop much faster as it heats up without the influx of more humid cool air to moderate the drying effect of a hot sunny day. Then again it did start the day @ only 61% RH, so there was some water evaporation from the vines & fruit even during the night.
10 AM local time & it's getting worse. The air in the central valley is really sucking up available water...but it still pales in comparison to the values at 1 PM local time today...
Fresno is at 29% while Santa Rosa is 45%; Monterey remains almost at 70% near the hottest part of the day. And it's not muggy either - the high temp in Monterey was only supposed to reach 65°F.
The beauty of the North and Central Coasts are that the temps and the RH will reverse course again, allowing the vines to get a rest from the continual drying that areas in the San Joaquin Valley & Central Valley experience. This recharging period for the vines allows much longer time on the vine itself, and a slow development of flavor without the loss of acidity that warmer areas produce. The results: deeper and more layered, flavorful wines.
That 94°F "cooking" and "dehydrating" on the fruit leaves a telltale note in the flavors and aromas of wines suffering from the "Big Valley" wine syndrome: flabby body, lack of acidity, flavors leaning toward the over-ripe and burnt areas of the flavor wheels I described before. Unfortunate as it is, this area still pumps out quite a bit of inferior wine when it coould be better used to produce grains and vegetables people need.
The biggest problem with stearing the current growers towards other crops is the most powerful one to combat: money. Winegrapes continue to be the most lucrative (legal) agricultural crop...